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  • 1.
    Al-Saadi, Munir
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. R&D Metallurgy, AB Sandvik Materials Technology, SE-811 81 Sandviken, Sweden.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Sandberg, Fredrik
    R&D Metallurgy, AB Sandvik Materials Technology, SE-811 81 Sandviken, Sweden.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hot Deformation Behaviour and Processing Map of Cast Alloy 825Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Alloy 825 is a nickel-based alloy that is commonly used in applications where both high strength and corrosion resistance are required. Applications include tanks in the chemical, food and petrochemical industries and oil and gas pipelines. Components made from Alloy 825 are often manufactured using hot deformation. However, there is no systematic study to optimise the processing conditions reported in literature. In this study, a processing map for as-cast Alloy 825 is established to maximise the power dissipation efficiency of hot deformation and correlate the processing conditions to final materials properties. The hot deformation behaviour of equiaxed Alloy 825 is characterized on the basis of the dynamic materials model and compression data in the temperature range of 950 °C to 1250 °C at an interval of 50°C and strain rate range of 0.01 s-1 to 10 s-1 to a true strain of 0.7 using a Gleeble-3500 thermomechanical simulator. Flow stress is modelled by the constitutive equation based on a hyperbolic sine function. The deformed material is characterized using Vickers hardness, optical microscopy and scanning electron microscopy, including electron backscattered diffraction. The true stress-true strain curves exhibit peak stresses followed by softening due to occurrence of dynamic recrystallization. The value of stress exponent in the hyperbolic sine-based constitutive equation, n=5.0. This suggests that the rate-limiting mechanism of deformation is climb (diffusion)-mediated dislocation glide. The activation energy for plastic flow in the temperature range tested is about 450 kJ mole-1, and the relationship between flow stress and temperature-compensated strain rate (via the Zener-Hollomon parameter) was found to be valid across this temperature range. The maximum power dissipation efficiency is over 35%. The highest efficiency is observed over temperature range of 1100 °C – 1250 °C and a strain rate of 0.01 s-1 – 0.1s-1. These are the optimum conditions for hot working. The optimum processing parameters for good strain hardening are obtained in the temperature range of between  950 °C  and  1100 °C with a strain rate between  0.3/s  and 10.0/s. 

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  • 2.
    Al-Saadi, Munir
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Sandberg, Fredrik
    AB Sandvik Materials Technology.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hot Deformation Behaviour and Processing Map of Cast Alloy 8252021Inngår i: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Alloy 825 is a nickel-based alloy that is commonly used in applications where both high strength and corrosion resistance are required, such as tanks in the chemical, food and petrochemical industries and oil and gas pipelines. Components made from Alloy 825 are often manufactured using hot deformation. However, there is no systematic study to optimise the processing conditions reported in literature. In this study, a processing map for as-cast Alloy 825 is established to maximise the power dissipation efficiency of hot deformation in the temperature range of 950 to 1250 °C at an interval of 50 °C and strain rate range of 0.01s−1 to 10.0s−1 to a true strain of 0.7 using a Gleeble-3500 thermomechanical simulator. The processing conditions are also correlated to the Vickers hardness of the final material, which is also characterised using optical microscopy and scanning electron microscopy, including electron backscattered diffraction. The true stress-true strain curves exhibit peak stresses followed by softening due to occurrence of dynamic recrystallization. The activation energy for plastic flow in the temperature range tested is approximately 450 kJ mol−1, and the value of the stress exponent in the (hyperbolic sine-based) constitutive equation, n=5.0, suggests that the rate-limiting mechanism of deformation is dislocation climb. Increasing deformation temperature led to a lower Vickers hardness in the deformed material, due to increased dynamic recrystallization. Raising the strain rate led to an increase in Vickers hardness in the deformed material due to increased work hardening. The maximum power dissipation efficiency is over 35%, obtained for deformation in the temperature range 1100-1250 °C and a strain rate of 0.01s−1-0.1s−1. These are the optimum conditions for hot working.

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  • 3.
    Al-Saadi, Munir
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer. Sandvik Materials Technology AB.
    Mu, Wangzhong
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Strukturer.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Sandberg, Fredrik
    Sandvik Materials Technology AB.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Effect of Trace Magnesium Additions on the Dynamic Recrystallization in Cast Alloy 825 after One-Hit Hot-Deformation2021Inngår i: Metals, ISSN 2075-4701, Vol. 11, nr 1, artikkel-id 36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Alloy 825 is widely used in several industries, but its useful service life is limited by both mechanical properties and corrosion resistance. The current work explores the effect of the addition of magnesium on the recrystallization and mechanical behavior of alloy 825 under hot compression. Compression tests were performed under conditions representative of typical forming processes: temperatures between 1100 and 1250 °C and at strain rates of 0.1–10 s−1 to a true strain of 0.7. Microstructural evolution was characterized by electron backscattered diffraction. Dynamic recrystallization was found to be more prevalent under all test conditions in samples containing magnesium, but not in all cases of conventional alloy 825. The texture direction ⟨101⟩ was the dominant orientation parallel to the longitudinal direction of casting (also the direction in which the samples were compressed) in samples that contained magnesium under all test conditions, but not in any sample that did not contain magnesium. For all deformation conditions, the peak stress was approximately 10% lower in material with the addition of magnesium. Furthermore, the differences in the peak strain between different temperatures are approximately 85% smaller if magnesium is present. The average activation energy for hot deformation was calculated to be 430 kJ mol−1 with the addition of magnesium and 450 kJ mol−1 without magnesium. The average size of dynamically recrystallized grains in both alloys showed a power law relation with the Zener–Hollomon parameter, DD~Zn, and the exponent of value, n, is found to be 0.12. These results can be used to design optimized compositions and thermomechanical treatments of alloy 825 to maximize the useful service life under current service conditions. No experiments were conducted to investigate the effects of such changes on the service life and such experiments should now be performed.

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  • 4.
    Al-Saadi, Munir
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. R&D, AB Sandvik Materials Technology, SE-811 81 Sandviken.
    Sandberg, Fredrik
    R&D, AB Sandvik Materials Technology, SE-811 81 Sandviken.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Modelling of strengthening mechanisms in wrought nickel-based 825 alloy subjected to solution annealing2021Inngår i: Metals, ISSN 2075-4701, Vol. 11, nr 5, s. 771-20Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Wrought nickel‐based Alloy 825 is widely used in the oil and gas industries, attributed toits high strength at temperatures up to 540 °C. However, differences in mechanical properties arisein finished components due to variations in both grain size and dislocation density. Numerous ex‐perimental studies of the strengthening mechanisms have been reported and many models havebeen developed to predict strengthening under thermomechanical processing. However, there aredebates surrounding some fundamental issues in modeling and the interpretation of experimentalobservations. Therefore, it is important to understand the evolution of strain within the materialduring the hot‐forging process. In addition, there is a lack of research around the behavior duringhot deformation and subsequent stabilization of Alloy 825. This article investigates the origin of thisstrength and considers a variety of strengthening mechanisms, resulting in a quantitative predictionof the contribution of each mechanism. The alloy is processed with a total forging strain of 0.45, 0.65,or 0.9, and subsequent annealing at a temperature of 950 °C, reflecting commercial practice. Themicrostructure after annealing is similar to that before annealing, suggesting that static recovery isdominant at this temperature. The maximum yield strength and ultimate tensile strength were348 MPa and 618 MPa, respectively, obtained after forging to a true strain of 0.9, with a ductility of40%. The majority of strengthening was attributed to grain refinement, the dislocation densities thatarise due to the large forging strain deformation, and solid solution strengthening. Precipitatestrengthening was also quantified using the Brown and Ham modification of the Orowan bowingmodel. The results of yield strength calculations are in excellent agreement with experimental data,with less than 1% difference. The interfacial energy of Ti(C,N) in the face‐centered cubic matrix of. These results can bethe current alloy has been assessed for the first time, with a value of 0.8 mJm−2used by future researchers and industry to predict the strength of Alloy 825 and similar alloys, es‐pecially after hot‐forging.

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  • 5.
    Al-Saadi, Munir
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi. R&D, AB Sandvik Materials Technology, SE-811 81Sandviken, Sweden..
    Sandberg, Fredrik
    R&D, AB Sandvik Materials Technology, SE-811 81Sandviken, Sweden..
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Karasev, Andrey
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    A study of the static recrystallization behaviour of cast Alloy 825 after hot-compressions2019Inngår i: Journal of Physics: Conference Series, 2019, Vol. 1270, artikkel-id 012023Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The static recrystallization behaviour of a columnar and equiaxed Alloy 825 material was studied on a Gleeble-3800 thermo-simulator by single-hit compression experiments. Deformation temperatures of 1000-1200 °C, a strain of up to 0.8, a strain rate of 1s-1, and relaxation times of 30, 180, and 300 s were selected as the deformation conditions to investigate the effects of the deformation parameters on the SRX behaviour. Furthermore, the influences of the initial grain structures on the SRX behaviors were studied. The microstructural evolution was studied using optical microscopy and EBSD. The EBSD measurements showed a relaxation time of 95 % for fractional recrystallization grains, 𝑡95, in both structures, was less than 30 seconds at the deformation temperatures 1100 °C and 1200 °C. However, fewer than 95% of recrystallized grains recrystallized when the deformation temperature was lowered to 1000 °C. From the grain-boundary misorientation distribution in statically recrystallized samples, the fraction of high-angle grain boundaries decreased with an increasing deformation temperature from 1000 °C to 1200 °C for a given relaxation time. This was attributed to grain coarsening

  • 6.
    Al-Saadi, Munir
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. R&D, AB Sandvik Materials Technology, SE-811 81Sandviken, Sweden..
    Sandberg, Fredrik
    R&D, AB Sandvik Materials Technology, SE-811 81Sandviken, Sweden..
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Influence of Strain Magnitude on Microstructure, Texture and Mechanical Properties of Alloy 825 during hot-forgingManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Alloy 825 is a nickel-base alloy that is common in applications with high stresses and corrosive environments. It is commonly processed by hot forging, but there are few data about how hot forging affects the microstructure, which is critical for both mechanical and corrosion performance. Here, the alloy was hot forged in a commercial thermomechanical process to three industrially-relevant strains and the microscture was examined using scanning electron microscopy and EBSD. The tensile properties were also measured after thermomechanical treatment. Dynamic recrystallization was prevalent during the process, so increasing the forging strain leads to smaller grains and also higher dislocation density. Data were combined to allow the 0.2% proof stress to be calculated as a function of forging strain. All forging strains were sufficient to meet the criteria of the relevant industrial standard for this material. The maximum yield strength and ultimate tensile strength were obtained after forging to a true strain of 0.9 were 413 MPa and 622 MPa, respecitvely, with a ductlity of 40%. This may be used to tailor thermomechanical treatments to achieve precise mechanical properties and serve as a basis for future studies into the corrosion performance of this alloy as a function of forging strain.

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  • 7.
    Ben Khedher, Nidhal
    et al.
    Univ Hail, Coll Engn, Dept Mech Engn, Hail 81451, Saudi Arabia.;Univ Monastir, Natl Sch Engn Monastir, Lab Thermal & Energet Syst Studies LESTE, Monastir 5000, Tunisia..
    Shahabadi, Mohammad
    Univ Oklahoma, Sch Aerosp & Mech Engn, Norman, OK 73019 USA..
    Alghawli, Abed Saif
    Prince Sattam Bin Abdulaziz Univ, Comp Sci Dept, Al Aflaj 11912, Saudi Arabia..
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Mehryan, Seyed Abdollah Mansouri
    Islamic Azad Univ, Yasooj Branch, Young Researchers & Elite Club, Yasuj 7591493686, Iran..
    Numerical Study of the Flow and Thermomagnetic Convection Heat Transfer of a Power Law Non-Newtonian Ferrofluid within a Circular Cavity with a Permanent Magnet2022Inngår i: Mathematics, E-ISSN 2227-7390, Vol. 10, nr 15, artikkel-id 2612Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study is to analyze the thermo-magnetic-gravitational convection of a non-Newtonian power law ferrofluid within a circular cavity. The ferrofluid is exposed to the magnetic field of a permanent magnet. The finite element method is employed to solve the non-dimensional controlling equations. A grid sensitivity analysis and the validation of the used method are conducted. The effect of alterable parameters, including the power law index, 0.7 <= n <= 1.3, gravitational Rayleigh number, 10(4) <= Ra-T <= 10(6), magnetic Rayleigh number, 10(5) <= Ra-M <= 10(8), the location of the hot and cold surfaces, 0 <= lambda <= pi/2, and the length of the magnet normalized with respect to the diameter of the cavity, 0.1 <= L <= 0.65, on the flow and heat transfer characteristics are explored. The results show that the heat transfer rate increases at the end of both arcs compared to the central region because of buoyancy effects, and it is greater close to the hot arc. The location of the arcs does not affect the heat transfer rate considerably. An increase in the magnetic Rayleigh number contributes to stronger circulation of the flow inside and higher heat transfer. When the Kelvin force is the only one imposed on the flow, it enhances the heat transfer for magnets of length 0.2 <= L <= 0.3.

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  • 8.
    Chipakwe, Vitalis
    et al.
    Luleå Tekniska Universitet.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Karlkvist, Tommy
    Luleå Tekniska Universitet.
    Rosenkranz, Jan
    Luleå Tekniska Universitet.
    Chelgani, Saeed Chehreh
    Luleå Tekniska Universitet.
    Effects of Chemical Additives on Rheological Properties of Dry Ground Ore: A Comparative Study2021Inngår i: Mineral Processing and Extractive Metallurgy Review, ISSN 0882-7508, E-ISSN 1547-7401Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is well documented that chemical additives (grinding aid “GA”) during grinding can increase mill throughput, reduce water and energy consumption, narrow the particle size distribution of products, and improve material flowability. These advantages have been linked to their effects on the rheology, although there is a gap in understanding GA effectiveness mechanism on the flow properties. The present study aims to fill this gap using different GAs (Zalta™ GR20-587, Zalta™ VM1122, and sodium hydroxide) through batch grinding experiments of magnetite ore and addressing the mechanisms of their effects on the rheology by an FT4 Powder Rheometer as a unique system. Experimental results showed that GA improved grinding efficiency (energy consumption and product fineness), which were well-correlated with basic flow energy, specific energy, aerated basic flow energy, and aerated energy. Moreover, the rheometry measurement showed strong linear correlations between basic flow energy, specific energy, and the resulting work index when GAs was considered for grinding, which confirmed the effect of GA on ground particles’ flowability. Zalta™ VM1122, a polysaccharide-based grinding aid, showed the best performance with 38.8% reduction of basic flow energy, 20.4% reduction of specific energy, 24.6% reduction of aerated basic flow energy, and 38.3% reduction of aerated energy. It also showed the strongest correlation between the grinding parameters and flow parameters (r > 0.93). The present investigation shows a strong indication that the predominant mechanism of GAs is based on the alteration of rheological properties and identify Zalta™ VM1122 as the best GA.

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  • 9.
    Dadbakhsh, Sasan
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Tillverkning och mätsystem.
    Zhao, Xiaoyu
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Tillverkning och mätsystem.
    Chinnappan, Prithiv Kumar
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Shanmugam, Vishal
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Zeyu, Lin
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Tillverkning och mätsystem.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Process and geometrical integrity optimization of electron beam melting for copper2022Inngår i: CIRP annals, ISSN 0007-8506, E-ISSN 1726-0604, Vol. 71, s. 201-204Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This work systematically analyzes and optimizes the process of electron beam melting for pure copper. It is shown that, for reliable manufacturing, the preheating temperature should be optimized to avoid porosity as well as part deformation. The electron beam should be fully focused to prevent shrinkage voids (correlated to negative defocusing) and material spattering (linked to positive defocusing). Smoother surfaces from lower hatch spacing (e.g., 100µm) can improve the density reliability, while longer overhangs are reached by a higher hatch spacing. A suitable starting contour strategy is also applied to mitigate border porosities, reduce side roughness and increase geometric precision.

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  • 10.
    Forsberg, Kerstin
    et al.
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemiteknik, Resursåtervinning.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Materials - a tangible challenge for the electrification of society2022Inngår i: Towards the energy of the future – the invisible revolution behind the electrical socket / [ed] Fredrik Brounéus & Christophe Duwig, Books on Demand , 2022Kapittel i bok, del av antologi (Annet (populærvitenskap, debatt, mm))
  • 11.
    Ghalambaz, Mohammad
    et al.
    Ton Duc Thang University.
    Mansouri Mehryan, Seyed Abdollah
    Islamic Azad University, Yasooj.
    Ayoubi Ayoubloo, Kasra
    Shahid Chamran University of Ahvaz.
    El Kadri, Mohamad
    Université Ferhat Abbas Sétif-1; Centre Scientifique et Technique du Bâtiment.
    Hajjar, Ahmad
    Université de Lyon.
    Younis, Obai
    Department of Mechanical Engineering, College of Engineering at Wadi Addwaser, Prince Sattam Bin Abdulaziz University.
    Saffari Pour, Mohsen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Thermal Energy Storage and Heat Transfer of Nano-Enhanced Phase Change Material (NePCM) in a Shell and Tube Thermal Energy Storage (TES) Unit with a Partial Layer of Eccentric Copper Foam2021Inngår i: Molecules, ISSN 1431-5157, E-ISSN 1420-3049, Vol. 26, nr 5, artikkel-id 1491Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermal energy storage units conventionally have the drawback of slow charging response. Thus, heat transfer enhancement techniques are required to reduce charging time. Using nanoadditives is a promising approach to enhance the heat transfer and energy storage response time of materials that store heat by undergoing a reversible phase change, so-called phase change materials. In the present study, a combination of such materials enhanced with the addition of nanometer-scale graphene oxide particles (called nano-enhanced phase change materials) and a layer of a copper foam is proposed to improve the thermal performance of a shell-and-tube latent heat thermal energy storage (LHTES) unit filled with capric acid. Both graphene oxide and copper nanoparticles were tested as the nanometer-scale additives. A geometrically nonuniform layer of copper foam was placed over the hot tube inside the unit. The metal foam layer can improve heat transfer with an increase of the composite thermal conductivity. However, it suppressed the natural convection flows and could reduce heat transfer in the molten regions. Thus, a metal foam layer with a nonuniform shape can maximize thermal conductivity in conduction-dominant regions and minimize its adverse impacts on natural convection flows. The heat transfer was modeled using partial differential equations for conservations of momentum and heat. The finite element method was used to solve the partial differential equations. A backward differential formula was used to control the accuracy and convergence of the solution automatically. Mesh adaptation was applied to increase the mesh resolution at the interface between phases and improve the quality and stability of the solution. The impact of the eccentricity and porosity of the metal foam layer and the volume fraction of nanoparticles on the energy storage and the thermal performance of the LHTES unit was addressed. The layer of the metal foam notably improves the response time of the LHTES unit, and a 10% eccentricity of the porous layer toward the bottom improved the response time of the LHTES unit by 50%. The presence of nanoadditives could reduce the response time (melting time) of the LHTES unit by 12%, and copper nanoparticles were slightly better than graphene oxide particles in terms of heat transfer enhancement. The design parameters of the eccentricity, porosity, and volume fraction of nanoparticles had minimal impact on the thermal energy storage capacity of the LHTES unit, while their impact on the melting time (response time) was significant. Thus, a combination of the enhancement method could practically reduce the thermal charging time of an LHTES unit without a significant increase in its size.

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  • 12.
    Ghalambaz, Mohammad
    et al.
    Ton Duc Thang University.
    Mehryan, Seyed Abdollah Mansouri
    Islamic Azad University.
    Hajjar, Ahmad
    Université de Lyon.
    Younis, Obai
    Prince Sattam Bin Abdulaziz University; University of Khartoum.
    Sheremet, Mikhail
    Tomsk State University.
    Saffari Pour, Mohsen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer. Shahid Bahonar University of Kerman.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Phase-Transition Thermal Charging of a Channel-Shape Thermal Energy Storage Unit: Taguchi Optimization Approach and Copper Foam Inserts2021Inngår i: Molecules, ISSN 1431-5157, E-ISSN 1420-3049, Vol. 26, artikkel-id 1235Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Thermal energy storage is a technique that has the potential to contribute to future energy grids to reduce fluctuations in supply from renewable energy sources. The principle of energy storage is to drive an endothermic phase change when excess energy is available and to allow the phase change to reverse and release heat when energy demand exceeds supply. Unwanted charge leakage and low heat transfer rates can limit the effectiveness of the units, but both of these problems can be mitigated by incorporating a metal foam into the design of the storage unit. This study demonstrates the benefits of adding copper foam into a thermal energy storage unit based on capric acid enhanced by copper nanoparticles. The volume fraction of nanoparticles and the location and porosity of the foam were optimized using the Taguchi approach to minimize the charge leakage expected from simulations. Placing the foam layer at the bottom of the unit with the maximum possible height and minimum porosity led to the lowest charge time. The optimum concentration of nanoparticles was found to be 4 vol.%, while the maximu possible concentration was 6 vol.%. The use of an optimized design of the enclosure and the optimum fraction of nanoparticles led to a predicted charging time for the unit that was approximately 58% shorter than that of the worst design. A sensitivity analysis shows that the height of the foam layer and its porosity are the dominant variables, and the location of the porous layer and volume fraction of nanoparticles are of secondary importance. Therefore, a well-designed location and size of a metal foam layer could be used to improve the charging speed of thermal energy storage units significantly. In such designs, the porosity and the placement-location of the foam should be considered more strongly than other factors.

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  • 13.
    Ghalambaz, Soodabeh
    et al.
    Payame Noor Univ PNU, Dept Management, POB 19395-4697, Tehran, Iran..
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    A Scientometric Analysis of Energy Management in the Past Five Years (2018-2022)2022Inngår i: Sustainability, E-ISSN 2071-1050, Vol. 14, nr 18, s. 11358-, artikkel-id 11358Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Energy management is an essential part of the integration of renewable energy in energy systems, electric vehicles, energy-saving strategies, waste-heat recovery, and building energy. Although many publications considered energy management, no study addressed the connection between scientists, organizations, and countries. The present study provides a scientometric analysis that addresses the trend of publications and worldwide dynamic maps of connectivity and scientists, organizations, and countries and their contribution to energy management. The results showed that Javaid Nadeem published the most papers in the field of energy management (90) while Xiao Hu received the most citations (1394). The university with the highest number of publications in energy management is the Islamic Azad University (144 papers), while the Beijing Institute of Technology has received the most citations (2061 citations) and the largest h-index (28). China and the United States are in the first and second rank in terms of total publications, citations, and h-index. Pakistan has the most publications relative to the country's research and development investment level. The maps of co-authorship show islands of isolated groups of authors. This implies that the researchers in energy management are not well-connected. Bibliographic coupling of countries revealed China and USA are influential contributors in the field, and other countries were coupled mostly through these two countries.

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  • 14. Hosseini, Zahra Shah
    et al.
    Abidi, Awatef
    King Khalid Univ, Coll Sci Abha, Dept Phys, Abha 61421, Saudi Arabia.;Monastir Univ, Energy Engn Dept, Natl Engn Sch, Res Lab Metrol & Energy Syst, Monastir City 5000, Tunisia.;Sousse Univ, Higher Sch Sci & Technol Hammam Sousse, Sousse City 4011, Tunisia..
    Mohammadi, Sajad
    Mehryan, Seyed Abdollah Mansouri
    Islamic Azad Univ, Yasooj Branch, Young Researchers & Elite Club, Yasuj 7591493686, Iran..
    Hulme, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    A Fully Resolved Computational Fluid Dynamics Study of the Boundary Layer Flow of an Aqueous Nanoliquid Comprising Gyrotactic Microorganisms over a Stretching Sheet: The Validity of Conventional Similarity Models2021Inngår i: Mathematics, E-ISSN 2227-7390, Vol. 9, nr 21, s. 2655-, artikkel-id 2655Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When materials are processed in the form of sheets that are stretched, cooling is often required. Coolants have been developed to maximize the rate of heat transfer away from the sheet, including by adding nanoparticles and microorganisms to control the physical properties of the fluid. Such coolants perform well, but the interaction between them and the sheet is not yet fully understood. Most of the articles found in the literature have used similarity models to solve the set of governing equations. In this method, the governing equations can be mapped into a set of 1-D equations and solved easily. However, care should be taken when using this method as the validity of this method is ensured only in the fully developed region, far away enough from the extrusion slit. The present study, therefore, aims to explore the reliability of a similarity model by comparing it with a full computational fluid dynamics (CFD) approach. In this work, the boundary layer flow of a nanoliquid comprising gyrotactic microorganisms in both the developed and undeveloped regions of a stretching sheet is studied using computational fluid dynamics with the finite difference approach, implemented using FORTRAN. The results of the CFD method are compared against the similarity analysis results for the length of the developed and undeveloped regions. This study, for the first time, distinguishes between the undeveloped and fully developed regions and finds the region in which the similarity analysis is valid. The numerical results show that the critical Reynolds numbers for the boundary layers of the concentration of the nano-additives and of density of the microorganisms are equal. To achieve an agreement between the CFD and the similarity model within 5%, the Grashof number for the hydrodynamic boundary layer must be Gr < 10(5). Nonetheless, this length reduces significantly when the Grashof number increases from 10(5) to 10(6). The reduced Nusselt number, Nu(r), increases when the density difference of the microorganisms increases.

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  • 15. Hou, T. P.
    et al.
    Li, Y.
    Wu, K. M.
    Peet, Mathew James
    Hulme-Smith, Christopher
    Guo, L.
    Magnetic-field-induced magnetism and thermal stability of carbides Fe6-xMoxC in molybdenum-containing steels2016Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 102, s. 24-31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A hybrid method combining first-principles calculations and Weiss molecular field theory with thermodynamic data has been implemented to explore the origin of magnetic-field-induced precipitation behaviors for alloy carbides. The paramagnetic Mo atom disturbed the order of magnetic moment and resulted in a decrease in the Curie temperature for alloy carbide Fe<sub><it>6-x</it></sub>Mo<sub><it>x</it></sub>C. The temperature dependence of magnetic moment and saturation magnetization of Fe atoms at different Wyckoff positions, as well as the saturation or induced magnetization of Fe<sub><it>6-x</it></sub>Mo<sub><it>x</it></sub>C, decreased with increasing temperature. The higher Fe content and external magnetic field greatly increased the magnetization of alloy carbides. Two kinds of stella quadrangula lattices were employed to account for the total magnetism which was derived from the contribution of different Wyckoff sites of Fe atoms and Fe-C distances. The calculated total free energy taking into account magnetic field, temperature and composition was sufficient to provide quantitative agreement with experiment. The investigation of the effects of external field on the carbide precipitation behaviors led to a better understanding of the magnetic-field-induced phase transformation mechanism in heat resistant steels.

  • 16. Hou, T. P.
    et al.
    Peet, Mathew James
    Hulme-Smith, Christopher
    University Of Cambridge.
    Wu, K. M.
    Li, Y.
    Guo, L.
    The determining role of magnetic field in iron and alloy carbide precipitation behaviors under the external field2016Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 120, s. 76-79Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A combined approach to calculate the thermodynamic properties of iron and alloy carbides including the thermal and magnetic contribution is derived. Special emphasis is placed on the role of Fe and Mo to the Gibbs free energy. Lower Mo concentration in the carbides corresponds to a higher thermal Gibbs free energy change. The higher Fe content and external magnetic field greatly increase the induced magnetization, reducing the magnetic Gibbs free energy substantially and therefore increase the formation temperature. The stability of M 2 C and M 3 C are mainly determined by the thermal factors, whereas magnetic field has a predominant contribution for M 6 C.

  • 17. Hou, T. P.
    et al.
    Wu, K. M.
    Liu, W. M.
    Peet, M. J.
    Hulme-Smith, Christopher
    University Of Cambridge.
    Guo, L.
    Zhuang, L.
    Magnetism and high magnetic-field-induced stability of alloy carbides in Fe-based materials2018Inngår i: Scientific Reports, E-ISSN 2045-2322, Vol. 8, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Understanding the nature of the magnetic-field-induced precipitation behaviors represents a major step forward towards unravelling the real nature of interesting phenomena in Fe-based alloys and especially towards solving the key materials problem for the development of fusion energy. Experimental results indicate that the a pplied high magnetic field effectively promotes the precipitation of M 23 C 6 carbides. We build an integrated method, which breaks through the limitations of zero temperature and zero external field, to concentrate on the dependence of the stability induced by the magnetic effect, excluding the thermal effect. We investigate the intimate relationship between the external field and the origins of various magnetics structural characteristics, which are derived from the interactions among the various Wyckoff sites of iron atoms, antiparallel spin of chromium and Fe-C bond distances. The high-magnetic-field-induced exchange coupling increases with the strength of the external field, which then causes an increase in the parallel magnetic moment. The stability of the alloy carbide M 23 C 6 is more dependent on external field effects than thermal effects, whereas that of M 2 C, M 3 C and M 7 C 3 is mainly determined by thermal effects.

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  • 18.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Flow behavior of magnetic steel powder2022Inngår i: Particulate Science and Technology, ISSN 0272-6351, E-ISSN 1548-0046, Vol. 40, nr 5, s. 576-588Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Flow occurs in most powder-based processes, opposed by various cohesive forces. Magnetism is often overlooked for metal powders. Here, flowability and magnetization were measured for a dual-phase steel powder in size fractions from (Formula presented.) to > 200 µm. The finest fraction did not flow through a Hall flowmeter, then flow time increased continuously with particle size from 12 ± 1 s for the next fraction ((Formula presented.)) to > 28 ± 0.5 s for > 200 µm. Drying had little effect. Key metrics derived from shear tests gave no overall relationship between flow behavior and particle size. Magnetism was considered the most likely reason for this behavior. Magnetometry showed a remanent magnetization of (Formula presented.) which causes ∼ 5 µN cohesion between 200 µm diameter particles. X-ray diffractometry showed that the powder contained 77 wt%-80 wt% of (magnetic) martensite. Liquid bridging, van der Waals forces and friction (in the Hall flowmeter geometry) contribute 50 µN, 0.08 µN and 4 µN, respectively, to cohesion in 200 µm particles. These results can be used to help explain flow behavior in other magnetic powders and allow optimization of powders and/or powder-based processes. 

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  • 19.
    Hulme-Smith, Christopher
    University Of Cambridge.
    Improving the thermal stability of bulk nanocrystalline steel2015Inngår i: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A recent innovation in steel metallurgy allows the formation of carbide-free bainite at temperatures below 300 °C, with plates of bainitic ferrite ≈100 nm wide separated by films of carbon-enriched retained austenite ≈50 nm wide, which are inexpensive to make and show an impressive combination of strength and toughness. Heating the material leads to the transformation of austenite to cementite and untempered martensite, rendering the steel weak and brittle. The current work uses thermodynamic modelling to design new alloys with increased resistance to thermal decomposition while retaining desirable mechanical properties. All three alloys studied were found to consist of nanostructured carbide-free bainite using electron microscopy and X-ray diffraction and exhibited improved thermal stability, compared to existing alloys.

  • 20. Hulme-Smith, Christopher
    et al.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Erratum to "Mechanical properties of thermally-stable, nanocrystalline bainitic steels" [Materials Science & Engineering A 700 (2017) 714-720]2017Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 704, nr AugustArtikkel i tidsskrift (Annet vitenskapelig)
  • 21.
    Hulme-Smith, Christopher
    et al.
    University Of Cambridge.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Mechanical properties of thermally-stable, nanocrystalline bainitic steels2017Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 700, s. 714-720Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two novel, thermally stable bulk nanocrystalline bainitic steels were subjected to a range of mechanical tests. One alloy, containing 0.72 wt% carbon exhibited an ambient-temperature 0.2% proof strength of 1500 MPa and a fracture toughness of 64.6 MPa m<sup>1/2</sup> after the bainite transformation. The other, containing 0.45 wt% carbon and 13.2 wt% nickel, had a 0.2% proof stress of 1000 MPa and a fracture toughness of 103.8 MPa m<sup>1/2</sup> . Both steels showed excellent creep resistance, with a rupture life at 450 ˚C and 700 MPa of 114 h and 94.8 h, respectively. Both displayed fatigue lives consistent with other steels of similar structure in the literature. After thermal exposure at 480 ˚C for 8 d, both steels increased in strength to 1800 MPa, and 1600 MPa, respectively. The latter steel reduced in fracture toughness to 19.6 MPa m<sup>1/2</sup> . These alloys are suitable for a range of engineering applications and remain so after thermal exposure. Combined with impressive high-temperature performance, this

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  • 22.
    Hulme-Smith, Christopher
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hari, Vignesh
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mellin, P.
    Benchtop Spreadability Measurement of Powder2020Inngår i: Proceedings - Euro PM2020 Congress and Exhibition, European Powder Metallurgy Association (EPMA) , 2020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The behaviour of metal powders when they are spread into thin layers is critical for powder bed additive manufacturing and other processes. However, there is no accepted test procedure to quantify this behaviour. There is not even an accepted metric that can be used to assess this property. This increases the difficulty of developing new powders for additive manufacturing. The current study proposes test and analysis procedures that minimise the influence of operators and are aimed at providing maximum repeatability and reproducibility while minimising the need for specialist analysis equipment. Initial testing shows that a powder with good flow properties behaves as expected as a function of recoater speeds and always exhibits superior spread metrics to powders with poor flow properties. This provides an important step towards the establishment of a robust, inexpensive test that can help additive manufacturing to grow in new industries. 

  • 23.
    Hulme-Smith, Christopher
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hari, Vignesh
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mellin, Pelle
    Swerim AB.
    Spreadability Testing of Powder for Additive Manufacturing2020Inngår i: Berg- und Huttenmännische Monatshefte (BHM), ISSN 0005-8912, E-ISSN 1613-7531, Vol. 166, nr 1, s. 9-13Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The spreading of powders into thin layers is a critical step in powder bed additive manufacturing, but there is no accepted technique to test it. There is not even a metric that can be used to describe spreading behaviour. A robust, image-based measurement procedure has been developed and can be implemented at modest cost and with minimal training. The analysis is automated to derive quantitative information about the characteristics of the spread layer. The technique has been demonstrated for three powders to quantify their spreading behaviour as a function of layer thickness and spreading speed.

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  • 24.
    Hulme-Smith, Christopher
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Kamalasekaran, Arun
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Sundin, Stefan
    Simulations of gas flow in gas atomisation of liquid metals and validation experiments2021Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The production of metal powder by gas atomisation generates feedstock for many manufacturing techniques, including hot isostatic pressing, laser cladding and, of current interest, powder bed additive manufacturing. While many thousands of alloys are commercially available in bulk form, fewer than fifty are widely available as powders suitable for additive manufacturing. This is due to difficulties in controlling droplet size distribution and avoiding particle defects. Indeed, a typical gas atomisation process that attempts to make powder for powder bed additive manufacturing achieves a yield of suitable powder below 50%. Several studies have simulated the gas atomisation process or part of it, but few validate the models directly. The current work aims to take a first step towards making a holistic and fully validated model for gas atomisation. The gas flow from de Laval nozzles under conditions similar to those used in gas atomisation has been simulated using computational fluid dynamics and experiments to validate these simulations have been performed using shadowgraphy. A validated model can be used as part of a larger model to predict the phenomena that occur in gas atomisation and thereby refine the process to improve the production yield of powders, especially for additive manufacturing.

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  • 25.
    Hulme-Smith, Christopher
    et al.
    Materials Science and Metallurgy, University of Cambridge, UK.
    Lonardelli, I.
    Materials Engineering and Industrial Technologies, University of Trento, Italy.
    Dippel, A. C.
    Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Materials Science and Metallurgy, University of Cambridge, UK.
    Experimental evidence for non-cubic bainitic ferrite2013Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 69, nr 5, s. 409-412Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first evidence is provided for the existence of a tetragonal or slightly orthorhombic unit cell of bainitic ferrite. It supports the hypothesis that the excess carbon that persists in the ferrite, which is in contact with austenite, is a consequence of an increased solubility due to the change in symmetry from the conventional cubic unit cell. The deviations from the cubic cell are maintained to elevated temperatures, as expected from an increased solubility of carbon in the ferrite.

  • 26.
    Hulme-Smith, Christopher
    et al.
    Materials Science and Metallurgy, University of Cambridge, UK.
    Lonardelli, I.
    Materials Engineering and Industrial Technologies, University of Trento, Italy.
    Peet, Mathew James
    Materials Science and Metallurgy, University of Cambridge, UK.
    Dippel, A. C.
    Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Materials Science and Metallurgy, University of Cambridge, UK.
    Enhanced thermal stability in nanostructured bainitic steel2013Inngår i: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 69, nr 2, s. 191-194Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report an attempt at increasing the thermal stability of nanocrystalline bainite to tempering heat treatments by enhancing the silicon concentration of the alloy. Validation experiments have been conducted using synchrotron X-irradiation during tempering heat treatment. It is found that the change in alloying successfully stabilizes the austenite at elevated temperatures by retarding cementite formation to temperatures as high as 500 ˚C. Other changes reflected in the lattice parameters of the major phases have revealed further information about the mechanisms involved.

  • 27.
    Hulme-Smith, Christopher
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Mellin, P.
    Marchetti, Lorenzo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hari, Vignesh
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Uhlirsch, M.
    Strandh, E.
    Saeidi, K.
    Dubiez-Le Goff, S.
    Saleem, S.
    Pettersson, V.
    Memarpour, A.
    Jakobsson, K.
    Meurling, F.
    A practicable and reliable test for metal powder spreadability: development of test and analysis technique2023Inngår i: Progress in Additive Manufacturing, ISSN 2363-9512, Vol. 8, nr 3, s. 505-517Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A crucial step in the powder bed metal additive manufacturing process is the formation of a thin layer of powder on top of the existing material. The propensity of the powder to form thin layers under the conditions used in additive manufacturing is critically important, but no test method has yet been established to measure this characteristic, which is sometimes referred to as spreadability. The current work spreads a single layer of powder using commercial equipment from the paint and food industries and derives the density of a layer of powder, which is of a similar thickness to that in additive manufacturing. Twenty-four powders from eight suppliers have been tested and the density of the layers has been measured as a function of various parameters. Twenty-two of the powders successfully form thin layers, with a density of at least 40% of each powder’s apparent density. Hall flow time did not correlate with the spread layer density, although the two powders that did not spread did not pass through the Hall funnel. The roughness of the plate onto which the powder was spread, the recoater speed, the layer thickness, particle size and aspect ratio all affect the measured layer density. Results of the new test are repeatable and reproducible. These findings can be used to develop a test for spreadability for metal powders that can be used for additive manufacturing, which will help to improve the quality of printed components. 

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  • 28.
    Hulme-Smith, Christopher
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi. Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England..
    Ooi, S. W.
    Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England..
    Bhadeshia, H. K. D. H.
    Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England..
    Intermetallic-strengthened nanocrystalline bainitic steel2018Inngår i: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 34, nr 16, s. 1976-1979Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A new thermally stable, nanocrystalline bainitic steel has been developed, rich in nickel and aluminium. During tempering, it is expected that a significant quantity of intermetallic precipitates will form. This was confirmed by X-ray diffractometry, scanning transmission electron microscopy, Fourier transform analysis of atomic column images, energy dispersive X-ray spectroscopy and selected area electron diffraction. These are the first intermetallics to be produced in a nanocrystalline bainitic steel.

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  • 29.
    Hulme-Smith, Christopher
    et al.
    Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
    Ooi, Shgh Woei
    Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, UK.
    Thermally Stable Nanocrystalline Steel2017Inngår i: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48, nr 10, s. 4957-4964Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Two novel nanocrystalline steels were designed to withstand elevated temperatures without catastrophic microstructural changes. In the most successful alloy, a large quantity of nickel was added to stabilize austenite and allow a reduction in the carbon content. A 50 kg cast of the novel alloy was produced and used to verify the formation of nanocrystalline bainite. Synchrotron X-ray diffractometry using in situ heating showed that austenite was able to survive more than 1 hour at 773 K (500 ˚šC) and subsequent cooling to ambient temperature. This is the first reported nanocrystalline steel with high-temperature capability.

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  • 30.
    Hulme-Smith, Christopher
    et al.
    Materials Science and Metallurgy, University of Cambridge, UK.
    Peet, Mathew James
    Materials Science and Metallurgy, University of Cambridge, UK.
    Lonardelli, I.
    Materials Engineering and Industrial Technologies, University of Trento, Italy.
    Dippel, Ann Christin
    Deutsches Elektronen-Synchrotron DESY, Hamburg, Germany.
    Bhadeshia, Harshad Kumar Dharamshi Hansraj
    Materials Science and Metallurgy, University of Cambridge, UK.
    Further evidence of tetragonality in bainitic ferrite2015Inngår i: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 31, nr 2, s. 254-256Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There is growing evidence that bainitic ferrite which retains a substantial amount of carbon in solid solution does not have cubic symmetry. We provide additional data on a different nanostructured bainitic steel to support this evidence, based on synchrotron X-ray diffraction experiments. The data are consistent only with a displacive transformation mechanism for bainite.

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  • 31.
    Hulme-Smith, Christopher
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi. University Of Cambridge.
    Pickering, Ed
    University of Cambridge.
    Steeling the Show2012Inngår i: The Naked Scientists: Science Articles and FeaturesArtikkel, forskningsoversikt (Annet (populærvitenskap, debatt, mm))
  • 32.
    Ibrahim, Mohammad
    et al.
    Department of Engineering Sciences, University of Agder (UiA), Grimstad, 4879, Norway.
    Du, Qiang
    SINTEF Industry, Department of Metal Production and Processing, Oslo, 0314, Norway.
    Hovig, Even Wilberg
    SINTEF Industry, Department of Metal Production and Processing, Oslo, 0314, Norway.
    Grasmo, Geir
    Department of Engineering Sciences, University of Agder (UiA), Grimstad, 4879, Norway.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Aune, Ragnhild E.
    Department of Engineering Sciences, University of Agder (UiA), Grimstad, 4879, Norway; Department of Materials Science and Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, 7491, Norway.
    Gas-Atomized Nickel Silicide Powders Alloyed with Molybdenum, Cobalt, Titanium, Boron, and Vanadium for Additive Manufacturing2023Inngår i: Metals, ISSN 2075-4701, Vol. 13, nr 9, artikkel-id 1591Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Nickel silicides (NiSi) are renowned for their ability to withstand high temperatures and resist oxidation and corrosion in challenging environments. As a result, these alloys have garnered interest for potential applications in turbine blades and underwater settings. However, their high brittleness is a constant obstacle that hinders their use in producing larger parts. A literature review has revealed that incorporating trace amounts of transition metals can enhance the ductility of silicides. Consequently, the present study aims to create NiSi-based powders with the addition of titanium (Ti), boron (B), cobalt (Co), molybdenum (Mo), and vanadium (V) for Additive Manufacturing (AM) through the process of gas atomization. The study comprehensively assesses the microstructure, phase composition, thermal properties, and surface morphology of the produced powder particles, specifically NiSi11.9Co3.4, NiSi10.15V4.85, NiSi11.2Mo1.8, and Ni-Si10.78Ti1.84B0.1. Commonly used analytical techniques (SEM, EDS, XRD, DSC, and laser diffraction) are used to identify the alloy configuration that offers optimal characteristics for AM applications. The results show spherical particles within the size range of 20–63 μm, and only isolated satellites were observed to exist in the produced powders, securing their smooth flow during AM processing.

  • 33.
    Kuthe, Sudhanshu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Swiss Fed Inst Technol, Composite Mat & Adapt Struct Lab, Dept Mech & Proc Engn, Leonhardstr 21, CH-8092 Zurich, Switzerland..
    Schlothauer, Arthur
    Swiss Fed Inst Technol, Composite Mat & Adapt Struct Lab, Dept Mech & Proc Engn, Leonhardstr 21, CH-8092 Zurich, Switzerland..
    Bodkhe, Sampada
    Swiss Fed Inst Technol, Composite Mat & Adapt Struct Lab, Dept Mech & Proc Engn, Leonhardstr 21, CH-8092 Zurich, Switzerland.;Polytech Montreal, Dept Mech Engn, CP 6079,Succ Ctr Ville, Montreal, PQ H3C 3A7, Canada..
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Ermanni, Paolo
    Swiss Fed Inst Technol, Composite Mat & Adapt Struct Lab, Dept Mech & Proc Engn, Leonhardstr 21, CH-8092 Zurich, Switzerland..
    3D printed mechanically representative aortic model made of gelatin fiber reinforced silicone composite2022Inngår i: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 320, s. 132396-, artikkel-id 132396Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive manufacturing (AM) is a useful technology to produce artificial aortic models for the training of transcatheter aortic valve replacement (TAVR) surgery. With AM, the models can be tailored towards the individualized aortic anatomy of patients. Most of these reported models so far are manufactured using single rubber-like materials. However, such materials do not replicate the mechanical properties of natural aortic tissue, especially the stress-strain response in higher strain (>0.1) regions. This could be problematic for surgeons training for surgeries using a model which does not exhibit properties of the real aorta. To overcome this limitation, we developed a 3D-printed, mechanically representative aortic model comprising gelatin fibers and silicone. The model is promising as a realistic analog of aortic sinus for mock TAVR surgery. Computerized tomography data was analyzed beforehand using medical imaging to identify the anatomy of a specific patient's aortic sinus and the surrounding blood vessels. A novel silicone matrix composite reinforced with gelatin fibers designed in this work was tested and compared with the stress-strain response of aortic tissue. Such a model comprising both patient-specific geometries as well as realistic material properties of aortic tissue can be helpful for the development of next-generation medical phantoms.

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  • 34.
    Law, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad processmetallurgi.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Matsushita, Taishi
    Jönköping University.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi.
    Assessment of Mechanisms for Particle Migration in Semi-Solid High Pressure Die Cast Aluminium-Silicon AlloysInngår i: Journal of Manufacturing and Materials Processing, ISSN 2504-4494Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract: In semi-solid metal high pressure die casting, as well as in conventional high pressure die casting, it is common to find a defect band just below the surface of the component. The formation of these bands are not yet fully understood. However, there are several theories as how they occur. Previous research by the lead author suggested that aluminium globules migrate toward the centre of the component, leaving a band behind. In the present work the formation of these bands is investigated theoretically by reviewing suitable potential mechanisms from literature. It was found that it is not possible to positively identify the mechanism responsible for the observed banding using theoretical considerations alone. However, from the mechanisms examined there are two that are identified as the most probable: Saffman lift force and the Mukai-Lin-Laplace effect. Further testing is required to identify the mechanism that is causing the migration of the aluminium globules and suitable tests are proposed.

    Fulltekst (pdf)
    fulltext
  • 35.
    Law, Madeleine
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Matsushita, Taishi
    Jönköping Universitet.
    Jönsson, Pär
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Assessment of Mechanisms for Particle Migration in Semi-Solid High Pressure Die Cast Aluminium-Silicon Alloys2020Inngår i: Journal of manufacturing and materials processing, ISSN 1042-6914, Vol. 4, nr 51Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In semi-solid metal high pressure die casting and in conventional high pressure die casting, it is common to find a defect band just below the surface of the component. The formation of these bands is not fully understood. However, there are several theories as how they occur, and it has been suggested that segregation is caused by the migration of aluminium-rich externally solidified crystals. In the present work the formation of these bands is investigated theoretically by reviewing suitable potential mechanisms for the migration of such crystals. Two mechanisms are identified as the most probable: Saffman lift force and the Mukai-Lin-Laplace effect. However, it was not possible to identify which of these two mechanisms acted in the case studies. Further testing is required to identify the mechanism that is causing the migration of the aluminium globules and suitable tests are proposed.

    Fulltekst (pdf)
    fulltext
  • 36.
    Lin, Zeyu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Produktionsutveckling.
    Surreddi, Kumar Babu
    Materials Technology School of Information and Technology Dalarna University SE‐791 88 Falun Sweden.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Dadbakhsh, Sasan
    KTH, Skolan för industriell teknik och management (ITM), Produktionsutveckling.
    Rashid, Amir
    KTH, Skolan för industriell teknik och management (ITM), Produktionsutveckling.
    Influence of Electron Beam Powder Bed Fusion Process Parameters on Transformation Temperatures and Pseudoelasticity of Shape Memory Nickel Titanium2023Inngår i: Advanced Engineering Materials, ISSN 1438-1656, E-ISSN 1527-2648Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electron beam powder bed fusion (PBF-EB) is used to manufacture dense nickel titanium parts using various parameter sets, including the beam current, scan speed and post cooling condition. The density of manufactured NiTi parts are investigated with relation to the linear energy input. The results implies the part density increases with increasing linear energy density to over 98% of the bulk density. With a constant energy input, a combination of low power and low scan speed leads to denser parts. This is attributed to lower electrostatic repulsive forces from lower number density of the impacting electrons. After manufacturing, densest parts with distinct parameter sets are categorized into three groups: i) high power with high scan speed and vacuum slow cooling, ii) low power with low scan speed and vacuum slow cooling and iii) low power with low scan speed and medium cooling rate in helium gas. Among these, a faster cooling rate suppresses phase transformation temperatures, while vacuum cooling combinations do not affect the phase transformation temperatures significantly. All the printed parts in this study exhibit almost 8% pseudoelasticity regardless of the process parameters, while the parts cooled in helium have a higher energy dissipation efficiency ( ), which implies faster damping of oscillations. 

    Fulltekst (pdf)
    fulltext
  • 37.
    Liu, Yu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer. KTH-Royal Institute of Technology.
    Ersson, Mikael
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer. KTH-Royal Institute of Technology.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer. KTH-Royal Institute of Technology.
    Liu, Heping
    Central Iron & Steel Research Institute, 76 Xueyuan Nanlu, Beijing 100081, P. R. China..
    Jönsson, Pär Göran
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer. KTH-Royal Institute of Technology.
    An Experimental and Mathematical Work on Single Bubble Behavior under Reduced PressureManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    During secondary steelmaking, argon bubbles are often passed through molten steel to ensure a clean and homogeneous product. The behavior of the bubbles and the capacity of the bubbles to stir the melt and remove impurities depends on their size, shape, and velocity. These factors depend on the ambient pressure of the melt, the temperature and flow rate of the gas and the geometry of the gas nozzles. There have been many studies that investigate the behavior of bubbles when the melt is under atmospheric pressure, but few when the melt is held under vacuum. This makes it difficult to optimize the argon blowing process. The current study addresses this lack of knowledge by studying bubble behavior when the melt is under vacuum. Physical modeling was used to analyze the effects of the reduced pressure and nozzle diameter on the bubbles’ initial diameter and ascent behavior in a molten steel. Moreover, a multiphase fluid dynamics solver for compressible fluids called ‘compressibleInterFoam’ was validated and used. Increasing the flow rate leads to larger initial bubble diameters and more frequent bubble formation, and increasing the nozzle diameter leads to larger initial bubble diameters and less frequent bubble formation. Decreasing the subjected pressure causes the bubble diameter to increase substantially but bubbles to form less frequently. For flow rates in the range of 5.0(mL·min-1)STP to 2000(mL·min-1)STP, the bubble diameter ranges from 6.0mm to 20.0mm. The frequency of bubble generation initially increases with flow rate before reaching a constant value. During the ascent, a bubble will shed several small bubbles at the bottom to reach a constant shape. In the steel-argon system, under laminar flow conditions, the maximum bubble width under a pressure of 0.2bar is 65mm and is 58mm under a pressure of 2.0bar. As the surrounding pressure increases, the maximum size of the bubble under the steady condition will decrease. These findings can be used to determine the bubble behaviors and to optimize the conditions of argon blowing to produce steel that is sufficiently clean, while minimizing argon usage.

  • 38.
    Marchetti, Lorenzo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Comparative study of metallic powder flowability testing methods2019Inngår i: Euro PM 2019 Congress and Exhibition, European Powder Metallurgy Association (EPMA) , 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The flowability of a powder is an important characteristic that depends on both the physical properties of the particle ensemble and the testing method, equipment and conditions. In additive manufacturing processes, flowability can be an indicator of the quality of the deposited powder layer and, therefore, the final component. In this study, we carried out a comparison of the flowability of different steel powders and the data generated by a range of testing methods. Each sample had a unique combination of composition and particle size range. Flowability testing equipment and methods were selected according to standards (angle of repose, Hausner Ratio, Hall flow) or published literature (FT4 Powder Rheometer). We measured the flowability of different samples for each testing method, in order to obtain a first dataset. Secondly, we evaluated the correlations between different flowability testing methods.

  • 39.
    Marchetti, Lorenzo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Flowability of steel and tool steel powders: A comparison between testing methods2021Inngår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 384, s. 402-413Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Theflow behaviour of a powder is critical to its performance in many industrial applications and manufacturing processes. Operations such as powder transfer, die filling and powder spreading all rely on powder flowability. Multiple testing methods can help in assessing flowability, but it is not always clear which may better represent specific flow conditions or how different metrics correlate. This study compares 8 different flowability testing methods using 11 steel powders varying in chemistries and size fractions. Regression analysis was used to test the relationship between each flowability metric obtained. Some metrics, such as the conditioned bulk density,relate to many flowability indicators. Others, such as the basic flowability energy, show poor correlations to othervariables, likely describing different aspects of the powder flow behaviour. When two metrics show a strong correlation, as between conditioned bulk density and Hausner ratio, a numerical relationship is derived: CBD =−(5.65 ± 0.86)HR g cm−3.

    Fulltekst (pdf)
    fulltext
  • 40.
    Marchetti, Lorenzo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Mellin, P.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Effects of Humidity on the Flowability of Steel Powders2020Inngår i: Proceedings - Euro PM2020 Congress and Exhibition, European Powder Metallurgy Association (EPMA) , 2020Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Humidity and temperature can vary across the world. For this reason, during storage and processing, batches of the same powder may interact with diverse environmental conditions and eventually vary in their properties. For example, a higher atmospheric water vapour content could increase the water adsorbed on the surface of individual powder particles. This adsorbed water can alter the surface interactions between particles, affecting its flow behaviour. In this study, we measured the flow behaviour of various sieve fractions and steel powders in different environmental conditions. We set the environmental conditions in a C1000-40 climate chamber to different levels of relative humidity and temperature. The powder samples and a Freeman FT4 powder rheometer were placed in the climate chamber and equilibrated for 72h. Subsequently, we tested the flow behaviour using two different programs of the powder rheometer. Ultimately, we found that powder flowability is adversely affected by increased humidity.

  • 41.
    Marchetti, Lorenzo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Mellin, P.
    Swerim AB, Kista, Sweden.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Negative impact of humidity on the flowability of steel powders2022Inngår i: Particulate Science and Technology, ISSN 0272-6351, E-ISSN 1548-0046, Vol. 40, nr 6, s. 722-736Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Atmospheric humidity is introduced into powders during handling, transportation, and storage. High moisture content can increase cohesive forces between particles and make it difficult to spread a powder into thin layers in powder bed processes or to fill a mold in processes such as press-and-sinter. Furthermore, water can cause porosity and uptake of oxygen in the final component, damaging its mechanical properties. In this study, a Freeman FT4 powder rheometer was placed inside a climate chamber. Both flowability and shear tests were performed on four steel powders under a range of humidity and temperatures. Basic flowability energy and specific energy were both found to increase significantly with humidity (typically increase by 50% for 80% of relative humidity compared to dry conditions) and were insensitive to temperature change (10–30 °C). Conversely, the behavior of the powders under shear was neither sensitive to relative humidity nor temperature. Measurements of moisture content revealed that finer powders contained more moisture than coarser ones, but the moisture content was not correlated with humidity, probably due to shortcomings with the measurement method. This knowledge can be used to optimize powder processing conditions.

    Fulltekst (pdf)
    fulltext
  • 42.
    Marchetti, Lorenzo
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Mellin, Pelle
    Swerim AB, Kista, Sweden.
    Neveu, Aurélien
    Granutools, Liege, Belgium.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    On Metal Powder Tribocharging and Humidity Adsorption2022Inngår i: World PM 2022 Congress Proceedings, European Powder Metallurgy Association (EPMA) , 2022Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this work, three characterization techniques were applied to a set of alloys in fine powder form (TiAl6V4, AlSi10Mg, AlSi7, 316L, ferritic stainless steel, martensitic stainless steel and WC-Co-mixes). We sought deeper understanding of response to humidity and flowability as a result of the powder alloy. Slight tribo-charging (induced and measured using a GranuCharge setup) against metal surfaces was found to occur for all alloys. Although the accumulated charge was small and dissipated quickly. Greater charging occurs if the environment is humid, and if the powder slides against plastic surfaces. Dynamic Vapor Sorption (DVS) was employed to understand the adsorption capacity of powders. It showed that WC-Co-mixes adsorbed much more humidity than the other materials. Some alloys retained some of the adsorbed mass when humidity returned to normal conditions. RPA was tested on powders during exposure to 20-98% RH, which above 80% RH caused declining flowability.

  • 43.
    Mellin, Pelle
    et al.
    Swerim AB.
    Rashidi, Masoud
    Chalmers University of Technology.
    Fischer, Marie
    Chalmers University of Technology.
    Nyborg, Lars
    Chalmers University of Technology.
    Marchetti, Lorenzo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Uhlirsch, Markus
    Swerim AB.
    Strondl, Annika
    Swerim AB.
    Moisture in Metal Powder and Its Implication for Processability in L-PBF and Elsewhere2020Inngår i: Berg- und Huttenmännische Monatshefte (BHM), ISSN 0005-8912, E-ISSN 1613-7531, Vol. 166, nr 1, s. 33-39Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The impact of moisture on flowability and spread- ability is discussed. More notably we also present research on the impact of moisture on built nickel-base material. One lot of a newly opened Hastelloy X (HX) L-PBF powder was split into two equal batches. One batch was moisturized using a programmable climate chamber, the other was un- treated. We built bars with both batches for mechanical testing, in an EOS M100, with a cold build plate. The mois- ture content of the two powder batches, before and after the build-jobs, were determined using Karl Fischer titration (KF). Regarding the periodical monitoring of moisture con- tent, it is not needed according to the findings of this paper. More moisture contributes to a slightly higher O-content in the built material, and in turn, a very slight reduction in im- pact toughness. If a newly purchased powder exhibits poor flowability or high oxygen content, the analysis using oven- desorption followed by KF is recommended. If the moisture content is high, a drying of the powder is recommended

    Fulltekst (pdf)
    fulltext
  • 44. Momeni Dolatabadi, Amir
    et al.
    Saffari Pour, Mohsen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mousavi Ajarostaghi, Seyed Soheil
    Poncet, Sébastien
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Last stage stator blade profile improvement for a steam turbine under a non-equilibrium condensation condition: A CFD and cost-saving approach2023Inngår i: Alexandria Engineering Journal, ISSN 1110-0168, E-ISSN 2090-2670, Vol. 73, s. 27-46Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Non-equilibrium phenomena and related damages have always been one of the great concerns among researchers, designers, and industry managers. In power plants, the overhaul of turbines during a pre-planned schedule includes checking, repairing, and replacing damaged parts, which always challenge industry investors with variable costs. In this study, a modified profile for the stationary cascade blades of a 200 MW steam turbine is predicted by help of the Computational Fluid Dynamics (CFD) according to a cost-saving approach for a power plant. Wet steam model is used to investigate the flow behavior between the turbine blades, due to the sonication and non-equilibrium phenomena. The numerical model based on the Eulerian-Eulerian approach accounts the turbulence caused by the presence of droplets, condensation shocks and aerodynamics. At first, such model has been carefully validated against the available experimental data. Then, the entrance edge of the blade is designed considering different shapes and sizes. The flow behavior at the entrance edge region has been fully investigated. Finally, according to the criteria for measuring the non-equilibrium flow phenomena (erosion rate, Mach number, entropy, exergy destruction and transfer of mass and heat between flow phases), a modified model for the steam turbine blade considering the economic aspects has been presented. The modified blade model exhibits 88%, 0.13% and 7% reduction in the erosion rate, entropy generation and exergy destruction, respectively. Furthermore, the application of this modified blade profile save 456$ of the total monthly maintenance costs.

    Fulltekst (pdf)
    fulltext
  • 45. Ooi, S. W.
    et al.
    Ramjaun, T. I.
    Hulme-Smith, Christopher
    Morana, R.
    Drakopoulos, M.
    Bhadeshia, H. K. D. H.
    Designing steel to resist hydrogen embrittlement Part 2: precipitate characterisation2018Inngår i: Materials Science and Technology, ISSN 0267-0836, E-ISSN 1743-2847, Vol. 34, nr 14, s. 1747-1758Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel, low-alloy steel has been designed for use in the oil and gas industry. Its high strength and hydrogen trapping potential are derived from a martensitic microstructure containing a dispersion of fine vanadium-molybdenum alloy carbides that evolve during tempering. In this second paper, the effect of quench rate from austenitisation and tempering conditions are investigated with respect to the microstructure. The alloy loses its tempering resistance following slow-cooling from austenitisation as a result of MC precipitation, leading to vanadium depletion and significant M2C coarsening. This is predicted using computer simulation and confirmed by high energy X-ray diffraction, combined with electron microscopy.

    Fulltekst (pdf)
    fulltext
  • 46. Peet, Mathew James
    et al.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processteknologi. University Of Cambridge.
    Stone, H. J.
    Partitioning and supersaturation of carbon in low-temperature bainite2015Inngår i: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, 2015Konferansepaper (Fagfellevurdert)
  • 47.
    Persson, Fredrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Jönsson, Pär Göran
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Particle morphology of water atomised iron-carbon powders2022Inngår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 397, s. 116993-, artikkel-id 116993Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Water atomisation can produce metal powders faster and at lower cost than gas atomisation, but it is well known that the powder particles are irregular and may contain a large number of pores. The current study analyses three iron-carbon alloys with different superheats, produced as powder by water atomisation and compares the particle shapes and porosity in each. The alloy with the most carbon (4.2 wt%) showed the highest circularity (0.72) for 20-40 µm particles, but the lowest (0.59) for 180-210µm particles. This is consistent with collisions between droplets affecting particle shape. The lowest-carbon melt (0.22 wt%) solidified fastest, so underwent fewest collisions and showed similar circularity for all particle sizes. The breakdown of water to form hydrogen and the formation of hydrogen bubbles was the most likely cause of porosity. The findings of this study may be used to inform future water atomisation process design to control particle shape and minimise porosity.

  • 48.
    Valizadeh, Reza
    et al.
    Sharif University of Technology.
    Abbaspour, Madjid
    Sharif University of Technology.
    Rahni, Mohammad Taeibi
    Sharif University of Technology.
    Saffari Pour, Mohsen
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Shahid Bahonar University of Kerman.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Improved Wells Turbine using a Concave Sectional ProfileManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The current need to develop sustainable power sources has led to the development of ocean-based conversion systems. Wells turbine is a widely used converter in such systems which suffers from a lack of operational range and power production capacity under operational conditions. The profile named IFS which is concave in the post-mid-chord region, can produce significantly larger lift forces and show better separation behavior than the NACA profiles. In the present study, we tested this profile for the first time in a Wells turbine. The performance of six different blade designs with IFS and NACA profiles were evaluated and compared using a validated computational fluid dynamic model. Although the substitution of the NACA profile with the IFS profile in all cases increased the torque generated, the most efficient power generation and the largest efficient range were achieved in the design with varying thickness from the hub with a 0.15 thickness ratio reaching to the ratio of 0.2 at the tip. The operational span of this design with the IFS profile was 24.1% greater and the maximum torque generation was 71% higher than the case with the NACA profile. Therefore, the use of the IFS profile is suggested for further study and practical trials.

    Fulltekst (pdf)
    fulltext
  • 49.
    Zhao, Xiaoyu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Tillverkning och mätsystem.
    Rashid, Amir
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Tillverkning och mätsystem.
    Strondl, A.
    Swerim AB, Isafjordsgatan 28A, S-16440 Kista, Sweden.
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Stenberg, N.
    Swerim AB, Isafjordsgatan 28A, S-16440 Kista, Sweden.
    Dadbakhsh, Sasan
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Tillverkning och mätsystem.
    Role of Superficial Defects and Machining Depth in Tensile Properties of Electron Beam Melting (EBM) Made Inconel 7182021Inngår i: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024, Vol. 30, nr 3, s. 2091-2101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Since there is no report on the influence of machining depth on electron beam melting (EBM) parts, this paper investigated the role of superficial defects and machining depth in the performance of EBM made Inconel 718 (IN718) samples. Therefore, as-built EBM samples were analyzed against the shallow-machined (i.e., only removal of outer surfaces) and deep-machined (i.e., deep surface removal into the material) parts. It was shown that both as-built and shallow-machined samples had a drastically lower yield strength (970 ± 50 MPa), ultimate tensile stress (1200 ± 40 MPa), and ductility (28 ± 2%) compared to the deep-machined samples. This was since premature failure occurred due to various superficial defects. The superficial defects appeared in two levels, as (1) notches and pores on the surface and (2) irregular pores and cracks within the subsurface. Since the latter occurred down to 2 mm underneath the surface, shallow machining only exposed the subsurface defects to outer surfaces. Thus, the shallow-machined parts achieved only 68% and 8% of UTS and elongation of the deep-machined parts, respectively. This low performance occurred to be comparable to the as-built parts, which failed prematurely due to the high fraction surface voids and notches as well as the subsurface defects.

    Fulltekst (pdf)
    fulltext
  • 50.
    Zhao, Xiaoyu
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion.
    Rashid, Amir
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Tillverkning och mätsystem.
    Strondl, Annika
    Hulme-Smith, Christopher
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Stenberg, Niclas
    Dadbakhsh, Sasan
    KTH, Skolan för industriell teknik och management (ITM), Industriell produktion, Tillverkning och mätsystem.
    Role of Superficial Defects and Machining Depthin Tensile Properties of Electron Beam Melting (EBM)Made Inconel 7182021Inngår i: Journal of materials engineering and performance (Print), ISSN 1059-9495, E-ISSN 1544-1024Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Since there is no report on the influence of machining depth on electron beam melting (EBM) parts, this paper investigated the role of superficial defects and machining depth in the performance of EBM made Inconel 718 (IN718) samples. Therefore, as-built EBM samples were analyzed against the shallow-machined (i.e., only removal of outer surfaces) and deep-machined (i.e., deep surface removal into the material) parts. It was shown that both as-built and shallow-machined samples had a drastically lower yield strength (970 ± 50 MPa), ultimate tensile stress (1200 ± 40 MPa), and ductility (28 ± 2%) compared to the deep-machined samples. This was since premature failure occurred due to various superficial defects. The superficial defects appeared in two levels, as (1) notches and pores on the surface and (2) irregular pores and cracks within the subsurface. Since the latter occurred down to 2 mm underneath the surface, shallow machining only exposed the subsurface defects to outer surfaces. Thus, the shallow-machined parts achieved only 68% and 8% of UTS and elongation of the deep-machined parts, respectively. This low performance occurred to be comparable to the as-built parts, which failed prematurely due to the high fraction surface voids and notches as well as the subsurface defects.

    Fulltekst (pdf)
    Zhao2021_Article_RoleOfSuperficialDefectsAndMac
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