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  • 51.
    Mu, Wangzhong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Shibata, H.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ferrite Formation Dynamics and Microstructure Due to Inclusion Engineering in Low-Alloy Steels by Ti2O3 and TiN Addition2016In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 47, no 4, p. 2133-2147Article in journal (Refereed)
    Abstract [en]

    The dynamics of intragranular ferrite (IGF) formation in inclusion engineered steels with either Ti2O3 or TiN addition were investigated using in situ high temperature confocal laser scanning microscopy. Furthermore, the chemical composition of the inclusions and the final microstructure after continuous cooling transformation was investigated using electron probe microanalysis and electron backscatter diffraction, respectively. It was found that there is a significant effect of the chemical composition of the inclusions, the cooling rate, and the prior austenite grain size on the phase fractions and the starting temperatures of IGF and grain boundary ferrite (GBF). The fraction of IGF is larger in the steel with Ti2O3 addition compared to the steel with TiN addition after the same thermal cycle has been imposed. The reason for this difference is the higher potency of the TiOx phase as nucleation sites for IGF formation compared to the TiN phase, which was supported by calculations using classical nucleation theory. The IGF fraction increases with increasing prior austenite grain size, while the fraction of IGF in both steels was the highest for the intermediate cooling rate of 70 °C/min, since competing phase transformations were avoided, the structure of the IGF was though refined with increasing cooling rate. Finally, regarding the starting temperatures of IGF and GBF, they decrease with increasing cooling rate and the starting temperature of GBF decreases with increasing grain size, while the starting temperature of IGF remains constant irrespective of grain size.

  • 52.
    Mu, Wangzhong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Shibata, Hiroyuki
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Jönsson, Pär Göran
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ferrite Formation Dynamics and Microstructures in Inclusion Engineered Steels with Ti2O3 and TiN AdditionsManuscript (preprint) (Other academic)
    Abstract [en]

    The dynamics of intragranular ferrite (IGF) formation in inclusion engineered steels with Ti2O3 and TiN additions were investigated using in-situ high temperature confocal laser scanning microscopy (CLSM). Furthermore, the chemical composition of the inclusions and the final microstructures after continuous cooling was investigated using electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD), respectively. The results show that there is a significant effect of the chemical composition of the inclusions, the cooling rate and the prior austenite grain size on the phase fractions and the starting temperatures of IGF and grain boundary ferrite (GBF) formation. The fraction of IGF is larger in the steel with Ti2O3 addition compared to the steel with TiN addition after the same thermal cycle has been imposed. This is because the TiOx phase provides more potent nucleation sites for IGF than the TiN phase does. The fraction of IGF in the steels was highest after at an intermediate cooling rate of 70 ºC/min since competing phase transformations were avoided, however, the IGF was refined with increasing cooling rate. In addition, the IGF fraction increases and the starting temperature of GBF decreases with the increasing prior austenite grain size, however, the starting temperature of IGF keeps almost the value when the grain size changes.

  • 53.
    Mu, Wangzhong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Shibata, Hiroyuki
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Combination of in situ microscopy and calorimetry to study austenite decomposition in inclusion engineered steels2015In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344XArticle in journal (Refereed)
    Abstract [en]

    In situ high-temperature confocal laser scanning microscopy and differential scanning calorimetry studies of ferrite formation in inclusion engineered (Ti2O3 and TiN) steels have been performed. The applied methodology allows distinction between intragranular ferrite, grain boundary ferrite, and pearlite. The effect of the inclusions and cooling rates on the initiation of phase transformation and the final microstructure is discussed. It is concluded that the applied hybrid methodology could provide vital details of solid-state phase transformations within the field of inclusion engineering.

  • 54.
    Nabeel, Muhammad
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Frykholm, R.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Influence of alloying elements on Ni distribution in PM steels2014In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 57, no 2, p. 111-118Article in journal (Refereed)
    Abstract [en]

    Powder metallurgical (PM) steels with elemental Ni additions exhibit non-homogenous microstructures with soft Ni rich areas, lean in C, after conventional sintering. Though, the exact correlation between the distribution of Ni and mechanical properties is not well known and depends on the conditions, e.g. the load state, it is desirable to be able to control the distribution of Ni since it plays a major role in the properties of Ni PM components. By introducing other alloying elements, the microstructure homogeneity of Ni containing PM steels, can be influenced. Thus, the effect of common alloying elements on the homogeneity of sintered microstructures has been investigated in the present work. It is found that additions of either C or Mo have minor effect on Ni distribution in the Fe-Ni system. However, addition of both C and Mo to Fe-Ni improves the Ni distribution. In addition, a strong interaction between Ni and Cu is observed and it enhances the Ni homogeneity. Furthermore, the influence of Cu is more pronounced in presence of C.

  • 55.
    Naraghi, Reza
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Spontaneous and Deformation-Induced Martensite in Austenitic Stainless Steels with Different Stability2011In: STEEL RES INT, ISSN 1611-3683, Vol. 82, no 4, p. 337-345Article in journal (Refereed)
    Abstract [en]

    The fraction and microstructure of spontaneous and deformation-induced martensite in three austenitic stainless steels with different austenite stability have been investigated. Samples were quenched in brine followed by cooling in liquid nitrogen or plastically deformed by uniaxial tensile testing at different initial temperatures. In-situ ferritescope measurements of the martensite fraction was conducted during tensile testing and complemented with ex-situ X-ray diffractometry. The microstructures of quenched and deformed samples were examined using light optical microscopy and electron backscattered diffraction. It was found that annealing twins in austenite are effective nucleation sites for spontaneous alpha'-martensite, while deformation-induced alpha'-martensite mainly formed within parallel shear-bands. The alpha'-martensite formed has an orientation relationship near the Kurdjumov-Sachs (K-S) relation with the parent austenite phase even at high plastic strains, and adjacent alpha'-martensite variants were mainly twin related (< 111 > 60 degrees or Sigma 3).

  • 56.
    Ning, Zhijun
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Yuan, Chunze
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Tian, Haining
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ågren, Hans
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Quantum rod-sensitized solar cells2011In: ChemSusChem, ISSN 1864-5631, Vol. 4, no 12, p. 1741-1744Article in journal (Refereed)
    Abstract [en]

    An electron injection highway: CdSe nanorods with CdS seed material were applied to a quantum rod-sensitized TiO 2 solar cell that showed a higher electron injection efficiency than analogous quantum dot-sensitized solar cells: reducing the nanocrystals carrier confinement dimensions can improve electron injection efficiency of nanocrystal-sensitized solar cells.

  • 57.
    Nosko, Oleksii
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Borrajo-Pelaez, Rafael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Porosity and shape of airborne wear microparticles generated by sliding contact between a low-metallic friction material and a cast iron2017In: Journal of Aerosol Science, ISSN 0021-8502, E-ISSN 1879-1964, Vol. 113, p. 130-140Article in journal (Refereed)
    Abstract [en]

    The wear of brakes in transport vehicles is one of the main anthropogenic sources of airborne particulate matter in urban environments. The present study deals with the characterisation of airborne wear microparticles from a low-metallic friction material / cast iron pair used in car brakes. Particles were generated by a pin-on-disc machine in a sealed chamber at sliding velocity of 1.3 m/s and contact pressure of 1.5 MPa. They were collected on filters in an electrical low pressure impactor, and an investigation was conducted to quantify their shape and porosity. Scanning electron microscopy revealed that most of the 0.1−0.9 µm particles are flakes and have a breadth-to-length aspect ratio of 0.7 ± 0.2. Particle porosity was determined by milling particles with a focused ion beam and subsequent analysis of the exposed particle cross-sections. Most of the 0.3–6.2 µm particles were revealed to have porosity of 9 ± 6%. Analysis of the relationship between effective particle density, particle material density, dynamic shape factor and porosity showed that the shape factor has a stronger influence on the effective density of airborne wear particles than the porosity factor. The obtained results are useful for accurate prediction of particle behaviour in the atmosphere and in the human respiratory system.

  • 58.
    Odqvist, Joakim
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ahierarchic modelling approach to phase separation of ferrite in stainless steels2015In: Stainless Steel: Microstructure, Mechanical Properties and Methods of Application, Nova Science Publishers , 2015, p. 107-121Chapter in book (Other academic)
    Abstract [en]

    The purpose of this chapter is to present a hierarchic modelling approach to phase separation of ferrite during low temperature aging of stainless steels. This phenomenon is responsible for the so-called 475C embrittlement in ferrite-containing stainless steels and enabling predictive modelling of the underlying phase transformation is of high technical importance, since such steels are vital in e.g., power generation applications. The suggested modelling approach is adopted in a project within the research center Hero-m at KTH in Sweden and currently steps towards predictive modelling of multicomponent alloys are taken. The hierarchic modeling utilizes: first-principles calculations to build fundamental understanding and to evaluate thermodynamic, kinetic and elastic data; CALPHAD-type thermodynamics modelling to build thermodynamic and kinetic databases; and phase-field modelling to simulate the nanostructure evolution. Experimental measurements are also an integrated part of the modelling approach. We demonstrate that the continuum modelling treatments in the literature are insufficient, but also that the suggested approach solving the non-linear Cahn-Hilliard equation, considering initial concentration fluctuations, and using accurate thermodynamic and kinetic input data, provide a viable path.

  • 59.
    Odqvist, Joakim
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Zhou, Jing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Xiong, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    3D analysis of phase separation in ferritic stainless steels2012In: Proceedings of the 1st International Conference on 3D Materials Science, John Wiley & Sons, 2012, p. 221-226Conference paper (Refereed)
    Abstract [en]

    The embrittlement of ferritic stainless steels during low temperature aging is attributed to the phase separation with Fe and Cr demixing. The small scale of the decomposed structure with only minor compositional fluctuations and short distances between the enriched and depleted regions has been a challenge for quite some time. A wide selection of experimental and modeling tools have been used to quantify these types of structures. These analyses often focus on rather late stages of decomposition where the mechanical properties are already seriously affected. The recent advance in 3D tools like phase-field and atom probe tomography have created a need for good quantitative procedures of evaluating the structure and also to link results from the continuum approach to the individual atom measurements. This work aims at addressing this need.

  • 60. Pettersson, N.
    et al.
    Wessman, S.
    Thuvander, M.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Pettersson, R. F. A.
    Hertzman, S.
    Nanostructure evolution and mechanical property changes during aging of a super duplex stainless steel at 300°C2015In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 647, p. 241-248, article id 32735Article in journal (Refereed)
    Abstract [en]

    The nanostructure evolution and the corresponding changes in mechanical properties of a super duplex stainless steel 2507 (UNS S32750) during aging at 300. °C up to 12,000. h have been investigated. Microstructural studies using transmission electron microscopy and atom probe tomography show that subtle Cr concentration fluctuations develop during aging. The amplitude of the concentration fluctuations is proportional to the hardness of the ferrite phase, and it is also proportional to the decrease in room temperature impact toughness during aging. The fracture behaviour of the alloy changes gradually from ductile to cleavage fracture, upon aging. The cracks were found to propagate through the ferrite phase, partly along deformation twin interfaces, and delamination between the austenite and ferrite phases was observed.

  • 61.
    Rahaman, Moshiour
    et al.
    Ferritico, Brinellvagen 85, S-10044 Stockholm, Sweden..
    Mu, Wangzhong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. Ferritico, Brinellvägen 85, S-10044 Stockholm, Sweden.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Ferritico, Brinellvägen 85, S-10044 Stockholm, Sweden.
    Machine Learning to Predict the Martensite Start Temperature in Steels2019In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 50A, no 5, p. 2081-2091Article in journal (Refereed)
    Abstract [en]

    The martensite start temperature (M-s) is a critical parameter when designing high-performance steels and their heat treatments. It has, therefore, attracted significant interest over the years. Numerous methodologies, such as thermodynamics-based, linear regression and artificial neural network (ANN) modeling, have been applied. The application of data-driven approaches, such as ANN modeling, or the wider concept of machine learning (ML), have shown limited technical applicability, but considering that these methods have made significant progress lately and that materials data are becoming more accessible, a new attempt at data-driven predictions of the M-s is timely. We here investigate the usage of ML to predict the M-s of steels based on their chemical composition. A database of the M(s)vs alloy composition containing 2277 unique entries is collected. It is ensured that all alloys are fully austenitic at the given austenitization temperature by thermodynamic calculations. The ML modeling is performed using four different ensemble methods and ANN. Train-test split series are used to evaluate the five models, and it is found that all four ensemble methods outperform the ANN on the current dataset. The reason is that the ensemble methods perform better for the rather small dataset used in the present work. Thereafter, a validation dataset of 115 M-s entries is collected from a new reference and the final ML model is benchmarked vs a recent thermodynamics-based model from the literature. The ML model provides excellent predictions on the validation dataset with a root-mean-square error of 18, which is slightly better than the thermodynamics-based model. The results on the validation dataset indicate the technical usefulness of the ML model to predict the M-s in steels for design and optimization of alloys and heat treatments. Furthermore, the agility of the ML model indicates its advantage over thermodynamics-based models for M-s predictions in complex multicomponent steels. (C) The Author(s) 2019

  • 62.
    Stormvinter, Albin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    A Transmission Electron Microscopy Study of Plate Martensite Formation in High-carbon Low Alloy Steels2013In: Journal of Materials Science & Technology, ISSN 1005-0302, Vol. 29, no 4, p. 373-379Article in journal (Refereed)
    Abstract [en]

    The martensitic microstructures in two high-carbon low alloy steels have been investigated by classical and automated crystallographic analysis under a transmission electron microscope. It is found that the martensitic substructure changes from consisting mostly of transformation twins for 1.20 mass% carbon (C) steel to both transformation twins and planar defects on {101}(M) for 1.67 mass% C steel. In the 1.67 mass% C steel it is further found that small martensite units have a rather homogeneous substructure, while large martensite units are more inhomogeneous. In addition, the martensite units in both steels are frequently found to be of zigzag patterns and have distinct crystallographic relationships with neighboring martensite units, e.g. kink or wedge couplings. Based on the present findings the development of martensite in high-carbon low alloy steels is discussed and a schematic of the martensite formation is presented. Moreover, whether the schematic view can be applied to plate martensite formation in general, is discussed.

  • 63.
    Stormvinter, Albin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Investigation of Lath and Plate Martensite in a Carbon Steel2011In: International Conference on Solid-Solid Phase Transformations in Inorganic Materials, 2011, Vol. 172-174, p. 61-66Conference paper (Refereed)
    Abstract [en]

    Martensite in carbon steels forms in different morphologies, often referred to as lath andplate martensite. The alloy composition has a strong effect on the morphology, for instance in car-bon steels there is a morphological change of the martensite microstructure from lath martensite atlow carbon contents to plate martensite at high carbon contents. In the present work a decarburizedhigh-carbon steel, enabling the isolation of carbons' influence alone, has been studied in order to in-vestigate the changes in morphology and hardness. From the results it is concluded that there is acontinuous change of hardness with increased carbon content. The increasing hardness slows down atabout 0.6 wt%C before decreasing at higher carbon contents. This is in accordance with the change inmorphology since it was found that lath martensite dominates below 0.6 wt%C and the first units ofgrain boundary martensite and plate martensite appear above 0.6 wt%C. At high carbon contents thedominating morphology is plate martensite, but retained austenite is also present.

  • 64.
    Stormvinter, Albin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Miyamoto, G.
    Furuhara, T.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Effect of carbon content on variant pairing of martensite in Fe-C alloys2012In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 20, p. 7265-7274Article in journal (Refereed)
    Abstract [en]

    The effect of carbon content on the variant pairing tendency of martensite formed in Fe-C alloys is investigated by means of electron backscattered diffraction analysis. The method used is based on experimentally determined orientation relationships between austenite and martensite. The results show that the carbon content has a strong effect on the martensite variant pairing tendency. This observed change in variant pairing tendency is discussed in relation to the well-known morphological transition from lath to plate martensite in Fe-C alloys and the formation of packets and plate groups. The results indicate that quantitative analysis of variant pairing, as demonstrated here, may facilitate martensite characterization in Fe-C alloys as well as in other alloy systems.

  • 65.
    Tahir, Abdul Malik
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Bergman, O.
    Chasoglou, D.
    Frisk, K.
    Behaviour of master alloy during sintering of PM steels: redistribution and dimensional variations2015In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 58, no 2, p. 133-141Article in journal (Refereed)
    Abstract [en]

    The addition of alloying elements in low alloyed PM steels in the form of a master alloy gives the advantage of introducing oxidation sensitive but less expensive elements and also allows manipulation in composition adjustment to achieve desired properties. In this work, interrupted sintering trials of the Fe-2MA-0.5C (%) (MA = Cu based master alloy) are performed. The behaviour of the liquid forming master alloy, for instance in terms of liquid phase formation, alloying element redistribution and effect on the dimensional changes, is investigated. The results show that master alloy particles melt over a range of temperature, which is also supported by the thermodynamic calculations. The low swelling in the master alloy system, compared to a reference system of Fe-2Cu-0.5C, is attributed to the progressive melting of the master alloy. The mean diffusion distance of Cu in Fe at the interparticle boundaries is 5.8 mu m after 34 min of isothermal holding.

  • 66.
    Tahir, Abdul Malik
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Bergman, Ola
    Chasoglou, Dimitris
    Frisk, Karin
    Behavior of master alloy during sintering of PM steels: redistributionand dimensional variationsManuscript (preprint) (Other academic)
  • 67.
    Tahir, Abdul Malik
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Bergman, Ola
    Frisk, Karin
    Cu redistribution during sintering of Fe–2Cu and Fe–2Cu–0·5C compacts2014In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 57, no 5, p. 373-379Article in journal (Refereed)
    Abstract [en]

    The effective use of alloying elements in powder metallurgical steels requires a deep understanding of their redistribution kinetics during sintering. In this work, interrupted sintering trials of Fe–2Cu and Fe–2Cu–0·5C compacts were performed. Moreover, diffusion simulations of Cu in γ-Fe using Dictra were performed. It is found that transient liquid phase penetrates the Fe interparticle and grain boundaries in less than 3 min of holding time. However, C addition limits the penetration of liquid Cu, particularly into grain boundaries of large Fe particles. The results also show that the mean diffusion distance of Cu in γ-Fe in the C added system is slightly lower than that in the C-free system at 3 min of holding time; however, after 33 min, the mean diffusion distance is similar in both systems. The diffusion distances of Cu in γ-Fe, predicted by Dictra, are in good agreement with the measured values.

  • 68.
    Tahir, Abdul Malik
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Amberg, Gustav
    KTH, School of Engineering Sciences (SCI), Mechanics, Physicochemical Fluid Mechanics.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Bergman, Ola
    Frisk, Karin
    Investigation of Cu distribution and porosity in Fe-2Cu and Fe-2Cu-0.5C compacts2013In: International Powder Metallurgy Congress and Exhibition, Euro PM 2013, 2013Conference paper (Refereed)
    Abstract [en]

    The distribution of the alloying element Cu in steel compacts is important in determining the properties of the sintered products. In this work, mixtures of Fe-2Cu and Fe-2Cu-0.5C were compacted at 600 MPa and sintered at 1120oC for the holding times of ts= 3, 13, 23, and 33 min. Dilatometry and light optical microscopy is used to investigate porosity, Cu distribution and its effect on the dimensional changes during sintering. The result shows that the molten Cu penetrates into the Fe interparticle and grain boundaries in less then 3 min holding time at 1120°C, however C addition hinders the liquid penetration of Cu. Furthermore, it is found that the C-added compact has lower volume expansion and porosity compared to the C-free system, after 33 min of holding time at 1120°C.

  • 69. Terner, Mark
    et al.
    Hedström, Peter
    Division of Engineering Materials, Luleå University of Technology.
    Almer, Jon
    Ilavsky, Jan
    Odén, Magnus
    Residual stress evolution during decomposition of Ti(1-x)Al (x)N coatings using high-energy x-rays2006In: RESIDUAL STRESSES VII / [ed] Reimers, W; Quander, S, 2006, Vol. 524-525, p. 619-624Conference paper (Refereed)
    Abstract [en]

    Residual stresses and microstructural changes during phase separation in Ti33Al67N coatings were examined using microfocused high energy x-rays from a synchrotron source. The transmission geometry allowed simultaneous acquisition of x-ray diffraction data over 360 degrees and revealed that the decomposition at elevated temperatures occurred anisotropically, initiating preferentially along the film plane. The as-deposited compressive residual stress in the film plane first relaxed with annealing, before dramatically increasing concurrently with the initial stage of phase separation where metastable, nm-scale c-AlN platelets precipitated along the film direction. These findings were further supported from SAXS analyses.

  • 70.
    Thuvander, Mattias
    et al.
    Tillämpad Fysik, Mikroskopi och mikroanalys, Chalmers Tekniska Högskola.
    Zhou, Jing
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hertzman, Staffan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Observations of copper clustering in a 25Cr-7Ni super duplex stainless steel during low-temperature aging under load2012In: Philosophical Magazine Letters, ISSN 0950-0839, E-ISSN 1362-3036, Vol. 92, no 7, p. 336-343Article in journal (Refereed)
    Abstract [en]

    Atom-probe tomography was used to investigate phase separation and copper (Cu) clustering in the ferrite phase of a 25Cr-7Ni super duplex stainless steel. The steel was subjected to a tensile load during aging at 325 degrees C for 5800 h. The degree of phase separation into alpha (Fe-rich) and alpha' (Cr-rich) was small, but still, it was the highest in the steel subjected to the highest load. Cu was found to cluster, and the number density of clusters increased with increasing load. In the material subjected to the highest load, Cu was enriched in regions that were neither Fe-rich nor Cr-rich. These regions also had the highest number density of Cu clusters.

  • 71.
    Tian, Ye
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A microstructural investigation of athermal and deformation-induced martensite in Fe-Cr-Ni alloys2015In: MATERIALS TODAY-PROCEEDINGS, Elsevier, 2015, Vol. 2, p. 687-690Conference paper (Refereed)
    Abstract [en]

    The microstructure of athermal and deformation-induced martensite in four high-purity Fe-Cr-Ni alloys has been investigated. The investigation is conducted using light optical microscopy, electron backscatter diffraction and electron channeling contrast imaging. It is found that epsilon-martensite, annealing twins and grain boundaries are preferred nucleation sites for athermal alpha'-martensite. Furthermore, when epsilon-martensite forms before alpha'-martensite during quenching it acts as nucleation sites as well as growth obstacles for narrow alpha'-martensite units producing a characteristic microstructure with sharp angular coupling, which is distinct from the packet-type alpha'-martensite that forms when athermal alpha'-martensite is able to grow without any hindrance from prior epsilon-martensite formation. It is also found that the transformation strain imposed by the martensitic transformation can be relieved by either autocatalytic martensitic transformation or generation of planar defects, i.e. shear bands. Finally the nucleation sites of alpha'-martensite induced by deformation seem to be mainly at intersections of shear bands and individual shear bands.

  • 72.
    Tian, Ye
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Comparing the deformation-induced martensitic transformation with the athermal martensitic transformation in Fe-Cr-Ni alloysManuscript (preprint) (Other academic)
    Abstract [en]

    The microstructure of martensite formed athermally or via deformation in Fe-Cr-Ni alloys with different austenite (γ) stability has been investigated using microscopy. Two different types of microstructures, viz. blocky and banded structure, are observed after athermal and deformation-induced martensitic transformation (AMT and DIMT, respectively). The blocky structure form during AMT or DIMT if the stability of γ is low. In both these cases, there is a significant chemical driving force for the transformation from γ to α’-martensite (α’), and if it is not hindered by e.g. planar defects it can grow uninhibited into a blocky morphology without the necessity to nucleate new crystallographic variants to accommodate the transformation strains. On the other hand, the banded structure is due to the formation of ε-martensite (ε) during AMT, or the wider concept shear bands in the case of DIMT. The shear bands, and in particular ε, lower the nucleation barrier for α’ that forms within individual shear bands if the stability of γ is low. Neighbouring α’ units predominantly have a twin-related orientation relationship to accommodate the transformation strains. With increasing γ stability during DIMT, variant selection becomes pronounced with preferred formation of variants favourable oriented with respect to the applied stress/strain field. The formation of α’ at individual shear bands is also rare, since no ε is present and instead α’ forms at the intersection of shear bands for more stable γ. In conclusion, AMT and DIMT for low γ stability lead to similar microstructures, whereas the DIMT microstructure for high γ stability is distinct.

  • 73.
    Tian, Ye
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Das, Yadunandan
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mechanical stability of austenite grains towards martensitic transformation in a TRIP-assisted duplex stainless steelManuscript (preprint) (Other academic)
    Abstract [en]

    The mechanical behavior of austenite was investigated in a TRIP duplex stainless steel (TDSS). Uniaxial tensile testing was performed and the microstructure was characterized using electron backscatter diffraction. A strong <111> texture develops along the loading direction (LD) due to preferential martensitic transformation and grain rotation. Austenite oriented with <112> and <100> parallel to the LD transform preferentially, since multiple slip planes activate for these orientations. These observations agree with observations in single-phase austenitic alloys with low stacking fault energy. In conclusion, it is indicated that the stability of austenite grains towards martensitic transformation is mainly dictated by crystallographic orientation.

  • 74.
    Tian, Ye
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Forsberg, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Comparing the deformation-induced martensitic transformation with the athermal martensitic transformation in Fe-Cr-Ni alloys2018In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 766, p. 131-139Article in journal (Refereed)
    Abstract [en]

    The microstructure of martensite formed athermally or via deformation in Fe-Cr-Ni alloys with different austenite (gamma) stability has been investigated using microscopy. Two different types of microstructures, viz. blocky and banded structure, are observed after athermal and deformation-induced martensitic transformation (AMT and DIMT, respectively). The blocky structure form during AMT or DIMT if the stability of gamma is low. In both cases, there is a significant chemical driving force for the transformation from gamma to alpha'-martensite (alpha'), and if it is not hindered by e.g. planar defects it can grow uninhibited into a blocky morphology without the necessity to nucleate new crystallographic variants to accommodate the transformation strains. On the other hand, the banded structure is due to the formation of epsilon-martensite (epsilon) during AMT, or the wider concept shear bands in the case of DIMT. The shear bands, and in particular epsilon, lower the nucleation barrier for alpha' that forms within individual shear bands if the stability of gamma is low. Neighbouring alpha' units predominantly have a twin-related orientation relationship to accommodate the transformation strains. With increasing y stability during DIMT, variant selection becomes pronounced with preferred formation of variants favorable oriented with respect to the applied stress/strain field. The formation of alpha' at individual shear bands is also rare, since nos is present and instead alpha' forms at the intersection of shear bands for more stable gamma. In conclusion, AMT and DIMT for low gamma stability lead to similar microstructures, whereas the DIMT microstructure for high y stability is distinct. 

  • 75.
    Tian, Ye
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Gorbatov, Oleg I.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Deformation Microstructure and Deformation-Induced Martensite in Austenitic Fe-Cr-Ni Alloys Depending on Stacking Fault Energy2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 1, p. 1-7Article in journal (Refereed)
    Abstract [en]

    The deformation microstructure of austenitic Fe-18Cr-(10-12)Ni (wt pct) alloys with low stacking fault energies, estimated by first-principles calculations, was investigated after cold rolling. The E >-martensite was found to play a key role in the nucleation of alpha'-martensite, and at low SFE, E > formation is frequent and facilitates nucleation of alpha' at individual shear bands, whereas shear band intersections become the dominant nucleation sites for alpha' when SFE increases and mechanical twinning becomes frequent.

  • 76.
    Tian, Ye
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lienert, Ulrich
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Fischer, Torben
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Martensite formation during incremental cooling of Fe-Cr-Ni alloys: An in-situ bulk X-ray study of the grain-averaged and single-grain behavior2017In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 136, p. 124-127Article in journal (Refereed)
    Abstract [en]

    The formation of martensite (epsilon and alpha') in metastable austenitic Fe-18Cr-(10-11.5)Ni alloys was investigated in situ during cooling. High-energy X-rays were used to study the bulk of the alloys. Both grain-averaged and single grain data was acquired. s played an important role in the formation of a' with an indistinguishable difference in the martensite start temperature. The single-grain data indicated that stacking faults appear as precursors to a An analogy can be made with deformation-induced martensitic transformation, where the generation of nucleation sites would significantly lower the driving force required to overcome the energy barrier in low stacking fault energy Fe-Cr-Ni alloys.

  • 77.
    Tian, Ye
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lin, Sen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ko, J. Y. P.
    Lienert, U.
    Forsberg, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Micromechanics and microstructure evolution during in situ uniaxial tensile loading of TRIP-assisted duplex stainless steels2018In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 734, p. 281-290Article in journal (Refereed)
    Abstract [en]

    Transformation-induced plasticity (TRIP) assisted duplex stainless steels, with three different stabilities of the austenite phase, were investigated by synchrotron x-ray diffraction characterization during in situ uniaxial tensile loading. The micromechanics and the deformation-induced martensitic transformation (DIMT) in the bulk of the steels were investigated in situ. Furthermore, scanning electron microscopy supplemented the in situ analysis by providing information about the microstructure of annealed and deformed specimens. The dependence of deformation structure on austenite stability is similar to that of single-phase austenitic steels with shear bands and bcc-martensite (α′) generally observed, and blocky α′ is only frequent when the austenite stability is low. These microstructural features, i.e. defect structure and deformation-induced martensite, are correlated with the micro- and macro-mechanics of the steels with elastoplastic load transfer from the weaker phases to the stronger α′, in particular this occurs close to the point of maximum rate of α′ formation. A clear strain-hardening effect from α′ is seen in the most unstable austenite leading to a pronounced TRIP effect. 

  • 78.
    Tian, Ye
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lin, Sen
    Peter Ko, J. Y.
    Lienert, Ulrich
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Micromechanics and microstructure evolution during in situ uniaxial tensile loading of TRIP-assisted duplex stainless steelsManuscript (preprint) (Other academic)
    Abstract [en]

    Two transformation-induced plasticity (TRIP) assisted duplex stainless steels, with three different stabilities of the austenite phase, were investigated by synchrotron X-ray diffraction characterization during in situ uniaxial tensile loading. The micromechanics and the deformation-induced martensitic transformation (DIMT) in the bulk of the steels were investigated in situ. Furthermore, scanning electron microscopy supplemented the in situ analysis by providing information about the microstructure of annealed and deformed specimens. The dependence of deformation structure on austenite stability is similar to that of single-phase austenitic steels where shear bands and bcc-martensite (α’) are generally observed, and blocky α’ is only frequent when the austenite stability is low. These microstructural features, i.e. defect structure and deformation-induced martensite, are correlated with the micro- and macro-mechanics of the steels with elastoplastic load transfer from the weaker phases to the stronger α’, in particular this occurs close to the point of maximum rate of α’ formation. A clear strain-hardening effect from α’ is seen in the most unstable austenite leading to a pronounced TRIP effect.

  • 79. Ukonsaari, Jan
    et al.
    McCarthy, Donald
    Prakash, Braham
    Hedström, Peter
    Division of Engineering Materials, Luleå University of Technology.
    Tribological studies on an eal lubricated bearing bronze - Steel pair under reciprocating sliding conditions2008In: Tribologia, ISSN 0780-2285, Vol. 27, no 1, p. 3-18Article in journal (Refereed)
    Abstract [en]

    Boundary lubricated journal bearings are found in various applications involving oscillatory sliding conditions. Environmental adaptation of hydraulic systems includes the introduction of synthetic esters. These new environmentally adapted lubricants (EALs) have shown very good boundary lubrication performance but also condition sensitivity. This study examines an oil lubricated bronze pin on hardened steel configuration in a reciprocating friction and wear test machine. Three synthetic esters were tested with a 1 mm stroke length. Results were compared with those for a mineral oil. The tribological performance with synthetic ester lubricant can, under certain conditions, be very good. SEM-EDS and XRD surface sensitive studies indicate the formation of a soft, copper enriched outer contact layer. The layer's nature and contact mechanisms clearly affect the performance of the different lubricants.

  • 80. Westraadt, J. E.
    et al.
    Olivier, E. J.
    Neethling, J. H.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Xu, X.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Steuwer, A.
    A high-resolution analytical scanning transmission electron microscopy study of the early stages of spinodal decomposition in binary Fe-Cr2015In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 109, p. 216-221Article in journal (Refereed)
    Abstract [en]

    Spinodal decomposition (SD) is an important phenomenon in materials science and engineering. For example, it is considered to be responsible for the 475 degrees C embrittlement of stainless steels comprising the bcc (ferrite) or bct (martensite) phases. Structural characterization of the evolving minute nano-scale concentration fluctuations during SD in the Fe-Cr system is, however, a notable challenge, and has mainly been considered accessible via atom probe tomography (APT) and small-angle neutron scattering. The standard tool for nanostructure characterization, viz, transmission electron microscopy (TEM), has only been successfully applied to late stages of SD when embrit-dement is already severe. However, we here demonstrate that the structural evolution in the early stages of SD in binary Fe-Cr, and alloys based on the binary, are accessible via analytical scanning TEM. An Fe-36 wt% Cr alloy aged at 500 degrees C for 1, 10 and 100 h is investigated using an aberration-corrected microscope and it is found that highly coherent and interconnected Cr-rich regions develop. The wavelength of decomposition is rather insensitive to the sample thickness and it is quantified to 2, 3 and 6 nm after ageing for 1, 10 and 100 h, which is in reasonable agreement with prior APT analysis. The concentration amplitude is more sensitive to the sample thickness and acquisition parameters but the TEM analysis is in good agreement with APT analysis for the longest ageing time. These findings open up for combinatorial TEM studies where both local crystallography and chemistry is required.

  • 81.
    Xiong, Wei
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Hedstrom, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, Mattias
    Chen, Qing
    An improved thermodynamic modeling of the Fe-Cr system down to zero kelvin coupled with key experiments2011In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 35, no 3, p. 355-366Article in journal (Refereed)
    Abstract [en]

    A thermodynamic modeling of the Fe-Cr system down to 0 K is performed on the basis of our recent comprehensive review of this binary system [W. Xiong, M. Selleby, Q. Chen, J. Odqvist, Y. Du, Evaluation of phase equilibria and thermochemical properties in the Fe-Cr system, Crit. Rev. Solid State Mater. Sci. 35 (2010) 125-152]. The model predicts a sign change for the magnetic ordering energy of mixing rather than the enthalpy of mixing in the bcc phase at 0 K. Designed key experiments are performed not only to check the validity of the present modeling but also to assist in understanding the mechanism for spinodal decomposition of the Fe-Cr alloy. Heat capacities and Curie temperatures of several Fe-rich alloys are determined between 320 and 1093 K by employing differential scanning calorimetry. The measured heat capacities are found to be in remarkable agreement with the prediction based on the present modeling. Microstructural patterns and frequency distribution diagrams of Cr are studied in alloys containing 26.65, 31.95, and 37.76 at.% Cr by using atom probe tomography. The observed phase separation results correspond well with our model-predicted boundary for the spinodal decomposition. Interestingly, a horn on the Cr-rich spinodal boundary is predicted below 200 K for the first time. This work demonstrates a way to bridge the ab initio calculations and CALPHAD approach. (C) 2011 Elsevier Ltd. All rights reserved.

  • 82.
    Xu, Xin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Colliander, M. H.
    King, S.
    Thuvander, M.
    Steuwer, A.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effect of cooling rate after solution treatment on subsequent phase separation during aging of Fe-Cr alloys: A small-angle neutron scattering study2017In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 134, p. 221-229Article in journal (Refereed)
    Abstract [en]

    The effect of cooling rate after solution treatment on the initial structure of concentrated binary Fe-Cr alloys and the effect of the initial structure on phase separation during subsequent aging has been investigated. The nano-scale compositional fluctuations in the bulk of the alloys are studied using small-angle neutron scattering and the results are compared with simulations using the Cahn-Hilliard-Cook (CHC) model. The alloys investigated represent different mechanisms of phase separation and at higher Cr content, when spinodal decomposition (SD) is favored, the initial Cr compositional fluctuations due to slow cooling after solution treatment reduce the kinetics of phase decomposition, whereas, at lower Cr composition when nucleation and growth is favored, the kinetics of phase decomposition is more rapid. Regardless of the nominal Cr composition of the alloy, the phase decomposition after extended aging up to 300 h at 748 K is always larger for the more non-random initial structure. The CHC modeling of the cooling process and subsequent initial aging (below 10 h) is in reasonable qualitative agreement with the experimental results for the Fe-40 wt.% Cr alloy decomposing via SD. However, the modeling approach must be refined for accurate quantitative modeling of the full SD process, including coarsening.

  • 83. Xu, Xin
    et al.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Colliander, Magnus Hornqvist
    Thuvander, Mattias
    Steuwer, Axel
    Westraadt, Johan E.
    King, Stephen
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Structural Characterization of Phase Separation in Fe-Cr: A Current Comparison of Experimental Methods2016In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 47A, no 12, p. 5942-5952Article in journal (Refereed)
    Abstract [en]

    Self-assembly due to phase separation within a miscibility gap is important in numerous material systems and applications. A system of particular interest is the binary alloy system Fe-Cr, since it is both a suitable model material and the base system for the stainless steel alloy category, suffering from low-temperature embrittlement due to phase separation. Structural characterization of the minute nano-scale concentration fluctuations during early phase separation has for a long time been considered a major challenge within material characterization. However, recent developments present new opportunities in this field. Here, we present an overview of the current capabilities and limitations of different techniques. A set of Fe-Cr alloys were investigated using small-angle neutron scattering (SANS), atom probe tomography, and analytical transmission electron microscopy. The complementarity of the characterization techniques is clear, and combinatorial studies can provide complete quantitative structure information during phase separation in Fe-Cr alloys. Furthermore, we argue that SANS provides a unique in-situ access to the nanostructure, and that direct comparisons between SANS and phase-field modeling, solving the non-linear Cahn Hilliard equation with proper physical input, should be pursued.

  • 84.
    Xu, Xin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    King, Stephen M.
    Venero, Diego. A.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Nuclear and magnetic small-angle neutron scattering in self-organizing nanostructured FexCr1-x alloysManuscript (preprint) (Other academic)
    Abstract [en]

    Nuclear and magnetic small-angle neutron scattering (SANS) in self-organizing nanostructured FexCr1-x (x=0.8, 0.6 and 0.5) alloys has been studied. A saturation magnetic field is applied to separate the scattering signals and it is shown that the relation between nuclear and magnetic scattering depend on both, the extent of self-organizing due to demixing of Fe and Cr, and the alloy composition. When the demixing is pronounced with large concentration amplitude, the two scattering signals are identical, whereas when the concentration amplitude is small IM(Q) is negligible compared to IN(Q). The relation between the scattering signals is critical when assessing demixing in FexCr1-x alloys by SANS, and it has been mostly ignored in prior works in the literature.

  • 85.
    Xu, Xin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Wessman, Sten
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy. KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    King, Stephen M.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Nanostructure and mechanical properties of duplex stainless steels 25Cr-7Ni and 22Cr-5Ni (wt.%) aged at 325 oCManuscript (preprint) (Other academic)
    Abstract [en]

    The nanoscale concentration fluctuations due to phase separation (PS) and the corresponding mechanical property changes of duplex stainless steels, standard grade 2205 and super grade 2507, during aging at 325 oC up to 6000 h have been studied. The nanostructure characterization is performed using small-angle neutron scattering (SANS) and the microstructure, including fracture surface and cross-section, is investigated by scanning electron microscopy and electron backscatter diffraction. The results show that the kinetics of phase separation (PS) in grade 2507 is faster than that in grade 2205, leading to greater hardening and deterioration in toughness for grade 2507 compared to 2205. The evolution of nanostructure in the ferrite changes the deformation mode from the original ductile fracture to a quasi-cleavage type where deformation twins form in the hardened ferrite. Delamination, grain fragmentation and plastic deformation of the austenite are suggested to dissipate most of the energy absorbed by the crack during brittle fracture.

  • 86.
    Xu, Xin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wessman, Sten
    Swerim AB, SE-16407 Stockholm, Sweden..
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    King, Stephen M.
    Rutherford Appleton Lab, ISIS Pulsed Neutron & Muon Source, Harwell Campus, Didcot OX11 0QX, Oxon, England..
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Nanostructure, microstructure and mechanical properties of duplex stainless steels 25Cr-7 Ni and 22Cr-5Ni (wt.%) aged at 325 degrees C2019In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 754, no ALGUE A, 1990, JOURNAL OF MATERIALS SCIENCE, V25, P4977, p. 512-520Article in journal (Refereed)
    Abstract [en]

    The nanoscale concentration fluctuation evolution due to phase separation (PS) and the corresponding mechanical property changes in two duplex stainless steels, 22Cr-5Ni (2205) and 25Cr-7N1 (2507), have been studied after aging at 325 degrees C for up to 6000 h. The nanostructure characterization is performed using small-angle neutron scattering (SANS) and the microstructure and fractography analyses, including observations on fracture surfaces and fracture cross-sections, are performed by scanning electron microscopy and electron backscatter diffraction. The results show that the kinetics of PS in grade 2507 is faster than that in grade 2205, leading to greater hardening and deterioration in toughness for grade 2507 as compared to grade 2205. The evolution of the nanostructure in the ferrite phase changes the deformation mode from the original ductile fracture to a quasi-cleavage type fracture where deformation twins form in the hardened ferrite. Delamination, grain fragmentation in ferrite and plastic slip deformation of the austenite are suggested to dissipate most of the energy absorbed by the crack during brittle fracture.

  • 87.
    Xu, Xin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Westraadt, J. E.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Youngs, T. G. A.
    King, S. M.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effect of heat treatment above the miscibility gap on nanostructure formation due to spinodal decomposition in Fe-52.85 at.%Cr2018In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 145, p. 347-358Article in journal (Refereed)
    Abstract [en]

    The effect of heat treatment at temperatures above the miscibility gap (MG) on subsequent nanostructure formation due to spinodal decomposition (SD) has been investigated in an Fe-52.85 at.%Cr alloy. In-situ total neutron scattering measurements were conducted above and inside the MG to shed light on the high temperature nanostructure. Thereafter, different quenched-in nanostructures were imposed by heat treatments at various temperatures above the MG, followed by rapid quenching. The effect of the quenched-in nanostructure on subsequent SD was investigated ex-situ by small-angle neutron scattering, analytical transmission electron microscopy and hardness testing. The critical temperature of the miscibility gap was found at ∼580 °C for the Fe-52.85 at.%Cr alloy and below that temperature, phase separation occurs, where the ferrite decomposes into Fe-rich α-phase and Cr-rich α′-phase. It was found that transient clustering of Cr occurs above the MG and that the tendency of clustering increases with decreasing temperature. The quenched-in clustering present in rapidly quenched materials treated above the MG has a significant effect on the kinetics of SD upon further aging within the MG. It is clear that the significant quenched-in Cr clustering present in samples heat treated at 600 and 700 °C accelerates SD. However, samples heat treated at 1000 °C demonstrate more rapid SD kinetics than samples heat treated at 800 °C. Cr clustering and other mechanisms affecting the kinetics of SD are discussed in the light of the results obtained. 

  • 88.
    Xu, Xin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Westraadt, Johan E.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Youngs, Tristan G. A.
    King, Stephen M.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Effect of heat treatment above the miscibility gap on nanostructure formation due to spinodal decomposition in Fe-52.85 at.%CrManuscript (preprint) (Other academic)
    Abstract [en]

    The effect of heat treatment at temperatures above the miscibility gap (MG) on subsequent nanostructure formation due to spinodal decomposition (SD) has been investigated in an Fe-52.85 at.%Cr alloy. In-situ total neutron scattering measurements were conducted above and inside the MG to shed light on the high temperature nanostructure. Thereafter, different quenched-in nanostructures were imposed by heat treatments at various temperatures above the MG, followed by rapid quenching. The effect of the quenched-in nanostructure on subsequent SD was investigated ex-situ by small-angle neutron scattering, analytical transmission electron microscopy and hardness testing. The critical temperature of the miscibility gap was found at ~570oC and below that temperature, thermodynamically stable α'-phase forms. It was found that transient clustering of Cr occurs above the MG and that the tendency of clustering increases with decreasing temperature. The quenched-in clustering present in rapidly quenched materials treated above the MG has a significant effect on the kinetics of SD upon further aging within the MG. It is clear that the significant quenched-in Cr clustering present in samples heat treated at 600 and 700oC accelerates SD. However, samples heat treated at 1000oC demonstrate more rapid SD kinetics than samples heat treated at 800oC. Cr clustering and other mechanisms affecting the kinetics of SD are discussed in the light of the results obtained.

  • 89.
    Yeddu, Hemantha Kumar
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    A phase-field study of the physical concepts of martensitic transformations in steels2012In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 538, p. 173-181Article in journal (Refereed)
    Abstract [en]

    A 3D elastoplastic phase-field model is employed to study various driving forces associated withmartensitic transformations, plastic deformation behavior as well as the habit plane concept. Usage ofthermodynamic parameters corresponding to Fe–0.3%C alloy in conjunction with anisotropic physicalparameters of steels as the simulation parameters have yielded the results in reasonable agreement withexperimental observations. From the simulation results, it is concluded that there exist three critical drivingforces that control the transformation and also that the plastic deformation behavior of the materialgreatly affects the transformation. The model predicts the initial habit plane of the first infinitesimalunit of martensite as (−1 1 1). The model also predicts that, as the transformation progresses, the abovementioned martensite domain rotates and finally orients along the new habit plane of (−2 1 1).

  • 90.
    Yildiz, Ahmet Bahadir
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Weidow, Jonathan
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Ryukhtin, Vasyl
    Nucl Phys Inst, Cp 130, Husinec Rez 25068, Czech Republic..
    Norgren, Susanne
    Sandvik, SE-12680 Stockholm, Sweden.;Uppsala Univ, Dept Engn Sci, Appl Mat Sci, SE-75121 Uppsala, Sweden..
    Wahnström, Göran
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Very-small angle neutron scattering study on grain coarsening inhibition by V-doping of WC-Co composites2019In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 173, p. 106-109Article in journal (Refereed)
    Abstract [en]

    The mechanical properties of cemented carbides can be tuned by controlling WC grain coarsening and the simultaneous growth of the binder pocket size during the sintering. So far, bulk studies considering this phenomenon are scarce, but here, we report the first very-small angle neutron scattering (VSANS) study on cemented carbides. VSANS is supplemented with electron backscatter diffraction (EBSD) and the microstructural refinement by increasing V-doping (0, 0.02, 022, and 0.76 wt%) is quantified. The capability of VSANS as a non-destructive bulk probe for cemented carbides is shown, paving way for forthcoming in-situ studies.

  • 91.
    Yvell, Karin
    et al.
    Materials Science, Dalarna University, Falun, Sweden.
    Grehk, Mikael
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Engberg, Göran
    EBSD analysis of surface and bulk microstructure evolution during interrupted tensile testing of a Fe-19Cr-12Ni alloy2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 141, p. 8-18Article in journal (Refereed)
    Abstract [en]

    The microstructure evolution in both surface and bulk grains in a pure Fe-19Cr-12Ni alloy has been analyzed using electron backscatter diffraction after tensile testing interrupted at different strains. Surface grains were studied during in situ tensile testing performed in a scanning electron microscope, whereas bulk grains were studied after conventional tensile testing. The evolution of the deformation structure in surface and bulk grains displays a strong resemblance but the strain needed to obtain a similar deformation structure is lower in the case of surface grains. Both slip and twinning are observed to be important deformation mechanisms, whereas deformation-induced martensite formation is of minor importance. Since the stacking fault energy (SFE) is low, ~17 mJ/m2, dynamic recovery by cross slip of un-dissociated dislocations is unfavorable. This reduces the annihilation of dislocations which in turn leads to a significant increase of low angle boundaries with increasing strain. The low SFE also favors formation of deformation twins which reduces the slip distance, leading to a hardening similar to the Hall-Petch relation. The combination of a low ability for cross-slip and a reduced slip distance caused by twinning is concluded to be the main reason for maintaining a high strain-hardening rate up to strains close to necking.

  • 92.
    Yvell, Karin
    et al.
    Materials Science, Dalarna University, Falun, Sweden.
    Grehk, T. M.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Engberg, G.
    Microstructure development in a high-nickel austenitic stainless steel using EBSD during in situ tensile deformation2018In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 135, p. 228-237Article in journal (Refereed)
    Abstract [en]

    Plastic deformation of surface grains has been observed by electron backscatter diffraction technique during in situ tensile testing of a high-nickel austenitic stainless steel. The evolution of low- and high-angle boundaries as well as the orientation changes within individual grains has been studied. The number of low-angle boundaries and their respective misorientation increases with increasing strain and some of them also evolve into high-angle boundaries leading to grain fragmentation. The annealing twin boundaries successively lose their integrity with increasing strain. The changes in individual grains are characterized by an increasing spread of orientations and by grains moving towards more stable orientations with < 111 > or < 001 > parallel to the tensile direction. No deformation twins were observed and deformation was assumed to be caused by dislocation slip only.

  • 93. Zhang, H.
    et al.
    Nakajima, Keiji
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Su, M.
    Shibata, H.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Wang, W.
    Lei, H.
    Wang, Q.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    He, J.
    Prediction of Influences of Co, Ni, and W Elements on Carbide Precipitation Behavior in Fe–C–V–Cr–Mo Based High Speed Steels2018In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 89, no 10, article id 1800172Article in journal (Refereed)
    Abstract [en]

    The effects of Co, Ni together with W addition on the precipitation sequence, amount, and composition of carbides and FCC matrix in Fe–C–V–Cr–Mo based alloys are investigated with the help of Partial Equilibrium (PE) approximation and thermodynamic calculations as well as differential scanning calorimetry (DSC) and electron backscatter diffraction (EBSD) - energy dispersive spectrometer (EDS) analyses. Results show that, individually, Co and Ni elements strengthen the matrix by their great solubility in FCC matrix; W element enlarges the hardness of the alloy through benefiting the formation of M6C carbide. Mutually, the addition of Co and Ni together with W increases the precipitation temperature of the eutectic carbides, although the addition of Co and Ni itself exerts little influence on the nature (type, amount, and composition) of the carbides. These predictions combined with the experimental verifications provide potentials for the alloy design and the property control in high speed steels.

  • 94.
    Zhou, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hertzman, Staffan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics. Outokumpu Stainless Research Foundation, Sweden .
    Thuvander, Mattias
    Tillämpad Fysik, Mikroskopi och mikroanalys, Chalmers Tekniska Högskola.
    A study of duplex stainless steels aged at 325°C under applied tensile load2011In: 7th European Stainless Steel Conference: Science and Market, Proceedings, Associazione Italiana di Metallurgia , 2011Conference paper (Refereed)
  • 95.
    Zhou, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, M.
    Barkar, Thomas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Initial clustering - A key factor for phase separation kinetics in Fe-Cr-based alloys2014In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 75, p. 62-65Article in journal (Refereed)
    Abstract [en]

    Clustering of alloying elements in solution-treated Fe-Cr-based alloys is of considerable importance for their microstructure stability upon aging. The clustering of Cr after solution treatment in three stainless steel alloy categories has been studied by atom probe tomography. Furthermore, phase-field simulations are applied to examine the effect of initial clustering on phase separation evolution. It is concluded that the clustering of Cr found in solution-treated ferritic and duplex alloys plays a critical role in the nanostructure evolution during aging.

  • 96.
    Zhou, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thuvander, M.
    Xiong, W.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Olson, G. B.
    Hedström, Peter
    Effect of solution treatment on spinodal decomposition during aging of an Fe-46.5 at.% Cr alloy2017In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, no 1, p. 326-335Article in journal (Refereed)
    Abstract [en]

    Spinodal decomposition is a key phase transition in advanced materials and a significant effort is paid to the quantitative modeling of the phenomenon. The initial materials condition is often assumed to be random during modeling, but this may be an oversimplification. In this work, the effect of solution treatment above the miscibility gap, on spinodal decomposition during subsequent aging, has been investigated for an Fe-46.5 at.% Cr alloy. By atom probe tomography (APT), it is found that different extents of quenched-in Cr clustering exist after solution treatments at different temperatures. The clustering is pronounced at 800 °C but decreases significantly with increasing temperature to 900 °C. Thermodynamic Monte Carlo simulations show that there is a difference in atomic short range order between the different solution treatment temperatures. By APT, it is, furthermore, found that the kinetics of spinodal decomposition at 500 °C, i.e., within the miscibility gap, is enhanced in the initial alloy condition, where Cr was less randomly distributed. These observations are supported by kinetic Monte Carlo simulations, predicting a similar but less pronounced qualitative effect on spinodal decomposition kinetics. Other possible reasons for the enhanced kinetics could be related to clustering of interstitial elements and/or sigma phase, but neither was found in the experiments. Nonetheless, the observations in this work suggest that it is necessary to implement a modeling strategy, where the initial structure is properly accounted for when simulating spinodal decomposition.

  • 97.
    Zhou, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, M.
    Hertzman, Staffan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Concurrent phase separation and clustering in the ferrite phase during low temperature stress aging of duplex stainless steel weldments2012In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 60, no 16, p. 5818-5827Article in journal (Refereed)
    Abstract [en]

    The concurrent phase separation and clustering of alloying elements in the ferrite phase of duplex stainless steel weldments after stress aging at 325 degrees C have been investigated by atom probe tomography analysis. Both phase separation, into Fe-rich and Cr-rich ferrite, and solute clustering were observed. Phase separation in the heat-affected zone (HAZ) is most pronounced in the high alloyed SAF 2507, followed by SAF 2205 and SAF 2304. Moreover Cu clustering was observed in the HAZ of SAF 2507. However, decomposition in the weld bead (25.10.4L) was more pronounced than in the HAZs, with both phase separation and clustering of Ni-Mn-Si-Cu. The observed differences in the decomposition behaviors in the HAZ and weld bead can be attributed to the high Ni content and the characteristic microstructure of the weld bead with high internal strains. In addition, an applied tensile stress during aging of weldments has been found to further promote the kinetics of phase separation and clustering.

  • 98.
    Zhou, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, Mattias
    Hedstrom, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Quantitative Evaluation of Spinodal Decomposition in Fe-Cr by Atom Probe Tomography and Radial Distribution Function Analysis2013In: Microscopy and Microanalysis, ISSN 1431-9276, E-ISSN 1435-8115, Vol. 19, no 3, p. 665-675Article in journal (Refereed)
    Abstract [en]

    Nanostructure evolution during low temperature aging of three binary Fe-Cr alloys has been investigated by atom probe tomography. A new method based on radial distribution function (RDF) analysis to quantify the composition wavelength and amplitude of spinodal decomposition is proposed. Wavelengths estimated from RDF have a power-law type evolution and are in reasonable agreement with wavelengths estimated using other more conventional methods. The main advantages of the proposed method are the following: (1) Selecting a box size to generate the frequency diagram, which is known to generate bias in the evaluation of amplitude, is avoided. (2) The determination of amplitude is systematic and utilizes the wavelength evaluated first to subsequently evaluate the amplitude. (3) The RDF is capable of representing very subtle decomposition, which is not possible using frequency diagrams, and thus a proposed theoretical treatment of the experimental RDF creates the possibility to determine amplitude at very early stages of spinodal decomposition.

  • 99.
    Zhou, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Thuvander, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Xiong, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Computational Thermodynamics.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Olson, Gregory B.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Effect of homogenization temperatureon subsequent spinodal decompositionduring aging in Fe-46.5Cr alloyManuscript (preprint) (Other academic)
  • 100.
    Zhou, Jing
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Ruban, Andrei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Multiscale Materials Modelling.
    Thuvander, Mattias
    Xiong, Wei
    Olson, Gregory B.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Direct atom probe tomography observations of concentration fluctuations in Fe-Cr solid solution2015In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 98, p. 13-15Article in journal (Refereed)
    Abstract [en]

    The local concentration of atoms in an Fe-46.5 at.% Cr alloy, solution treated at four different temperatures above the miscibility gap, has been investigated using atom probe tomography. It is experimentally found that Cr atoms cluster in the solid solution and that the clustering tendency decreases with increasing temperature above the miscibility gap. These findings are corroborated by Monte Carlo simulations of the atomic short-range order, which show that clustering markedly decrease with increasing temperature from 800 to 1200 degrees C.

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