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Publications (10 of 61) Show all publications
Dong, Y., Guo, S., Mao, H., Xu, C., Xie, Y., Deng, J., . . . Sun, J. (2020). In Situ Growth of CVD Graphene Directly on Dielectric Surface toward Application. ACS Applied Electronic Materials, 2(1187), 238-246
Open this publication in new window or tab >>In Situ Growth of CVD Graphene Directly on Dielectric Surface toward Application
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2020 (English)In: ACS Applied Electronic Materials, ISSN 2637-6113, Vol. 2, no 1187, p. 238-246Article in journal (Refereed) Published
Abstract [en]

A technique for the in situ growth of patterned graphene by CVD has been achieved directly on insulating substrates at 800 degrees C. The graphene growth is catalyzed by a Ni-Cu alloy sacrificial layer, which integrates many advantages such as being lithography-free, and almost wrinkle-free, with a high repeatability and rapid growth. The etching method of the metal sacrificial layer is the core of this technique, and the mechanism is analyzed. Graphene has been found to play an important role in accelerating etching speeds. The Ni-Cu alloy exhibits a high catalytic activity, and thus, high-quality graphene can be obtained at a lower temperature. Moreover, the Ni-Cu layer accommodates a limited amount of carbon atoms, which ensures a high monolayer ratio of the graphene. The carbon solid solubility of the alloy is calculated theoretically and used to explain the experimental findings. The method is compatible with the current semiconductor process and is conducive to the industrialization of graphene devices.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2020
Keywords
in situ growth, lithography-free, graphene, chemical vapor deposition, insulating substrate
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-268805 (URN)10.1021/acsaelm.9b00719 (DOI)000510530100030 ()
Note

QC 20200224

Available from: 2020-02-24 Created: 2020-02-24 Last updated: 2020-02-24Bibliographically approved
Wang, W., Hou, Z., Lizarrága, R., Tian, Y., Babu, P., Holmström, E., . . . Larsson, H. (2019). An experimental and theoretical study of duplex fcc+hcp cobalt based entropic alloys. Acta Materialia, 176, 11-18
Open this publication in new window or tab >>An experimental and theoretical study of duplex fcc+hcp cobalt based entropic alloys
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2019 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 176, p. 11-18Article in journal (Refereed) Published
Abstract [en]

Martensitically formed duplex fcc + hcp Co-based entropic alloys have been investigated both experimentally and theoretically. Theoretical predictions are in good agreement with experimental observations. A fair correlation is found between calculated driving forces for a partitionless fcc→hcp transformation and experimentally obtained phase fractions.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Metallurgy and Metallic Materials
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-258027 (URN)10.1016/j.actamat.2019.06.041 (DOI)000482247800002 ()2-s2.0-85068362090 (Scopus ID)
Note

QC 20190917

Available from: 2019-09-09 Created: 2019-09-09 Last updated: 2020-02-19Bibliographically approved
Churyumov, A. Y., Pozdniakov, A. V., Bazlov, A. I., Mao, H., Polkin, V. I. & Louzguine-Luzgin, D. V. (2019). Effect of Nb Addition on Microstructure and Thermal and Mechanical Properties of Fe-Co-Ni-Cu-Cr Multiprincipal-Element (High-Entropy) Alloys in As-Cast and Heat-Treated State. JOM: The Member Journal of TMS, 71(10), 3481-3489
Open this publication in new window or tab >>Effect of Nb Addition on Microstructure and Thermal and Mechanical Properties of Fe-Co-Ni-Cu-Cr Multiprincipal-Element (High-Entropy) Alloys in As-Cast and Heat-Treated State
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2019 (English)In: JOM: The Member Journal of TMS, ISSN 1047-4838, E-ISSN 1543-1851, Vol. 71, no 10, p. 3481-3489Article in journal (Refereed) Published
Abstract [en]

The microstructure and thermal and mechanical properties of (FeCoNiCuCr)(100-x)-Nb-x multiprincipal-element alloys have been investigated in the as-cast and heat-treated state. The alloys were smelted by arc-melting in argon atmosphere. As-cast samples were produced by copper mold casting. The structure was studied by scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The calculated phase diagrams of the Fe-Co-Ni-Cu-Cr-Nb system were used to predict the phase composition. The predicted thermodynamic temperatures and phase areas were compared with those obtained using differential scanning calorimetry (DSC) and the results of SEM observation, respectively. Addition of 10 at.% Nb caused phase separation of the alloy in the liquid state. Addition of Nb caused an increase in the yield strength by solid-solution hardening and by the formation of intermetallic compounds. Heat treatment also affected the mechanical properties of the studied alloys.

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-263359 (URN)10.1007/s11837-019-03644-z (DOI)000487659800019 ()2-s2.0-85068856817 (Scopus ID)
Note

QC 20191119

Available from: 2019-11-18 Created: 2019-11-18 Last updated: 2019-11-18Bibliographically approved
Tabeshian, A., Mao, H., Arnberg, L. & Aune, R. E. (2019). Investigation of glass forming ability in the Zr-rich part of the Zr-Fe-Al ternary system. Journal of Applied Physics, 125(6), Article ID 065101.
Open this publication in new window or tab >>Investigation of glass forming ability in the Zr-rich part of the Zr-Fe-Al ternary system
2019 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 125, no 6, article id 065101Article in journal (Refereed) Published
Abstract [en]

In the present study, the CALPHAD (CALculation of PHAse Diagrams) methodology and thermodynamic data were used to calculate the equilibrium phase diagram of the Zr-Fe-Al system. Furthermore, the information for the enthalpy of mixing (ΔH mix ) and the atomic radius of the constituent elements, in terms of the generalized topological instability factor (λ), were combined with the ternary phase diagram to predict compositions with high Glass Forming Ability (GFA). Compositions with a Zr content ranging from 67 to 73 at. % were proposed and later produced by rapid cooling using suction casting. The obtained results revealed that 12 out of the initial 14 compositions were successfully made into glassy structures with a critical diameter ranging from 0.5 to 2.5 mm. The achieved results show good agreement between the predictions made and the experimental results, and the corresponding λ value obtained for the highest GFA was used to identify the optimum area of interest for producing Zr-Fe-Al metallic glasses. It is believed that the proposed computational approach can be used as a guideline to predict glass forming areas/compositions in even other systems.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2019
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-244326 (URN)10.1063/1.5066554 (DOI)000458877500026 ()2-s2.0-85061368608 (Scopus ID)
Note

QC 20190220

Available from: 2019-02-20 Created: 2019-02-20 Last updated: 2019-03-18Bibliographically approved
Yin, J., Ersson, M., Mao, H. & Jönsson, P. G. (2019). Mathematical Modelling of the Initial Mold Filling with Utilization of an Angled Runner. Metals, 9(6)
Open this publication in new window or tab >>Mathematical Modelling of the Initial Mold Filling with Utilization of an Angled Runner
2019 (English)In: Metals, ISSN 2075-4701, Vol. 9, no 6Article in journal (Refereed) Published
Abstract [en]

The flow pattern plays a crucial role in the uphill teeming process. The non-metallic inclusion generation due to interaction with the mold flux is believed to be influenced by the flow pattern. In this study, a three-dimensional mathematical model of the filling of a gating system for 10, 20, and 30 degrees angled runners was used to predict the fluid flow characteristics. Moreover, a mathematical model with a horizontal runner was applied as a reference. The predictions indicate that the angled-runner-design decreases the hump height during the initial filling stage, which results in less entrapment of mold flux into the mold. Nevertheless, increasing the angle of runner can result in a lower hump height, while the 30 degree angled runner gives a much more stable increase of the hump height during the initial filling stage. Besides CFD calculations, some thermodynamic calculations are taken into account for the chemical reactions between liquid steel and gas. The results show that the bubble shrinks due to the fact that N and O are dissolved into steel. The present findings strongly suggest that changing the horizontal runner to an angled runner would be an effective means of reducing flow unevenness during the initial filling of ingots, if the added steel losses are deemed acceptable.

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
CFD, bubble, uphill teeming, ingot casting, mathematical modelling, gating system, thermodynamic calculations
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-255577 (URN)10.3390/met9060693 (DOI)000475356500077 ()2-s2.0-85070457970 (Scopus ID)
Note

QC 20190802

Available from: 2019-08-02 Created: 2019-08-02 Last updated: 2019-10-04Bibliographically approved
Zhou, J., Wu, Y., Jiang, S., Song, W., Huang, H., Mao, H., . . . Lu, Z. (2019). Simultaneously enhancing the strength and plasticity of Ti-based bulk metallic glass composites via microalloying with Ta. MATERIALS RESEARCH LETTERS, 8(1), 23-30
Open this publication in new window or tab >>Simultaneously enhancing the strength and plasticity of Ti-based bulk metallic glass composites via microalloying with Ta
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2019 (English)In: MATERIALS RESEARCH LETTERS, ISSN 2166-3831, Vol. 8, no 1, p. 23-30Article in journal (Refereed) Published
Abstract [en]

Characteristics of deformation-induced transformation under loading dictate the mechanical performance of TRIP (transformation-induced plasticity)-reinforced bulk metallic glass composites (BMGCs), which have shown great potential as engineering materials. Here, we report that the addition of 0.3 at.% Ta in the Ti45Cu41Ni9Zr5 alloy could induce the formation of uniform glassy composite structure with B2-(Ti,Zr)(Ni,Cu) precipitates. More interestingly, nanosized A2-(Ti,Zr)(Ni,Cu) particles also formed inside B2 grains which effectively impede rapid propagation of martensite plates and lead to the formation of multi-oriented martensites, eventually homogenizing the involved plastic flow during deformation-induced transformation. Consequently, high fracture strength (similar to 3000 MPa), large plasticity (similar to 25%) and pronounced work-hardening ability were achieved. [GRAPHICS] IMPACT STATEMENT Microalloying of Ta not only homogenizes the B2 distribution, but also facilitates formation of multi-orientated martensites during deformation, resulting in simultaneously enhanced strength and plasticity of a Be-free Ti-based BMGC.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS INC, 2019
Keywords
Metallic glass composites, microalloying, transformation-induced plasticity, martensitic transformation, strengthening
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-270855 (URN)10.1080/21663831.2019.1680454 (DOI)000498029100001 ()
Note

QC 20200316

Available from: 2020-03-16 Created: 2020-03-16 Last updated: 2020-03-16Bibliographically approved
Dong, Y., Guo, S., Mao, H., Xu, C., Xie, Y., Cheng, C., . . . Sun, J. (2019). The Growth of Graphene on Ni-Cu Alloy Thin Films at a Low Temperature and Its Carbon Diffusion Mechanism. Nanomaterials, 9(11), Article ID 1633.
Open this publication in new window or tab >>The Growth of Graphene on Ni-Cu Alloy Thin Films at a Low Temperature and Its Carbon Diffusion Mechanism
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2019 (English)In: Nanomaterials, ISSN 2079-4991, Vol. 9, no 11, article id 1633Article in journal (Refereed) Published
Abstract [en]

Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni-Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni-Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni-Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2/Si substrate at a low temperature (similar to 600 degrees C).

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
transfer-free, lithography-free, graphene, chemical vapor deposition, insulating substrate, low temperature growth
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-266236 (URN)10.3390/nano9111633 (DOI)000502271700128 ()31744237 (PubMedID)2-s2.0-85075273340 (Scopus ID)
Note

QC 20200103

Available from: 2020-01-03 Created: 2020-01-03 Last updated: 2020-01-03Bibliographically approved
Omori, T., Bigdeli, S. & Mao, H. (2018). A Generalized Approach Obeying the Third Law of Thermodynamics for the Expression of Lattice Stability and Compound Energy: A Case Study of Unary Aluminum. JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, 39(5), 519-531
Open this publication in new window or tab >>A Generalized Approach Obeying the Third Law of Thermodynamics for the Expression of Lattice Stability and Compound Energy: A Case Study of Unary Aluminum
2018 (English)In: JOURNAL OF PHASE EQUILIBRIA AND DIFFUSION, ISSN 1547-7037, Vol. 39, no 5, p. 519-531Article in journal (Refereed) Published
Abstract [en]

Recently, Hillert and Selleby proposed a simple method for expression of the lattice stability or Gibbs energy of formation that does not violate the third law of thermodynamics. This method describes the derivation of the Gibbs energy function from high temperatures down to 0 K by interpolation, instead of extrapolation from room temperature to 0 K. In the present work, their original method is discussed in terms of determination of the characteristic parameter values. Keeping the essential interpolation character of their method, a generalized approach is presented for expressing the lattice stability through parameter optimizations. This approach retains the zero point entropy of substances and is in line with the development of the third generation CALPHAD databases. Using the Al unary system as a case study, the lattice stabilities of the hcp and bcc phases are investigated. The respective Einstein temperatures are also evaluated. At high temperatures, the present descriptions reproduce the lattice stabilities suggested by SGTE for the existing second generation of databases, with a reasonable accuracy. More importantly, information from ab initio calculations (total energy at 0 K) is also used for this optimization and the present method results in a physically sounder description of thermodynamic properties at lower temperatures down to 0 K. The present approach provides a simple and flexible way to estimate the lattice stabilities, with potential applicability for the Gibbs energy of formation of stoichiometric compounds and the excess energy of solution phases, in accordance with the third law of thermodynamics.

Place, publisher, year, edition, pages
Springer, 2018
Keywords
aluminum, excess energy, Gibbs energy of formation, lattice stability, thermodynamic database, third generation of CALPHAD databases
National Category
Other Physics Topics
Identifiers
urn:nbn:se:kth:diva-236002 (URN)10.1007/s11669-018-0641-4 (DOI)000444765000007 ()2-s2.0-85048360999 (Scopus ID)
Funder
VINNOVA, 2012-02892
Note

QC 20181016

Available from: 2018-10-16 Created: 2018-10-16 Last updated: 2018-12-03Bibliographically approved
Chen, H.-L., Mao, H. & Chen, Q. (2018). Database development and Calphad calculations for high entropy alloys: Challenges, strategies, and tips. Materials Chemistry and Physics, 210, 279-290
Open this publication in new window or tab >>Database development and Calphad calculations for high entropy alloys: Challenges, strategies, and tips
2018 (English)In: Materials Chemistry and Physics, ISSN 0254-0584, E-ISSN 1879-3312, Vol. 210, p. 279-290Article in journal (Refereed) Published
Abstract [en]

The development of a reliable multicomponent thermodynamic database for high entropy alloys (HEAs) is a daunting task and it faces new challenges comparing to the development of databases for conventional single principal element alloys, such as the assessment of a large number of ternary systems, the proper estimation of phase stability within metastable compositional and temperature ranges, and the reasonable extrapolation into higher order systems. We have recently established a thermodynamic database (TCHEA1) especially for HEAs within a 15-element framework. This work highlights the usage of high throughput density functional theory (OFT) calculations for validating and refining the binary and ternary parameters of the solid solution phases, and having a more reliable extrapolation into metastable regions and higher order systems. TCHEA1 consists of 105 binaries and 200 ternaries and contains nearly all the stable solution phases and intermetallic compounds in each of the assessed systems. Together with Thermo-Calc, this database enables us to predict the stability of the desired multicomponent solid solution relative to intermetallic compounds and other solid solutions. Calculation examples are presented not only for case studies but also for bridging the knowledge gap between Calphadian and people who do not have a background of the Calphad approach.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
High entropy alloys, Calphad, Thermodynamic database, Thermodynamic calculation
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-226744 (URN)10.1016/j.matchemphys.2017.07.082 (DOI)000429762200037 ()2-s2.0-85028308669 (Scopus ID)
Note

QC 20180503

Available from: 2018-05-03 Created: 2018-05-03 Last updated: 2018-05-03Bibliographically approved
Abu-Odeh, A., Galvan, E., Kirk, T., Mao, H., Chen, Q., Mason, P., . . . Arróyave, R. (2018). Efficient exploration of the High Entropy Alloy composition-phase space. Acta Materialia, 152, 41-57
Open this publication in new window or tab >>Efficient exploration of the High Entropy Alloy composition-phase space
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2018 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 152, p. 41-57Article in journal (Refereed) Published
Abstract [en]

High Entropy Alloys (HEAs), Multi-principal Component Alloys (MCA), or Compositionally Complex Alloys (CCAs) are alloys that contain multiple principal alloying elements. While many HEAs have been shown to have unique properties, their discovery has been largely done through costly and time-consuming trial-and-error approaches, with only an infinitesimally small fraction of the entire possible composition space having been explored. In this work, the exploration of the HEA composition space is framed as a Continuous Constraint Satisfaction Problem (CCSP) and solved using a novel Constraint Satisfaction Algorithm (CSA) for the rapid and robust exploration of alloy thermodynamic spaces. The algorithm is used to discover regions in the HEA Composition-Temperature space that satisfy desired phase constitution requirements. The algorithm is demonstrated against a new (TCHEA1) CALPHAD HEA thermodynamic database. The database is first validated by comparing phase stability predictions against experiments and then the CSA is deployed and tested against design tasks consisting of identifying not only single phase solid solution regions in ternary, quaternary and quinary composition spaces but also the identification of regions that are likely to yield precipitation-strengthened HEAs.

Place, publisher, year, edition, pages
Acta Materialia Inc, 2018
Keywords
Alloy design, CALPHAD, Constraint satisfaction problem, High-Entropy Alloys
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-227544 (URN)10.1016/j.actamat.2018.04.012 (DOI)000436650600005 ()2-s2.0-85045696607 (Scopus ID)
Note

QC 20180509

Available from: 2018-05-09 Created: 2018-05-09 Last updated: 2018-07-17Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-8493-9802

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