Understanding the Metallurgy of High Entropy Alloys

From Professor Stéphane Gorsse

I am a material scientist focused on metallurgy, which integrates chemistry, physics, mechanics and engineering. Part of my scientific studies is to practice computational thermodynamics. I find metals both fascinating and familiar, as they are found in a wide variety of applications. Behind what seems banal because of daily familiarity, there is prowess achieved by metallurgy to control and improve the structural and functional properties of metallic alloys. There is also a freedom to scientific research, the opportunity of meeting great minds, and the fortune of sitting on the shoulders of giants [1]. I also find teaching a most enriching experience. The student’s engagement is rewarding.

I study the genesis and evolution of microstructure in metallic alloys, and the effects of microstructure parameters on properties. My current work is aimed to contribute in gaining a better understanding the metallurgy of High Entropy Alloys (HEAs) and the holistic view of Complex Concentrated Alloys (CCAs) and Multi-Principal Elements Alloys (MPEAs). I am also designing and implementing methodologies that could help to accelerate the discovery of new high-performance alloys, this with a combination of interesting properties and operating processability.

My research involves collaboration with researchers from all over the world. It is carried out in strong cooperation with Dan Miracle and Oleg Senkov from the Air Force Research Laboratory, and Rajarshi Banerjee from the University of North Texas, all based in the USA. From Asia-Pacific, An-Chou Yeh from the National Tsing Hua University in Taiwan, Hideyuki Murakami from National Institute for Material Science in Japan, and Christopher Hutchinson from Monash University in Australia are scientist who I work closely with. In Europe, I have close research relationships with Stéphane Godet from Université Libre de Bruxelles, and Geoffroy Hautier from Université Catholique de Louvain, who both are based in Belgium.

High Entropy Alloys Research

High Entropy and multi-principle elements concepts are a shift in design principle of alloys, from the boundaries to the center of the compositional space, which gives both unprecedented opportunities and challenges [2, 3]. It expands the range of possibilities and offers metallurgists more degrees of freedom to develop novel alloys. It involves the exploration of vast and uncharted multi-dimensional compositional space, which requires the development of more efficient approaches and tools. Even though only crumbs of the design space have been explored so far, it has been observed that HEAs can exhibit unique and highly tunable properties compared to traditional single principal element alloy [2, 4].

In general, HEA research breathes new inspiration that revisits the main metallurgical concepts and revitalizes the metallurgy. The number of papers and conferences on HEAs are booming, impact factors of journals on metallurgy are increasing, student interest is fueled. The concept spreads from metals to other materials families, for example ceramics and polymers. Commercial industry though, is waiting for innovation trigger with potentially impactful applications.

For example, in gas turbine engines used in the aerospace and energy industries, to meet the demand for high-temperature structural materials and to cut down in CO2 emissions, High Entropy Superalloys (HESAs) [5], refractory HEAs (RHEAs), refractory complex concentrated alloys (RCCAs) and Refractory Superalloys (RSAs) [6] currently attract great attention and efforts with the aim to overcome the temperature limit of advanced Ni-based superalloys.

Computational Thermodynamics in Professor Gorsse’s Work

In my research, I use Thermo-Calc products and the CALPHAD approach mainly for two purposes [7]. The first one is to understand and rationalize experimental observations on the genesis and evolution of microstructures during thermomechanical treatments of alloys [8-12]. The second is to anticipate the effects of composition and processing parameters on microstructures and properties of alloys which enables to guide the experiments [13-15].

I am excited to experience data-science in conjunction with computational science. This to virtually explore more efficiently the vast design space toward the most interesting regions, with the aim to accelerate the discovery and development of new alloys. Also, to improve the reliability and accuracy of the predictions [16]. One can say that when there are no simple physics-based “equations” to describe, a phenomenon or a property, or when the “equations” exist but are very “expensive” to evaluate. To reach these goals, I build databases [17], and implement active learning cycles combining computational thermodynamic, designed experiments and machine learning. I particularly enjoy the new TC-Python, which enables automation and the coupling with third-party data-science and data-visualization tools.

Stéphane Gorsse, Associate Professor, CNRS, University of Bordeaux, Bordeaux INP, ICMCB, has used Thermo-Calc software in his research for 20 years. Learn more about Prof. Gorsse at ResearchGate, Publons and LinkedIn. For further information about TC-Python do not hesitate to contact info@thermocalc.com.

References

[1] Expression attributed to Bernard de Chartres and taken up by Yves Bréchet in the preface of the book Georges Vendryes le “père” des réacteurs à neutrons rapides.

[2] S. Gorsse, D.B. Miracle, O.N. Senkov, Mapping the world of complex concentrated alloys, Acta Materialia 135 (2017) 177–187, DOI: 10.1016/j.actamat.2017.06.027.

[3] S. Gorsse, J.-P. Couzinié, D. B. Miracle, From high-entropy alloys to complex concentrated alloys, C. R. Physique 19 (2018) 721–736, DOI: 10.1016/j.crhy.2018.09.004.

[4] B. Gwalani, S. Gorsse, D. Choudhuri, Y. Zheng, R.S. Mishra, R. Banerjee, Tensile yield strength of a single bulk Al0.3CoCrFeNi high entropy alloy can be tuned from 160 MPa to 1800 MPa, Scripta Materialia 162 (2019) 18–23, DOI: 10.1016/j.scriptamat.2018.10.023.

[5] Y.-T. Chen, Y.-J. Chang, H. Murakami, S. Gorsse, A.-C. Yeh, Designing high entropy superalloys for elevated temperature application, Scripta Materialia 187 (2020) 177–182, DOI: 10.1016/j.scriptamat.2020.06.002.

[6] D.B. Miracle, M.H. Tsai, O.N. Senkov, V. Soni, R. Banerjee, Refractory high entropy superalloys (RSAs), Scripta Materialia 187 (2020) 445–452, DOI: 10.1016/j.scriptamat.2020.06.048.

[7] S. Gorsse and F. Tancret, Current and emerging practices of CALPHAD toward the development of high entropy alloys and complex concentrated alloys, Journal of Materials Research 33(19) (2018) 2899-2923, DOI: 10.1557/jmr.2018.152.

[8] B. Gwalani, S. Gorsse, D. Choudhuri, M. Styles, Y. Zheng, R.S. Mishra and R. Banerjee, Modifying transformation pathways in high entropy alloys or complex concentrated alloys via thermo-mechanical processing, Acta Mater. 153 (2018) 169-185, DOI: 10.1016/j.actamat.2018.05.009.

[9] O.N. Senkov, S. Gorsse, D.B. Miracle, High temperature strength of refractory complex concentrated alloys, Acta Mater. 175 (2019) 394-405, DOI: 10.1016/j.actamat.2019.06.032.

[10] B. Gwalani, S. Gorsse, V. Soni, M. Carl, N. Ley, J. Smith, A.V. Ayyagari, Y. Zheng, M. Young, R.S. Mishra, R. Banerjee, Role of copper on L12 precipitation strengthened fcc based high entropy alloy, Materialia 6 (2019) 100282, DOI: 10.1016/j.mtla.2019.100282.

[11] D. Choudhuri, B. Gwalani, S. Gorsse, M. Komarasamy, S.A. Mantri, S.G. Srinivasan, R.S. Mishra, R. Banerjee, Enhancing strength and strain hardenability via deformation twinning in fcc-based high entropy alloys reinforced with intermetallic compounds, Acta Mater.165 (2019) 420-430, DOI : 10.1016/j.actamat.2018.12.010.

[12]  ACL-2020. S. Dasari, A. Jagetia, Y.-J. Chang, V. Soni, B. Gwalani, S. Gorsse, A.-C. Yeh, R. Banerjee, Engineering multi-scale B2 precipitation in a heterogeneous FCC based microstructure to enhance the mechanical properties of a Al0.5Co1.5CrFeNi1.5 high entropy alloy, Journal of Alloys and Compounds 830 (2020) 154707, DOI: 10.1016/j.jallcom.2020.154707.

[13] S. Dasari, V. Chaudhary, B. Gwalania, A. Jagetia, V. Soni, S. Gorsse, R.V. Ramanujan, R. Banerjee, Highly Tunable Magnetic and Mechanical Properties in an Al0.3CoFeNi Complex Concentrated Alloy, Materialia 12 (2020) 100755, DOI: 10.1016/j.mtla.2020.100755.

[14] S. Dasari, A. Jagetia, V. Soni, B. Gwalani, S. Gorsse, and R. Banerjee, Engineering Transformation Pathways in an Al0.3CoFeNi Complex Concentrated Alloy Leads to Excellent Strength-Ductility Combination, Materials Research Letters, 8(11) (2020) 399, DOI: 10.1080/21663831.2020.1777215.

[15] S. Dasari, B. Gwalani, A. Jagetia, V. Soni, S. Gorsse, R. Banerjee, Hierarchical Eutectoid Nanolamellar Decomposition in an Al0.3CoFeNi Complex Concentrated Alloy, Scientific Reports 10 (2020) 4836, DOI : 10.1038/s41598-020-61538-6.

[16] S. Gorsse and O.N. Senkov, About the Reliability of CALPHAD Predictions in Multicomponent Systems, Entropy 20(12) (2018) 899, DOI: 10.3390/e20120899.

[17] S. Gorsse, M.H. Nguyen, O.N. Senkov, D.B. Miracle, Database on the mechanical properties of high entropy alloys and complex concentrated alloys, Data in Brief 21 (2018) 2664–2678. DOI: 10.1016/j.dib.2018.11.111.