Microstructures and elementary deformation mechanisms of single-phase fcc and bcc high-entropy alloys
Metallurgical, Thermal and Thermomechanical Treatment of Materials
Final Report Abstract
During this research project, processing routes were established to produce chemically homogeneous, nearly texture-free and single-phase FCC medium- and high-entropy alloys (MEAs and HEAs) from the Cr-Mn-Fe-Co-Ni system with well-controlled grain sizes. This served as basis for further fundamental investigations with several research partners including the characterization of the physical and mechanical properties, oxidation resistance, and phase stability of these materials. The temperature dependence of magnetism, coefficient of thermal expansion, and elastic moduli of a set of medium entropy subsystems of the CrMnFeCoNi HEA were documented in the present project as they are useful for many fields of materials science and for engineers who need them to design components. Another key outcome of this project was the contribution to a better understanding of the elementary deformation mechanisms responsible for the outstanding mechanical properties of MEAs and HEAs at cryogenic temperatures. We showed that deformation twinning plays a key role in overcoming the strength/ductility trade-off. Deformation twinning was found to take place above a critical stress that is temperature independent but depends of chemical composition. In another study, we investigated whether the sluggish diffusion in HEAs would result in enhanced oxidation resistance. Based on oxidation tests in laboratory air followed by microstructural and chemical analyses, it was shown that sluggish diffusion, if any, does not improve the oxidation resistance of the CrMnFeCoNi HEA. This alloy has a rather low oxidation resistance above 600°C due to the fast growth of non-protective Mn-rich oxides and the formation of pores in the matrix close to the oxide scale. Based on a careful comparison with literature data, we suggested that the underlying rate-controlling mechanism corresponds to the diffusion of Mn through the oxides. Finally, we performed a phase-stability and precipitation-kinetics study using an off-equiatomic HEA. This work allowed to establish a simple pseudo-binary phase diagram and, to our knowledge, to report the first TTT-diagram in the field of HEAs.
Publications
- Microstructural evolution of a CoCrFeMnNi high-entropy alloy after swaging and annealing. Journal of alloys and compounds, volume 647, pages 548-557
G. Laplanche, O. Horst, F. Otto, G. Eggeler, E.P. George
(See online at https://doi.org/10.1016/j.jallcom.2015.05.129) - Microstructure evolution and critical stress for twinning in the CrMnFeCoNi high-entropy alloy. Acta Materialia, volume 118, pages 152-163
G. Laplanche, A. Kostka, O.M. Horst, G. Eggeler, E.P. George
(See online at https://doi.org/10.1016/j.actamat.2016.07.038) - Oxidation Behavior of the CrMnFeCoNi High-Entropy Alloy. Oxidation of Metals, volume 85, pages 629-645
G. Laplanche, U.F. Volkert, G. Eggeler, E.P. George
(See online at https://doi.org/10.1007/s11085-016-9616-1) - Reasons for the superior mechanical properties of medium-entropy CrCoNi compared to high-entropy CrMnFeCoNi. Acta Materialia, volume 128, pages 292-303
G. Laplanche, A. Kostka, C. Reinhart, J. Hunfeld, G. Eggeler, E.P. George
(See online at https://doi.org/10.1016/j.actamat.2017.02.036) - Thermal activation parameters of plastic flow reveal deformation mechanisms in the CrMnFeCoNi high-entropy alloy. Acta Materialia, volume 143, pages 257-264
G. Laplanche, J. Bonneville, C. Varvenne, W.A. Curtin, E.P. George
(See online at https://doi.org/10.1016/j.actamat.2017.10.014) - Elastic moduli and thermal expansion coefficients of medium-entropy subsystems of the CrMnFeCoNi high-entropy alloy. Journal of alloys and compounds, volume 746, pages 244-255
G. Laplanche, P. Gadaud, C. Bärsch, K. Demtröder, C. Reinhart, J. Schreuer, E.P. George
(See online at https://doi.org/10.1016/j.jallcom.2018.02.251) - Phase stability and kinetics of σ-phase precipitation in CrMnFeCoNi high-entropy alloys. Acta Materialia, volume 161, pages 338-351
G. Laplanche, S. Berglund, C. Reinhart, A. Kostka, F. Fox, E.P. George
(See online at https://doi.org/10.1016/j.actamat.2018.09.040) - Effect of temperature and texture on Hall-Petch strengthening by grain and annealing twin boundaries in the MnFeNi medium-entropy alloy. Metals, volume 9, pages 84-101
M. Schneider, F. Werner, D. Langenkämper, C. Reinhart, G. Laplanche
(See online at https://doi.org/10.3390/met9010084) - Data compilation on the effect of grain size, temperature, and texture on the strength of a single phase FCC MnFeNi medium-entropy alloy. Data in brief, volume 28, article number: 104807
M. Schneider, F. Werner, D. Langenkämper, C. Reinhart, G. Laplanche
(See online at https://doi.org/10.1016/j.dib.2019.104807) - Effects of cryogenic temperature and grain size on fatigue-crack propagation in the medium-entropy CrCoNi alloy. Acta Materialia, volume 200, pages 351-365
J. Rackwitz, Q. Yu, Y. Yang, G. Laplanche, E.P. George, A.M. Minor, R.O. Ritchie
(See online at https://doi.org/10.1016/j.actamat.2020.09.021)
