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Stacking fault energies of CrMnFeCoNi-based high entropy alloys from ab initio

Thursday (27.09.2018)
09:15 - 09:30 S1/01 - A2
Part of:

High entropy alloys (HEAs) including CrMnFeCoNi-based alloys have attracted remarkable attention due to their excellent mechanical properties. Recent experiments supported the concept of transformation-induced plasticity (TRIP) HEAs to further improve strength and ductility simultaneously [1].

The key quantity determining whether an alloy tends to show TRIP or, e.g., TWIP (twinning induced plasticity) is the stacking fault energy (SFE). TRIP alloys require very low SFEs. Since the SFE is directly accessible via atomistic calculations, it provides an elegant link between macroscopic plastic deformation mechanisms and ab initio calculations. Since interstitials are well-known to affect the SFE, the key challenge in exploring and designing new interstitially alloyed TRIP HEAs is to activate the TRIP effect by balancing the SFE via compositional tuning. This concept is supported by recent experiments which show that interstitial alloying can indeed enhance mechanical properties [2]. To systematically explore this strategy, it is essential to quantify the SFE of HEAs as well as to evaluate the impact of interstitial atoms, alloy composition and temperature effects.

To achieve this goal, we employ two complementary ab initio techniques. We utilize a mean field approximation (i.e. coherent potential approximation) to efficiently screen SFEs in a wide range of compositions [3]. To study local relaxations and impact of interstitials we resort for selected alloys to explicit supercell models based on special quasirandom structures. Temperature effects are included and found to increase the SFE. Based on these results we discuss the effect of compositional fluctuations on the SFE and show how the SFE is related to a sensitive interplay between the deformation behavior and chemical short-range order.

[1] Z. Li, K. G. Pradeep, Y. Deng, D. Raabe, and C. C. Tasan, Nature 534, 227 (2016).

[2] Z. Li, C. C. Tasan, H. Springer, B. Gault, and D. Raabe, Sci. Rep. 7, 40704 (2017).

[3] Z. Li, F. Körmann, B. Grabowski, J. Neugebauer, and D. Raabe, Acta Mater. 136, 262 (2017).

Dr. Yuji Ikeda
Max-Planck-Institut für Eisenforschung GmbH
Additional Authors:
  • Dr. Fritz Körmann
    Max-Planck-Institut für Eisenforschung GmbH
  • Prof. Dr. Jörg Neugebauer
    Max-Planck-Institut für Eisenforschung GmbH