Metastable HEAs have shown to be able to overcome the work hardening deficiency of conventional HEAs, allowing the destabilization of the γ-fcc phase [1]. As such,  ε-hcp forms during deformation, which is known as the TRIP effect and hence these alloys are referred as TRIP-HEAs. Recent studies on tailoring the metastability of a Fe40-Mn20-Co20-Cr15-Si5 (at.%) TRIP-HEA, resulted in an excellent strength and ductility relationship [2]. The addition of 1 at.% Al in this system, followed by friction stir processing causing an ultra-fine grained microstructure, and by subsequent annealing treatment was seen to result in remarkable mechanical properties, without, however, revealing the involved deformation mechanisms [3]. In this contribution, a detailed investigation following the formation of ε-hcp and the subsequent deformation mechanisms upon further straining is undertaken in a fine-grained Fe39-Mn20-Co20-Cr15-Si5-Al1 (at.%) TRIP-HEA.  

In situ synchrotron X-ray diffraction tests in transmission geometry during uniaxial tensile deformation were undertaken to study the evolution of the TRIP effect and the interplay of deformation mechanisms. Post-mortem EBSD was performed to verify some the observations from the synchrotron XRD investigation [4]. Three distinct deformation regimes are detected: 1) the initial elastic and early dislocation-based plasticity deformation in the γ-fcc phase is followed by 2) a moderate work hardening rate regime, which is associated with the deformation-induced phase formation of ε-martensite, as well as slip in the parent γ-fcc phase. 3) During the third deformation regime, the phase transformation continues to occur in combination with 2 modes of hcp twinning (extension twinning and contraction twinning) and slip in the unfavourably oriented grains for twinning. The interplay of all these co-existing deformation mechanisms can be evidenced by synchrotron X-ray diffraction and it is verified by post-mortem EBSD. 

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

2. S.S. Nene, M. Frank, K. Liu, S. Sinha, R.S. Mishra, B. McWilliams, K.C. Cho, Scri. Mater., 154, (2018), 163. 

3. S.S. Nene, S. Sinha, M. Frank, K. Liu, R.S. Mishra, B.A. McWilliams, K.C. Cho, Apl. Mater. Today, 13, (2018), 198.

4. E. Polatidisa, S.Shukla, J.Čapek, S.Van Petegem, N.Casati, R.S.Mishra, Mat. Today Com., 30, (2021), 103155.