Complex deformation behavior of a partially recrystallized metastable medium-entropy alloy: In-situ synchrotron X-ray diffraction study

Ferrous medium-entropy alloys (FeMEAs), leveraging deformation-induced martensitic transformation (DIMT), demonstrate excellent strain-hardening ability attributed to the transformation-induced plasticity (TRIP) effect. To improve the low yield strength of FeMEAs, the initial microstructure was controlled by utilizing partial recrystallization. The intricate initial microstructure, a blend of recrystallized (ReX) and non-recrystallized (non-ReX) regions, results in complex deformation behavior where DIMT in both the ReX and non-ReX regions are simultaneously activated, posing significant analytical challenges. In this paper, we perform in-situ synchrotron X-ray diffraction during the tensile loading on a partially recrystallized metastable Fe_57.5Co₁₈Cr₁₃Ni_7.5Mo₃C₁ (at%) FeMEA to quantitatively analyze each deformation mechanism. The innovative idea of peak deconvolution enables separate tracing of the deformation behavior of the ReX and non-ReX FCC domains, revealing the stress partitioning between them. DIMT kinetics in each domain are investigated by the evolution of domain fractions, and we provide a detailed discussion on how both of them exhibit rapid DIMT kinetics. Furthermore, we measure the contributions of DIMT occurring in each domain on the global strain-hardening rate. The results suggest that the predominant contribution shifts from DIMT in the ReX domain to DIMT in the non-ReX domain as deformation progresses, highlighting the distinctive strain-hardening mechanisms between the ReX and non-ReX domains. This work demonstrates how a partially recrystallized metastable FeMEA exhibits superior mechanical properties and provides insights into analyzing the complex deformation behavior.