Strain rate sensitive microstructural evolution in a TRIP assisted high entropy alloy: Experiments, microstructure and modeling

Abstract

Compressive response of a novel Fe38·5Mn20Co20Cr15Si5Cu1.5 high entropy alloy with transformation induced plasticity made by laser powder bed fusion was studied at quasi-static, medium and high strain rates. Mechanical response and variation in work hardening rate with strain rate were correlated with γ (f.c.c.) → ε (h.c.p.) martensitic transformation, subsequent phase evolution and adiabatic heating. A strong near basal {0 0 0 1} texture observed in the transformed ε (h.c.p.) phase after deformation was correlated with the initial texture, γ (f.c.c.) → ε (h.c.p.) transformation orientation relationship, as well as the activated deformation mechanisms in ε (h.c.p.) phase. The initial c/a ratio of 1.612 for the ε (h.c.p.) phase evolved with deformation and this was quantified to understand the propensity of non-basal <c+a> slip activation. Metastable γ (f.c.c.) dominant microstructure in the as-built alloy enabled excellent hardening via γ (f.c.c.) → ε (h.c.p.) transformation accompanied by activation of non-basal <c+a> slip and twinning. Experimental results were correlated with existing empirical constitutive models such as Johnson-Cook, Modified Zerilli-Armstrong, Khan-Huang-Liang and Khan-Liu; the Khan-Liu model evidenced the best correlation with experimental results.