Dependence of Mechanical Properties and Deformation Behavior of TRIP-FeMnCoCrAl Dual-phase High-entropy Alloy on Grain Size and Strain Rate

Abstract

Fe₅₀Mn₃₀Co₁₀Cr₁₀ dual-phase metastable high-entropy alloys (HEAS) have gained significant attention for their outstanding mechanical properties. However, limited research has explored the relationship between grain size and strain rate sensitivity (SRS) in dual-phase HEAS. Current investigations primarily focus on pure metals and single-phase FCC HEAS. To address this gap, this study examines the impact of grain size on the deformation behavior and SRS of TRIP-(Fe₅₀Mn₃₀Co₁₀Cr₁₀)₉₇Al₃ dual-phase HEAS. Two variants of dual-phase HEAS were prepared, distinguished by their grain sizes (2.86 µm, labeled Fine Grain or FG, and 5.25 µm, termed Coarse Grain or CG), via the vacuum melting method. Subsequent tensile tests were conducted at varying strain rates, ranging from 0.001/s to 0.02/s. The findings unveil a robust grain size dependency in the phase transformation and deformation twinning of the (Fe₅₀Mn₃₀Co₁₀Cr₁₀)₉₇Al₃ dual-phase HEA during tensile deformation. Within the FeMnCoCrAl HEA system, characterized by a dual-phase structure, both TRIP (Transformation-Induced Plasticity) and TWIP (Twinning-Induced Plasticity) effects intensify with increasing grain size. Additionally, as the strain rate increases, the TRIP effect gradually diminishes while the TWIP effect strengthens. Notably, the strain rate sensitivity index ‘m’ exhibits a downward trend with an increase in grain size, distinguishing it from the behavior observed in single-phase FCC HEAS. This study conducts an in-depth analysis of grain size’s impact on the SRS of (Fe₅₀Mn₃₀Co₁₀Cr₁₀)₉₇Al₃ dual-phase HEA, scrutinizing micro-level aspects encompassing phase transformation, deformation twinning, and grain boundary slip. The findings provide essential theoretical insights for designing HEAS tailored for applications requiring high strain rates.