Microstructural evolution and deformation behavior of an interstitial TRIP high-entropy alloy under dynamic loading

The mechanical properties and microstructural evolution under dynamic loading conditions are of paramount importance in the development and utilization of interstitial high-entropy alloys (iHEAs). This study focuses on the investigation of a currently trending material, C-doped TRIP-assisted HEA Fe49.5Mn30Co10Cr10C0.5 (at.%). By subjecting the alloy to uniaxial quasi-static and dynamic tensile loading, the study systematically elucidates mechanical property testing under different strain states, characterizes the microstructural evolution during deformation, analyzes deformation mechanisms, and delves into the essence of mechanical responses. Particularly, by employing digital image correlation (DIC) techniques, local severe deformation regions under highspeed deformation conditions are sampled to investigate microstructural changes under extreme deformation conditions. The results indicated that, in comparison to quasi-static tensile deformation, the dynamic tensile deformation of the HEA demonstrated a slight increase in yield strength, a decrease in ultimate tensile strength, and a trend toward an increase in total elongation. Specifically, at a strain rate of 103 s- 1, the tensile strength was -825.5 MPa, and at a strain rate of 10 s- 1, the elongation was -57.7 %. In quasi-static deformation, the TRIP and TWIP effects served as the primary deformation mechanisms. In dynamic deformation, the proportion of epsilon-martensite phase transformation was significantly reduced, with deformation twinning (DT) and dislocations becoming the dominant mechanisms, originating from the impact of adiabatic heating on the stacking fault energy (SFE). Furthermore, in the locally severe deformation region, multiple twinning systems were activated, coupled with a substantial accumulation of dislocations. A minor presence of dual-oriented martensite also contributed to this complex mechanism. Additionally, the carbides formed through C-doping exerted a significant hindrance on dislocation slip during high-speed deformation and under high-strain conditions. Simultaneously, they promoted the activation of multiple twinning systems, making an indispensable contribution to maintaining the strain hardening rate (SHR) of the HEA.