Sequential activation of TRIP and TWIP enables multi-stage hardening in a metastable FeMnCoCrN high-entropy alloy at elevated temperature

초록

The deformation behavior of a metastable Fe46Mn35.5Co9Cr9N0.5 (at.%) high-entropy alloy was examined under uniaxial tensile testing at 400 degrees C. Although transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) mechanisms are typically suppressed at elevated temperatures due to increased stacking fault energy, the elemental partitioning inherent to the as-cast microstructure enables their localized activation resulting in a sequential, multi-stage rapid hardening (bump hardening) behavior. Notably, a localized shear-induced reversion from HCP to FCC was observed within transformed regions, supported by misorientation and pole figure analyses that deviated from the ideal orientation relationship. This intermediate-stage reduction in HCP fraction is attributed to shear-induced reversion, highlighting the highly dynamic nature of phase transformations at elevated temperatures. The concurrent operation of TRIP, TWIP, and phase reversion emphasizes the role of local phase stability and provides new insights into enhancing strain-hardening capability of metastable HEAs under high-temperature conditions.

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