Schmid factor and temperature control of ε martensite evolution in a Co$_{34}$Cr$_{23}$Fe$_{25}$Ni$_{18}$ metastable compositionally complex alloy

Research on transformation-induced plasticity in compositionally complex alloys (CCAs) has focused on alloy design, but activating specific mechanisms also requires consideration of the Schmid factor and deformation temperature. The effective stacking fault energy model captures the effect of orientation and temperature on twinning, but does not predict ε martensitic transformation because it considers only twinning and full dislocation cross-slip. The specific roles of Schmid factor and temperature in ε martensite nucleation are not well understood. To investigate this, tensile and compression tests were conducted on a CCA single crystal (Co$_{34}$Cr$_{23}$Fe$_{25}$Ni$_{18}$, wt. %) along the [001] direction at 298 and 77 K, where the Schmid factor for partial dislocations varies with loading mode. Direct observations show that ε martensite does not form under tensile test at 298 K, but it nucleates at 77 K or under compressive stress. By combining generalized stacking fault energy analysis, molecular dynamics simulations, and experimental observations, this work links temperature and Schmid factor to dislocation-mediated ε martensitic transformation. ... mehrSchmid factor and temperature influence ε martensite nucleation by modulating the glide behavior of Shockley partial dislocations, providing insights into ε martensite formation and guiding microstructure tailoring to improve material properties.