Influence of short-range order on pressure-induced fcc to hcp transformations in high entropy alloys

Metastable high-entropy and medium-entropy alloys exhibit a pressure-induced FCC→HCP phase transformation governed by stacking-fault–mediated mechanisms. While the transformation pressure is known to depend on composition and microstructure, the role of chemical short-range order (CSRO) remains unclear. Recent work by the group of Gil Coury demonstrated that CSRO in CoCrNi can be systematically tuned through controlled thermal treatments without introducing long-range order, enabling isolation of chemical ordering effects from other variables. We propose in-situ high-pressure synchrotron X-ray diffraction measurements on two well-defined CoCrNi specimen states, one with minimal and one with enhanced CSRO. By compressing both states quasi-statically in the large volume press at ESRF, we will directly determine the onset (critical) pressure of the FCC→HCP transformation as a function of CSRO.