Hall-Petch and grain growth kinetics of the low stacking fault energy TRIP Cr₄₀Co₄₀Ni₂₀ multi-principal element alloy

The Cr40Co40Ni20 multi-principal element alloy (MPEA) displays a single-phase face centered cubic initial structure, which partially transforms to hexagonal close packed (HCP) phase by transformation-induced plasticity (TRIP) during straining, as evidenced by nanometric HCP lamellae that provide enhanced mechanical properties. This MPEA also exhibits significant yield strength-grain size dependence, given by the high Hall-Petch coefficients (k = 667 MPa/mu m(-0.5) and sigma(0) = 299 MPa). The high activation energy for grain growth (Q(G) = 533 kJ/mol) leads to refined grain structures after conventional heat treatments. These features, combined with the large solid solution strengthening of Cr-rich Cr-Co-Ni MPEAs, grant the Cr40Co40Ni20 alloy a great combination of strength and ductility under tension. Finally, an empirical equation is proposed to describe the stacking fault energy (SFE) of Cr-Co-Ni alloys, contributing to the prediction of the acting deformation mechanisms. Such findings highlight the potential of compositional tuning to enhance multiple strength and deformation mechanisms in the Cr-Co-Ni system.