Chemical Short-Range Order (CSRO) has attracted recent attention from many researchers, creating intense debates about its impact on material properties. The challenges lie in confirming and quantifying CSRO, as its detection proves exceptionally demanding, contributing to conflicting data in the literature regarding its true effects on mechanical properties. Our work uses high-precision calorimetric data to unambiguously prove the existence and, coupled with atomistic simulations, quantify the type of CSRO. This methodology allows us to propose a mechanism for its formation and destruction based on the heat evolution during thermal analysis and facilitates a precise identification of local ordering in CoCrNi alloys. Samples of CoCrNi (Co₃₃Cr₃₃Ni₃₃) and CrNi₂ (Cr₃₃Ni₆₆) alloys are fabricated in varying ordered states, extensively characterized via synchrotron X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy. Samples with considerably different ordered states are submitted to tensile tests with in-situ synchrotron X-ray diffraction. We demonstrate, despite inducing varied CSRO levels in CoCrNi, no significant alterations in overall mechanical behavior emerge. However, the CrNi₂ alloy, which undergoes long-range ordering, experiences significant shifts in yield strength, ultimate tensile stress and ductility.

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/μm^−0.5 and σ₀ = 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.

Multi-principal element alloys (MPEAs) are an emergent class of metallic materials that displays a huge range of possible properties and applications. CrCoNi MPEAs attract great interest because they show good strength–ductility combinations, especially in Cr-rich non-equiatomic compositions. In this work, the Cr₄₀Co₃₀Ni₃₀ MPEA was produced and characterized at different annealing conditions. This alloy displays a great strength–ductility balance, evidenced by the high uniform deformation (55–70%) and high estimated toughness. It also exhibits high strengthening by grain refining, given by the high Hall–Petch slope (k = 655 MPa/μm^−0.5). The grain growth kinetics analysis provides estimates that can aid the design and processing of this alloy for future applications. Deformed samples displayed both TWIP and TRIP effects, once mechanical twins and HCP martensitic phase, arranged in nanometric lamellae, are formed during straining, greatly increasing the number of interfaces in the microstructure and providing good mechanical properties in tension. Graphical abstract