Effect of Ni and Fe content on the plastic deformation behavior of Co–Cr–Fe–Ni–Mo alloys: A combined computational and experimental study

ASTM F1058 Co–22Cr–17Fe–15Ni–4Mo (mol%) alloys (equivalent to Co–20Cr–16Fe–15Ni–7Mo in mass%) are widely used in biomedical applications, particularly in balloon-expandable stents, which require a combination of high ultimate tensile strength (UTS), good ductility, and low 0.2 % proof strength. To optimize the mechanical properties of these alloys, it is essential to understand their plastic deformation behavior. In this study, first-principles calculations, microstructural analysis, and mechanical property evaluation were used to investigate the stacking fault energy (SFE) and plastic deformation behavior of these alloys as a function of their Ni and Fe content. First-principles calculations indicated that their SFE increased with increasing Ni and Fe content, with Ni influencing the SFE more than Fe. Experimentally, increasing the Ni content suppressed the γ-to-ε stress-induced martensitic transformation during plastic deformation, resulting in improved ductility without compromising strength. With increasing Ni content, the plastic deformation mechanism in the early stage changed from martensitic transformation and/or deformation twinning to dislocation slip, attributable to an increase in the SFE. This study indicates that SFE evaluation by first-principles calculations is an effective approach for designing Co–Cr-based multicomponent systems from the perspective of plastic deformation mechanisms. • Ni effects the stacking fault energy (SFE) more than Fe in Co–Cr–Fe–Ni–Mo alloys. • Cr in Co-based alloys may reduce the SFE-enhancing ability of Fe. • Ni suppresses γ-to-ε strain-induced martensitic transformation. • Ni shifts the early plastic deformation mechanism from non-slip to slip. • Combining computational and experimental approaches in alloy design.