Effect of Cr content on the mechanical behaviour of a high entropy alloy

High entropy alloys (HEAs) are a relatively novel class of materials with unique properties. Unlike traditional alloys, which are typically based on a single primary metal combined with smaller amounts of other elements, HEAs are composed of five or more principal elements, each usually present in significant amounts. This study investigates the influence of chromium content on the microstructure and mechanical properties of Cr x CoFeMnNi HEAs focusing on three compositions: HEA10Cr, HEA20Cr, and HEA30Cr. Using Vickers hardness and shear punch testing at both room temperature and 400 °C, the research identifies a strong correlation between increasing Cr content and enhanced strength-based properties. Contrary to conventional behavior, grain size and secondary dendrite arm spacing exhibited limited influence, with mechanical performance instead dominated by chemical composition, lattice distortion, and elemental segregation. The HEA30Cr alloy displayed the highest hardness and shear strength, attributed to more severe lattice distortion, Cr-induced dendritic growth, and sigma phase formation. Elevated temperatures reduced strength and strain hardening due to increased dislocation mobility, though ductility remained largely unaffected. Strain rate sensitivity was found to be modest at room temperature and negligible at 400 °C. These findings underscore the critical role of Cr in tuning the mechanical response of FCC-based HEAs and highlight the need for compositional control to balance strength and ductility for high-performance applications.