An Investigation into the Impact of Cobalt Replacement by Silicon in FeCrMnNiCo Non-Stoichiometric High Entropy Alloys

Non-stoichiometric high entropy alloys have garnered significant attention in recent years. The current research aims to investigate the effects of substitution of the quasi-metallic element Silicon on FeCrMnNiCo high entropy alloy. Cobalt, a costly element, was replaced with silicon in varying concentrations (3, 6, and 9 at.%) to form alloys of composition Fe28Cr18Mn18Ni18Co18-xSix (x = 3, 6, or 9). The alloys were designed and manufactured using the vacuum arc remelting method. Comprehensive characterizations, including microstructural studies, solidification calculations, investigation of phase analysis, mechanical behavior, magnetic response, and measurement of thermal analysis and specific heat capacity were done. Microstructural analyses revealed that high silicon contents often separate from the primary phase and form silicon-rich phases. All four alloys seem to exhibit either a single phase or consist of two face-centered cubic (FCC) phases. Analysis indicates the presence of Cr₃Si intermetallic particles in Cr9Si9 alloy. Mechanical testing showed significant improvements in hardness (up to 80%), strength (over 60%), and Young’s modulus (up to 140%) with increasing silicon content, though at the cost of reduced ductility. While the reduction in flexibility was minimal for alloys containing 3 and 6 atomic percent silicon (less than 10%), a substantial drop in ductility was observed at 9 atomic percent, where fracture mode shifted from ductile to brittle. These findings offer valuable insights into the design of silicon-substituted HEAs for high-performance applications.