While many high-entropy and medium-entropy alloys (HEAs/MEAs) exhibit exceptional mechanical, wear, corrosion, and oxidation performance, their reliance on costly elements, such as cobalt, limits broader industrial adoption. In this study, CALPHAD-based equilibrium and non-equilibrium simulations were used to screen the Co-free Al–Cr–Fe–Ni quaternary system for compositions that favour BCC/B2 phase formation under rapid solidification while suppressing FCC and brittle intermetallic phases. The selected composition, Al 1.2 Cr 0.5 Fe 0.5 Ni MEA, was produced via ultrasonic atomization and subsequently deposited as a coating on 316 stainless steel using laser cladding. Characterization of the atomized powder feedstock revealed a microstructure consisting of primary B2 dendrites and eutectic BCC + B2 interdendritic regions. Detailed analysis of the laser-clad coating demonstrated excellent metallurgical bonding and confirmed retention of this dual-phase BCC/B2 structure, even in the dilution zone at the coating-substrate interface where Fe enrichment occurs. The coating achieved a high microhardness of 489 ± 9 HV 0.3 , demonstrating mechanical performance comparable to Co-containing systems. In addition, nanoindentation mapping revealed a highly uniform nanohardness, reflecting balanced strengthening contributions of the BCC and B2 phases. Overall, this study validates the use of CALPHAD-guided design for developing cost-effective, high-performance Co-free surface coatings. • CALPHAD guided the design of a Co-free Al-Cr-Fe-Ni MEA targeting BCC/B2 formation. • Powder and laser-clad coating validated the dual-phase BCC/B2 structure. • The Co-free coating achieved microhardness comparable to Co-containing alloys. • Balanced B2 and BCC strengthening provided uniform nanohardness through the coating.
Bosi et al. (2026) studied this question.