Tribological wear behavior of thermal-sprayed AlCoCr2FeMo0.5Ni-Zrx high-entropy alloy coatings

The exceptional mechanical and thermal characteristics of high-entropy alloys (HEAs) have attracted substantial attention; however, their potential as protective coatings continues to be a major focus of ongoing research. This study examines the influence of zirconium (Zr) addition on the microstructural evolution, and the mechanical and tribological performance of flame-sprayed AlCoCr 2 FeMo 0.5 Ni-Zrₓ (x = 5, 10, and 15 wt%) coatings synthesized on SS 316 L substrates. Mechanical properties were evaluated via microhardness testing, while tribological behavior was assessed through multi-pass scratch wear experiments. Phase analysis revealed a dominant body-centred cubic (BCC) solid-solution phase, along with secondary phases such as ZrO₂, Cr₂O₃, and spinel oxide. The incorporating Zr significantly improved the coating hardness, with AlCoCr 2 FeMo 0.5 Ni-Zr 5 (585 HV 0.3 ), AlCoCr 2 FeMo 0.5 Ni-Zr 10 (720 HV 0.3 ), and AlCoCr 2 FeMo 0.5 Ni-Zr 15 (907 HV 0.3 ) exhibiting microhardness values ~3.7, 4.6, and 5.7 times higher than that of SS 316 L (158 HV 0.3 ), respectively, owing to the combined contributions of solid-solution strengthening and ZrO 2 -induced oxide dispersion hardening. Among the coatings, AlCoCr 2 FeMo 0.5 Ni-Zr 10 exhibited the lowest coefficient of friction (COF) of 0.11 the minimum specific wear rate of 4.48 × 10 −3 mm 3 /N·m, with reductions of 68.3% in COF and 72.5% in specific wear rate compared to uncoated SS 316 L. The superior performance was attributed to a well-balanced combination of hardness and toughness, reflected by high H / E and H 3 / E 2 ratios. These findings demonstrate that Zr-modified AlCoCr 2 FeMo 0.5 Ni HEA coatings deposited via flame spraying exhibit enhanced multi-pass scratch wear resistance, providing new insights into the design of wear-resistant HEA coatings for industrial applications involving severe sliding and abrasive environments.