Heterostructure-reinforced CoCrFeNiTax (x = 0.5 and 1) high-entropy alloy coatings fabricated by combining mechanical alloying and hot-pressing sintering

Abstract

The high-performance CoCrFeNiTa_0.5 (Ta0.5) and CoCrFeNiTa (Ta1) high-entropy alloy coatings (HEACs) consolidated on the Q235 substrate were synthesized via mechanical alloying and vacuum hot-pressing sintering. The final milled Ta0.5 and Ta1 powders consist of dual body-centered cubic phases, with the Ta1 powder additionally containing an amorphous phase. Both HEACs comprise double face-centered cubic solid-solution matrix with intermetallic compound. Distinct precipitate distribution patterns are observed across four characteristic regions: the transition boundary, fine-grained layer, coarse-grained layer, and normal region. These microstructural features contribute to excellent interfacial bonding, as evidenced by the bending strengths of 586 MPa (Ta0.5) and 531 MPa (Ta1). Due to the thicker fine-grained layer adjacent to the substrate, the Ta0.5 coating exhibits superior resistance to shearing forces and bending moment, resulting in higher bending strength. The Ta1 coating achieves optimized microhardness, showing 256 % and 28 % improvements over the substrate and Ta-free CoCrFeNi coating, respectively. Furthermore, wear resistance tests confirm that both HEACs outperform the substrate. The enhanced microhardness and wear resistance are attributed to solid-solution strengthening (from larger Ta atoms), second-phase strengthening (via nanoscale Laves phases), and the synergistic effect of the dual FCC matrix with uniformly distributed nanoscale hard phases. Electrochemical corrosion tests display that both HEACs demonstrate superior comprehensive corrosion resistance in a 3.5 wt% NaCl solution, primarily due to the formation of protective Ta oxides.