Microstructure evolution, work-hardening-dynamic softening transition and wear performance of a NiAl-based high-entropy alloy

This study fabricated a NiAl-CoCrxZryFez high-entropy alloy (HEA) with a valence electron concentration (VEC) value of 7 via vacuum arc melting. The influence of Zr content on the alloy's microstructure, mechanical properties, and wear performance was systematically investigated. Microstructural analysis revealed that increasing Zr progressively enhanced the volume fraction of eutectic microstructure, while the phase composition evolved from a single BCC phase to a dual-phase FCC + BCC structure. The Ni₃₀Al₂₈Co₁₅Zr₇Fe₂₀ alloy exhibited exceptional resistance to high-temperature softening, achieving yield strengths of 1316 MPa at 600 °C, 960 MPa at 800 °C, and 300 MPa at 1000 °C. However, thermal stability assessments indicated that eutectic secondary phases in both Ni₃₀Al₂₈Co₁₅Cr₅Zr₅Fe₁₇ and Ni₃₀Al₂₈Co₁₅Zr₇Fe₂₀ alloys became unstable at 1000 °C, exhibiting a tendency for phase ablation. Furthermore, Zr addition broadened the temperature window for the transition from work-hardening to dynamic softening during deformation by approximately 200 °C. High-temperature tribological tests (600–800 °C) revealed a transition in the dominant wear mechanisms from abrasive to adhesive wear with increasing temperature. The Ni₃₀Al₂₈Co₁₅Zr₇Fe₂₀ alloy exhibited superior wear resistance at 800 °C, achieving the lowest wear rate of 8.92 × 10⁻⁶ (mm³/N·m). This enhancement is attributed to Zr-induced solid solution strengthening, which improved hardness and effectively mitigated delamination wear mechanisms, thereby maintaining excellent high-temperature wear resistance.