Abstract: High-entropy alloy matrix solid-lubricating composites (HSLCs) are promising anti-wear and friction-reduced materials to meet the demands of complicated engineering applications. Here we present a strategy to develop HSLCs by using the coupled high-entropy phases of (BCC + FCC + L2₁) with near-equal volume fraction as the matrix material, instead of using the usual single phase-dominated high-entropy phases, which can preserve the intrinsic strength and deformability of the matrix while activating adaptive wear protection during sliding. This enables a low coefficient of frictions of 0.23-0.31 and wear rates within the order of 10^-6-10^-5 mm³ N m^-1 for the (CrFeNi)₈₃(AlTi)₁₇-Ag-BaF₂/CaF₂ HSLC between room-temperature and 800 °C, considerably outperforming the reported HSLCs and conventional alloy matrix solid-lubricating composites. At low and moderate temperatures, the synergistic Ag-BaF₂/CaF₂ lubricating films eliminate the surface stress concentration upon wear, thus suppressing three-body abrasion and surface roughening during the groove multiplication process. At elevated temperatures, the high-entropy composite tribo-layers provide the friction interface with strong and deformable stress shielding, which avoids the oxidative and adhesive wear triggered by the delamination of the tribo-layer. Developing similar coupled high-entropy matrix phases may open an avenue for further optimization of the tribological properties of the HSLCs.

Key words: Solid-lubricating composites, High-entropy alloys, Wear mechanism, High temperature, Tribochemical reaction