Microstructural evolution, mechanical properties and tribological behavior of SiCw-composite rock-salt/spinel biphasic high-entropy oxide ceramics over a wide temperature range

High-entropy oxide ceramics (HEOCs) suffer from low fracture toughness despite their excellent high-temperature stability. Herein, silicon carbide whiskers (SiCw) were introduced into the rock-salt/spinel biphasic HEOC system via solid-state reaction sintering. The composite ceramic prepared with 5% SiCw at a forming pressure of 80 MPa exhibited the best overall mechanical properties, with a Vickers hardness of 784.60 HV, a flexural strength of 272.80 MPa, and a fracture toughness of 3.43 MPa·m 1/2 . The improved fracture toughness was mainly associated with crack bridging, crack deflection, and whisker pull-out. Wide-temperature tribological tests (25 - 900°C) showed friction coefficient decreasing from 0.883 to 0.353, while wear rate increased from 7.21 × 10 -5 to 26.24 × 10 -5 mm 3 /(N·m). During high-temperature sliding, Cu and Zn species migrated and enriched on the worn surface, and together with SiO 2 /SiO x generated by local tribo-oxidation of SiCw, participated in the formation of a friction reaction layer. This reaction layer possessed relatively low interfacial shear resistance, thereby reducing the friction coefficient. However, its limited load-bearing capacity and shear stability made it prone to softening, flow, and delamination under high-temperature cyclic shearing, resulting in an increased wear rate. This study provides a new pathway for designing HEOCs with improved mechanical properties and tunable tribological behavior.