Chromium Diboride Effect on Wear Resistance and Adaptation Mechanisms in Dry Friction of ZrB2‒SiC and ZrB2‒MoSi2 Ceramics against a Steel Counterface

The use of ZrB₂‒SiC and ZrB₂‒MoSi₂ ultrahigh-temperature ceramics with and without CrB₂ additions as antifriction materials for operation in dry friction conditions at high speeds and loads was examined. The friction process was studied under low-speed and high-speed sliding against a steel counterface at speeds of 2, 4, and 6 m/sec and loads of 0.8, 1.2, and 2 MPa. The surface structure and phase composition of the ceramic samples after friction were analyzed by X-ray diffraction, optical microscopy, and electron microscopy. Intensive tribooxidation of the composite components, along with the formation of an intermediate layer between the friction surfaces, was observed at a sliding speed of 6 m/sec. Wear followed a decreasing trend with increasing sliding speed at constant load. Analysis of the friction tracks using scanning electron microscopy and energy-dispersive X-ray spectroscopy revealed an intermediate layer between the friction surfaces, consisting of tribooxidation products from both the ceramic and steel components. This layer reduced frictional losses, facilitated the formation of a smooth wear surface, and protected the brittle ceramics. Chromium diboride additions reduced the sintering temperature (through the formation of lower-melting compounds), increased the corrosion resistance (through the formation of zircon), and improved the mechanical properties of the composites (through the formation of solid solutions). The effect of these additions on the tribological properties of ZrB₂–SiC and ZrB₂–MoSi₂ composites was examined. The results showed that they favorably influenced the friction process and enabled the formation of a dense glass-like intermediate layer with complex phase composition. This layer demonstrated strong adhesion to the ceramic surface and promoted its self-restoration. The layer consists of tribooxidation products and metallic particles transferred from the steel counterface. The most significant reduction in the friction coefficient was observed for the ZrB₂–15% MoSi₂–5% CrB₂ composite, from 0.44 to 0.29.