Tribological behavior of h-BN/Al2O3 self-lubricating composites in extreme environment—Part Ⅱ: Self-lubrication and mechanism in water-oxygen environment from 300 °C to 1200 °C

The hBN/Al₂O₃ composites exhibit well self-lubricating properties over a wide temperature range in high temperature water-oxygen environments. At temperatures from 300 °C to 1100 °C, the composites maintain a consistently low friction coefficient (0.11–0.16) and show low wear rates of about 10⁻⁶ mm³·N⁻¹∙m⁻¹ orders of magnitude. The thermal expansion effect of h-BN and dynamic water vapor interlaminar diffusion reduced the critical shear strength of h-BN and enhanced interlaminar slip, which in turn improved the tribological properties of the composites. In addition, the stability of the friction interface structure and phase composition was effectively maintained at 1100 °C by the self-volatility of boric acid and the competitive adsorption ability of H₂O molecules.