Temperature-driven wear behavior of WC/Co against Si3N4 exposed to air conditions

Abstract

WC/Co coatings are indispensable wear-resistance material to withstand harsh environments in aerospace engines and power generation turbines. This study systematically investigates the reciprocating wear behavior of high-velocity oxygen-fuel (HVOF) sprayed WC/Co coatings against Si₃N₄ counterparts across temperatures ranging from 25 °C to 800 °C in ambient air. The WC/Co-Si₃N₄ tribo-pair displays relatively constant friction and desirable wear resistance at RT and 400 °C, nevertheless friction rises, and wear deterioration occurs for the WC/Co-Si₃N₄ tribo-pair as temperature exceeds 500 °C. The friction coefficient rises from 0.38 ± 0.03 at 25 °C to 0.68 ± 0.05 at 600 °C, peaking at 0.83 ± 0.07 at 800 °C, while the specific wear rate of WC/Co escalates exponentially from 2.1 × 10⁻⁷ mm³/Nm at 25 °C to 1.4 × 10⁻⁴ mm³/Nm at 800 °C, representing a three-order-of-magnitude increase from RT to 800 °C. X-ray diffraction (XRD) and Raman spectroscopy confirm the formation of tribo-oxidized products. At higher temperatures, though the in-situ formation of tribo-chemically oxidized products initially helps to suppress wear to some extent, 600 °C as the critical threshold for stable tribological performance, beyond which contact fatigue and oxidative wear dominates. WC/Co coating demonstrates the temperature stimulated wear worsening phenomenon, which relates to the interfacial tribochemistry during friction. Resulting WO₃ layer on WC/Co coating rubbed against SiO₂ of Si₃N₄ counterpart substantially undermines the tribological compatibility and thereby poor wear resistance.