Mo-doped Cr-Ti-Mo ternary o-MAX with ultra-low wear at elevated temperatures

In this work, the Cr-Ti-Mo ternary o-MAX ceramics based on the Cr2TiAlC2 phase are synthesized, and their tribological performance at elevated temperatures up to 800 ºC in the air is evaluated. With Si3N4 as a tribocouple, an unexpected ultra-low wear rate reaching 6.1 × 10−8 mm3 N−1 m−1 is observed in Cr1.9Ti0.9Mo0.2AlC2 at 800 ºC, accompanied by a stable coefficient of friction (COF) around 0.33 in a wide temperature range. X-ray photoelectron spectroscopy (XPS) depth profiling confirms a tribofilm with gradient composition, which simultaneously offers fluid lubricating at elevated temperatures and self-healing after cooling. Particularly, confirmed by the theoretical simulations, the doping of Mo improves the interlayer binding as well as alters the oxidation behaviors of Cr2TiAlC2. With an optimal interlayer binding strength and oxidation rate, the Cr1.9Ti0.9Mo0.2AlC2 can generate a tribofilm possessing ideal composition, which simultaneously promotes lubrication and anti-wear performance at elevated temperatures.