Synthesis of Ti-Nb-Hf quinary M₂AlC MAX ceramics and the effects of Hf incorporation on the anti-wear performance up to 800 °C

The (TiNb)₂AlC MAX ceramic exhibits superior high-temperature oxidation resistance, mechanical, and lubricating properties due to the solid solution of second transition metal elements. However, it demonstrates relatively poor wear resistance. In this work, (Ti_0.5-xNb_0.5-xHf_2x)₂AlC MAXs with varying Hf contents are synthesized. Their mechanical property and tribological behaviors from room temperature to 800 °C are investigated. From nanoindentation, Hf incorporation reduces the capacity of energy dissipation and resistance to plastic deformation of the MAXs. Accordingly, the wear rate is raised under the conditions of friction coupled with insufficient oxidation (400 °C and below). On the other hand, under oxidative wear-dominated conditions (600 and 800 °C), hafnium oxide alters the properties of the oxide tribofilm, and thus dramatically reduces the wear rate by 83 % of (Ti_0.4Nb_0.4Hf_0.2)₂AlC compared to (Ti_0.5Nb_0.5)₂AlC. Eventually, the enhanced high-temperature wear resistance of (Ti_0.5−xNb_0.5-xHf_2x)₂AlC proves the effectiveness of Hf solid solution in the system.