Fabrication of composite coatings containing in-situ reacted Ti₂AlC/Ti₂AlN MAX phases by laser cladding and investigation of fretting wear mechanism

Ti–Al–C–N protective coatings were prepared using laser cladding on the TC4 in this work. MAX phase is generated in situ in the coating. Moreover, as an in-situ autogenous reinforcing phase, MAX phase has good compatibility with the substrate and good bonding force, which is conducive to the full realization of the cladding performance. The results show that the amount of MAX phase increased with the proportion of ceramic phase in the composition design. Among them, the best coating performance is achieved when the component ratio is TiAl: TiN: TiC = 1:1:1. The coating shows the highest hardness of 712–950 HV, which was about twice the hardness of the substrate. It also shows the best resistance to fretting wear at both room temperature and 400 °C. The analysis of the wear mechanism reveals that twins are formed in C1 coatings during fretting wear at both room temperature and 400 °C. The twins not only can rapidly relax the local stress concentration and maintain the plasticity of the material, but also can promote the continuation of slip, and play an obvious strengthening effect without causing serious stress concentration. This work can provide the theoretical basis and data support for the functional-structural integration of protection design of components under actual working conditions.