High Temperature Tribological Properties of Nano La₂O₃-Doped MoSi₂ Composite Coatings Sintered in Vacuum

The MoSi₂ composite coatings were synthesized and doped with La₂O₃ nano-particles by high temperature sintering in vacuum on substrate of high speed steel. The influence of the content of La₂O₃ nano-particles on the high temperature tribological behavior of the coatings was investigated with X-ray diffraction (XRD) and conventional mechanical probes. The results show that depending on its content, doping of La₂O₃ significantly affected the high temperature tribological properties of the coatings. For example, as the La₂O₃ contentincreased, the compactness, hardness and wear-resistance of the coatings changed in an increase-decrease mode, and the friction coefficient varied in a decrease-increase way; 1% and/or 5%(wt) of La₂O₃ significantly increased the wear-rate. Doped at 3% of La₂O₃, the MoSi₂ coating, with a friction coefficient of 0.1, displayed an excellent tribological performance at 200℃ and 800℃, respectively. A combination of abrasive, adhesive and dominate oxidative wear was responsible for the wear mechanisms.