Design and high-temperature tribological properties of CoCrW with rare earth fluoride composites

CoCrW matrix containing rare earth LaF3 self-lubricating composites were fabricated by using hot-pressing method. The microstructure, phases and high-temperature tribological properties of obtained composites were systematically studied. Friction and wear behaviors were evaluated by using ball-on-disc tribo-tester from RT (24 °C) to 1000 °C. Metal matrix consisted of two allotropes: e (hcp) and γ (fcc). Mo had a solid solution strengthening effect and lubricating effect when it changed into compounds. Rare earth LaF3 and its compounds showed lubricating effect at elevated temperatures. The friction coefficients and wear resistance of reinforced composites were greatly enhanced with little hardness dropping. It was ascribed to the synergistic effect of in-situ formed and extra added solid lubricants (silver, LaCrO3, Ag2MoO4, AgF3 and metal oxides) as well as oxides film which changed the wear model of tribo-couples during sliding. The wear rate of CoCrW-10LaF3-8Mo-9Ag was about 10 times lower than those of reported Ni and ZrO2 matrix composites. The composites showed the slight abrasive wear and oxidative wear at elevated temperatures.