High temperature tribological behaviors of (WAl)C-Co ceramic composites with the additions of fluoride solid lubricants

The tribological behaviors of the (W0.67Al0.33)C0.67-Co/fluoride (CaF2, BaF2, CaF2/BaF2) composites against SiC ball from room temperature to 600 °C were investigated. A marked increase in the friction coefficient resulting from fluoride oxidation was observed as the temperature increased. The composites containing BaF2 or (Ca, Ba)F2 displayed better integrated wear resistance over a wide temperature range compared with (W0.67Al0.33)C0.67-Co/CaF2. The high temperature tribological characteristics of the three composites were distinct, which originated from the composition difference on the worn surfaces. First, the SiO2/SiC film formed on the worn surfaces of the composites with BaF2 or (Ca, Ba)F2 was favorable for their wear resistance. Second, the oxidation of WC matrix was an important factor influencing the wear resistance of the composites. When mixture oxides of WO2 and WO3 appeared on the surface, wear is severe. In addition, single WO3 formed on the worn surfaces, appeared more adhesive to the underlying substrate and decreased the wear rate.