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

The tribological behaviors of the (W_0.67Al_0.33)C_0.67-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 (W_0.67Al_0.33)C_0.67-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.