Composition versus friction and wear behavior of plasma sprayed WC–(W,Cr)2C–Ni/Ag/BaF2–CaF2 self-lubricating composite coatings for use up to 600 °C

Abstract

This paper reports the composition optimization of self-lubricating composite coatings containing WC–(W,Cr)2C–Ni, silver and fluoride eutectics. Various ingredients obtained by powder blending were studied to determine their optimum content in as-prepared composite coatings. An atmospheric plasma spraying (APS) system was used to deposit promising WC–(W,Cr)2C–Ni/Ag/BaF2–CaF2 self-lubricating composite coatings. The friction and wear behavior of the composite coatings sliding against Si3N4 ball was investigated from room temperature to 600°C. Results show that silver and fluoride eutectics can effectively reduce the friction coefficient of the coatings and the wear volume loss of counterpart balls over the whole temperature range. Thanks to the highest hardness, WC–(W,Cr)2C–Ni coating without silver and fluoride eutectics has the lowest wear rate at room temperature and 600°C. However, it has a high friction coefficient and a very high wear rate at 200 and 400°C, due to severe adhesion wear and fatigue wear thereat. Fortunately, introducing appropriate amount of silver and fluoride eutectics contributes to effectively reduce the wear rate of the composite coatings at 200 and 400°C. The optimized composite coating consists of 70wt.% WC–(W,Cr)2C–Ni, 15wt.% Ag and 15wt.% BaF2/CaF2, and it has excellent friction and wear performance over a wide range of temperature.