Effect of heat treatment on the wear behavior of WC-Ni-Cr and WC-Ni-Cr + Cr₃C₂ coatings fabricated by high-velocity oxy-fuel method

In this study, a tungsten carbide (WC)-Ni-Cr composite and a coating composition of Cr₃C₂ in WC-Ni-Cr were selected and fabricated using a high-velocity oxy-fuel (HVOF) method, to explore their applicability as wear-resistant coatings on cast iron substrates used in automotive brakes. Furthermore, to investigate the effect of post-annealing on the wear performance of the coatings, the coated samples were heat-treated at 500 and 850 °C. The microstructure, phase formation behavior, composition, and wear rate of the coated samples and post-annealed coatings were analyzed. Furthermore, the wear characteristics of the coatings were analyzed using a ball-on-disk method with a Si₃N₄ ball. By comparing the wear and friction characteristics of each coating, before and after heat treatment, the wear resistance performance of the coating could be related to the surface oxidation caused by heat treatment. In summary, the oxidation and phase change caused by the heat treatment reduced the wear resistance; however, if appropriate heat treatment conditions are satisfied, the frictional force required for automotive braking can be increased. Furthermore, the WC-Ni-Cr + Cr₃C₂ coating, where Cr₃C₂ was added to WC-Ni-Cr, exhibited an improved wear resistance compared to the coating with only WC-Ni-Cr. This was predicted to be an enhancement effect produced by the addition of Cr₃C₂.