Effects of cyclic heating and water-cooling on the mechanical properties of WC-Co coatings

Abstract

To determine the effect of heating and water-cooling on the mechanical properties of the WC-Co coatings, we conducted a series of mechanical tests on the HVOF (high-velocity oxygen-fuel) sprayed WC-Co samples. These coatings were first heated to the target temperatures (200–800 °C), followed by rapid cooling with water. Mechanical properties were tested after thermal treatments. Microstructural changes were also observed using a scanning electron microscope and optical microscope. According to experimental results, the microhardness, residual stress and adhesive strength of the heated WC-Co coating changed significantly after water-cooling. As heating temperature rises, changes in these properties become more pronounced. However, the number of cycles has less effect on the mechanical properties of the coatings and the effect mainly occurs in the first 30 cycles. Compared with the argon-cooling method, water-cooling induces greater changes in the mechanical properties at higher target temperatures. This indicates that water-cooling can damage the heated WC-Co coatings more remarkably than the other cooling treatment. Nevertheless, after about 30 cycles, changes in mechanical become less pronounced. Additionally, cobalt content has little impact on the mechanical properties of the coating after heating and water-cooling.