Effect of heat treatment on characteristics of high velocity oxygen fuel flame sprayed coatings (WC-27 mass%NiCr)

The effect of heat treatment on the characteristics of WC-27 mass%NiCr sprayed coatings on 13%Cr steel made by the High Velocity Oxygen-Fuel Flame Spraying (HVOF) was studied. Specimens were heated to 673 K and held at 5, 10, 20 and 30 h in air. Corrosion resistance was measured by a salt-spray test (CASS test) and strength was measured by a three-point bend test. The results obtained were as follows: (1) Corrosion resistance increased with heating time. This increase is dependent on the surface void ratio of the sprayed coatings which decreases as the temperature increases. (2) The three-point bending strength decreases at 5 h heating, and increases again with continued heating. The initial decrease at 5 h heating was due to release oi compressive stress in the coatings, and the increase afterwards was due to the surface void ratio decreasing.