Improvement in High-Velocity Air-Fuel-Sprayed Cr3C2-NiCr/(NiAl, NiCr) Composite Coatings by Annealing Heat Treatment

NiAl/Cr 3 C 2 -NiCr and NiCr/Cr 3 C 2 -NiCr gradient coatings were sprayed on mold copper plate (CuCrZr) by high-velocity air-fuel spraying technology. The effects of annealing treatment on the performance of sprayed coatings were investigated systematically. The results showed that the corrosion and wear resistance of the coating is increased first and then decreased with the increase of temperature. Annealing treatment caused the precipitation of secondary carbides and led to the variation of hardness and wear resistance, which have weak relationship with the bond layers. With annealing temperature rising, the adhesion strength of NiCr/Cr 3 C 2 -NiCr coatings gradually increased but NiAl/Cr 3 C 2 -NiCr coatings decreased, which is closely linked to the diffusion behavior at the interfaces. Moreover, the change in anti-corrosion properties of the coating is also related to the bond layers, and the coating with NiCr bond layer shows better corrosion resistance. The weak bonding of Cr 3 C 2 -NiCr and NiAl and the reaction between Ni and Al led to the increase of the corrosion rate to some extent. After annealing at 600 °C, the coating got the highest hardness as well as the best wear and corrosion resistance.