Relation between microstructure and properties of HVOF sprayed Cr ₃C₂-NiCr cermet coating

Cr₃C₂-25 %NiCr cermet coatings were deposited by HVOF spray process. The carbon content, carbide grain size and carbide content were estimated quantitatively. The mechanism of carbon loss in spraying and the effect of carbide grain size on the properties of sprayed coating were examined. The main conclusions obtained are as follows. (1) Carbon content of Cr ₃C₂-25 %NiCr cermet coating deposited by HVOF spraying was lower than that of the powder. It was found that the carbon loss during particle in-flight is much limited. It can be suggested that the main mechanism of carbon loss is due to the rebound-off of large carbide particles. (2) It was recognized that the grain size and content of carbide in sprayed coating were lower than those in starting powder. (3) With the increase in carbide grain size and decrease in carbide content, the abrasive wear loss of HVOF sprayed coating was increased. Moreover, it was recognized that the erosion rate of HVOF sprayed coating was proportional to the ratio of carbide grain size to carbide content.