Optimizating Spray Parameters of High Velocity Oxy Fuel (HVOF) for Cr<sub>3</sub>C<sub>2</sub> - NiCr Coating

Abstract

Porosity, hardness, and adhesion mainly affect the performance of thermal spray coating and significantly depend on spray parameters. Therefore, determining value of the spray parameters and their effects on the coating properties are always taken into consideration. This paper studies optimization as well as evaluates influences of HVOF spray parameters which include powder feed rate (M), rotational speed of the details per minute (N) and step movement of the nozzle per revolution (S) to the adhesion, porosity, micro-hardness of Cr3C2 - 20(80Ni20Cr) coating on 40Cr steel shaft substrate. Taguchi experimental design L9 combined with analysis of variance (ANOVA) was used to determine optimum spray parameters and percentage of effect of each spray parameter on properties of the coating. From obtained results, the optimal spray parameters are m = 35 g.min-1, n = 130 rpm, S = 6 mm for the highest hardness coating of 658.2 HV; with m = 45g.min-1, n = 130rpm, S = 3 mm for the smallest porosity of 1.27%; with m = 35g.min-1, n = 130 rpm, S = 3 mm for the coating with a maximum adhesion of 44.07 MPa. The percent effects of the parameters m, n, S to adhesion, porosity and hardness were (2.8%, 33.6%, 63.6%), (0.1%, 1.3%, 98.6%), (32.7%, 43.3%, 24%), respectively. The percent effects of spray parameters on corresponding coating property allows adjustment of spray parameters to obtain the desired coating. Verified experiment results shows that the results are reliable. Taguchi method and ANOVA can find optimal parameters of the HVOF spray to acquire high-performance coating.