Analysis of HVOF parameters on the tribological properties of the Cr-Ni Multilayer coatings on SS316 by response surface Methodology

The influence of spray distance, gun speed, and number of layers on the wear behavior, coefficient of friction (COF), and microhardness of Cr-Ni multilayer coating deposited on SS316 substrate with High Velocity Oxy-Fuel (HVOF) process is considered in this study. The experimental data showed that these parameters significantly affect coating performance. The wear rate ranged from 185 mm to 263 mm at a distance of 300 mm from the spraying gun, with a gun speed of 100 mm/s and 7 layers; the minimum wear rate was 185 mm. The COF varied between 0.808 and 1.17, with smoother coating at higher degrees of densification registering lower COF. Microhardness ranged from 705 to 1021 HV, with the highest value of 1021 HV achieved under the same optimized parameters, indicating better coating adhesion. The ANOVA showed that all factors were statistically significant, and the model F-values and all p-values were below the 0.0001 threshold. The wear rate was 53.22, the COF was 28.61, and the hardness was 25.72. Spraying distance was the dominant parameter, with an F-value of 225.02 (p < 0.0001) for wear rate, 119.51 for COF, and 114.83 for hardness. The regression models developed achieved optimal predictive accuracy, with R2 values of 0.9795, 0.9626, and 0.9586. The perturbation and 3D surface analysis indicated that the optimal spraying distance is 300 mm, the moderate gun speed range is 100-150 mm/s, and six to seven layers achieve the best coating performance.