Developing partially oxidized NiCr coatings using the combined flame spray and plasma spray process for improved wear behaviour at high temperature

Abstract

The powders of NiCrBSiFe and NiCr are partially oxidized using a flame spray process and are deposited on MDN321 steel substrate using a plasma spray process. The effect of partial oxidization on microstructure, microhardness, density, bond strength, and porosity of the coatings is analyzed. The friction and wear behaviour of the coatings was assessed using a pin-on-disc tribometer by varying loads (10, 20 and 30 N), sliding velocities (1, 2 m/s) and temperatures (RT, 200, 400 and 600 °C). Worn surfaces of NiCrBSiFe and NiCr coatings consist of oxide phases of SiO2, NiO, Cr2O3 and NiCr2O4 at elevated temperatures. These phases contributed to reducing the wear rate by five folds in coated steels compared to uncoated steels at 600 °C. The wear rate in coating decreases with an increase in temperature. The coefficient of friction was reduced gradually with the temperature in coatings and substrate. The wear rate coefficient of NiCr coating was 1.7 times higher than the NiCrBSiFe coating.