Effect of Dilution on High-Temperature and High-Vacuum Tribological Behaviour of Ni-Cr-B-Si Hardfaced Coating

Influence of dilution on high-temperature-high-vacuum-friction behaviour of Ni-Cr-B-Si coating made on AISI 316L (N) stainless steel using plasma transferred arc welding process is studied. Two coatings with different dilution levels are made by using two different welding currents. With increase in dilution (Ni/Fe change from 4.4 to 2.5 and hardness from 46 & PLUSMN; 3 to 30 & PLUSMN; 5 R-C), microstructure changed from hypereutectic to eutectic with variations in the distribution of borides and carbides as well as their relative contents. Sliding wear tests were conducted for coatings using SiC ball as the counterbody, at 823 K under vacuum of 10(-5) mbar. Friction coefficient increased from 0.17 & PLUSMN; 0.04 to 0.42 & PLUSMN; 0.12 with increase in dilution, with the change of wear coefficient from 0.60 x 10(-14) to 0.92 x 10(-14) (m(3)/Nm). Results revealed the dependence of friction on dilution, the effect of which influences the nature of the triboinduced film which in turn controls wear.