Effect of plasma nitriding temperature on microstructure and wear properties of electroless nickel-boron coatings

Abstract

This study investigates the effects of plasma nitriding (PN) temperature on the microstructural properties and wear behavior of electroless nickel‑boron (ENB) coatings. To this end, the ENB coatings are deposited on the mild steel substrates and submitted to PN treatment at 350, 400, and 450 °C. The Morphology, roughness, microstructure, microhardness and wear resistance of the coatings are evaluated and compared to the conventional heat-treated ENB coatings. The results indicate that a crystalline structure has appeared in the as-deposited amorphous ENB coatings through PN treatment, leading to enhancement of their hardness. The highest hardness value (1406 HV0.1) and consequently the highest wear resistance are obtained for the PN-treated ENB coating at 350 °C. These results could be assigned to the grain growth suppression achieved by doping nitrogen atoms into the coating through PN treatment. Moreover, the precipitation of the lubricant h-BN phase during PN treatment of the ENB coatings has decreases the coefficient of friction in the sliding wear test.