Wear mechanism of medium carbon steel after its plasma electrolytic nitrocarburising

Abstract

This article considers the change in the tribological characteristics of medium carbon steel after its anodic plasma electrolytic nitrocarburising in a carbamide electrolyte. Phase and elemental composition of the nitrocarburised layer was studied using X-ray analysis and nuclear backscattering of protons. Optical and electron microscopes were used to observe friction tracks. It has been found out that the wear process in nitrocarburised samples is followed by plastic displacement of the metal in the friction contact zone according to the molecular-mechanical and fatigue theory of wear and application of the Kragelsky criterion. It has been shown that an increase in the sliding velocity of 0.5 m/s to 1.5 m/s results in a linear decrease in the friction coefficient from 0.65 to 0.45. The minimum wear rate is achieved after nitrocarburising of steel at 750 °C for 7 min and a sliding speed of (0.4–0.55) m/s. Anodic nitrocarburising increases the wear resistance of steel by 40% compared to quenching at a sliding speed of 0.9 m/s.