Tribological properties of pulsed ion nitrided AISI 4140 steel

Abstract

The present study was conducted in order to investigate the tribological behaviour of plasma nitrided AISI 4140 steel by using a dc pulsed glow discharge technique. Microstructure and structural characterisations were performed by using scanning electron microscopy and X-ray diffraction techniques. A compound layer with a thickness between 6 and 8 μm containing ɛ (Fe₃ N) and to a lesser extent γ′ (Fe₄ N) was identified. Wear tests were performed with a pin on disc configuration. The tests were carried out at room temperature in air using two different pin materials (AISI 1086 and WC–6Co). A sliding speed of 0·1 m s^-1, 5 N load, and 700 m maximum sliding distance were used on both substrate and nitrided specimens. The friction coefficients found for the tribological pairs under study, tungsten carbide pin and plasma nitrided disc, AISI 1086 pin and plasma nitrided disc, and AISI 1086 pin and AISI 4140 disc, were 0·34–0·6, 0·49–0·6, and 0·475–0·57 respectively. Wear volumes of 0·0453, 0·0511, and 0·00077 mm³ have been determined for the tribological pairs mentioned above. The surface top ography of the wear scars on both specimens and pins have been determined using scanning electron micros copy and three-dimensional stylus profilometry.