Rapid surface treatment of grey cast iron for reduction of friction and wear by alumina coating using gas tunnel plasma spray

Abstract

Gas tunnel plasma spray (GTPS) technique produces a high energy density plasma jet for rapid fabrication of ceramic coatings. In this paper, alumina powder was sprayed onto a grey cast iron (GCI) substrate as friction and wear-resistant coating. GTPS parameters such as plasma input power, powder flow rate and nozzle to substrate distance were fixed at 2.8 kW, 2.4 ml/min and 10 mm, respectively. The microstructure and composition of the alumina coating were examined under a light microscope, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The physical properties of the alumina coating were evaluated by surface roughness measurement and pull-off adhesion test. A uniform, crack-free alumina coating of an average thickness of 3.0 µm and surface roughness of 0.2 µm was obtained after 10 s of deposition time. The adhesion of the alumina coating to the GCI substrate was measured around 9.5 MPa due to adhesive/glue failure. The tribological behavior of the alumina coating was studied using the ball on disc sliding wear test. Under a lubricated condition, the alumina coated specimens exhibit a relatively stable coefficient of friction (CoF) between 0.077 and 0.080 in which the values were lower as compared to the uncoated GCI specimens for all different applied loads (25 N, 50 N and 75 N). It was demonstrated that the alumina coating can decrease the CoF value and wear mass loss of the GCI substrate by at least 10% and 50%, respectively.