Abstract:

Material performance in many industrial applications is strongly affected by the behaviour of the surfaces. For example, corrosion response reactivity with environments, wear characteristics, and thermal properties are all critically dependent on surface character. Utilization of coatings to upgrade component performances is often a cost effective alternative to substitution of superior bulk materials. The advantage of coating technology, in general is that it marries two dissimilar materials to improve the performance of the whole. Usually mechanical strength and fracture toughness are being provided by the substrate and the coating provides protection against environmental degradation processes including wear, corrosion, erosion and biological and thermal attack.Steel alloys as a substrate material have very wide applications for blades, mill rolls, printing, piston rings, drilling equipment, gearbox, worm wheel and power generators. In such applications, the steel alloys substrates are subjected to higher thermal and mechanical loads. Increasing the anti-wear resistance and decrease of friction requires surface modification by other high wear resistant coatings. Recently, there are many surface modification processes to steel by the evolution of effective lubrication with higher performance to keep the lubricating systems running reliably and to avoid bearing and other component failures (1), and plasma thermal spray coatings process (2-6). Plasma spraying is the most versatile of the coating technologies. It may serve for "metalizing" all sorts of articles and has great advantages over the known galvanizing process in cases where it can be used to coat electrically non-conductive surfaces with metal. Spray materials must be melted and sprayed without decomposition or excessive vaporization in plasma flame through the optimum spray parameters. In plasma spray process, the spray material in the form of powder is rapidly brought to molten or near molten state by the plasma flame and then accelerated by a gas stream to impact a suitably prepared substrate. Upon impact, the molten metal droplets are rapidly flattened and solidify to form their splats. Microstructure and physical properties of sprayed coatings are linked to dynamic properties of molten particles impinging on a substrate.