Effect of air plasma sprays parameters on the coating performance in Al2O3-TiO2-based high temperature, wear and corrosion resistance coatings applications on 304 H- austenitic steel alloy of Aero-turbine Engine.

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. 304 H- austenitic steel alloy as a substrate material have very wide applications for: blades, mill rolls, printing, press of cylinders, piston rings, drilling equipments, gearbox, worm wheel and power generators. In such applications, the austenitic steel alloy substrate is 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. There are many spray parameters that affects the properties of the sprayed plasma coating, the most common control parameters are: Chemical compositions, phase structure and crystal size of the powder input, substrate temperature, plasma gas, plasma torch, powder feeder (.e.g. grain size chemical and phase composition, shape, internal porosity (correlated with apparent density), spray angle, and finally spray distance.The objective of this study is to improve the temperature wear, and corrosion resistant, properties of steel alloys materials via plasma using ceramic powder. Plasma spraying of ceramic coating is a prime candidate for the surface modification of steel alloys for anti-wear corrosion, erosion and thermal resistance. Ceramic powder during spraying is not quite easy process because of rapid solidification of flattened particles. There are two approaches to improve the ceramic coating in plasma spraying. One method is the optimization of the spray parameters to improve the adhesion properties and decrease the solidification rate. The other method is using high alumina content powder (97% Al2O3 + 3% TiO2) .Our objective is not only to spray high content alumina, but also to get the best optimum spray parameters, by studying the effect of these parameters in microstructure, adhesion, reaction layer, micro-hardness, corrosion and pore formation.