Processing and Tribological Behaviour of Flyash-Illmenite Coating

Abstract

A unique way to tailor the surface properties of a component, suit to a specific operating environment without sacrificing the bulk characteristics of the structure, is by deposition of a surface coating. Thermal spraying processes have been known for producing hard overlay coatings especially ceramic coatings, to improve tribological properties. Amongst the thermal spray techniques conventional atmospheric plasma spray technique is widely used to develop coatings of ceramic materials. Though plasma spray coatings deposition is very promising and drawn extensive attention, a major hindrance to its wide spread application is due to high cost of spray grade powders. To overcome this problem, research has been carried out to find the possibility of using some low grade ore mineral and industrial wastes as coating material so that the cost of raw material used for coating can be minimized. In this work plasma spray deposition of alumino-silicate composite coatings onto metal substrates is done using industrial waste i.e. fly ash with addition of illmenite, a titanium bearing ore mineral. To overcome the poor interface mechanical properties arising due to the mismatch of thermal expansion coefficients of ceramics and metals, generally metallic bond coat is provided onto the substrate for better interface adherence of ceramic coating. An improvement of coating properties when pre-mixed metal–ceramic powders are used (instead of using a bond coat), has already been reported . It is well established that, addition of titania to alumina provide dense coating & better adherence on substrate. Therefore, illmenite a low grade ore mineral plentily available in India, is premixed with fly ash so as to further reduce the raw material cost.