WEAR BEHAVIOUR OF COMPOSITE COATINGS BY THERMAL SPRAY PROCESS FOR HIGH TEMPERATURE APPLICATIONS

Abstract

The aim of this research is to study the comparative wear behaviour of pure Al2O3 with varying TiO2 content due to the high demand in the industry for high-temperature applications such as the automotive industry (piston ring and liner), petrochemicals industry (pump sleeves) and textile industry tools which require the hard bearing surface, abrasion resistance and particle corrosion at the higher temperature. In the present study, three coatings of Al2O3, Al2O3-13%(TiO2) and Al2O3-40%(TiO2) composite coatings were deposited by the thermally flame spray process. The comparative wear behaviour of the Al2O3-TiO2 coatings has been studied under high temperatures of up to 400°C using a high-temperature tribometer at a constant load of 40N. Before the tribo-test, the coating morphology and elemental analysis were examined with the help of field emission scanning electron microscope (FESEM), elemental dispersion spectroscopy (EDS) and X-ray powder diffraction (XRD) techniques. The thermal behaviour and corrosion rate of the deposited coatings were examined. Before the experimentation, the mechanical properties of the coated samples, such as microhardness and surface roughness, have also been analysed and reported. The results reveal that the specific wear rate decreases with an increase in temperature for all the deposited coating except Al2O3 coating at 400°C. The overall friction coefficient of the coatings decreases with increasing temperature. The Al2O3-40%TiO2 coating showed maximum sustainability against wear and a low coefficient of friction because of its low hardness and high adhesion properties. The examined worn surface validates the presence of brittle fracture and abrasive wear behaviour mechanism along with the oxidation wear, from room temperature to 400°C. The thermal conductivity of the deposited coating decreases with the increase in TiO2 content. The Al2O3- 40% TiO2 coating has the lowest average thermal conductivity. The Al2O3-40% TiO2 coating possesses a low corrosion rate (mmpy) compared to pure Al2O3 and Al2O3-13% TiO2 coatings.