Studies on solid particle erosion behaviour of D-Gun sprayed WC-Co, Stellite 6 and Stellite 21 coatings on SAE213-T12 boiler steel at 400 °C temperature

Abstract

Erosion wear of boiler tubes occurs from room temperature to high temperature and is accelerated by oxidation and hot corrosion above 400 °C temperature. The demand for hard coatings compatible in improving erosion, oxidation and hot corrosion resistance while maintaining the desired mechanical properties of the base material is increasing with the advancement of technology. In this work, WC-12Co coating, Stellite 6 coating and Stellite 21 coatings have been deposited on SAE213-T12 boiler steel using a Detonation gun (D-gun) spray method, and their erosion performances have been evaluated at 400 °C temperature using an air jet erosion tester. The erosion tests have been carried out using the alumina erodent particles at 30° and 90° impact angles. The surfaces of the as-sprayed coatings and the specimens eroded at 400 °C temperature were analysed using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscope (EDS). Stellite 21 coating has shown comparatively lower erosion rate than the Stellite 6 and WC-Co coatings at 400 °C temperature attributed to the formation of protective oxides of chromium and cobalt at 400 °C. The effects of microhardness and temperature on the erosion behaviours of the coatings at 400 °C temperature are discussed. The oxide layers of chromium and cobalt and accumulation of hard phases of nickel, molybdenum and carbon contributed in the protective behaviour of the deposited Stellite 6 and Stellite 21 coatings at 400 °C. The oxidation enhanced erosion wear is observed at 400 °C temperature for all the coatings.