Plasma Spray Deposition of Fly Ash + Aluminum Coatings on Steel Substrates

Abstract

Through plasma spray technology, it is possible to develop metallic and ceramic coatings on a wide range of substrates and it also has the advantage of being able to process various low grade ore minerals and wastes to obtain value added products like near-homogeneous coatings of desired microstructure. Fly ash is such an industrial waste which is produced in huge quantities during power generation in a coal based power plants. The chemical analysis of fly ash indicates its tremendous potential to be used as a coating material on structural and engineering components, which are generally used in aggressive environments. In view of this, the present work describes the development and characterization of a new class of coatings made of fly ash pre-mixed with aluminium (Al) powder in different weight proportions (0, 5, 10, 15, 20, 25 and 30 wt%) on mild steel substrates by atmospheric plasma spraying route. The coating depositions are made at different torch input power levels ranging from 9 kW to 18 kW DC. The coatings are characterized in terms of their thickness, adhesion strength and deposition efficiency. Maximum adhesion strength of about 29 MPa is recorded with fly ash + 15 wt% Al mixture deposited at 12 kW power level. Similarly, coating deposition efficiency as high as about 35% is obtained for fly ash + 30 wt% of Al mixture at 18 kW power level. It is further noticed that the quality and properties of the coating are significantly affected by the operating power level of plasma sprayer and also by the Al content in the feed-stock. This work opens up a new avenue for the utilization of an industrial waste by identifying fly ash and fly ash pre-mixed with Al as potential and cost effective coating materials for engineering applications.