D-gun sprayed alumina-silicon carbide coating on steel substrate for mechanical applications

Abstract

Sand blasting is a popular method to prepare steel substrates prior to the thermal spray coating application to obtain good coating-substrate adhesion. Die-Sinking EDM is a non-conventional machining process which also produces rough surfaces. In this study, steel (EN 31) surfaces are prepared by both methods to obtain the same average roughness (Ra) of 3, 5 and 7 µm. The prepared surfaces are studied and compared to investigate whether the rough EDMed surface is suitable for applying thermally sprayed Ni-5Al coating on it or not. XRD and SEM analysis of the samples are carried out. Nano-hardness behavior of the samples is also studied. Failing to obtain well-adhered D-Gun sprayed Ni-5Al coating on EDMed surface is due to the presence of hard cementite and austenite phases on the surface. It is concluded that for thermal spraying, adhesion of coating material on substrate cannot be achieved without proper metallurgical compatibility. Also, for thermally sprayed Ni-5Al coating application on steel substrate grit blasting method is the suitable process to adopt for substrate preparation.