A comparative study of sand-blasted and electro-discharge-machined surfaces of steel substrates

Abstract

Sand blasting is a common process to prepare steel surfaces prior to thermal spray coating application to obtain better coating adhesion. Die-sinking electro-discharge machining (EDM) is a non-conventional machining process that 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 scanning electron microscopy analysis of the samples are carried out. Nano-hardness behaviour of the samples is also studied. Failure in obtaining 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 for substrate preparation. © 2020, Indian Academy of Sciences.