Linear reciprocating wear test is carried out on atmospheric plasma-sprayed Al₂O₃–Cr₂O₃ coatings applied on steel substrates. Linear bi-directional sliding wear test of the coatings is performed at different loading and sliding conditions such as load (10, 20 and 30 N), reciprocating amplitude (1.5, 3 and 6 mm) andfrequency (5, 10, 15 and 20 Hz) using ball on flat linear reciprocating tribometer. The patterns of tribological behaviour of the coatings, as manifested at the tribo-contact surface, are judged. Results have shown that the wear rate increases with increasing applied load and frequency and that decreases with increasing reciprocating amplitude. Plastic deformation, detachments of unmelted core, reattachments, delamination and adhesive wear dominate the main failure mechanism of coating.

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 (R_a) of 3, 5 and 7μm. 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. Nanohardness 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 isconcluded 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.