Parallel laser melted tracks: Effects on the wear behaviour of plasma-sprayed Ni-based coatings

A frequently used deposition method for alloys with a high Ni content is plasma spraying (Ni-PS). However, this technique produces highly porous, uneven coatings with no homogeneity and poor adherence. Laser melting is now used to correct these defects, since it homogenizes and densifies the coating and also increases adherence to the substrate. However, complete melting of the whole surface of a coating generates great heat, which in turn often leads to cracking. Another drawback of complete melting is that treatment time is high and the method becomes very costly. In an attempt to strike a balance between the two processes – plasma spraying and total laser melting – this paper describes a partial treatment of a plasma-sprayed Ni-based coatings (Ni-PS + L), using a CO2 laser, which scanned separated parallel lines along the coating. This technique blends the advantages of plasma-sprayed coatings, with its excellent wear performance in lubricated contact, and those of laser melting, with its high wear resistance in general.Microstructural analysis of the coatings of the laser melted area indicated a homogenized microstructure, enhanced hardness, less roughness, no porosity and increased adherence of the coating. Our study of the wear performance of the coatings indicates that partial laser melting improves wear resistance in lubricated contact compared to both plasma-sprayed coatings with no melting and totally melted plasma-sprayed coating. Our study also considered the effects of the angle formed by the laser tracks and the percentage of surface that was melted on wear performance in lubricated contact. Optimum results were obtained with laser tracking at a 45° angle and with 25% melted surface.