Comparison of microstructure in Ni-Al single splats and millimeter sized drops

Paper in proceeding, 2011

Splat studies are a central area of research because they can provide fundamental knowledge on the phenomena controlling the final coating properties such as coating microstructure and adhesion. Wetting and heat transfer are expected to influence the final splat shape while they are in turn controlled by the presence of oxides and adsorbed species on the substrate surface. It is however difficult to follow the flattening of a sprayed droplet at the micrometer scale. Since the mid nineties, so-called free falling experiments have been developed with which it is possible to simulate the thermal spray process. The millimetre sized drops allow investigating the flattening and solidification occurring in milliseconds instead of in microseconds. In this study, the microstructure of plasma sprayed Ni-Al splats and millimetre sized droplets produced on TiAlV and pure Ti substrates, respectively, are compared. By use of scanning electron microscopy (SEM), especially the cross-section of splats and droplets has been investigated. In the splats, diffusion across the splat-substrate interface and the formation of an interface layer is detected. In the droplets, up to 3 different layers are formed at the interface to the substrate. The microstructure at the interface and the phases present are discussed and their influence on heat transfer and coating properties are described.In this study, the microstructure of plasma sprayed Ni-Al splats and millimetre sized droplets produced on TiAlV and pure Ti substrates, respectively, are compared. By use of scanning electron microscopy (SEM), especially the cross-section of splats and droplets has been investigated. In the splats, diffusion across the splat-substrate interface and the formation of an interface layer is detected. In the droplets, up to 3 different layers are formed at the interface to the substrate. The microstructure at the interface and the phases present are discussed and their influence on heat transfer and coating properties are described.