Characterization of single splats produced by plasma spraying

Paper in proceeding, 2009

When sprayed particles impinge on the substrate, they flatten, cool down and build-up – splat by splat – the laminar structure of the thermal spray coating. Splat studies are therefore 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. In the present study, Ni-5Al single splats on 2 different Ti-6Al-4V substrates (one pre-heated and the other maintained at room temperature prior to spraying) have been investigated. Splat morphology has been analyzed by use of scanning electron microscopy (SEM). Analytical techniques like energy dispersive X-ray spectrometry (EDS) and Auger electron spectrometry (AES) have been used to determine the composition of the splats and of the splat-substrate interface. Adhesion was found to determine the splat microstructure. Two microconstituents are observed in the microstructure when delamination occurs. In case of good contact between splat and substrate, the microstructure consists of single-phase solid solution and an additional layer was found at the splat-substrate interface. Site-specific focused ion beam (FIB) milling and transmission electron microscopy (TEM) has been used to investigate this layer in more detail.