Study of the microstructure of NiCr splats plasma sprayed on to stainless steel substrates by TEM

In the plasma spraying process fine particles are melted and sprayed onto a substrate using a plasma jet to form splats. However, the mechanisms of formation of these splats, and their dependency on the chemical state of the substrate, are not yet fully understood. Transmission electron microscopy was used here to study NiCr splats sprayed onto a stainless steel substrate in order to perform detailed microstructural characterization of the splat and the splat–substrate interface. These studies provided evidence of localized substrate melting, inter-diffusion and/or inter-mixing between the splat and the substrate. Furthermore, nickel, chromium and iron oxide phases were identified at various locations around the splat using a combination of energy dispersive spectroscopy and electron diffraction. Mechanisms of formation of the microstructural features observed are discussed.