Surface study of process contamination of plasma spray metal deposition process
Olivas, John Daniel
Barrera, Enrique V.
Doctor of Philosophy
The purpose of the present study was to analyze the contamination which resulted from processing steps applied to substrate surfaces for the metal coating process known as plasma spray metal deposition. Additionally, the surface effects resulting from different solvent cleaning steps applied to a Ni based alloy were investigated in detail using incident, angle resolved and thermal desorption x-ray photoelectron spectroscopic methods. In particular, the study focused on contaminant O and C species interactions with the polycrystalline substrate prior to coating deposition. Differences in XPS features were noted between the various solvents used. Each solvent resulted in evaporation and ambient adsorption behavior which produced characteristic contaminants. Combining conventional desorption theory and surface spectroscopic techniques, a method of determining desorption behavior which was independent of weight measurements was developed. By comparing ambient O species to substrate oxides, changes in adsorbate coverage were estimated for the denuding surfaces. Experimental values for desorption behavior and relative desorption energetics were determined for ambient air on a polycrystalline substrate resulting from solvent/substrate interactions. Differences were discriminated between preparation methods and shown to vary as a function of solvent used. The nature of a surface with contamination was explained on this basis.
Engineering; Materials science; Metallurgy