Synthesis of highly oriented TiNx coatings by free-electron laser processing of titanium in nitrogen gas

Titanium substrates were irradiated in pure nitrogen gas by means of a free-electron laser. The treatment resulted in the formation of delta-TiNx coatings, with surface stoichiometry x approximate to 1 and thickness of about 15 mu m. Under specific experimental conditions the nitride phase had a remarkable crystallographic texture with the delta-TiNx(200) planes parallel to the irradiated surface, and well aligned dendrites growing normal to the surface. The mechanism of the dendritic alignment and the origin of the texture correlate with the existence of a solidification front starting at the surface, which is very peculiar for laser surface treatments. This phenomenon is explained with the help of numerical simulations.