The influence of nitrogen to hydrogen ratio and temperature on thickness and phase composition in plasma nitrided Ti-6Al-4V

Ti-6Al-4V was plasma nitrided using several N-2/H-2 ratios and substrate temperatures. In order to investigate the combined influence of these parameters on phase composition and thickness of the coatings, the phases in the as received, annealed, and nitrided Ti-6Al-4V samples were identified with Rietveld refinement. In the as-received and annealed samples the structure parameters of alpha-Ti and beta-Ti were slightly changed, due to the substitution of titanium atoms by Al or V in the alpha- and beta-Ti unit cells. A combination of multiple angle grazing incidence X-ray diffraction, nuclear reaction analysis and cross sectional micrographs showed compound layers consisting of an outer layer of stoichiometric delta-TiN over a phase mixture of delta-TiN and epsilon-Ti2N, formed on top of a nitrogen diffusion region in the alloy. Higher nitriding temperatures induced thicker compound layers, and higher nitrogen content of the plasma induced thicker fine-grained delta-TiN top layers.