Experimental Investigation in the Quaternary Systems Ti-Ni-Al-N and Ti-Ni-Al-O

The experimental evaluation of phase equilibria in the Ti-Ni-Al-N and Ti-Ni-Al-O phase diagrams are based on alloy samples, which were prepared of elemental powder blends by argon-levitation melting in a Hukin crucible. The experimental investigation employed X-ray powder diffraction, metallography, SEM, and EMPA techniques in the as-cast state as well as after annealing at 900°C. Two quaternary compounds Ti3NiAl2N and Ti3NiAl2O deriving from the filled Ti2Ni type (eta phase) were observed. The novel phases are in equilibrium with the Ti2Ni-type solid solution phase (Ti1-xAlx)2Ni, which exhibits a maximum solubility of 14 at.% Al in binary Ti2Ni. Atom order in all these phases was monitored by quantitative X-ray powder diffraction (Rietveld analyses). The difference of X-ray spectra among the various phases deriving from parent Ti2Ni type was analyzed and the complex atom site occupation mode was discussed in terms of the general classification scheme for etaphases