Parametric Optimization of Ti-Ni Powder Mixtures Produced by Mechanical Alloying

In this study, a set of Ti-50 at.% Ni elemental powder mixtures were processed through mechanical alloying (MA). The objectives were to induce during MA the formation of a lamellar microstructure and to apply a design of experiments, based on the Taguchi method, to optimize the MA parameters. Enthalpy measurements associated to the high temperature reaction between Ni and Ti powders were used to evaluate the effect of the MA parameters. It is known that different ball-impact energies lead to different reaction pathways. The results indicate that milling time affects significantly (74% contribution) the enthalpy of the high temperature reaction while the milling speed has a lower effect (25% contribution). Moreover, whatever the milling conditions, the powder was a mixture of both crystalline phases and an amorphous phase. Their microstructure was composed of a multilayer of alternating Ni and Ti that in some cases was constituted by nanolayers. The oxygen and nitrogen contents of the milled powders ranged between 0.29 and 0.79 wt%, and 0.15 and 0.90 wt%, respectively.