Microstructure and thermodynamic investigation of NiTi system produced by mechanical alloying

In this study, an equiatomic mixture of Ni and Ti powders has been mechanically milled for 180 h in a planetary mill in order to study the product phase of milling process. Miedema's semi empirical method has been used in order to calculate the energy of solid solution and amorphous phases and the effect of defects like dislocations and grain boundaries have been considered in this thermodynamic approach. The results showed that amorphous phase is more stable than solid solution after mechanical milling process. It seems these results are in contrast with Mousavi et al. [1] results but there are some points that we should consider in this approach. Applying of common tangent rule and considering the grain boundaries and dislocation energies in this thermodynamic approach lead to anticipating of amorphous phase as the stable phase after mechanical alloying process while lack of considering these terms in Mousavi et al. study led to different results. The milled powders has been heat treated at 950ᵒC for 20 min and finally, XRD and SEM analysis have been performed in order to evaluate experimental phases and compare experimental and theoretical results. Crystallite size and lattice strain have been calculated using Williamson-Hall equation and XRD patterns.