lt is apparent from Table 2that there is a rise in the content of mono- clinic and cubic structures, while a decrease of the tetragonal phase is observed; these findings partially agree with results of Gupta et al. [19], who stated that a tetragonal/monoclinic transformation occurs during fracture; thus, this phase transformation is possible during the milling since the mechanism of reduction of average particle size is the fracture event. This phase transition is described as a first-order displacive martensitic phase transformation, and details of the specific mechanism can be found elsewhere [20]. On the other hand, the mechanism to obtain the cubic structure by means of ball milling has been previously reported by Gateshki et al. [21l, who described it in terms