Phase transformations under ball milling

How to predict which phase is stabilized as a function of milling conditions? Two systematic experimental studies of phase transformations under ball milling (crystal-to-amorphous transition in Ni_xZr_y and order-disorder in FeAl) have demonstrated that the end product of a milling treatment and the path to this latter state depend on the milling temperature and intensity (to be defined in the text). A simple model for the competition between shear-induced disorder and thermally activated atom jumps yields a dynamic equilibrium phase diagram for FeAl under milling in good agreement with experimental findings. Atomistic Monte Carlo simulations of an ordered compound under sustained shearing reproduces most behaviours observed in FeAl; moreover the microstructure achieved is found to depend on the amplitude and geometry of the disorder introduced by each shearing event, as well as the number of vacancies produced by non-conservative dislocation motions. Advantage is taken from the above results for practical purposes. An example is given of optimizing the milling treatment for synthesizing nanocomposite materials for electrical applications. The approach as described can be taken advantage of for assessing the effect of subsurface transformations on wear.