An investigation was made of changes in the density of vacancies during ball milling, and a model was proposed for the evolution of vacancies. The results of simulation showed that the density of vacancies increased asymptotically with collision time, and the rate of increase became slower with further ball-milling. The accumulation of vacancies in the powder particles was dramatically accelerated at lower milling temperature. Vacancies were shown to accumulate more easily in powder materials having higher vacancy migration energies. The simulations indicated that a higher collision frequency resulted in a faster accumulation of vacancies and therefore a higher density of vacancies could be obtained. In addition, a higher impact energy introduced a higher density of vacancies per collision. It was suggested that a low milling temperature, high collision frequency and high collision energy could be advantageous for the formation of new alloys, but a low migration rate of vacancies at low temperature could reduce the rate of formation of new alloys if the milling temperature was too low.

Evolution of Vacancy Densities in Powder Particles during Mechanical Milling. B.Q.Zhang, L.Lu, M.O.Lai: Physica B, 2003, 325, 120-9