  We propose and develop a model as an attempt to describe the local mechanism
of mechanical alloying. This model is based on the observation of global
parameters, such as the volumes of the various phases present in the material,
and their transformations during the process. The model is applied to milled
Fe-Cu and Fe-N experimental results obtained in previous works. In the milling
of Fe-Cu system, four stages, whose features are in accordance with
experimental observation, are identified:(i) energy storage; (ii) start of the
reaction and speed up of it; (iii) decrease of the reaction rate and (iv)
stationary stage. No energy storage stage is observed and no saturation is
achieved in the milling of Fe-N system. Moreover, we propose a modification on
the global kinetic law introduced by Matteazzi et al. based on the different
nature of Fe-Cu and Fe-N systems. This modification allows the extension of the
validity of this law.
