Kinetics behaviour of metastable equiatomic Cu-Fe solid solution as function of the number of collisions induced by mechanical alloying

We have addressed a new study by mechanical alloying on the nominally immiscible Cu50Fe50 system with the aim of relating the solid state transformation process, with formation of a disordered unstable solid solution having the face centered cubic habit, to parameters reflecting the impulsive, discontinuous nature of the process. The milling set-up, tools and powder were adjusted in order to ensure completely anelastic hits. Phase analysis, structure and microstructure parameters of such powder system have been followed accurately in the course of the kinetics by X-ray Diffraction using the Rietveld method. The experimental kinetics data points of the amount of transformed solid solution show a typical sigmoidal behavior. It was assumed that dissolution only occurs in the volumes of material that have undergone the necessary critical loading conditions, which is accounted by a discrete series expansion. The mass fraction effectively processed at each collision can be regarded as an apparent rate constant for the microstructural refinement and phase transformation processes. Analysis of model curves fitting the experimental data suggests that it takes up an average of 6 impacts of coupled powder particles to drive the system to the new unstable nano-crystalline state.