Thermodynamic Approach to the Description of the Steady-State Phase Composition of Alloys Obtained by Mechanical Alloying Techniques

摘要

Deformation mechanism of mechanical alloying (MA) process is discussed. Deformation considered as a superplastic flow ― sliding of relatively hard nanocrystals along relatively soft grain boundaries (GB). In the steady state nanostructured MA materials consist of at least two phases: crystalline phase of grains and GB amorphous phase, which coexist in local equilibrium. Amorphisation of alloy can be described as an increase in the amount of GB phase during MA. At MA of immiscible systems the mutual solubility of components decreases with an increase in the mixing enthalpy. It is considered that in such systems the energy barrier for solid solution formation, which MA method allows to reach, is close to the heat of amorphous phase formation. For systems with low positive or negative enthalpies of solid solution formation, the final structure of MA materials most likely contains only one phase, which has the lowest Gibbs energy among all of possible phases.