Abstract The objective of this work is proposing a simple thermodynamic model to explain the increase in the solubility limit of the powders of the Cu–Mo systems or other binary systems processed by mechanical alloying. In the regular solution model, the effects of crystalline defects, such as; dislocations and grain boundary produced during milling were introduced. The model gives results that are consistent with the solubility limit extension reported in other works for the Cu–Cr, Cu–Nb and Cu–Fe systems processed by mechanical alloying.