Study on the solid solubility extension of Mo in Cu by mechanical alloying Cu with amorphous Cr(Mo)

This paper presents the extension of the solid solubility of Mo in Cu by a mechanical alloying technique. Two binary systems, Cu–10 wt.% Mo and Cr–50 wt.% Mo, and one ternary system, Cu–20 wt.% Cr(Mo), are investigated. The solid solubility of Mo in Cu has been shown to be less than 4.3 at.% when the Cu–Mo system is mechanically alloyed, whereas when the Cr–Mo system is mechanically alloyed all of Mo dissolves into Cr, forming an amorphous Cr(Mo). Similarly, all of 10 wt.% Mo dissolve into Cu when Cu–20 wt.% amorphous Cr(Mo) is mechanically alloyed. Based on Miedema’s model, the Gibbs free-energy changes in these three alloy systems during the formation of solid solutions are calculated to be positive, which means that thermodynamic barriers exist for the formation of these three alloy systems in solid solution states. The mechanism of solid solubility extension in these mechanical alloyed systems is discussed. The conclusion is that the extension of solid solubility is favoured by adding a third element, such as Cr, to the Cu–Mo system.