Structural investigation on nano-crystalline Cu–Cr supersaturated solid solution prepared by mechanical alloying

In this paper, elemental Cu–7 wt.% Cr powder mixture was mechanically alloyed in order to study the solid solubility extension during the alloying process. By mechanical alloying in a high energy ball mill, a nano-structured and homogeneous Cu–Cr powder was obtained. The effect of toluene as a process control agent (PCA) was investigated. The structural changes were characterised by X-ray diffraction (XRD) technique. The Gibbs free energy change in this system during the formation of solid solution was calculated and shown to be positive, which means that a thermodynamic barrier exist for the formation of this alloy system in solid state. It was found that the additional energy stored in the nano-crystalline Cu–Cr alloy during mechanical alloying process as a result of crystallite size reduction and increased dislocation density, would be high enough to overcome the thermodynamic barrier in the formation of a solid solution.