Mechanical alloying of the immiscible Cu-60wt%Cr alloy: Phase transitions, microstructure, and thermodynamic characteristics

Abstract Solid state alloying of immiscible alloy systems such as Cu-Cr is an important field of physical metallurgy. Currently, non-equilibrium techniques are successfully applied in the synthesis of Cu-Cr alloys; however, the mechanism of formation of these alloys remains unclear due to the unavailability of data regarding their microstructure evolution and thermodynamic characteristics. In this work, a mechanical alloying (MA) Cu-60wt%Cr alloy is prepared by high-energy milling. The phase transitions, thermodynamic properties, and microstructure of this alloy are analyzed using X-ray diffraction, differential scanning calorimetry, and transmission electron microscope techniques. The obtained results demonstrate that the supersaturated Cr(Cu) solid solution alloy has a supra-nanometer-sized microstructure and is composed of crystalline and amorphous phases. To form the alloy, the localized Cu is first transformed into an amorphous state, then the disordered Cu atoms diffuse into the Cr matrix during the MA process. The diffusivity of Cr atoms in the Cu lattice is significantly hindered, even when the lattice is heavily defected.