Microstructural Evolution and Properties of Aged Cu-3Ti-3Ni Alloy

The effect of aging treatment on the microstructure and the properties of Cu-3Ti-3Ni alloy was studied. The microstructure and the precipitated phase were characterized by X-ray diffractometer, scanning electron microscope and transmission electron microscope, and hardness, electrical conductivity and elastic modulus were measured as well. The results show that a number of Ni3Ti and β′-Cu4Ti phases precipitate from the Cu matrix after aging treatment. With the increase of secondary aging time, partial alloying elements dissolve into the Cu matrix, and the metastable Cu4Ti phase transforms into incoherent equilibrium Cu3Ti phase. The enhanced electrical conductivity is ascribed to the decrease of Ti solubility in the Cu matrix by the formation of the Ni3Ti and β′-Cu4Ti precipitates. After an appropriate aging treatment of Cu-3Ti-3Ni alloy, the Ni3Ti and coherent metastable β′-Cu4Ti phases precipitate completely, giving rise to the increase of hardness. Aging treatment has no obvious effect on the elastic modulus of Cu-3Ti-3Ni alloy. In the scope of the experiments, the optimal two-step aging treatment parameter for Cu-3Ti-3Ni alloy is to age at 300 °C for 2 h followed by aging at 450 °C for 7 h. The HV hardness, the electrical conductivity and elastic modulus are 1.83 GPa, 31.34 %IACS (International Annealed Copper Standard) and 148.62 GPa, respectively.