Microstructure and properties of Cu-3Ti-1Ni alloy with aging process

The effects of Ni addition and aging treatment on the microstructure and properties of Cu-3Ti alloy were investigated. The microstructure and phase constituents were characterized by optical microscopy, scanning electron microscopy, X-ray diffractometer and high-resolution transmission electron microscopy, and the hardness and electrical conductivity were measured as well. The results show that NiTi phase forms with addition of Ni into as-cast Cu-3Ti alloy during solidification, and the as-cast microstructure evolves from dentrite to equiaxial structure. After aging treatment, coherent metastable β'-Cu4Ti precipitates from the Cu matrix. However, β'-Cu4Ti precipitation phase transforms into equilibrium, incoherent and lamellar Cu3Ti phase after overaging. Meanwhile, aging treatment results in appearance of annealing twins in the residual NiTi phase, and dislocation lines exist in the Cu matrix. Ni addition enhances the electrical conductivity, but decreases the hardness of Cu-3Ti alloy. In the range of experiments, the optimum aging treatment for Cu-3Ti-1Ni alloy is 300 °C for 2 h and 450 °C for 7 h. The hardness and electrical conductivity were HV 205 and 18.2%IACS (international annealed copper standard), respectively.