Abstract
Ti and Zr were added as “dopants” to a Cu-15%Al-4%Ni (in weight percentages) shape memory alloy in order to study their effect on grain refinement, grain growth rates, the shape memory effect and fracture mode. Small amounts of Ti and Zr (0.55% and 1.1% of each) had a significant effect in refining the grain size. It was found that the degree of grain refinement is independent of the amount of dopants added once a certain additive level is reached. Both Zr and Ti suppressed the subsequent grain growth rate essentially to zero. Ti-rich and Zr-rich second phase particles were observed in the Ti- and Zr-doped alloys. However, there was no evidence that these second phase particles were a major factor in grain refinement. Various solution treatment times did not change the Ms temperatures of all alloys studied. The Ms temperatures for most doped alloys were modified only slightly, and therefore the shape memory effect was retained. Auger electron analysis was performed on both dopant free and doped alloys, and showed that oxygen segregation at the grain boundaries of dopant free CuAlNi may be the major cause of intergranular fracture. Additions of Ti and Zr to the base CuAlNi alloy changed its fracture mode from intergranular to transgranular.
