TENSILE PROPERTIES AND MICROSTRUCTURE OF MICROALLOYED CU-AL-NI-X SHAPE MEMORY ALLOYS

Abstract

The effects of microalloying additions (0.3Ti, 0.3Ti-0.2Mn, and 0.3Ti-0.6Zr) to a beta Cu-13Al-3Ni shape memory alloy on the tensile properties, shape recovery capacity and microstructure were investigated. It was found that the tensile properties (sigma-t, sigma-f and epsilon-f) lie roughly on a straight line according to a Hall-Petch relationship. The highest fracture stress (903 MPa) and fracture strain (8.6%) were obtained in the Cu-13.4Al-3.05Ni-0.24Ti-0.63Zr alloy. Fractography revealed a change from the intergranular to the transgranular fracture mode. Grain boundary cracking was markedly suppressed by the microalloying additions and the fracture mode also changed from brittle to ductile with decreasing grain size of the beta phase. The investigated alloys were fully martensitic consisting of internally faulted M18R and internally twinned N2H types.