Continuously cast Cu-Al-Ni shape memory wires with a unidirectional morphology

Abstract

The possibility of applying the Ohno continuous casting (OCC) process to the fabrication of Cu-Al-Ni shape memory alloy wires has been investigated. It was established that Cu-Al-Ni shape memory alloy wires of ∼2-mm diameter can be continuously cast by the OCC process. Cast wires were found to be of unidirectional structure with a matrix phase of β1 in which γ2 particles were precipitated in the form of dendrites along the subgrain boundaries. The γ2 precipitates became fewer and the size became finer with an increase in casting speed. The Ms transformation temperature was in the range −19 °C to −3 °C depending on casting speed, giving rise to stress-induced martensitic transformations at room temperature. The wires cast at slower speeds (50 to 90 mm min−1) displayed shape memory attributes on heating to 90 °C, whereas the wires produced at higher casting speeds (110 to 150 mm min−1) exhibited superelasticity at room temperature. In addition, the fatigue failure of the wires cast at 150 mm min−1) occurred after 6500 to 7500 bend cycles, which is comparable to that of a single crystal of similar composition.