Thermal Cycling Effects in a Cu–Al–Ni Shape Memory Alloy

Abstract

Thermal cycling effects in a Cu-13.7 Al-4.0 Ni (mass%) alloy have been studied by optical and electron microscopy observations and X-ray diffraction. Transformation temperatures, M_s and A_f, decrease gradually with increasing thermal cycles, the magnitude of the decrease reaching about 40 K after 10000 cycles. Martensite plates tend to become smaller with increasing thermal cycles, but their morphology is not so different even after 10000 cycles. The reproducibility of martensite plate formation becomes to be recognized after 10000 cycles, although it is not so perfect as in Cu–Zn and Fe–Pt alloys. Dislocations in the parent phase increase in density with increasing thermal cycles, and a characteristic array of the dislocations is seen after 10000 cycles. The degree of DO₃ order of the parent phase decreases with thermal cycling, although that of B2 order remains almost constant, and this results in the decrease of transformation temperatures.