Ageing Behaviour of Sc-Doped Cu–Zn–Al Shape Memory Alloys

Abstract

The effect of scandium (Sc), when added in trace, on the ageing behaviour of Cu–Zn–Al shape memory alloy was investigated in the present work. Cu–Zn–Al shape memory alloy was prepared by melting 70:30 brass using commercial grade Cu strips and Al chips. Sc was added using Al–Sc 2 wt% master alloy at the time of melting, and the final composition was adjusted to 0.1 wt% Sc. Chemical composition of the alloys was analysed by using EDAX and spectrometer. The influence of Sc on mechanical properties under different ageing conditions were primarily evaluated by Vickers hardness test. Optical and scanning electron microscopy (SEM) was used to analyse the microstructure. Differential scanning calorimetry was used to measure the transformation temperatures, correspond to martensite to austenite or the reverse transformation. Thermo-Calc software was used to construct a phase fraction diagram as a function of temperature to obtain the evolving phases during quenching and subsequent ageing process for both of the alloy systems. The ageing behaviour was also examined using XRD and SEM characterization and explained in the light of phase predictions obtained from the thermodynamic calculations. Subsequently, transmission electron microscopy investigation was carried out to evaluate the influence of Sc on the size and habit planes of the precipitates in Cu–Zn–Al ternary alloy system. Sc has been found to reduce the transformation temperature and consequently increase the mobility of the martensite/austenite interface.