On the influence of austenitization on the morphology of α-phase in tempered Cu-Zn-Al shape memory alloys

The paper reports some austenitization effects on the α-phase morphology in a tempered martensitic Cu-21.57 Zn-7 Al (wt.%) shape memory alloy (SMA). By means of differential scanning calorimetry, X-ray diffraction and optical and electron microscopy, it has been shown that the effects of the stress-state induced in austenite persist even after martensitic transformation and tempering at 773 K. The two analyzed austenitization states, hot-pressed and homogenized, respectively, aimed to reproduce two steps of an industrial technologic flow for SMA manufacturing. Basically, austenitic hot-working diminished the size of disoriented α-phase precipitates while austenitic homogenization enabled the formation of a Widmanstaetten structure with oriented long α-phase needles, among which those corresponding to α(1 1 1) intersect at about 70 deg. and those corresponding to α(2 0 0) at 90 deg