Thermally and stress induced changes in three phase structure of Cu–Zn–Al–Fe shape memory alloy

Abstract

In order to explain the stabilised shape memory behaviour observed during the thermal and mechanical cycling of a Cu–14·86Zn–5·81Al–0·5Fe (wt-%) alloy, X-ray diffraction and optical microscopy studies have been performed. The former have shown that the previously reported reorientation of the α brass phase crystallites from α(111) to α(200), observed during the heating up to 500°C, also occurs during a complete heating–cooling cycle up to 325°C. Optical microscopy studies confirm the increasing tendency for α phase preferred formation when the temperature is increased from 325 to 500°C. This texturing effect that occurs during thermal cycling is accompanied by an increase in the amount of α phase with a reduction in the amount of β 2 austenite. Finally, a tensile completely recoverable pseudoelastic strain of almost 0·6%, determined during a loading–unloading cycle applied to a heat treated specimen that contained no austenite, has been ascribed to the reversible formation of a specific martensite variant.