Effect of indium in Cu-Zn-Al shape memory alloys

Abstract

Shape memory alloys (SMAs) are among the "smart" materials that can virtually remember their original shape; after being deformed, they may return to their initial shape through heating. The shape memory effect derives from a martensitic transformation induced by stress and/or temperature change. Copper-based SMAs are a more economical alternative compared to Ni-Ti alloys. They have low cost and various interesting mechanical and thermal properties and high practical value for the applications. In this present work, Cu-Zn-Al shape memory alloys with 0.1-0.5 wt.% In were studied. Investment casting (lost-wax casting) was performed at 1100 °C melting temperature and 650 °C mold temperature. Shape memory effect of the alloys was investigated with bending test and then heating for shape recovery. Scanning and transmission electron microscopes were used for microstructural characterization along with Energy X-ray diffraction and selected area diffraction spectroscopy. XRD measurement was also performed to understand effect of indium on microstructure. The results clearly presented that the addition of In in Cu-Zn-Al SMAs caused a precipitation of the second phase and significantly alternated the shape memory effect. The microstructure and orientation relationship of the typical and twinned martensite were discussed.