A new type of Cu-Al-Ta shape memory alloy with high martensitic transformation temperature

In this study, a new type of Cu-Al-Ta (Cu₈₆Al ₁₂Ta₂ wt%) shape memory alloy with high martensitic transformation temperature is explored. The microstructure, reversible martensitic transformation and shape memory properties are investigated by means of optical microscopy, back-scattered electron, electron probe microanalysis, x-ray diffraction, differential scanning calorimetry and tensile tests. It is proposed that Cu₈₆Al₁₂Ta₂ alloy consists of a mixture of primarily β^′₁ martensite and a little γ^′₁ martensite and some different precipitates. The tiny thin-striped Ta₂(Al,Cu)₃ precipitate is predominant in the as-quenched condition, whereas the particle-shaped Cu(Al, Ta) precipitate is dominant after hot-rolling. Additionally, the dendritic-shaped γ₁(Cu₉Al ₄) phase begins to appear after hot-rolling, but it disappears when the sample is re-quenched. All studied samples have reversible martensitic transformation temperatures higher than 450°C. The results show that two-step martensitic transformation behavior is observed for Cu ₈₆Al₁₂Ta₂ alloy in all three different conditions due to the transformations between (β^′ ₁ + γ^′₁) martensites and the austenite parent phase. The results further show that the recovery ratios are almost 100% when the pre-strains are ≤2.5%, then they gradually decrease with further increase of the pre-strains. The shape memory effects clearly increase as a result of increase of the pre-strains, up to a maximum value of 3.2%.