Effect of Be content on some characteristics of Cu–Al–Be shape memory alloys

Two kinds of shape memory alloys with the composition Cu–11.6 wt.%Al–0.42 wt.%Be and Cu–11.8 wt.%Al–0.47 wt.%Be were investigated. The structure of some part of sample 1 and the whole of sample 4 of the alloy with 0.47 wt.%Be content was determined as austenitic DO3 superlattice and the structure of the alloy with 0.42 wt.%Be content was determined as 18R martensitic phase by using X-ray diffraction techniques. From the differential scanning calorimeter (DSC) measurements and microscopic observations, the suitable heat treatment stages for the shape memory characteristics of these two alloys were determined as: annealing at 650 °C for 15 min aging at 97 °C for 5 min and cooling in water at room temperature. Samples of these two alloys having other heat treatment stages did not show any shape memory properties in the −50 to +200 °C temperature range. The difference in the Be contents of these alloys is 0.05 wt.%Be. It has largely affected the transformation temperatures and the As (austenitic phase starting temperature), Amax (maximum phase transformation rate temperature) and Af (austenitic phase finish temperature) temperatures for sample 4 of alloy having 0.47 wt.%Be content were found to be −21.5, −13.1 and 2.2 °C, respectively. The As, Amax and Af temperatures for sample 6 of alloy having 0.42 wt.%Be were found to be 99, 115 and 146 °C, respectively. The As, Amax and Af temperatures for sample 8 of alloy having 0.42 wt.%Be were also found to be 60.8, 77.0 and 93.0 °C, respectively.