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

摘要

Two kinds of shape memory alloys with the composition Cu-11.6 wt. percent Al-0.42 wt. percent Be and Cu-11.8 wt. percent Al-0.47 wt. percent Be were investigated. The structure of some part of sample 1 and the whole of sample 4 of the alloy with 0.47 wt. percent Be content was determined as austenitic DO_3 superlattice and the structure of the alloy with 0.42 wt. percent 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 deg C for 15 min aging at 97 deg 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 deg C temperature range. The difference in the Be contents of these alloys is 0.05 wt. percent Be. It has largely affected the transformation temperatures and the A_s (austenitic phase starting temperature), A_(max) (maximum phase transformation rate temperature) and A_f (austenitic phase finish temperature) temperatures for sample 4 of alloy having 0.47 wt. percent Be content were found to be -21.5, -13.1 and 2.2 deg C, respectively. The A_s, A_(max) and A_f temperatures for sample 6 of alloy having 0.42 wt. percent Be were found to be 99, 115 and 146 deg C, respectively. The A_s, A_(max) and A_f temperatures for sample 8 of alloy having 0.42 wt. percent Be were also found to be 60.8, 77.0 and 93.0 deg C, respectively.