Study of shape memory effect developed by helical springs made from Cu-Al-Ni base alloy by lost-wax casting

By means of displacement-temperature variation curves, the occurrence of both free-recovery and work-developing shape memory effects (SME) were revealed in the case of compression helical springs made from a Cu-Al-Ni based shape memory, by lost-wax casting. The corresponding critical temperatures of the martensitic transformation, determined during heating-cooling cycling, were compared to the results obtained during thermal cycling performed by dilatometry and differential scanning calorimetry (DSC). The results showed a decreasing tendency of critical temperatures. The corresponding microstructure was analyzed by scanning electron microscopy (SEM) in order to reveal the formation of β₁’ martensite and its morphological changes produced by cycling.