S. Stanciu, L. G. Bujoreanu, N. Cimpoesu, I. Ionita, The Gheorghe Asachi Technical University from Iasi, Iasi, Romania
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.
Summary: From a Cu-Al-Ni base Shape Memory Alloy (SMA) specimens were obtained under cylindrical form and under the form of helical springs, by lost-wax casting which were homogenized and solution treated.
By scanning electron microscopy (SEM) the microstructure was analyzed in order to reveal the existence and morphological changes of beta one prime thermally induced martensite.
During heating-cooling cycles, performed by means of a dilatometer at a temperature variation rate of 2 deg./ sec, the decreasing tendency of critical temperatures of forward martensitic transformation was observed. After the first heating-cooling cycle, the contraction occurring during forward martensitic transformation was replaced by expansion which increased more than four times during cycling.
Critical transformation temperatures were also determined by differential scanning analysis (DSC).
The shape memory behavior of helical springs during compression was investigated, under the form of displacement vs. temperature variation curves. In this way, their capacity to experience free-recovery shape memory effect, to produce work and to increase their thermal memory by training was revealed.
