Abstract
In a polycrystalline Cu-13.9 mass% Al-3.8% Ni-0.03% B shape memory alloy, the pseudoelastic loop and electric resistance during straining and unloading above Ms were observed. The results were discussed in comparison with the predictions made from the modified Taylor model and observations in single crystals in the literature, which suggest that either γ1′- or β1′-martensite could be stress-induced. The observed yield stress was close to the predictions made assuming these martensites, but definitely smaller than either of them, the difference being larger as temperature increased. This disagreement is primarily attributed to the simultaneous formation of the two types of martensites, which is facilitated by the effect of intergranular constraint. The difference of the observed value for the SIM formation rate to the prediction, on the other hand, was far larger than that for the yield stress, so that the work done by the applied stress was significantly larger than the energy consumed for the formation of SIM. Although various uncertainties are involved in this comparison, this apparent energy unbalance is considered to be real, being likely to be caused by energy storage in the form of elastic energy.
