抄録
The reversible shape memory effect (RSM) was found to appear in Cu-Zn-AI alloys after a heat-treatment under constraint without severe deformation. A series of detailed investigations have been performed to understand this phenomenon. This paper represents the results of mechanical test associated with the RSM as well as those of the corresponding metallographic examinations.
Three stages of stress variation were observed with respect to temperature in tensile tests under a fixed elongation of polycrystalline specimens. In the first stage the stress increases with temperature where the reverse transformation (β′1→β1) of stress-induced martensites (SIMs, β′1) occurs. The second one with a lower increasing rate follows at temperatures greater than about 60°C, the decrease in rate being caused by the yielding of SIMs. The last one at temperatures higher than 180°C shows a decrease in stress with temperature, where the bainitic transformation takes place.
The RSM was produced by heating the specimen under constraint only at the temperatures corresponding to the second stage in the above test, i.e., about 60∼180°C. The metallographic examinations reveals that the yielding stabilizes the β′1 SIMs, and also that the RSM is predominant in the grains where a large amount of the stabilized SIMs remains to form complex structures in the matrix. The result that the stabilized β′1 has a different crystal structure from 9R, i.e., 3R called α′1, will be described in the next paper.
