| The practical application of the Cu-Al-Ni shape memory alloys has been restricted because of their brittleness and degradation of shape memory ability, that are mainly caused by their high elastic anisotropy(A=13) and large grain size. In order to clarify the way of the improvement of the aforementioned properties, the effects of grain refining on the ductility and thermocycling properties of the alloys has been studied by adding small quantity of B, Ti, Zr. The addition of such elements to Cu-Al-Ni alloys caused significant decrease of grain size and the increase of elongation from 5% to 7-10%, in comparison to those of Cu-Al-Ni base alloys. After 30 cycles under 200g load, recovery displacement was decreased to 55% in the Cu-Al-Ni alloys with large grain size but decreased to 81% in Cu-Al-Ni-Zr alloys with fine grain size. The change of transformation, temperature were found smaller in the grain refined Cu-Al-Ni-Zr alloys. It is thus concluded that the grain refining by adding small amount of Zr to the Cu-Al-Ni allay improved the ductility and the stabilization of thermocycling properties. |
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