Influence of Al and Ni concentration on the martensitic transformation in Cu-Al-Ni shape-memory alloys

The martensitic transformation temperatures and the types of martensitic phases have been determined in a wide concentration range of technological interest for Cu-Al-Ni shape-memory alloys (SMAs) A stability diagram of martensitic phases as a function of alloy concentration has been determined. It is found that when the aluminum, content increases, the transformation changes from beta(3) double right arrow beta'(3) to beta(3) double right arrow gamma'(3), with an intermediate concentration range where both martensites coexist due to a beta(3) double right arrow gamma'(3) + beta'(3) transformation. On the other hand, an increase of nickel content stabilizes the martensite beta'(3), changing from a mixed beta(3) == gamma'(3) + beta'(3) to a single beta(3) double right arrow beta'(3) transformation. Furthermore, linear relationships between M-s and Al and Ni concentrations have been obtained for all types of martensitic phases.