In the ternary Cu-Zn-Al alloys the bcc β phase is stable at high temperatures at electron concentrations (e/a) in the range from about 1.4 to 1.6 electrons per atom. Cu, Zn and Al atoms contribute with 1, 2 and 3 electrons, respectively. This region of stability is bounded by a β + γ twophase region at the high electron concentration border. If the P phase is retained at room temperature (RT) it transforms martensitically to a close packed structure. This transformation occurs without diffusion and provides information on the relative phase stability of the bcc and close packed structures. A detailed characterization of the microstructure of the parent bcc β phase and the martensite is thus essential for an adequate study of the transformation.
To retain the β phase at RT Cu-Zn-Al alloys must usually be quenched.