Influence of neutron irradiation on the martensitic transformations in 18R Cu-Zn-Al single crystals

The Cu-Zn binary and ternary alloys have a low vacancy formation energy in the high temperature β-phase. This implies that a high vacancy concentration can be quenched in, considerably higher than in the close packed α phases, which are stable at lower electron concentrations. The β-phase transforms martensitically to close packed lattices (fcc, 18R or hexagonal); the high concentration of vacancies can then be retained in these closed packed structures. At sufficiently high temperatures, which include already room temperature, the vacancies become mobile, leading to a change in phase stability, which manifests itself in a change in transformation temperature or stress, and which is called stabilization. When a material is irradiated with particles, vacancies are created, among other effects. If it is only these vacancies which are important in the structural changes, then a quench and an irradiation experiment should yield the same results, if the excess vacancy concentration is similar. In order to investigate this possibility, CuZnAl alloys slowly cooled to avoid excess vacancies were irradiated with fast neutrons in the martensitic phase. The results are compared with the stabilization which is known to occur in samples with quenched-in vacancies. The results of reactor-neutron irradiations at about 70 degrees C are described