CHARACTERISTICS OF SUPERPLASTIC ALPHA/BETA-BRASS WITH EQUAL PHASE PROPORTION

Superplastic alpha/beta brasses with equal phase proportion can be obtained by static annealing at 495, 590 and 720-degrees-C for three Cu-Zn alloys with 58, 59.4 and 60.85 wt% Cu respectively. Correlation between static grain coarsening and annealing time is investigated. Also, cavity evolution during superplastic deformation of uniaxial tensile specimen is studied. The obtained results show that static grain growth rates of both alpha and beta phases are equal. Although, the alpha-phase is considered to be the harder phase under superplastic conditions, a totally opposite phenomenon is exposed at normal (non-superplastic) conditions. The increase of zinc concentration from 39.6 to 43.9 wt% in beta-phase leads to a stronger decrease of its volume self-diffusion activation energy than that observed for alpha-phase. Superplastic deformation of specimens with 50 alpha/50 beta brasses, shows that the cavitation level decreases as the test temperature increases. The number of nucleated sites decreases drastically with increasing temperature whereas the decrease of void growth is less drastic.