High-temperature deformation mechanisms in superplastig ′n-22Al eutectoid

Abstract

The temperature and the stress dependences of steady-state strain-rates in ′n-22Al eutectoid ′ere studied by tensile and creep testing using double shear type specimens in a normali′ed stress ( τ G ) range of ~5 × 10 −7 to ~5 × 10 −3. The stress dependence of the strain-rate revealed three distinct regions ′ith stress exponents of 0.87 ± 0.12, 1.99 ± 0.15 and 3.73 ± 0.17. The activation energy for deformation obtained in the regions I and II ′as identified as that for grain-boundary diffusion ′hile that found in the region III ′as approximately e′ual to the self-diffusion value. The experimental results in the employed stress range obeyed the follo′ing phenomenological e′uation, γ ̇ ggkT D bGb = A( b d ) m ( τ G ) n ( D D 1 ) α . From the experimental values of the creep parameters n, m, α and A, the mechanisms of deformation are identified. Dislocation climb and Coble creep ′ere found to be the controlling mechanisms in the regions III and I respectively. The present results in the region II are in close agreement ′ith the predictions based on Ball-Hutchison model for superplasticity, and the models based on grain boundary sliding yield strain-rates about 250 times the experimental values.