Kunio Suzuki1, Yoichi Ishida2 and Masaki Ichihara1
1Institute for Solid State Physics, The University of Tokyo, Tokyo
A typical superplastic alloy, fine-grained Zn-22 wt%Al eutectoid, was strained at elevated temperatures in a 500 kV electron microscope in order to understand the mechanism of apparently ``superplastic'' elongation of zinc-rich grains.
Superplasticity is generally thought as a grain boundary phenomenon and not as the elongation of individual grains. Thus, the unusual elongation of zinc-rich grains was a puzzling feature of the deformation in favor of the grain deformation as the cause of superplasticity. The ``in situ'' observation proved that the elongated grain in fact grew at the grain boundary under the influence of the applied tensile stress. The growth rate is determined by the diffusion of zinc through the grain boundary. The apparently superplastic elongation was a diffusional creep that prevails when bulk super-plasticity is prohibited due to the thin foil geometry.
The phenomenon is not only important the for elucidation of the mechanism but also is interesting as a process to grow whiskers.
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