| Present investigation has been made to study the superplastic deformation behavior of Ti-6Al-4V alloy with respect to the variation of α/β volume fraction. Load relaxation and superplastic deformation tests have been carried out at 600℃ and 800℃, to obtain stress-strain rate curves and tensile elongations for the microstructures of 3 and 11㎛ grain sizes. The experimental results have been analyzed by the theory of inelastic deformation which consists of two mechanisms, i.e., the grain matrix deformation and the phase/grain boundary sliding. Grain matrix deformation observed at 600℃ is consistent with an iso-stress model for the deformation of fine grain microstructures (3㎛) in which the β volume fractions are varied. However, the coarse grain microstructures (11㎛) reveal the deformation behavior of mixed type between. iso-stress mode and iso-strain rate mode. Phase boundary sliding occurring at 800℃ is the most effective in 48% β structure, resulting in the largest elongation, The sliding resistance in the different types of grain boundary is increased in the order of α/β≫α/α≒ β/β. |
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