| Abstract |
| Superplasticity of ultra-fine grained (UFG) Ti-6A1-4V alloy processed by equal channel angular (ECA) pressing was investigated with the variation of strain rate and temperature. Initial coarse equiaxed grains (11 μm in diameter) were significantly refined to =0.3 μm without changing volume fraction after 4 times of isothermal ECA pressing at 600℃. Tensile tests of both coarse grained specimens and UFG specimens were performed at temperatures of 600℃, 650℃ and 700℃, respectively, and at strain rates of 10^(-4)/s to 10^(-2)/s. UFG structures exhibited considerably higher elongations than those of coarse grained specimens at the same conditions of temperatures and strain rates. The results indicated low-temperature superplasticity (LTS) could be achieved by using UFG structures. Also, it was found in this study that, in spite of non-equilibrium state due to intense plastic straining, grain size were found to be an important factor in controlling overall superplasticity of UFG structure. A plastic instability during superplastic deformation of UFG Ti-6A1-4V alloy was discussed in relation to Hart`s criterion. (Received June 2, 2004) |
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| Key Words |
| ECA pressing, Ultra-fine grain, Ti-6Al-4V alloy, Superplasticity |
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