Superplasticity of Fine-Grained Titanium Alloys Obtained through Protium Treatment

To obtain fundamental data on superplasticity of fine-grained α+β titanium alloys obtained through protium treatment, superplasticity tensile tests were carried out in vacuum. Changes in the microstructure after the tensile test were observed using an optical and scanning electron microscope. The experimental results are as follows: A fine-grained material having a grain size of 1µm to 3µm exhibits a significant elongation of over 8000% at a testing temperature of 1123K and a strain rate of 1×10^-3s^-1. The m-value of the fine-grained material is much higher than that of a coarse-grained material, with the maximum m-values being 0.80 and 0.64, respectively. These results indicate that it is not easy for necking to occur in fine-grained material. In the observation of the structure after the superplastic-tensile test, a coarse-grained material did not exhibit grain growth, but the fine-grained material did.