Abstract
In this work, several important problems related to the fabrication of ultrafine grained UFG alpha+beta titanium alloys have been investigated, taking Ti-6.5Al-3.3Mo-1.8Zr-0.26Si wt- as the model material. It has been shown that UFG titanium alloys can be produced by deformation at relatively low temperatures or high strain rates. There were different Zenner-Holloman parameter-grain size relationships in the relatively high temperature region 750-920C and the relatively low temperature region 650-750C for the present titanium alloy. During the compression of a martensite microstructure at 890C, both the alpha and beta phases were dynamic recrystallised and the lamellae were broken up by means of grain boundary sliding and phase penetration along the subgrain boundaries. During compression at 650C, alpha phases were dynamically recrystallised, and beta phases precipitated and grew in the matrix of alpha phases. It was suggested that the martensite microstructure should be preferred to other lamellar microstructures for the fabrication of UFG Ti alloys. The UFG Ti alloy demonstrated good superplasticity at relatively high strain rates and low temperatures.
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