Features of the superplastic deformation development in ultrafine-grained α + β titanium alloys with a high β-phase volume fraction

Investigations of the features of the superplastic deformation development and the evolution of the structural-phase state of ultrafine-grained VT22 and VT35 alloys under tension in the temperature range 823-973 K and strain rate 6.9×10^-3 s^-1 have been carried out. It is shown that, for the VT35 alloy, the evolution of the structural-phase state under tension at temperatures of 873 and 973 K has a qualitatively different character. After deformation at 873 K, a stable micro-duplex α-β structure with an average grain-subgrain size of about 0.2 μm is formed in the alloy. In this case, the main mechanism of deformation under the considerate conditions is grain boundary sliding. At the same time, after deformation of the VT35 alloy at 973 K, there is a significant increase in the grain size with strain degree and an increase in the volume fraction of the β-phase to 95%. In this case, the α-phase is observed mainly in the form of individual particles along the grain boundaries of the β-phase. It was found that the evolution of the structural state of the VT22 alloy at a deformation temperature of 973 K is qualitatively similar to the evolution of the structural state of the VT35 alloy at 873 K. Based on a comparative analysis of the evolution of the structural-phase state during the deformation of VT22 and VT35 alloys at 973 K, it is assumed that the relatively low ductility of VT35 alloy samples under the conditions is due to the rapid grain growth, the transition of the alloy to an almost single-phase state and, as a result, the hindered development of grain boundary sliding.

Keywords

Authors

References