Effect of Subcritical ? Solution Treatment on the Primary a Phase, Element Partitioning and Aging Precipitation of TB17 Titanium Alloy

Subcritical ss solution treatment of TB17 titanium alloy was carried out at the solution temperature range from 800 degrees C to 835 degrees C and the solution time range from 0.5 h to 9 h, and the distribution of Al, Mo and Nb elements in the primary a phase, element partitioning and ss matrix was studied by electron probe microanalysis (EPMA). Effect of subcritical ss solution on precipitation of primary a phase and secondary a phase of the alloy was investigated. The experimental results show that primary a phase presents two typical morphologies of needle- type and lamellae-type structure, which the needle-type a phase is distributed at grain interior and lamellae-type a phase is distributed at grain boundaries. The amount of primary a phase decreases with the increasing of solution temperature. No primary a phase is observed at the solution temperature higher than 825 degrees C. The amount of primary a phase increases with the decreasing of solution temperature. The precipitation of primary a phase will reach a steady state at the temperature of 815 degrees C and the solution time higher than 2 h. Al element tends to be enriched in the primary a phase, and Mo and Nb elements tend to be enriched in the ss matrix. The Al concentration in the center of the a phase is higher than that in the edge, while the Mo and Nb concentration in the center is lower than that in the edge. Increasing the amount of primary a phase will decrease Al concentration and increase Mo and Nb concentration in the ss matrix. When the amount of primary a phase is low, the secondary a phase near primary a phase presents the morphologies of needle-type or lamellae- type structure, and morphology of the basketweave structure for the secondary a phase far from primary a phase. When the amount of primary a phase is high, the secondary a phase presents the morphologies of needle-type or lamellae-type structure.