The effect of microstructure on porosity healing mechanism of powder near-β titanium alloys under hot isostatic pressing in α plus β-region: Ti-10V-2Fe-3Al

The relation between phase and structural changes and porosity healing that occurred during hot isostatic pressing (HIP) in the near-beta Ti-10V-2Fe-3Al alloy obtained by powder metallurgy was studied. The powders were pressed at room temperature at 750 MPa in air, and then sintered at 1250 degrees C in vacuum. The residual porosity did not exceed 4.1 vol%. After sintering the HIP treatment was carried out in an argon atmosphere without a container. At the optimal HIP regimes (750 degrees C, 200 MPa), at which the porosity was completely healed, the structure transformed into the alpha + beta-lamellar type of basket weaving. The dislocation density after HIP treatment mainly increased in the interphase boundaries due to the action of hydrostatic stresses. Nucleation and growth of the secondary alpha-phase occurs during HIP on the omega-phase particles inside the beta-phase. It is shown that the main mechanism of porosity healing in the Ti-10V-2Fe-3Al alloy during HIP is the diffusion of vacancies along cores of the dislocations accumulated at the interphase boundaries. The plasticity of the alloy after HIP increased 2.5 times compared to the state after sintering. It was found out that the mechanism of tensile deformation after HIP, as well as after sintering, is controlled by the alpha-phase.