Hydrogen treatment technology of titanium and its alloys is a relatively active research direction in the field of materials science and engineering. At present, hydrogen treatment technology has been applied in research on thermal processing, mechanical processing, powder consolidation, composite material preparation, microstructure refinement, etc. of titanium alloys, and has formed a unique research field. The use of hydrogen treatment technology to improve the superplastic properties of titanium alloys is an important research aspect. So far, many scholars have used the hydrogen treatment effect to improve the superplastic properties of cast titanium, deformed titanium alloys and titanium-aluminum intermetallic compounds.
At present, there are two ways to use hydrogen treatment technology to improve the superplasticity properties of titanium alloys:
(1) Utilize the plasticizing effect of hydrogen, add an appropriate amount of hydrogen before superplastic forming of titanium alloy, increase the proportion of B phase in titanium alloy, reduce the flow stress during superplastic deformation, and achieve the purpose of improving the superplastic properties of titanium alloy.
(2) Hydrogen treatment is used to refine the microstructure of titanium alloys, and combined with plastic deformation technology to prepare ultra-fine-grained titanium alloys, so that titanium alloys have excellent superplastic properties at lower deformation temperatures and higher deformation rates.
Modern superplastic deformation theory believes that grain boundary slip is the main mode of superplastic deformation, and diffusion and dislocation movement within grains and grain boundaries are the main coordination mechanisms of grain boundary slip. In the superplastic forming of titanium alloys, the B phase is dominated by diffusion creep or dislocation creep; the A phase is dominated by grain boundary slip, coordinated through diffusion and dislocation motion; the flow between the A and B phases is dominated by A Completed with B phase boundary migration. Hydrogen mainly plays the following roles in the superplastic forming of titanium alloys:
(1) The addition of hydrogen improves the diffusion ability of alloy elements, leading to the enhancement of diffusion creep of B phase and intergranular slip of A phase.
(2) The diffusion of hydrogen activates the pinned dislocations, promotes the climbing and sliding of dislocations, improves the sliding ability of B grains, and is conducive to the dislocation coordination required for A/A grain boundary sliding.
(3) The weak bond effect caused by hydrogen reduces the diffusion activation energy, enhances the atomic diffusion ability, and improves the superplastic flow ability.
(4) It can be seen from the Ti2H phase diagram that the addition of hydrogen significantly reduces the B\A+B transition temperature and increases the volume fraction of the B phase, which directly leads to the improvement of plasticity and the reduction of flow stress, allowing titanium alloys to Superplastic forming is performed at lower deformation temperatures and higher deformation rates.