The 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 the research of thermal processing, mechanical processing, powder consolidation, composite material preparation, and microstructure refinement of titanium alloys, and has formed a unique research field. Using 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 superplastic properties of titanium alloys:
(1) Using the plasticizing effect of hydrogen, adding appropriate amount of hydrogen before superplastic forming of titanium alloy to increase the proportion of phase B in titanium alloy, reduce the flow stress during superplastic deformation, and achieve the purpose of improving the superplastic performance of titanium alloy.
(2) Using hydrogen treatment to refine the microstructure of titanium alloy, combined with plastic deformation technology to prepare ultrafine-grained titanium alloy, so that the titanium alloy has excellent superplastic properties at lower deformation temperature and higher deformation rate.
Modern superplastic deformation theory believes that grain boundary slip is the main method of superplastic deformation, and diffusion and dislocation movement within and between grain boundaries are the main coordination mechanism of grain boundary slip. In superplastic forming of titanium alloys, phase B becomes the main by diffusion creep or dislocation creep: phase A is mainly grain boundary slippage, which is coordinated by diffusion and dislocation movement; the flow between A and B phases is A Completed with B phase migration. Hydrogen plays the following roles in superplastic forming of titanium alloys:
(1) The addition of hydrogen improves the diffusivity of alloying elements, resulting in the enhancement of the phase B diffusion creep and phase A intergranular slip.
(2) The diffusion of hydrogen activates the pinned dislocations, promotes the climbing and sliding of the dislocations, improves the sliding ability of the B grains, and is beneficial to the dislocation coordination required by the A / A grain boundary sliding.
(3) Hydrogen weakens the bond effect, 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 an increase in plasticity and a reduction in flow stress, which allows the titanium alloy to Superplastic forming is carried out at lower deformation temperature and higher deformation rate.