Superplastic titanium alloy hydrogen treatment technology

Hydrogen treatment of titanium and its alloys is an active research direction in the field of materials science and engineering. At present, hydrogen treatment technology has been applied in the research of titanium alloy hot processing, mechanical processing, powder consolidation, composite material preparation, microstructure refinement, etc., and has formed a unique research field. Hydrogen treatment technology is an important aspect of research to improve the superplastic properties of titanium alloys. So far, many scholars have used the hydrogen treatment effect to improve the superplastic properties of cast titanium, deformed titanium alloys and Ti-Al intermetallic compounds.

At present, there are two ways to use hydrogen treatment technology to improve the superplastic properties of titanium alloys:

(1) Using the plastic effect of hydrogen, adding an appropriate amount of hydrogen before the superplastic forming of titanium alloy can 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) The use of hydrogen treatment to refine the microstructure of titanium alloy, combined with plastic deformation technology to prepare ultra-fine crystalline titanium alloy, so that titanium alloy has excellent superplastic properties at a lower deformation temperature and a higher deformation rate.

Modern superplastic deformation theory holds that grain boundary slip is the main mode of superplastic deformation, and diffusion and dislocation movement within and at grain boundaries are the main coordination mechanism of grain boundary slip. In the superplastic forming of titanium alloy, the B phase is dominated by diffusion creep or dislocation creep, and the A phase is dominated by grain boundary slip, which is coordinated by diffusion and dislocation movement. The flow between A and B is completed by A and B phase boundary migration. Hydrogen mainly plays the following roles in the superplastic forming of titanium alloy:

(1) The addition of hydrogen increases the diffusion capacity of alloying elements, leading to the enhancement of B-phase diffusion creep and A-phase intergranular slip.

(2) Hydrogen diffusion activates the pinned dislocation, promotes the climbing and sliding of the dislocation, improves the sliding ability of B grain, and facilitates the dislocation coordination required by A/A grain boundary sliding.

(3) hydrogen-induced weak bond effect reduces the diffusion activation energy, enhances the atomic diffusion ability, and improves the superplastic flow ability.

(4) As can be seen from the Ti2H phase diagram, the addition of hydrogen significantly reduces the B\A+B transition temperature and increases the volume fraction of B phase, which directly leads to the improvement of plasticity and the reduction of flow stress, so that titanium alloy can be superplastic forming at a lower deformation temperature and a higher deformation rate.