Introduction to hydrogen treatment technology for titanium alloy materials
Hydrogen treatment technology for titanium and titanium 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, which has formed a unique research field. The improvement of superplastic properties of titanium alloys by hydrogen treatment technology is an important research area, and many scholars have improved the superplastic properties of cast titanium, deformed titanium alloys and titanium-aluminum intermetallic compounds by using hydrogen treatment effect up to now.
At present, there are two ways to improve the superplasticity of titanium alloys by using hydrogen treatment technology.
(1) Using the plasticizing effect of hydrogen, we add an appropriate amount of hydrogen to the titanium alloy before superplastic forming to increase the proportion of B-phase in the titanium alloy and reduce the flow stress during superplastic deformation, so as to improve the superplastic properties of titanium alloy.
(2) Using hydrogen treatment to refine the microstructure of titanium alloy, combined with plastic deformation technology to prepare superfine grain titanium alloy, so that the titanium alloy has excellent superplastic properties at lower deformation temperature and higher deformation rate.
Modern superplastic deformation theory suggests that grain boundary slip is the main mode of superplastic deformation, and diffusion and dislocation movement in the grain and grain boundary are the main coordination mechanisms of grain boundary slip. In titanium alloy superplastic forming, phase B is dominated by diffusion creep or dislocation creep: phase A is dominated by grain boundary slip, which is coordinated by both diffusion and dislocation motion; the flow between phases A and B is completed by the migration of phase A and B boundaries. Hydrogen 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 in B-phase and intergranular slip in A-phase.
(2) The diffusion of hydrogen activates the dislocations in the pegging, promotes the dislocation climbing and sliding, improves the sliding ability of B grains, and facilitates the coordination of dislocations required for A/A grain boundary sliding.
(3) Hydrogen causes weak bonding effect, reduces the diffusion activation energy, enhances the atomic diffusion ability, and improves the superplastic flow ability.
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