The Titanium Alloy Was Refined By Hydrogen Treatment

The titanium alloy was refined by hydrogen treatment

Ultrafine titanium alloy has a series of outstanding advantages, its room temperature strength can be improved to a certain extent, and it has a great elongation at high temperature. Grain refinement is usually obtained by large deformation methods, such as equal diameter Angle extrusion, high pressure torsion, multi-axis forging and cumulative roll welding. In addition, the titanium alloy can also be hydrogen treatment.

In the 1970 s, aircraft manufacturing research institute in Moscow, study the effect of hydrogen on the properties of titanium alloy processing, put forward the concept of "hydrogen plasticizing", as temporary alloying element to hydrogen, by hydrogen permeability and eutectoid decomposition, vacuum than hydrogen, and utilization of hydrogen induced plasticity, hydrogen induced phase transition, and reversible hydrogen in titanium alloy alloying effect, improve the processing performance, refine microstructure of materials.

Hydrogen treatment can be used to refine the grain structure of titanium alloy castings and forgings and improve their mechanical properties. It has been reported that the microstructure of TiAl alloy can be refined by hydrogen treatment, and the compression strength and yield strength of TiAl alloy can be significantly improved. In practice, hydrogen treatment technology can usually be combined with the corresponding subsequent heat treatment and thermal deformation treatment to obtain very fine grain structure. Some studies have shown that when hydrogenated titanium alloy is deformed at high temperature and large scale, equiaxed fine grains with a grain size of about 1μm can be formed, and even nano-scale grains can be formed. The study of Ti-6.3Al-3.5Mo-1.7Zr (%, mass fraction) alloy shows that the hydrogen fraction is 14% ~ 16% in hydrogen treatment, the deformation temperature is reduced to 550℃, and through the deformation process and the decomposition process of metastable phase, the nanocrystalline grain size of 40nm is finally obtained. Comparing the engineering stress-strain curves of Ti-6AL-4V alloy with different grain sizes, it can be seen that the ultra-fine grain material exhibits high yield strength and elongation compared with coarse grain or general fine grain material.

By allowing a titanium alloy to absorb a large number of hydrogen atoms and by allowing those hydrogen atoms to desorption under vacuum at high temperatures, a process called ADH-treatment. With respect to α+β titanium alloy, the treatment by pyh includes the following three processes :(1) by hydrogen absorption in hydrogen atmosphere; (2) Martensite transformation and thermal processing eventually lead to dispersion of hydride precipitation; (3) Final desorption treatment and recrystallization by hydrophyzation. It was reported that by treating Ti-6AL-4V alloy with additional hydrogen, the alloy adsorbed 0.5% by additional hydrogen and desorbed at 873K, showed ultra-fine isoaxed crystal structure with large angular grain boundaries and grain size in the range of 300 ~ 500nm. The results showed that the β-phase content in the α matrix was increased by the prophyton treatment method. Tensile test shows that the yield strength of the alloy increases at room temperature, and the maximum elongation reaches 9000% at 1123K.

The test results show that the superplastic elongation and other mechanical properties of the alloy increase obviously with the decrease of grain size

Although the hydrogen treatment method shows great potential for refining titanium alloys, compared with other conventional methods, the hydrogen treatment method has higher cost, and for large structural parts, the treatment method also has the problems of uneven distribution of hydrogen and high requirements of equipment conditions, which need to be further studied to solve.