Due to the shortage of energy, Marine environment has been paid more and more attention by various countries. China in the "13th Five-Year plan" outline pointed out that to strengthen the deep sea, deep earth, deep space and deep blue field of high-tech deployment, among them, the deep sea bear the brunt, visible China's determination to build a maritime power. The deep sea is not only the position of oil, gas and mineral resources exploration and development, but also the main battlefield of Marine scientific exploration and advanced deep-sea technology competition. Many countries have accelerated the development and deployment of deep-sea equipment. However, the deep sea environment is complex and harsh. In addition to high hydrostatic pressure, temperature, salinity, pH, dissolved oxygen and other factors are also greatly different from shallow sea environment, which brings unknown risk of corrosion failure for deep-sea equipment. At the same time, the harsh deep-sea environment also brings challenges to the application of deep-sea equipment and the study of deep-sea corrosion of materials.

Compared with stainless steel, aluminum alloy and other corrosion resistant materials, titanium alloy has better pitting corrosion resistance, gap corrosion, intergranular corrosion and uniform corrosion resistance. And in the high-speed flow of seawater, its corrosion resistance is still good. Titanium alloy is the only high strength material with almost no significant difference in fatigue limit between sea water and air. So titanium alloy is called the ocean metal. Although titanium alloy thermal conductivity, wear resistance, weldability poor, some problems such as thermal hydrogen absorption, but the excellent comprehensive performance makes it an important Marine materials, in the depths of the equipment, application, and gradually by the parts to develop in the direction of the key structure, research on deep sea corrosion behavior of titanium alloy and the corrosion resistance evaluation has been become a hot topic of current.

Although titanium alloy shows excellent corrosion resistance in surface seawater, the passivation performance of titanium alloy decreases with the continuous increase of its service depth and the influence of deep sea low temperature, low oxygen and high pressure, which will increase the risk of local corrosion, especially stress corrosion cracking. Pang and Blackwood found that TA2 and TC4 showed a tendency of crevice corrosion under low oxygen conditions. Yang Xiaojia et al. "studied the electrochemical behavior and stress corrosion behavior of TA2 in simulated deep-sea environment by electrochemical method and U-bending experiment. The results show that hydrostatic pressure promotes the anodic dissolution and cathodic hydrogen evolution of TA2. On the other hand, alloying titanium alloy will also cause changes in microstructure.

By studying Ti-8AI-1Mo-1V alloy, Pilchak et al. found that the crystallographic orientation was generated by alloy cracking. Dong Yuecheng et al. studied the service performance of TC4ELI titanium alloy in Marine environment, and the results show that the organizational structure has an important influence on the service performance of titanium alloy. In addition, the microstructure defects and internal stress caused by welding, machining and other post-treatment processes, as well as the synergistic effect with electrochemical corrosion, are also important factors causing deep sea stress corrosion of titanium alloys.