Some examples of hydrogen embrittlement show that hydrogen embrittlement is local.Crack corrosion, pitting corrosion, galvanic corrosion, stress corrosion and so on can cause hydrogen absorption and partial hydrogenation of titanium rod.
Although the causes of crevice corrosion and pitting corrosion are different, their development is based on the principle of block cell.After a certain stage of corrosion, hydrolysis reaction will occur, resulting in a large amount of H+ :
Due to the large amount of H+ formation, the pH value of the solution in the gap or point is significantly lower, reaching 1-1.6 or even as low as 0.7.This will further promote the dissolution of titanium, resulting in so-called autocatalysis, which allows local corrosion to develop at a high rate.At the same time, H is precipitated in the cathode region, and part of it is titanium absorption, so partial hydrogenation will be caused.Stress corrosion has a similar situation, leading some scholars to believe that stress corrosion is a phenomenon of hydrogen embrittlement.
Many cases of hydrogen embrittlement caused by galvanic corrosion have been reported.The electric couple is formed by the contact between titanium and steel in the high-temperature seawater melting equipment, and the electric couple is formed by the connection between the titanium tube and the copper and gold tube plate in the power station condenser.Hydrogen absorption of titanium in contact with foreign metals in deaerated salt and pure water.Titanium's potential decreases after contact with certain metals.For example, the potential of titanium in seawater is 0.14v/SCE, the potential in contact with zinc is -0.79v/SCE, and the potential in contact with steel is -0.8v/SCE in 6%Na solution.When the titanium in seawater and in contact with these metals drops to a potential of -0.65--0.7V/SCE, it causes hydrogen absorption.The results of galvanic corrosion are related to the stable potential, contact area and polarization characteristics of the metal in contact with each other.
According to the hydrogen absorption in 1MFe(OH)2 solution of tube expansion specimens of different materials.It appears that steel tube plates give the most hydrogen to titanium (whether or not the tube is pickled after expansion), and brass tube plates in the navy also add a lot of hydrogen after expansion without pickling.
According to the results of cathode treatment of samples with different surface states at 30℃ 0.1mh2so4.Obviously, because the scratch on the titanium surface caused heavy hydrogen absorption.The state of supply followed, indicating that the surface was also contaminated to a considerable extent.
Hydrogen embrittlement of titanium tubes in electrolyte solution is a complex problem, which involves many factors of the "material" environment "system.