Titanium alloy is an alloy composed of titanium and other elements. Titanium alloy has the advantages of low density, high specific strength, good corrosion resistance, good process performance, etc. It is an ideal structural material for aerospace engineering. In the actual production environment, different kinds of corrosion will occur, mainly in the following categories:
1, crevice corrosion
In the metal component crevices or defects, due to electrolyte stagnation constitutes an electrochemical battery and cause localized corrosion phenomenon, in neutral and acidic solution, titanium alloy crevices at the probability of contact corrosion is much greater than the alkaline solution, the contact corrosion does not occur in the entire crevice surface, but ultimately lead to localized perforation damage.
2,Pitting phenomenon
Titanium in most salt solutions without pitting phenomenon, which occurs in non-aqueous solutions and boiling highly concentrated chloride solution, halogen ions in the solution on the surface of the titanium passivation film corrosion, and diffusion to the titanium internal pitting occurs, pitting aperture is less than its depth. Certain organic media and titanium alloys in halogen solution pitting phenomenon, titanium alloys in halogen solution pitting generally occurs in the high concentration of high temperature environment, in addition, in the sulfide and chloride pitting requires specific conditions and limited.
3, Hydrogen embrittlement
Hydrogen embrittlement (HE), also known as hydrogen cracking or hydrogen damage, is one of the reasons for early damage failure of titanium alloys, titanium and its titanium alloy surface passivation film has a high strength, hydrogen embrittlement sensitivity increases with the intensity, so the passivation film hydrogen embrittlement is very sensitive.
4,Contact corrosion
The passivated oxide film on the surface of titanium promotes the titanium potential to move to a positive potential, which improves the resistance of titanium to corrosion by acidic and aqueous media. Due to the higher potential of the surface of titanium alloy, it is bound to cause contact corrosion with other metals in contact with the formation of electrochemical circuits and cause contact corrosion. Titanium alloy is easy to contact corrosion in the following two types of media: the first type is tap water, salt solution, seawater, the atmosphere, HNO3, acetic acid, etc., the solution Cd, Zn, Al stable electrode potential is more negative than Ti, anodic corrosion of the rate of the surge of 6 to 60 times, said the second type is H2SO4, HCl, etc., Ti in these solutions, may be in the passivation state, may be in the activation state, the actual contact Corrosion process is common for the first type of solution corrosion. Anodization is usually used to form a modified layer on the surface of the substrate to prevent contact corrosion.
