Titanium is a metal with a strong tendency to passivation, in air and oxidizing or neutral aqueous solutions can quickly generate a stable oxidizing protective film, even if the film is destroyed for some reason, it can be quickly and automatically restored. Therefore, titanium has excellent corrosion resistance in oxidizing and neutral media.
Because of titanium's great passivation properties, in many cases with dissimilar metals in contact, does not accelerate corrosion, but may accelerate the corrosion of dissimilar metals. Such as in the low concentration of non-oxidizing acid, if the Pb, Sn, Cu or Monel alloy and titanium in contact with the formation of galvanic coupling, these materials corrosion accelerated, while titanium is not affected. And in hydrochloric acid, titanium and mild steel contact, due to the titanium surface produces newborn hydrogen, destroying the titanium oxide film, not only cause titanium hydrogen embrittlement, but also accelerate the corrosion of titanium, which may be due to the titanium has a high degree of activity on hydrogen.
Iron content in titanium has an effect on the corrosion resistance of certain media, the reason for the increase in iron in addition to the cause of raw materials, often welded stained iron penetration of the weld channel, so that the weld channel in the local iron content increases, when the corrosion has an uneven nature. The use of iron parts to support titanium equipment, iron staining on the iron titanium contact surface is almost inevitable in the iron stained area corrosion acceleration, especially in the presence of hydrogen. When mechanical damage occurs to the titanium oxide film on the stained surface, hydrogen penetrates into the metal, and depending on the temperature, pressure and other conditions, hydrogen diffusion occurs accordingly, which makes titanium produce varying degrees of hydrogen embrittlement. Therefore, titanium is used in medium temperature and medium pressure and hydrogen-containing systems to avoid surface iron contamination.
Titanium also has corrosion fatigue stability.
Titanium crevice corrosion resistance is better, especially Ti-0.3Mo-0.8Ni and Ti-0.2Pd alloys, so Ti-0.3Mo-0.8Ni and Ti-0.2Pd alloys are widely used in sealing surface materials for container equipment to solve the problem of crevice corrosion of equipment sealing surfaces.
Uniform corrosion occurs on the surface of titanium specimens or workpieces, forming a layer of corrosion products of uniform thickness, clinging to the surface of titanium, and generally do not extend inward with the extension of time, but there are exceptions. In many corrosive media, the corrosion performance of titanium with a protective layer of other metals (such as aluminum) as good or better. Corrosion of titanium is usually electrolytic in nature, so there is a relationship between corrosion and electrode potential and electric current. Anodic and cathodic polarization also have a strong influence on the corrosion mechanism and rate. The potential of titanium depends largely on the insulating properties of the oxide film. Therefore, the characteristics of the oxide film on the surface of titanium play a decisive role in its corrosion resistance. Any factor that improves the density of the oxide film, increases the thickness of the oxide film, and improves the insulating properties of the oxide film contributes to the corrosion resistance. Conversely, any factor that reduces the effective protective capacity of the oxide film, whether mechanical or chemical, will cause a sharp decline in the corrosion resistance of titanium.
