Titanium general corrosion testing

It is important to know where titanium might exhibit susceptibility to corrosion attack in order to establish which corrosion test methods may be applicable or relevant to titanium alloys. Table 2 presents a list of specific environments where some form of corrosion susceptibility has been observed on titanium alloys in laboratory tests or service experience. The table indicates the relevant mode of corrosion degradation that can be expected, general scope of titanium alloys susceptible, and comments on critical factors that strongly influence each corrosion phenomenon. 

In general, it is fair to state that one of the major difficulties in interpreting, and consequently in establishing definitive tests of, corrosion phenomena in fused metal or salt environments is the large influence of very small, and therefore not easily controlled, variations in solubility, impurity concentration, temperature gradient, etc. . For example, the solubility of iron in liquid mercury is of the order of 5 x 10 at 649°C, and static tests show iron and steel to be practically unaltered by exposure to mercury. Nevertheless, in mercury boiler service, severe operating difficulties were encountered owing to the mass transfer of iron from the hot to the cold portions of the unit. Another minute variation was found substantially to alleviate the problem the presence of 10 ppm of titanium in the mercury reduced the rate of attack to an inappreciable value at 650°C as little as 1 ppm of titanium was similarly effective at 454°C . 

Biocompatibility studies have been conducted in various media chosen to simulate the conditions of the mouth and the human body. In general, no corrosion of titanium-nickel alloys has been reported. For example, in tests where coupons of titaniiun-nickel were sealed at 37 °C (97 °F) for 72 h, the mass corrosion rate was on the order of 10 mpy for such media as synthetic saliva, synthetic sweat, 1% NaCl solution, 1% lactic acid, and 0.1% HNaS04 acid (Ref 29) see also Ref 30. 

---