THE STRESS-CORROSION CRACKING AND HYDROGEN EMBRITTLEMENT OF TITANIUM IN METHANOL IODINE SOLUTIONS

Weight loss experiments were performed on IM125 (low-oxygen, commercia lly pure titanium) coupons exposed to methanol with varying additions of iodine and water. The corrosion rate was observed to increase as th e weight per cent additions of iodine were increased to 5%. Increasing additions of water to MeOH/0.5% I2 were observed to reduce the corros ion rate. Water additions of 15 vol% were observed to cause passivatio n of the titanium in this solution. Constant crosshead speed SCC tests were also performed in MeOH/I2/H2O Mixtures. The predominant mode of fracture was transgranular cleavage with small amounts of intergranula r fracture being evident in the lower crosshead speed tests. Additions to the solutions of selenium ions were observed to increase crack pro pagation rates, while additions of platinum ions were observed to redu ce crack velocities and, in some cases, completely arrest SCC. The fra cture surfaces from specimens tested in platinum-containing solutions showed significantly less transgranular cleavage and intergranular fra cture than specimens tested in the platinum-free solutions. These obse rvations support the view that the transgranular cleavage and intergra nular fracture occurring during the SCC of titanium in MeOH/I2/H2O mix tures is caused by hydrogen embrittlement.