Stress corrosion cracking of pure titanium in CH3OH/HCl solutions

The susceptibility to stress corrosion cracking (SCC) and its fracture morphology of pure titanium in CH3OH/HCl solutions with various HCl concentrations at room temperature were examined fractographically.It was found from the stress-free immersion tests in CH3OH/HCl solutions that the weight loss increased gradually with the immersion time, and that the intergranular corrosion occurred scarcely. In the subsequent tensile tests in air, however, the mechanical properties deteriorated greatly due to the intergranular embrittlement, especially during the prior immersion at a concentration of 0.4% HCl. The SCC susceptibility under constant load conditions also increased in a CH3OH/0.4% HCl solution. The fracture mode was changed from an intergranular into a transgranular fracture, and finally into a ductile fracture. A similar tendency was revealed by SCC tests under slow strain rates: In the crosshead speed of 5×10-2-5μm/s, all three modes of intergranular, transgranular and ductile fracture were observed. The aging treatment after stress-free immersion improved the mechanical properties, and thus decreased the area fraction of intergranular fracture. From the evidence introduced here, a possible mechanism for SCC of pure titanium was discussed.