STRESS-CORROSION CRACKING OF TITANIUM AND TI-AL ALLOYS IN METHANOL- IODINE SOLUTIONS
Interim rept. no. 1
MARTIN MARIETTA CORP BALTIMORE MD RESEARCH INST FOR ADVANCED STUDIES
Pagination or Media Count:
Studies of the mechanical behavior of unalloyed titanium in methanol- halogen solutions have led to the suggestion that stress-corrosion cracking SCC in these environments occurs by localized anodic dissolution at the crack tip. The validity and generality of this model for SCC has been examined by means of comparative studies of the corrosion characteristics and susceptibility to SCC of pure titanium and Ti-Al binary alloys in methanol-iodine solutions. Evidence is presented which indicates that two distinct SCC mechanisms may be operative, namely i stress accelerated intergranular corrosion involving dissolution of metal at a crack tip, and ii a transgranular cracking process which has the characteristics of mechanical failure. The characteristics of SCC failures of pure titanium and the Ti-2.1 wo Al alloy appear to be consistent with the dissolution model. In the higher alloys 5 wo Al, however, dissolution appears to be responsible only for the crack initiation stage, propagation involving transgranular cracking. Stress-corrosion failure in the higher alloys may therefore be prevented by inhibiting the initiation process via cathodic polarization or the introduction of passivators i.e. water into the testing environment.
- Properties of Metals and Alloys