STRESS CORROSION OF TI ALLOYS IN METHANOLIC SOLUTIONS

Stressed specimens of Ti and its alloys suffer intergranular cracking in methanol. If the A1 content is high (≥ 5%) the α-phase is subject to rapid transgranular cracking. The addition of HCl to the methanol shortens the time to failure considerably and causes a slow intergranular embrittlement, which does not require any applied stress and results in a total loss of strength in all the single phase α-alloys. This slower form of attack was not found in the α + β Ti-6Al-4V alloy. It is suggested that there are two operative processes: transgranular hydride formation and selective dissolution from α-grain boundaries. The former can occur in any environment that discharges hydrogen in reaction with Ti and that can cause breakdown of the protective film. © 1962 Pergamon Press, Great Brittain.