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Chemical composition and heat treatment were found to have an effect on the aqueous-stress corrosion of titanium. Aluminum contents greater than 5 per cent and oxygen contents greater than about 0.3 per cent caused appreciable sensitivity to stress corrosion. The additions of beta-isomorphous type alloying elements, such as molybdenum, were beneficial for titanium-aluminum alloys but showed no improvement for titanium-oxygen alloys. The amount of oxygen that could-be tolerated was reduced substantially by the addition of aluminum.
Heat-treatment effects were very pronounced and not similar for the alloy systems investigated. The heat-treatment temperature for maximum sensitivity to stress corrosion increased from 1000 F for Ti-6Al alloys to 1200 F for Ti-8Al alloys. This corresponds to about 150 F below the estimated Ti3Al transus. The stress-corrosion resistance of Ti-6Al-4V alloy was reduced as a result of long annealing times prior to exposure in the Ti3Al region. Long annealing times also promoted stress corrosion in titanium-oxygen alloys. Microscopic examination did not reveal significant changes with annealing time. This finding indicates the metallurgical factors affecting the stress corrosion resistance are related to submicroscopic changes.
stress corrosion, titanium alloys, embrittlement, heat treatment, fracture toughness
Supervisor, Reactive Metals, Inc., Niles, Ohio
Research metallurgist, Reactive Metals, Inc., Niles, Ohio
Graduate student, Lehigh University, Bethlehem, Pa.