SEDL / STP / STP432-EB / STP33624S

The Influence of Composition and Heat Treatment on the Aqueous-Stress Corrosion of Titanium

Seagle, SR
Supervisor, Reactive Metals, Inc., Niles, Ohio

Seeley, RR
Research metallurgist, Reactive Metals, Inc., Niles, Ohio

Hall, GS
Graduate student, Lehigh University, Bethlehem, Pa.

Pages: 19    Published: Jan 1968

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Abstract

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.