The Effect of Oxygen on the Structure and Mechanical Behavior of Aged Ti-8 WT. %Al.
Final rept. 26 Jan 71-25 Jan 72,
PENNSYLVANIA UNIV PHILADELPHIA SCHOOL OF METALLURGY AND MATERIALS SCIENCE
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It is shown that for a Ti-8 wt.Al alloy aged at a temperature high in the two-phase region 695C to precipitate the ordered alpha 2 phase, an increase in oxygen content from 600 ppm to 12 ppm increases the yield strength by approximately 10 and decreases the fracture strain from 20 to 1 elongation at room temperature. The fracture mode is changed from dimpled rupture to cleavage. It is demonstrated that oxygen additions alter the position of the alphaalpha alpha 2 coherent solvus, resulting in formation of coherent alpha 2 in specimens containing approximately or more than 1000 ppm oxygen aged at 695C. For a given aging time the volume fraction of alpha 2 increases with increasing oxygen up to 1300 wt.ppm and then levels off. The changes in mechanical behavior are attributed to the presence of alpha 2. The experimental evidence suggests that oxygen partitions preferentially into alpha 2.
- Properties of Metals and Alloys