The effect of oxygen on the structure and mechanical behavior of Aged Ti-8 Wt pct Al
- PDF / 2,563,615 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 142 Views
IT
is generally accepted that when a solution treated Ti-8 wt pct A1 alloy is aged to precipitate the ~2 phase, the alloy becomes brittle and fails by cleavage at r o o m temperature. ~-s Recently, however, it has been demonstrated that this does not occur if the oxygen content is low enough. 4'~ For example, Truax and McMahons showed that solution-treated samples with 450 ppm or 1000 ppm oxygen had essentially the same ductility (~15 pet); however, when the samples were aged at 550~ for 600 h to precipitate ~x~the 450 ppm oxygen samples still had a ductility of 15 pet, while the ductility of the 1000 ppm sample had dropped to about 4 pct. Since the precipitation of a~ is known to result in drastic ductility losses, ~'a it seems reasonable to inquire whether the present large change in ductility with oxygen content is related to a concomitant change in a2 content. There are no direct data in the literature to help decide the above question. The Ti rich side of the Ti-A1 phase diagram is r e produced in Fig~ 1. The ~/c~2 phase boundary marked "low oxygen" was determined by Namboodhiri e t al~ and is consistent with the results of Ltiterjing and W e i s s m a n J Using this "low oxygen" a/cz + ot2 phase boundary, it can be seen from Fig. 1 that for a Ti-8 wt pct A1 alloy the a / ~ transformation begins at about 700~ If oxygen additions increase the amount of ~2 at a given temperature, then samples with differing oxygen contents aged at t e m p e r a t u r e s just below the ~/o~ + ~2 boundary ~ i l show differing amounts of c~2. F u r t h e r m o r e an increase in oxygen would presumably increase the amount of ~ , based on the results of Truax and McMahon. s Accordingly, a study was initiated to determine the mechanism by which oxygen produces such large ductility changes in aged Ti-8 A1 alloys. J. Y, LIM, formerly a Graduate Student in the Department of Metallurgy and Materials Science, Universityof Pennsylvania, is now setf employed in Lansdaie, PA. C. J. McMAHON,Jr. and D. P. POPEare Professor and Associate Professor,respectively, Department of Metallurgy and Materials Science and LRSM,University of Pennsylvania, Philadelphia, PA 19174. J. C. WILLIAMSis Associate Professor, Department of Metallurgy and Materials Science, Carnegie-Melton University, Pittsburgh, PA 152I 3. Manuscript submitted February 1,1974. METALLURGICALTRANSACTIONSA
EXPERIMENTAL PROCEDURE The material was obtained from the Titanium Metals Corporation of A m e r i c a in the form of hot roiled 1.27 c m (1/2 in.) diam rods with the following composition (in wt pct): Nominal Ti-8 A1
At
Fe
N
O
7.82
0.010
0.005
0.058
Specimen preparation was c a r r i e d out as in previous work. ~ Strips 2.3 mm (0.090 in.) thick were prepared by swaging and roiling from 1223 K (950~ in air; s u r face contamination was removed by grinding 0.38 mm (0.015 in.) from each surface. Oxygen was added by heating specimens in Vycor capsules filled with various p r e s s u r e s of 80 pct argon-20 pct oxygen at 1223 K (950~ 456 h (19 days) which was sufficient tim
Data Loading...
