Phase transformations and tensile properties of Ti-10V-2Fe-3AI
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D E M A N D S for high strength light-weight alloys have been steadily increasing in recent years. Although the well established ot and ot +/3 titanium alloys (such as Ti-6AI-4V) have successfully met many of these demands, they are unsuited for thick section applications due to their extremely rapid decomposition kinetics. This has shifted research interests to the /3-Ti alloys, so called because the high temperature bcc phase (/3) is chemically stabilized and can be retained upon quenching. When compared to the c~ and oL +/3 alloys, B alloys enjoy the advantages of increased strength-to-density ratios, (some 20 pct higher than Ti-6A1-4V, for example), improved formabilities, lower thermal processing costs, and most importantly, improved deep hardenabilities. Ti-10V-2Fe-3A1 is a relatively new B-Ti alloy, in which the high temperature/3-phase is stablized by nominal alloying additions of 2 wt pct Fe and 10 wt pct V. The 3 pct AI is a natural ingredient in the master alloy and acts as a solid solution strengthener for the low temperature precipitating o~-phase (HCP). This particular alloying combination results in a nominal /3-transus of - 8 0 0 ~ which is relatively high when compared to other/3 alloy systems. Generally the more heavily B-stabilized alloys (such as/3-11I, Ti-8V8Mo-2Fe-3AI, and so forth) suffer from higher densities, higher manufacturing costs, and slower age hardening kinetics than Ti-10V-2Fe-3A1. This paper describes the results of a research program conducted to identify the various phase transformations of Ti-10-2-3, and to relate these to basic tensile properties.
T. W. DUERIG, formerly at Carnegie-Mellon University, is now at Brown, Boveri & Cie, AG, Baden, Switzerland, G. T. TERLINDE and J. C. WILLIAMS are with the Department of Metallurgical and Materials Science, Carnegie-Mellon University, Pittsburgh, PA 15213. Manuscript submitted August 2, 1979.
EXPERIMENTAL The material used in this study originated from Timet heat No. P-1452. The specific heat chemistry is: Element Concentration, (wtpct)
V
Fe
10.3 2.2
AI
O
3.2 0.15
N
C
0.009
0.016
Si
Ti
0.04 Balance
The/3-transus was measured as 805 _ 3 ~ somewhat high compared to other 10o2-3 heats. This probably reflects the oxygen content which is on the high side of the normal range. The thermomechanical processing began with a 3200 kg pound ingot which was upset forged 35 pct at 1120 ~ drawn to an 40 cm 2, and subsequently forged to a plate of 18 cm x 4.5 cm cross-section. The slab was then cut and hot rolled from 730 ~ to a 2.5 cm x 11.5 cm plate. All subsequent heat treatments were done in laboratory-type apparatus using small specimens. Treatments above 600 ~ were done by vacuum encapsulating specimens wrapped with Ta foil. Below 600 ~ treatments were performed in a liquid nitrate salt bath. Metallographic specimens were electropolished in a 5 pct n 2 s o 4 -t- 1 pct HF + balance methanol solution at a closed circuit voltage of 21 V. The primary etchant was prepared with equal parts of 10 pct oxalic acid and 1 pct HF in water.
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