1. Field of the Invention
This invention relates to the field of metallurgy and particularly to the field of titanium base alloys for high temperature applications.
2. Description of the Prior Art
Alpha phase alloys of titanium are known to retain strength at high temperatures. Two of the strongest high temperature creep resistant alpha phase alloys presently available are known commercially as IMI 685 and Ti-11. Both these alloys have a nominal aluminum content of 6% and a creep rate of about 0.1% per hour at a stress of 40,000 psi and at a temperature of 1000.degree. F.
To increase the performance of jet aircraft, there is an ever present need to improve the strength and creep resistance of high temperature titanium alloys. Therefore, metallurgists have added increasing amounts of alloy elements (particularly aluminum) to titanium in order to increase the strength. However, when the aluminum content exceeds 6% an ordered precipitate of Ti.sub.3 Al generally called .alpha..sub.2 is formed. The .alpha..sub.2 precipitate causes a loss ductility of these alloys. Such problem is well documented in U.S. Pat. No. 2,892,705 to R. I. Jaffee, et al., covering a Ti-(3-6)Al-(4-15)Zr alpha phase titanium alloy and a Ti-(3-6)Al-(4-10)Sn-(5-10)Zr alpha phase titanium alloy.
Consequently, prior art alpha phase titanium alloys have generally been limited to a maximum of about 6% aluminum. This limitation in turn has limited the strength obtainable in such alloys.