High strength alpha-beta titanium-base alloy

Abstract: An alpha-beta titanium base alloy comprising, in weight percent, .04 to .10 silicon and .03 to .08 carbon, characterized by an increase in strength over that of the alloy absent said silicon and carbon additions. The alloy may additionally comprise 6 aluminum, 4 vanadium, up to .3 iron and up to .25 oxygen.

Description: This invention relates to an alpha-beta titanium-base alloy having improved strength to facilitate the use of the alloy in the form of castings. The most widely used titanium-base alloy is Ti-6A1-4V, which is particularly adapted for use in producing castings . It is advantageous with respect to this alloy to increase the strength thereof without significantly adversely affecting the ductility and toughness. This would contribute to the overall utility of the alloy, particularly in the form of castings. It is accordingly an object of the present invention to provide an alpha-beta titanium-base alloy characterized by improved strength. A more specific object of the invention according to a preferred embodiment, is to provide the alpha-beta, titanium-base alloy comprising 6% aluminum and 4% vanadium, with additional elements for improving the strength thereof. In according with the invention, an alpha-beta, titanium-base alloy is provided which comprises an alpha-beta titanium-base alloy comprising in weight percent, 6.0 aluminium, 4.0 vanadium, 0.04 to 0.10 silicon and 0.03 to 0.08 carbon, optionally up to 0.3 iron, optionally up to 0.25 oxygen, and balance titanium and incidental impurities, and possessing an increase in strength over that of the alloy absent said silicon and carbon additions. US 2906654 discloses a titanium base alloy comprising 6% aluminium, 4% vanadium and up to 0.1 % carbon as an impurity. The alloy does not however comprising silicon. In the examples and throughout the specification and claims, all parts and percentages are by weight percent unless otherwise specified. In the evaluations leading to and demonstrating the invention, silicon and carbon additions, either singly or in combination, were added to a designated base composition and compared to nitrogen additions made to the same base compositions from the standpoint of achieving increased strength. The results of this evaluation with respect to as-cast 100-gm button ingots are presented in Table I. As may be seen from the data presented in Table I, the additions of carbon and silicon, in combination, resulted in a drastic improvement with respect to increased strength far exceeding that of nitrogen, silicon, and carbon alone. Also evaluated were 250-gm buttons that were rolled to 0.5 inch (1.27cm) diameter rod and then beta annealed to simulate an as-cast microstructure. The test results are presented in Table II. Again strength was significantly improved by additions of carbon and silicon in accordance with the invention, without a significant deleterious effect on ductility. A series of 50 pound (22.68kg) heats were produced and tested, and the results are presented in Table III. Again, a beta anneal was used to simulate the as-cast structure. The test results show a strength increase of 6-7 ksi with about a 2-4% loss in ductility for an alloy having carbon and silicon additions. The toughness was unchanged. The alloy was then examined after a simulated recrystallization anneal thermal cycle, and the results are set forth in Table IV. Although the strength levels for all of the alloys tested were reduced as a result of the anneal, nevertheless the alloy in accordance with the invention having carbon and silicon additions continued to demonstrate superior properties. It may be noted from the data set forth above that the combined effect of carbon and silicon as addition agents is greater than the sum of the individual contributions.

Claims: An alpha-beta titanium-base alloy comprising in weight percent, 6.0 aluminium, 4.0 vanadium, 0.04 to 0.10 silicon and 0.03 to 0.08 carbon, optionally up to 0.3 iron, optionally up to 0.25 oxygen, and balance titanium and incidental impurities, and possessing an increase in strength over that of the alloy absent said silicon and carbon additions.

Inventors: BANIA PAUL J, PARRIS WARREN M, BANIA, PAUL J., PARRIS, WARREN M.
Applicants: TITANIUM METALS CORP, TITANIUM METALS CORPORATION OF AMERICA
Application year: 1990
Main classification: C22C14
IPC codes: C22C14