Processing of titanium-aluminum-vanadium alloys and products made thereby

Abstract

A method of forming an article from an alpha-beta titanium including, in weight percentages, from about 2.9 to about 5.0 aluminum, from about 2.0 to about 3.0 vanadium, from about 0.4 to about 2.0 iron, from about 0.2 to about 0.3 oxygen, from about 0.005 to about 0.3 carbon, from about 0.001 to about 0.02 nitrogen, and less than about 0.5 of other elements. The method comprises cold working the alpha-beta titanium alloy.

Description

FIELD OF THE INVENTION[0001] The present invention relates to novel methods of processing certain titanium alloys comprising aluminum, vanadium, iron, and oxygen, to articles made using such processing methods, and to novel articles including such alloys.DESCRIPTION OF THE INVENTION BACKGROUND[0002] Beginning at least as early as the 1950's, titanium was recognized to have properties making it attractive for use as structural armor against small arms projectiles. Investigation of titanium alloys for the same purpose followed. One titanium alloy known for use as ballistic armor is the Ti-6Al-4V alloy, which nominally comprises titanium, 6 weight percent aluminum, 4 weight percent vanadium and, typically, less than 0.20 weight percent oxygen. Another titanium alloy used in ballistic armor applications includes 6.0 weight percent aluminum, 2.0 weight percent iron, a relatively low oxygen content of 0.18 weight percent, less than 0.1 weight percent vanadium, and possibly other trace ele...

AI Technical Summary

Benefits of technology

[0004] The above titanium alloys have been used to produce ballistic armor because when evaluated against many projectile types the titanium alloys provide better ballistic performance using less mass than steel or aluminum. Despite the fact that certain titanium alloys are more "mass efficient" than steel and aluminum against certain ballistic threats, there is a significant advantage to further improving the ballistic performance of known titanium alloys. Moreover, the process for producing ballistic armor plate from the above titanium alloys can be involved and expensive. For example, the '655 patent describes a method wherein a Kosaka alloy that has been thermomechanically processed by multiple forging steps to a mixed .alpha.+.beta. microstructure is hot rolled and annealed to produce ballistic armor plate of a desired gauge. The surface of the hot rolled plate develops scale and oxides at the high processing temperatures, and must be conditioned by one or more surface treatment steps such as grinding, machining, shotblasting, pickling, etc. This complicates the fabrication process, results in yield losses, and increases the cost of the finished ballistic plate.

[0010] The inventors have determined that any suitable cold working technique may adapted for use with the Kosaka alloy. In certain non-limiting embodiments, one or more cold rolling steps are used to reduce a thickness of the alloy. Examples of articles that may be made by such embodiments include a sheet, a strip, a foil and a plate. In the case where at least two cold rolling steps are used, the method also may include annealing the alloy intermediate to successive cold rolling steps so as to reduce stresses within the alloy. In certain of these embodiments, at least one stress-relief anneal intermediate successive cold rolling steps may be conducted on a continuous anneal furnace line.

Problems solved by technology

Moreover, the process for producing ballistic armor plate from the above titanium alloys can be involved and expensive.

This complicates the fabrication process, results in yield losses, and increases the cost of the finished ballistic plate.

However, it is generally believed that it is not possible to readily apply fabrication techniques other than simple hot rolling to many of these high-strength titanium alloys.

The process is expensive and may have a low yield given the necessity to grind and pickle the surfaces of the individual sheets.

In particular, it was conventionally believed that the Kosaka alloy's resistance to flow at temperatures significantly below the .alpha.-.beta. hot rolling temperature range was too great to allow the alloy to be worked successfully at such temperatures.

), it becomes possible to produce myriad product forms that are not possible through hot rolling and / or are significantly more expensive to produce using hot working techniques.