Titanium is one of the most plentiful elements on the earth’s surface, being fourth among the structural elements. Because of this abundance and the unique properties that titanium offers, it was the natural choice of aircraft designers to become the favored material for constructing airplanes. When compared on a strength-to-weight ratio basis, Titanium alloy has demonstrated superiority over most other structural aerospace materials. The low density, slightly over half that of steel, and high strength combination have increased titanium usage so that every modern military and commercial aircraft contains significant quantities of this material.
Because of the very stringent demands of the aerospace industry, the development of many titanium alloys has occurred. These alloys greatly increase the strength of pure titanium while retaining the weight advantage. An alloy of titanium was needed as a tubing material that would decrease the weight of the hydraulic system while offering high-strength properties. The Ti-6Al-4V alloy was the first choice, as it was already the workhorse of this industry. Efforts to make tubing from this alloy were unsuccessful, so an alternate was sought. CP Titanium proved to be useful for ducting but did not have the strength for most hydraulic applications. 
A leaner alloy, using the same alloying elements as the Ti-6Al-4V, proved to be sufficiently malleable for tube manufacture and provided a very useful set of properties for application in hydraulic systems. This alloy, Ti-3Al-2.5V, can be cold worked by standard tube making processes, is weldable and can be strengthened by a combination of cold working and subsequent heat treatment to a wide range of strengths inductivities. Since the late 1960s the aircraft hydraulic systems have used more and more of this titanium alloy tubing. While unalloyed titanium is still used in some aircraft hydraulic tubing, most of the new hydraulic tubing applications use the Ti-3Al-2.5V alloy. This alloy has also found application as strip which can be formed and welded into ducting and in foil which is used in honeycomb structures.
The first military aircraft production program to use the new titanium alloy tubing was the Lockheed C-5A. Ti-3Al-2.5V tubing was chosen for the hydraulic system of the Concorde Supersonic Transport, and Sandvik was chosen as the supplier. The next uses were back into military fighter programs. Boeing was the first to adopt the alloy for a subsonic commercial airliner, the 767. Since that time, this alloy has been chosen for most of the other commercial transports and commuter aircraft. Ti-3Al-2.5V tubing is used extensively in the space shuttle and has found application in satellites. Most of the new military programs in the Western world are now using this alloy in their tubular applications, including helicopters.
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In the early 1970s, the Ti-3Al-2.5V tubing was first used in sports products. The titanium golf shaft produced by Zirtech was introduced as a shaft with the same benefits as this titanium alloy offered for the Aerospace uses. These were high strength topweight ratio, corrosion resistance, shock dampening, torsional resistance and fatigue resistance.
Following on the heels of the golf shaft were bicycle frames made from Ti-3Al-2.5V seamless tubing. Prototype wheelchair frames were also built of this material as well as arrows, ski poles and tennis racquets. The sports applications were not successful their first time out, but with the advent of new processing technology have all been re-introduced in the 1980s.
In the late 1980s, Ti-3Al-2.5V seamless tubing, listed as ASTM Grade 9, was approved by the American Society of Mechanical Engineers (ASME) as a material for use in boiler and pressure vessels.
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