Titanium is one of the space age metals. As strong as steel but only half as heavy, it brides the gap between steel aluminum. It is silvery and attractive in appearance, while extremely resistant to corrosion. Most titanium alloys are capable of continuous operation at temperature of about 800°F (427°C), making them ideal in use in high speed aircraft components. Aluminum fails rapidly at temperatures about 250°F (121°C).
Titanium is a low-density, corrosion-resistant metal designed for specialized applications. Titanium has a relatively high melting temperature and a high strength-to-weight ratio, so it can be used for parts that must withstand stress at high temperatures. It is commonly alloyed with aluminum, tin, and vanadium to produce strong, lightweight materials.
The most common titanium alloy, R56400, is made up of mostly titanium, plus 6% aluminum and 4% vanadium. It is also known as Ti-6A1-4V. The alloy additions permit great increases in strength through precipitation hardening.
The use of titanium is limited in commercial applications because it is difficult to extract from rutile (a common mineral of titanium). Titanium processing must be closely controlled to prevent contamination of the metal. For these reasons, titanium is quite expensive as compared to steel or aluminum. Titanium is suitable only for specialized applications where its superior properties are critically necessary.
Titanium is processed from its ore in three stages. It is first reduced from titanium ore to sponge, a porous metal. The sponge is then melted into ingots in an electric arc vacuum furnace. Melting must occur in vacuum or inert gas conditions to prevent the presence of gases dissolved in the metal. In the last stage of processing, ingots are converted into primary products (such as billets) for production of final shapes. Each stage of processing must be closely regulated to ensure high purity of the final product.
Applications of Titanium
Titanium and its alloys are used for many aircraft components and other applications requiring light weight and strength at high temperatures and speeds. Compressor blades in jet engines are commonly made from titanium. These blades must withstand very high stresses at elevated temperatures. Large amounts of titanium are also used in the manufacture of wings for fighter planes. The skin of the wing shown reaches temperatures as high as 300°F (150°C).
Titanium can be formed easily when it is heated above 1400°F (760°C). Complex air-frame sections for fighter planes are often made in this manner. However, titanium reacts readily with air when it is heated, so high-temperature forming procedures must occur in vacuum or inert (shielded) atmospheres. Titanium can also be welded if it is shielded with an inert gas cover or welded in a vacuum. Electron beam welding, which uses a beam of high-energy electrons to make joints in a vacuum chamber, works very well with titanium. Complex structures can be formed in this process. The titanium forward boom shown is strong but lightweight.
The high strength and low density of titanium makes the metal suitable for many other applications requiring light frame construction. Titanium bicycle frames are the result of modern advances in engineering. This design allows the frame to maintain its rigidity at less weight.