The density of titanium alloys is usually about 4.5g/cm3, which is only 60% of steel. The strength of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys are stronger than many structural steel alloys. As a result, titanium alloys have a much greater specific strength (strength/density) than other metallic structural materials and allow the manufacture of parts and assemblies with high specific strength, good stiffness, and low weight. Currently, titanium alloys are used in aircraft engine components, skeletons, skins, fasteners, and landing gear. Titanium alloys exhibit excellent corrosion resistance in harsh environments, which is the main reason for their use in chemical equipment manufacturing. It has good high and low-temperature characteristics, non-magnetizability and low thermal conductivity, and thermal expansion coefficient. On the downside, titanium fasteners are difficult to machine. Also, when installing and locking threaded fasteners, the threads can easily get scratched or seized. Below are some examples of titanium alloys that are susceptible to stress corrosion at moderately high temperatures. But this can be mitigated with some special techniques. Pure titanium is not heat treatable. In general, almost no fasteners use pure titanium as a raw material. There are many titanium alloys, most of which are sold exclusively. Research has shown that only a small fraction of planed titanium alloys are suitable for making threaded fasteners. Ti-6Al-4V is a heavy-duty alloy. This titanium alloy fastener has a minimum tensile strength of 135,000 psi, high strength, and satisfactory toughness. Ti-6Al-4Mn has good creep resistance and is easy to cast. Its strength properties are comparable to Ti-6Al-4V alloys, but the toughness is slightly worse. The tensile strength of Ti-1Al-8V-5Fe is about 200,000 psi. Exaggerated is its excellent strength-to-mass ratio. Fasteners made from this alloy have a tightening force equal to that of a steel fastener of the same mass with a tensile strength of 350,000 psi. Two other titanium alloys are sometimes used in fastener manufacturing - Ti-6Al-12Zr and Ti-6Al-6V-2Sn. The most attractive feature of titanium is its extremely high strength-to-weight ratio. They are only 57% the mass of steel of the same volume, yet have comparable strength to heat-treated iron-carbon alloys. Titanium is an ideal material for aerospace, jet aircraft, and missiles. But its biggest disadvantage is the high cost. Titanium is not recommended for fasteners unless there is no other option.
