The density of titanium alloy is generally 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 exceed the strength of many alloy structural steels. Therefore, the specific strength (strength / density) of titanium alloy is much greater than that of other metal structural materials, and parts and components with high unit strength, good rigidity and light weight can be produced. At present, titanium alloys are used for aircraft engine components, skeletons, skins, fasteners and landing gear.
Titanium alloy exhibits superior corrosion resistance in harsh environments, which is the main reason why it is used in the manufacture of chemical equipment. It has better high and low temperature characteristics, non-magnetizability, and low thermal conductivity and thermal expansion coefficient. From its negative aspect, the processing of titanium fasteners is very difficult. Moreover, when the threaded fastener is installed and locked, the thread is easily scratched or stuck. Here are some examples of titanium alloys that are sensitive to stress corrosion at moderately high temperatures. But this situation can be alleviated by some special processes.
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 exclusively sold. Studies have shown that only a small portion of planed titanium alloys are suitable for threaded fasteners. Ti-6Al-4V is a heavy-duty alloy. The minimum tensile strength of this titanium alloy fastener is 135,000 psi, which has high strength and satisfactory toughness. Ti-6Al-4Mn has great creep resistance and is easy to cast. Its strength characteristics are comparable to Ti-6Al-4V alloy, but its toughness is slightly worse. The tensile strength of Ti-1Al-8V-5Fe is about 200,000 psi. To be exaggerated is its outstanding strength-to-mass ratio. The fastening force of fasteners made of this alloy is comparable to that of steel fasteners of the same quality with a tensile strength of 350,000 psi. The other two titanium alloys-Ti-6Al-12Zr and Ti-6Al-6V-2Sn are sometimes used in the manufacture of fasteners.
The most attractive feature of titanium is their extremely high strength-to-mass ratio. Their mass is only 57% of the same volume of steel, but their strength is comparable to the heat-treated iron-carbon alloy. Titanium is an ideal material for manufacturing aerospace, jet aircraft and missiles. But its biggest disadvantage is the high cost. Unless there is no other choice, the use of titanium as a material for fasteners is discouraged.