Titanium alloys exhibit superior corrosion resistance in harsh environments, which is the main reason why they are used in chemical equipment manufacturing. It has good high and low temperature characteristics, non-magnetizability and low thermal conductivity and thermal expansion coefficient. On its negative side, titanium fasteners are very difficult to machine. Moreover, when installing and locking threaded fasteners, the threads are easily scratched or stuck. Here are some examples of titanium alloys being susceptible to stress corrosion at moderately high temperatures. But this situation can be alleviated through some special processes.
Pure titanium is not heat treatable. Generally speaking, almost no fasteners use pure titanium as raw material. There are many titanium alloys, most of which are specialty. Research shows that only a small proportion 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 and has high strength and satisfactory toughness.
Ti-6Al-4Mn has great creep resistance and is easy to cast. Its strength characteristics are equivalent to those of Ti-6Al-4V alloy, but its toughness is slightly worse. The tensile strength of Ti-1Al-8V-5Fe is approximately 200,000 psi. What should be exaggerated is its outstanding strength-to-mass ratio. The tightening force of fasteners made of this alloy is equivalent to that of steel fasteners of the same quality with a tensile strength of 350,000 psi. Two other titanium alloys, Ti-6Al-12Zr and Ti-6Al-6V-2Sn, are sometimes used in the manufacture of fasteners.
The most attractive property 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 that of heat-treated iron-carbon alloys. Titanium is an ideal material for manufacturing aerospace, jet aircraft and missiles. But its biggest drawback is its high cost. The use of titanium as a fastener material is discouraged unless there is no alternative.
