As an engineering material, titanium has been developed over the past 50 years. This seems to be a long time, but in fact, as engineering materials, this time is relatively short. It takes many years to build a credible database, and the credibility of the data in the library is based on controllability studies confirmed by application experience.
The most attractive feature of titanium is their extremely high strength-to-mass ratio. They are only 57% of the same volume of steel, and their strength is comparable to that of heat-treated iron-carbon alloys. Titanium is an ideal material for aerospace, jet aircraft and missiles. But its biggest drawback is that the cost is too high. Unless there is no alternative, the use of titanium as a material for fasteners is discouraged.
Titanium alloy exhibits superior corrosion resistance in harsh environments, which is the main reason why it is used in chemical equipment manufacturing. It has good high and low temperature characteristics, non-magnetability and low heat transfer coefficient and thermal expansion coefficient.
From its negative side, titanium fasteners are very difficult to machine. 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 appropriate elevated temperatures. But this situation can be alleviated by some special process.
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 monopoly. Studies have shown that only a small portion of the planed titanium alloy is suitable for the manufacture of threaded fasteners.
Ti-6Al-4V is a heavy-duty alloy with fasteners with a minimum tensile strength of 135,000 psi, high strength and satisfactory toughness.
Ti-6Al-4Mn has great creep resistance and is easy to cast. Its strength characteristics are comparable to those of Ti-6Al-4V alloy, but the toughness is slightly poor.
Ti-1Al-8V-5Fe has a tensile strength of about 200,000 psi. To exaggerate is its outstanding strength-to-mass ratio, the fasteners made of this alloy have the same fastening force as 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 mechanical properties of the externally threaded fasteners made of titanium are described in ASTM F468 on page B-158 and in ASTM F467 on page B-184. In these specifications, the Ti-6Al-4V alloy has an identification alloy number of 5.