Some typical performance parameters of titanium alloys for fasteners

On both military and civilian aircraft and spacecraft, there are many carbon fibre composites in addition to metal components.

Titanium and carbon fibre composites have similar electrode potentials, and titanium alloy has become the only connection material for composite materials. Therefore, with the increasing amount of titanium alloy and composite materials in advanced military and civil aircraft, the demand for titanium alloy fasteners is increasing. Titanium alloy used as aviation fasteners, at least the following four advantages: 1) good weight reduction. A Russian IL-96 aircraft with 14.2 million pieces of fasteners, can reduce the mass of nearly 600 kg. China's aerospace system of titanium alloy fasteners used also have obvious weight reduction effect. Aircraft and spacecraft to reduce the mass, you can improve thrust, increase range, save fuel, reduce launch costs.

(2) Titanium alloy excellent corrosion resistance, especially its positive potential and carbon fibre composite material matching, can effectively prevent the fasteners from galvanic coupling corrosion.3) In the aircraft structure, fastener parts due to the high temperature, can not be used in aluminium alloys, only the use of titanium alloys.4) Titanium has a good elasticity and non-magnetic, is essential to prevent the loosening of the tightening bolts and anti-magnetic field interference.

Modern aircraft using a variety of titanium alloy fasteners are mainly ordinary titanium bolts, interference bolts, special fasteners. The United States, France and other aviation developed countries, more than 95% of the titanium alloy fasteners are made of Ti-6Al-4V (TC4) material. Besides, there are TB2, β III, Ti-44.5, Ti-15-3 (TB5), TB8 and TB3, whose typical performance parameters are listed in Table 7.

The Ti-6Al-4V (TC4) alloy has the lowest β-stability coefficient of 0.27. It has the advantage of having the lowest density, good strength and fatigue properties, a simple alloy composition, and the lowest cost of semi-finished products. However, because the room temperature plasticity is not high enough, processing of fasteners requires induction heating for hot upsetting, as well as vacuum solution treatments and aging treatments for higher processing costs.

TB2, TB3, TB8 and TB16 are sub-stable β Ti alloys with higher β stability coefficients than the alloys, with the disadvantages of higher density, lower fatigue properties than Ti-6Al-4V although the strength is comparable to that of Ti-6Al-4V, and a complex composition with a high cost of semi-finished products. Because of the same need for vacuum aging treatment, so the cost of finished fasteners is higher than Ti-6Al-4V.