Application advantages of titanium alloy

An important driving force for the large number of titanium alloys used in civil aircraft is structural weight reduction, and the weight reduction effect directly determines the overall cost of the aircraft. Titanium alloy is 40% less dense than steel of the same strength, and when titanium alloy is used instead of steel and nickel-based alloys or even high-strength steel, a lot of weight can be lost. For example, in some cases, replacing steel with titanium alloy Ti-6Al-4V for engine fans, compressor discs and blades can reduce weight by 30%; Replacing 30CrMnSiA steel with Ti-10V-2Fe-3Al can reduce the weight of parts by about 40%. Titanium alloy structures using superplastic forming and diffusion joining technology (SPF/DB) are widely used, such as the leading edge slat retracting mechanism cover of A300 and A310/320, which can reduce weight by 10%; A330, A340 wing access port cover, cockpit top cover, seam drive mechanism, etc. have been reduced by 46%, and the economic benefits are remarkable.

Another advantage of using titanium alloy for civil aircraft body structure is to break through the volume limit. When the structural load is relatively high and the aluminum alloy is limited by the structural space, the titanium alloy with higher strength becomes the ideal material. Very large titanium forgings are used on Boeing aircraft to reduce structural volume, such as the landing gear beams on the Boeing 757 and 747. The landing gear is the part between the landing gear beam and the rear beam of the wing, although the aluminum alloy is low in cost and can be used as an alternative material, but due to the high operating load, the aluminum alloy needs to be very large and difficult to wrap in the wing, so the choice of titanium alloy is more suitable.

The higher operating temperature is also a major advantage of titanium alloys. Traditional aluminum alloy can only be applied to 130 ~ 150℃, in the high temperature area, the use of titanium alloy is more suitable, can improve the structural efficiency. Steel and nickel-based alloys are also available, but both are denser than titanium alloys. Engine support structures, such as the B787 suspension structure and the auxiliary power Unit (APU) area, have temperature as a major design consideration.

Titanium alloys have excellent corrosion resistance, which makes them widely used in areas with severe corrosion. In fact, titanium alloys in the civil aircraft operating environment, almost no corrosion phenomenon. In corrosion-prone areas, such as floor support structures located under kitchens and lavatories, titanium alloys can be used instead of aluminum alloys to connect seats to the floor.

With the extensive use of carbon fiber composite (CFRP), the good compatibility between titanium alloy and carbon fiber composite has become an important reason for its extensive use. There is a large potential difference between aluminum alloy and CFRP, which will lead to serious electrochemical corrosion, although protective measures such as adding glass cloth can be taken to isolate aluminum alloy and carbon fiber, but any damage to the surface coating will lead to rapid corrosion of aluminum alloy. For the key structure, it is difficult to check or replace, in order to avoid the appearance of electrochemical corrosion, titanium alloy should be preferred. This characteristic of titanium alloy also makes it widely used in the interface between aluminum alloy and composite material structure. Compared with aluminum alloy, titanium alloy can increase the structural life by 60%. Moreover, its coefficient of thermal expansion is low, and when connected with CFRP structure, high thermal load can be reduced.