Why do we have to use grade 5 titanium alloy as the material of air transport aircraft?

 First of all, the thermal conductivity of grade 5 titanium alloy is only 1 / 4 of that of steel, 1 / 13 of that of aluminum and 1 / 25 of that of copper. Due to the slow heat dissipation in the cutting area, it is not conducive to the heat balance. In the process of cutting, the heat dissipation and cooling effect is very poor, which is easy to form high temperature in the cutting area. After processing, the deformation and springback of the parts are large, resulting in the increase of cutting tool torque, rapid wear of cutting edge and the decrease of durability.

Secondly, the thermal conductivity of grade 5 titanium alloy is low, which makes the cutting heat accumulate in a small area near the cutting tool and is not easy to dissipate. The friction of rake face is increased, so it is not easy to remove chips and the cutting heat is not easy to dissipate, which accelerates the tool wear. Finally, because of its high chemical activity, titanium alloy is easy to react with cutting tool materials at high temperature, forming solution deposition and diffusion, resulting in knife sticking, knife burning and knife breaking.

The highest speed of modern aircraft has reached more than 2.7 times the speed of sound. At such a high supersonic speed, a large amount of heat will be generated by the friction between the aircraft and the air. When the speed of flight reaches 2.2 times the speed of sound, the aluminum alloy will not be able to withstand. High temperature resistant grade 5 titanium alloy must be used. When the thrust to weight ratio of aeroengine increases from 4 to 6 to 8 to 10, and the outlet temperature of compressor increases from 200 to 300 ℃ to 500 to 600 ℃, the low pressure compressor disk and blade made of aluminum must be made of titanium alloy.

In recent years, scientists have made new progress in the study of the properties of grade 5 titanium alloys. The maximum working temperature of the original titanium alloy composed of titanium, aluminum and vanadium is 550 ℃ ~ 600 ℃, while the maximum working temperature of the newly developed aluminum titanide (TiAl) alloy has been increased to 1040 ℃. Using grade 5 titanium alloy instead of stainless steel to make high pressure compressor disk and blade can reduce the structural weight. Every 10% reduction in weight of aircraft can save 4% of fuel. For a rocket, a range of 15 km can be increased by reducing the weight of 1 kg.