Since the 1950s, the application of titanium machining parts in the aerospace field has been rapidly developed. In recent years, the research projects of aerospace titanium alloy applications have made great progress, and many alloys have also been greatly developed. This article mainly talks about the application of titanium machining parts in aerospace products.
The characteristics of titanium alloys for aerospace
(1) High strength. Titanium machined parts have high strength. Its tensile strength is 686-1176MPa, and its density is only about 60% of steel, so its specific strength is very high.
(2) Excellent high temperature performance. Titanium alloy can still maintain good mechanical properties at high temperatures, its heat resistance is much higher than that of aluminum alloy, and its working temperature range is wider.
(3) Strong corrosion resistance. In the air below 550C, a thin and dense titanium oxide film will quickly form on the surface of titanium machined parts, and its corrosion resistance is better than that of most stainless steels.
What are the applications of titanium alloy machined parts in aerospace?
In the aviation industry, the application of titanium machining parts is divided into aircraft structure titanium alloy and engine structure titanium alloy. In aerospace, titanium alloys are mainly used as materials for the structure and container manufacturing of rockets, missiles and spacecraft.
Aircraft structural titanium alloys are generally required to be used at temperatures below 350°C, requiring high specific strength, good toughness, excellent fatigue resistance, and good welding process performance. Titanium alloys for engines require high specific strength, good thermal stability, oxidation resistance, and creep resistance. In addition to the performance requirements of titanium machined parts for aviation, aerospace vehicles also require high temperature resistance and radiation resistance.
For aerospace engines, the application areas of titanium machining parts include compressor discs, blades, drums, high-pressure compressor rotors, compressor casings, and so on. About 30% of the structural weight of modern turbine engines is made of titanium alloy materials. The application of titanium machined parts reduces the quality of compressor blades and fan blades, and at the same time extends the life and inspection intervals of titanium machined parts. The leading edge and tip of the fan blades of the Boeing 747-8GENX engine use a titanium alloy protective sleeve, which has only been replaced three times during the 10-year service period.
Aerospace vehicles work under extreme conditions such as ultra-high temperature, ultra-low temperature, high vacuum, high stress, and strong corrosion. In addition to superb structural design technology, they also rely on the excellent characteristics and functions of titanium alloy materials. Titanium alloy processing and manufacturing fuel tanks, rocket engine shells, rocket nozzle ducts, artificial satellite shells, etc. have been typical applications.
Aerospace titanium machining parts need to go through the processes of ingot casting, billeting, die forging, and machining to obtain the required material structure and performance. They are often used to manufacture aircraft skeleton main bearing components and engine rotors. According to HB5024-1989, the outer diameter of large forgings is not less than 500 mm. With the development of aircraft and engines, the quality requirements of aviation titanium machined parts are getting higher and higher, the size is getting bigger and bigger, and the shape is getting more and more complicated.
The shape of the structural parts of aircraft titanium machined parts is complex, and the material utilization rate generally does not exceed 10%. The material of the four large main bearing reinforcement frames of the F-22 aircraft is Ti-6Al-4V ELI, and the projected area of ??the die forgings is 4.06～5.67 square meters. In recent years, my country’s specialized forging equipment for aerospace titanium machining parts has been greatly improved, and it is now possible to produce 5 square meters of titanium alloy integral forgings.
Due to the excellent performance of titanium alloy materials, some key parts of aerospace vehicles are also processed and manufactured by titanium alloy. For example, the air inlet lip is a part manufactured by 3D printing of titanium alloy material, which realizes the integrated design and manufacturing of structural parts and functional parts.
Titanium alloy fasteners commonly used in the aerospace industry mainly include rivets, bolts and special fasteners.
The main application parts of aircraft titanium machining parts are landing gear parts, frames, beams, fuselage skins, heat shields, etc. Russia’s Il-76 aircraft uses high-strength BT22 titanium alloy to process and manufacture key components such as landing gear and load-bearing beams. The material of the main landing gear transmission beam of the Boeing 747 is Ti-6Al-4V. The forging is 6.20 meters long, 0.95 meters wide, and has a mass of 1,545 kilograms.
The high-strength and high-toughness Ti-62222S titanium alloy is used in key parts of the C-17 aircraft horizontal stabilizer shaft. The rear fuselage area and the rear heat shield where the F-22 aircraft engine is located are designed with titanium alloy thin-walled structure, which has good temperature resistance.
The titanium machining parts used on the American F-22 aircraft include: high-strength titanium alloy bolts, ring-grooved nails, polished rod taper high-lock bolts, self-clamping bolts, titanium-niobium rivets and bonding nuts. my country’s first domestic commercial large aircraft C919, which flew in 2014, used more than 200,000 pieces of single-machine titanium machining parts.
The development and application of titanium alloy fasteners provide the possibility for further weight reduction of aircraft structures. The structural weight of Boeing 747 aircraft is reduced by 1,814 kg after replacing steel with titanium. Russia’s Il-96 aircraft uses 142,000 fasteners and replaces steel with titanium to reduce its weight by 600 kilograms.
Summarize
Titanium alloy is a material with high specific strength, excellent high temperature performance, and strong corrosion resistance. In the future, the demand for titanium machining parts for aviation aircraft should be both higher strength, higher toughness, higher damage performance, and higher temperature resistance. Performance, etc. Therefore, the application development direction of titanium alloy materials will be more demanding.