Titanium Alloy For Large Aviation Forgings
Due to its high specific strength, specific stiffness, corrosion resistance and other excellent properties, titanium alloy has been widely used in the aviation industry, and has a significant effect on the weight loss of aircraft structures and the improvement of the service life of parts. Especially for military aircraft, some important structural components such as spars, spacers, landing gear, etc. are widely made of titanium alloy forgings, with high single-piece weight and large size and cross-sectional area.
For example, the 8 pieces of the main landing gear support beam of the Boeing B747 aircraft are made of Ti-6Al-4V titanium alloy forgings, with a single piece weighing 1724kg, a length of 6.2m, and a projection area of 4.1m2. The two six-wheeled three-axle trolley-type main landing gear load beams of Airbus A380 aircraft are made of Ti-10V-2Fe-3V titanium alloy forgings, with a length of 4.255m and a weight of 3210kg. The fourth-generation fighter F22 spacer frame developed by Lockheed in the United States adopts Ti-6Al-4V ELI forgings, with a single piece weighing more than 771kg and a projection area of 4.06m2.
At present, the main grades of titanium alloys for aviation are TC4, TC18, TC21, TA15, TB6 (U.S. Ti-10V-2Fe-3Al alloy) and so on. Among them, TC18 is suitable for manufacturing large-scale forgings due to its maximum hardenability, and currently is the most used in China. According to the needs of civil aircraft such as Boeing and Airbus, Russia has developed Ti-55531 titanium alloy based on TC18 alloy by reducing the content of Fe, which is easy to isolate. Ti-55531 has high strength, superior hardenability and a wider processing window. It has been used on parts such as A380 aircraft hanger joints and landing gear struts.
Domestic C919 aircraft have also carried out the development of domestic materials, and domestic heavy-duty helicopters are also using this material to develop large-scale helicopter hub centers. The data currently collected show that Ti-55531 has higher tensile strength and lower plasticity and fracture toughness than TC21 and TC18, but Ti-55531's crack-spreading resistance under Δk=11 MPa·m1.2 conditions is significantly better than TC21 and TC18 alloys, indicating that its crack germination life is long and the fatigue limit is high, which is suitable for long-life designs.
