In order to meet the requirements of damage tolerance design, the international community attaches great importance to the development of medium-strength or high-strength titanium alloys with high fracture toughness and very slow crack growth rate, namely high damage tolerance titanium alloys (or damage tolerance titanium alloys). At present, damage tolerance titanium alloys with high fracture toughness and low crack growth rate have been developed abroad, namely, low gap Ti-6Al-4V (β-ELI) and Ti-6-22-22S. A new two-phase high-strength and high-toughness TC21 alloy developed in China.
Ti-6Al-4V (β-ELI) belongs to the high damage tolerance type titanium alloy with 900MPa strength level. The content of interstitial elements C, O, N and impurity element Fe in the alloy is significantly less than that of Ti-6A1-4V alloy. Reduce the strength of the alloy, but improve the toughness of the alloy. The main performance of alloy forgings can reach: o.≥895MPa, 00.2≥ 795MPa, 8≥8%, w≥15%, ic≥75MPa·m1/2Ti-6Al-4V(β-ELI) alloy has been applied to Boeing 777 passenger aircraft The stabilizer is connected to the joint and the body of the F/A-22 aircraft.
Ti-6-22-22S (Ti-6Al-2Sn-2Zr-2Mo-2Cr-0.2Si) alloy is a type of α+3 titanium alloy for aviation developed by RMI Corporation of the United States in the 1970s. By adding Si, the alloy can maintain high strength at medium temperature. The advantages of this alloy are: the typical toughness can reach 100mm in diameter; and the excellent superplastic forming performance. Ti-6-22-22S alloy has been selected by the US Air Force as the material for F-22 fighters. For example, the wing chord of the lower keel of the aircraft is Ti-6-22-22S alloy forgings, and the alloy is also planned to be used X-33 trainer, reusable launch vehicle and joint attack fighter.
TC21 (Ti-Al-Mo-Sn-Zr-Cr-Si-X series) titanium alloy is a new two-phase, high-strength, high-toughness, and high-damage-tolerant titanium alloy with my country's independent intellectual property rights. At present, the large bars of this alloy below D300mm have the conditions for stable batch supply. TC21 titanium alloy has the properties of high strength, high toughness, high weldability and low fatigue crack growth rate. Its comprehensive mechanical properties are more widely used than Ti-6-22-22S and Su-27 series aircraft used in American F-22 aircraft. The BT20 titanium alloy is more excellent, especially with very excellent electron beam welding performance, which is suitable for manufacturing important load-bearing components of large integral frame beams of aircraft.
Titanium has more than 30 years of experience in damage tolerance design abroad, but my country started late in damage tolerance design. With the rapid popularization of damage tolerance design technology for domestic aviation systems, the demand for high damage tolerance titanium alloys will become increasingly urgent. my country needs to deeply study the damage tolerance performance mechanism of titanium alloys and improve the characterization and evaluation technology of damage tolerance performance.
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