Performance characteristics of titanium materials for aviation industry

Titanium and titanium alloy materials have low density, high specific strength (the highest among metal materials at present), corrosion resistance, high temperature resistance, non magnetism, good structural properties and stability. They can be directly connected with the composite structure, and the thermal expansion coefficient between them is similar, which is not easy to produce electrochemical corrosion, and have excellent comprehensive properties. Therefore, titanium alloy is more and more widely used in aviation field. Lockheed's "blackbird" high altitude high-speed strategic reconnaissance aircraft SR-71 has a flight speed of more than Mach 3. When flying at high speed, the body surface temperature will exceed the limit of conventional aluminum alloy skin. If it is made of steel, the aircraft weight will be greatly increased, affecting the flight speed, ceiling and other performance. Therefore, the fuselage of SR-71 is heavily made of titanium alloy, with a total weight of more than 30 tons, accounting for 93% of the weight of the aircraft structure. With the continuous improvement of people's requirements for aircraft performance, the amount of titanium alloy used in civil aircraft is also increasing. The amount of titanium alloy parts on the early Boeing 707 accounted for only 0.2% of the total weight of the structure, and up to 15% of the latest Boeing 787.

In addition, titanium alloy is also the main material for manufacturing aeroengines. The j79 engine used in early American F-4 fighters used only 50kg titanium alloy, less than 2% of the total weight. At present, the titanium consumption of most aeroengines has reached 25% - 30% of the total weight of the engine. For example, for jt9d engines of Boeing 747 and 767, the amount of titanium used is 25% of the total weight; The V2500 engine of Airbus A320 uses 31% of the total weight of titanium. Another major use of titanium alloy is as fastener materials such as bolts and rivets. Although these fasteners are small, they are used in a large amount. The use of titanium alloy fasteners can greatly reduce the weight. It is estimated that 70% of the fasteners of C-5 large transport aircraft are titanium alloy fasteners, which reduces the weight of the aircraft by about 1 ton. Now titanium alloy 3D printing technology has been used in aircraft manufacturing. Titanium alloy 3D printing technology gets rid of the traditional mold manufacturing, which significantly prolongs the research and development time, and can manufacture metal parts with high precision, high performance, high flexibility and very complex structure. Therefore, it provides a powerful technical means for the rapid research and development of advanced aircraft structure.

航空工业用钛材料的性能特点:

钛及钛合金材料密度低、比强度高（目前金属材料中最高）、耐腐蚀、耐高温、无磁、组织性能和稳定性好，可以与复合材料结构直接连接，而且两者之间的热膨胀系数相近，不易产生电化学腐蚀，具有优良的综合性能。因此，钛合金在航空领域得到越来越广泛的应用。洛克希德公司的“黑鸟”高空高速战略侦察机 SR-71，飞行速度超过 3马赫，在高速飞行时，机体表面温度将超过常规铝合金蒙皮的极限，如果用钢制造，飞机重量会大大增加，影响飞行速度和升限等性能。因此，SR-71的机身大量采用了钛合金，总重达 30多吨，占飞机结构重量的 93%。随着人们对飞机性能要求的不断提高，民用飞机的钛合金用量也在逐渐增加。早期波音 707上的钛合金部件用量仅占结构总重量的 0.2%，到最新的波音 787，占比高达 15%。

此外，钛合金也是制造航空发动机的主要材料。早期美国 F-4战斗机使用的 J79发动机，钛合金的用量只有50千克，不到总重量的2%。而现在大多数航空发动机的钛用量已经达到发动机总重量的25%〜30%。如波音 747、767的发动机 JT9D，其用钛量为总重量的 25%；空客A320的V2500发动机，其用钛量为总重量的 31%。钛合金的另一大用途是作为螺栓、铆钉等紧固件材料。这些紧固件虽小，但用量却很大，使用钛合金紧固件可以大大减轻重量。据估算，C-5大型运输机有 70%的紧固件为钛合金紧固件，飞机因此而减重 1吨左右。现在钛合金 3D打印技术已用于飞机制造。钛合金3D打印技术由于摆脱了传统的模具制造这一显著延长研发时间的环节，可以制造高精度、高性能、高柔性和快速制造结构十分复杂的金属零件，因而为先进飞机结构的快速研发提供了有力的技术手段。

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