Heat-resistant titanium alloys, also known as high-temperature titanium alloys, possess high strength in the range of 400 to 600°C. These alloys can be categorized into α+β type and near α type based on their microstructure. An example of a typical α+β titanium alloy is BT9, with a composition of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si and a service temperature of 500°C. Near α alloys are more common, such as the Ti-6242 alloy composed of Ti-6Al-2Sn-4Zr-2Mo, which has a usage temperature of 540°C. Another example is the IML-834 alloy with a composition of Ti-5.8Al-4Sn-3.5Zr-0.7Nb-0.5Mo-0.35Si, capable of withstanding a service temperature of 600°C. These alloys find significant application in manufacturing aero-engine compressor discs and rotor blades. Compressor discs require high creep resistance strength and are suitable for double-state or basket-like structures. Rotor blades, on the other hand, necessitate high fatigue strength at both room and high temperatures and should be equiaxed in shape.
Titanium and its alloys are lightweight, high-strength, and corrosion-resistant materials extensively utilized in various industries such as aviation, aerospace, marine, defense, chemical, petrochemical, metallurgy, power generation, light industry, salt production, construction, ocean engineering, medicine, sports goods, and everyday utensils.
Aero-engines have been one of the earliest and most promising fields for the application of titanium alloys. As early as the 1870s, the usage of titanium alloys in Russian aero-engines accounted for 50% of the metal parts production. In recent years, there has been a noticeable decline in the use of titanium alloys in military aircraft engines, while conversely, their use in large civil engines has been on the rise. This increase can be attributed to the widespread utilization of gas turbine engines in large passenger aircraft, the accumulated experience in titanium alloy production and application, and the enhancement of titanium alloy performance and reliability. Currently, the most advanced engines are turbofan engines used in large passenger jets and transport aircraft, where the application of titanium alloys for weight reduction purposes is evident. Production of these engines has witnessed significant growth and is expected to continue increasing.
In contrast, the usage of titanium alloys in military engines, particularly for turbojet engines used in supersonic military aircraft, has shown a downward trend. This reduction can be attributed to lower production volumes of military engines and the relatively lesser need for titanium in turbojet engines.
Titanium is employed in the manufacturing of engine fans, compressors, disks, blades, isolators, intake boxes, air collectors, and other components. Heat-resistant titanium alloys can operate at temperatures of 500 to 550°C, and even at 600°C, they can function normally, while structural titanium alloys are suitable for temperatures of 300 to 350°C.
Structural titanium alloys exhibit superior specific strength, plasticity, and fracture resistance compared to heat-resistant titanium alloys, making them particularly suitable for the production of blades and vanes in large-scale turbofans.
Various data and studies indicate that replacing steel materials with titanium alloys in aircraft engines can reduce the weight of the engine structure by 30% to 40%. The extent of weight reduction depends on the quantity and design of structural titanium alloys used, thus influencing the economic benefits of weight reduction.
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