Titanium alloys have also encountered some bottlenecks in development, hindering further application. In this regard, all countries are stepping up the research of more "geili" titanium alloy and production technology, striving for a new breakthrough in high dosage, high performance and low cost. The main research directions are as follows: based on type titanium alloy, high temperature titanium alloy can be developed by means of precise control of strengthening element content, rapid solidification and powder metallurgy technology, and the working temperature can be raised to 600℃ or even above 800℃ to meet the requirements of large thrust ratio engine. On the basis of titanium alloy, the tensile strength, fracture toughness and fatigue resistance are improved continuously, and alloy steel is replaced by titanium alloy with high strength and high toughness to manufacture bearing beam, landing gear, helicopter hub and other important components. The common titanium alloy is prone to failure combustion under high temperature and pressure, so it is necessary to study the flame retardant titanium alloy with special coating, which is used in the high-pressure compressor, blade and vector nozzle of the engine. The high damage tolerance titanium alloy with better toughness can reduce the crack propagation speed in important parts of the aircraft and extend the service life. The titanium matrix composites with high specific strength, heat and corrosion resistance and easy to be machined will be developed vigorously to replace the more expensive titanium alloy. In terms of processing technology, in addition to improving traditional processes such as casting, welding and heat treatment, new technologies such as superplastic forming and laser forming are also introduced to manufacture complex aircraft integral components, effectively reducing the weight of finished products and production cycle.
The internal microstructure of titanium is phase with a dense hexagonal structure at room temperature, and changes to phase with a volumetric cubic structure at high temperature. Different titanium alloys can be obtained by adding different elements and conducting heat treatment. Industrial pure titanium contains a small amount of impurities, and is mainly used to manufacture general components with operating temperature below 350℃, such as aircraft skin and heat shield, spacecraft cryogenic vessels, etc. The type titanium alloy with aluminum, tin, zirconium as the main added elements has good thermal stability and oxidation resistance, easy to welding, suitable for aircraft plate or pipe structure with little stress, and engine parts working at 500℃ for a long time. The titanium alloy with molybdenum, vanadium and chromium as the main added elements is better in strength and toughness, fatigue resistance is also very good, is conducive to significantly reduce the weight of the aircraft, but the heat resistance is not high, can be used in aircraft internal frame, fasteners, landing gear and helicopter rotor assembly. The type titanium alloy with two kinds of stable elements is widely used because of its good comprehensive mechanical properties and easy processing and forming. The typical brand ti-6al-4V (TC4) accounts for more than half of the titanium alloy used, which can be used in fuselage and wings as well as engine parts.
