Gas turbine engine, which originated in 1930, was first studied as an aero-engine and is also widely used in ships. The engine is small in size, light in weight and large in output power.
Japan kawasaki heavy industry began to develop 200kW class backup generator gas turbine in 1974, and the world's top 6000kw class standby generator gas turbine with axial flow compressor structure was put into the market in 1994. These gas turbines use titanium.
Kawasaki heavy industries produces the 1 500kW class M1A -- 13 gas turbine, with two stages using titanium alloy impeller, rated speed of 22 000r/min. Ti-6al -- 4V forgings (maximum diameter 450mm) are used for primary turbine discs, and ti-6ai-2sn -- 4zr-2mo forgings are used for secondary turbine discs. The 6000kw-class m7a-01 gas turbine has a speed of 14000r/min. The moving blades of the low-temperature part in the first half of the axial flow compressor adopt ti-6al-4v forging with high specific strength and good corrosion resistance.
The aviation gas turbine requires as light as possible, so Al alloy and Mg alloy were developed in early use. The first titanium alloys to be mass-produced were the compressed motor blades and turbine discs of pratt & Whitney's j-57 jet engine in the 1950s. Precision castings made of titanium alloys, which account for 36% of the weight of the latest gas turbines, are also used. Suitable for large fan blades at the front of the engine, dynamic and static blades of the compressor, compressor disc, housing for rotating parts, etc. The titanium alloy low-pressure compressor disc of the V2500 turbofan engine (maximum diameter 900mm) USES Ti -- 6al-4v triple vacuum smelting material.
Ti-6a1-4v is also used in the compressed air powered blades inserted in the outer circle of the disc. In order to pursue the lightweight, also has made the large-scale hollow air fan blade with the titanium alloy, and already practical. The V2500 USES a ti-6al-4v fan housing with titanium material in the shape of a drum with a diameter of 1700mm and a height of 820mm. The development of high-temperature titanium alloy expands the application scope of parts. The typical high-temperature titanium alloy includes ti-6242si, IMl829, IMl834 and ti-1100, etc., which makes most of the gas turbine compressor use titanium.
The defects of titanium alloy used in gas turbine must be paid attention to. In 1989, the ti-6a1-4v fan disc of the second engine of a dc-10 aircraft broke. The ti-6a1-4v-2sn-4zr-2mo high pressure compressor disc of the first engine of an A300 aircraft broke during takeoff in 1994. Both events were the result of fatigue crack development induced by LDI(low density nitride inclusion) called hard phase. Based on this lesson, we seek to improve the smelting technology and nondestructive testing technology of aviation titanium alloy with high quality.
In addition to the traditional three times vacuum arc melting (VAR), the LDI is removed once more by electron beam cold bed furnace or plasma cold bed furnace smelting. This smelting technology has been stipulated as the technical requirement of smelting method (American aerospace material standard AMS4280).
High strength and high temperature are required for titanium materials used in gas turbines in the future. -intermetallic compound is a kind of light and heat-resistant material with excellent oxidation resistance, stiffness and specific strength. In terms of practical application, it mainly focuses on the research on castings. It has been planned to replace ni-based superalloy non-important parts of aviation gas turbine high-temperature components with -capital since 1997. At the same time, the evaluation test of gas turbine blade is also in progress. On the other hand, there is also titanium for the main turbine.
In titanium matrix composites (TMC), SiC long fiber reinforced TMC has excellent specific strength and specific stiffness, and is now being evaluated for various parts for practical use. The biggest problems with these practical aspects of TMC are manufacturing costs and nondestructive testing techniques.