powder superalloy : material of choice for aero engine turbine discs (HY-industry technical centre)
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Turbine disk is an important core hot-end component of aeroengine. Its metallurgical quality and performance level play a decisive role in the improvement of engine and aircraft reliability, safety life and performance. Superalloys (turbine disks, turbine blades, etc.) are known as the heart of gas turbines and have always been the focus of metallurgical workers. The use of powdered superalloys can significantly improve the mechanical properties and thermal process performance of the turbine disk. In recent decades, with the rapid development of alloys and preparation technologies, powdered superalloys have become the preferred material for high-performance aero-engine turbine disks. -
Superalloy refers to a type of metal material that uses nickel, iron and cobalt as the matrix, can work for a long time at a high temperature above 600 ℃ and a certain stress, can withstand relatively large and complex stresses, and has surface stability.
01 properties of superalloy
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Superalloys have high high temperature strength, good oxidation resistance, corrosion resistance and good fracture toughness, plasticity and other comprehensive properties, which are of great significance in modern national defense construction and national economic development. Superalloys have excellent high-temperature properties and are widely used and indispensable in many fields such as aerospace, energy, and transportation.
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However, high-temperature alloys are typical difficult-to-machine materials, and there are problems of poor thermal processing performance and difficult cutting processing. This not only increases the processing cost, but also seriously affects the application of high-temperature alloy materials.
02 Classification of superalloys
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High-temperature alloys are divided into iron-based, nickel-based and cobalt-based alloys according to the main elements of the alloy.
Iron-based superalloys are used at low temperatures (600~850℃), and are generally used in parts of the engine with low operating temperatures, such as turbine discs, casings and shafts.
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Nickel-based deformed superalloys are mainly used for turbine discs and turbine blades in engines, and the temperature range is generally 650°C-1000°C. Nickel-based casting superalloys are mainly used for turbine guide vanes and rotor blades in engines, and the operating temperature can reach above 1100°C.
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Cobalt has a small reserve on the earth and is more expensive. At present, the enthusiasm for research and development of cobalt-based alloys has declined.
03 Development status of powder superalloy
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Because powder metallurgy superalloys (referred to as: powder superalloy) have the advantages of fine powder, uniform alloy composition, stable part performance, good hot working deformation performance and high degree of alloying, the application prospect is very broad, in aerospace, petrochemical industry, Transportation, nuclear reactors and other aspects all occupy a pivotal position.
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Powder superalloys are a new generation of superalloys that appeared in the 1960s. Metal powders are used as raw materials and subjected to subsequent thermal processing to obtain alloys with higher tensile strength and good fatigue resistance. So far, it has gone through three generations of research and development. European and American countries and Russia have established their own superalloy systems.
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The research on powdered superalloys in China started relatively late, beginning in the late 1970s. The powder superalloy models mainly include FGH95, FGH96, FGH97, FGH98, etc. Shanghai HY Industry Co., Ltd has a corresponding enterprise brand
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With the continuous development of powdered superalloys, in recent years, some scholars have proposed the research direction of the fourth generation of powdered superalloys. The design goal of the fourth-generation powder superalloy is to meet the requirements of aeroengines with a thrust-to-weight ratio of 15-20. The development goal of the fourth-generation powder superalloy is to inherit the high strength and high damage tolerance of previous generations of powder superalloys. On the basis of this, increase its working temperature in order to prepare an alloy with high strength, high damage tolerance and high working temperature.
04 Preparation method of powder high temperature alloy
At present, the preparation of superalloy powder mainly includes two methods: gas atomization method (AA powder) and plasma rotating electrode method (PREP powder).
4.1 Gas atomization method
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Schematic diagram of the vacuum induction melting gas atomization (VIGA) pulverizing equipment is shown in Figure 1. It is mainly divided into vacuum system, induction melting system, gas source, atomization system and powder collection system. The corresponding powder making process is divided into four processes: smelting, atomization, droplet solidification and powder collection. The master alloy prepared by vacuum induction melting is heated to a molten state by medium frequency induction in the melting furnace; affected by the suction force of gravity and atomizing air flow, it overcomes the friction force on the surface of the porcelain crucible and the internal viscosity of the melt, and flows in through the draft tube The atomization chamber is subjected to the shearing force of the high-speed airflow at the end of the draft tube, which overcomes the surface tension and breaks into millimeter or micrometer-scale droplets; the fully broken droplets are affected by airflow drag, inertial force, gravity, and thermophoresis. Under the action of the resultant force, it disperses and flies in the atomization chamber, has a strong heat exchange effect with the airflow, and quickly solidifies into powder particles of different sizes, which are finally collected in the powder tank by the classification system. -
Advantage of gas atomization powder milling is that it can prepare relatively small spherical superalloy powders, and remove larger inclusion particles through sieving, thereby reducing the harmful effects of inclusions.
4.2 Plasma rotating electrode method (PREP)
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In the plasma rotating electrode method (PREP), the rotating electrode is placed in the atomization chamber, and an external heating source is used to form a molten metal film on the electrode end surface. When the electrode rotates at a high speed, the molten metal forms a fine liquid under the action of centrifugal force. Drop, crystallize to form metal powder. The powder prepared by this method has better sphericity, uniform particle size distribution and smooth powder surface.
05 summary
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After nearly half a century of research and development, powder superalloy technology has made breakthrough progress. Some powdered superalloys have been applied to the aero-engine field.
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With the continuous maturity and improvement of powder superalloy preparation technology, the future superalloy powder technology will continue to develop in the direction of high purity, refinement, narrow particle size, less inclusions, high sphericity, high efficiency and low cost. In the near future, a series of alloys with better properties will be developed, and their application scope will become wider and wider.
