1 Classification by matrix elements
According to matrix elements, superalloys can be divided into iron-based superalloys (14.3%), nickel-based superalloys (80%) and cobalt-based superalloys (5.7%).
(1) Iron-based superalloys can also be called heat-resistant alloy steels. The base body of the iron-based superalloy is Fe, with a small amount of alloying elements such as Ni and Cr, which can be divided into martensite, austenite, pearlite, and ferritic heat-resistant steel according to their normalizing requirements.
(2) The nickel content of nickel-based superalloys is more than half, which is suitable for working conditions above 600 ℃. The use of solid solution and aging processing can greatly improve the creep resistance and compressive and yield strength. From the current application situation, under high-temperature working conditions, the range of nickel-based superalloys exceeds that of the other two types of superalloys. At the same time, nickel-based superalloys are also the largest high-temperature alloys in China. Most turbine engines have turbine blades and combustion Chambers and even turbochargers use nickel-based alloys as the preparation material.
(3) Cobalt-based superalloys use cobalt as the matrix, and the cobalt content accounts for about 60%. At the same time, the alloy needs to add Cr, Ni and other elements to improve the heat resistance of the high-temperature alloy, but the cobalt resource output is relatively small, and the processing is difficult. It is usually only used in high temperature conditions (600-1000 ℃) and for a long time under extreme complex stress. Components such as working blades, turbine disks, hot end parts of combustion chambers and aerospace engines for aero engines.
2 Classification by preparation process
According to the preparation process, it is divided into deformed superalloys (70%), cast superalloys (including equiaxed superalloys, directional solidified columnar superalloys, single crystal superalloys, 20%) and new superalloys (powder metallurgy superalloys) , Intermetallic superalloys, etc.).
Deformed superalloys are the most used in aircraft engines. Taking GH4169 alloy as an example, it is currently the most widely used main high-temperature alloy variety. Deformation high-temperature alloys can be used to prepare main parts in the combustion chamber and turbine disk of aircraft engines. As other alloy products become more mature, deformed high-temperature alloys The amount of use may gradually decrease, but will remain dominant in the coming decades.
Casting superalloys can be divided into the following three categories according to the operating temperature. The first category: equiaxed crystal casting superalloys used at -253-650 ° C, have good comprehensive properties in a wide range of temperatures, especially at low temperatures to maintain strength and plasticity without falling. The second category: equiaxed crystal superalloys used at 650-950 ° C, have high mechanical properties and thermal corrosion resistance at high temperatures. The third category: directional solidified columnar crystals and single crystal superalloys used at 950-1100 ℃, with excellent comprehensive performance, oxidation resistance and thermal corrosion resistance in this temperature range.
Powder metallurgy superalloys use atomized superalloy powders, which are manufactured by hot isostatic pressing or hot isostatic pressing and then forged to produce high temperature alloy powder products. Due to the small powder particles and fast cooling speed, it has the characteristics of uniform composition, no macro-segregation, fine grains, good hot workability, high metal utilization, etc. The yield strength and fatigue performance of the alloy have been greatly improved. Powder metallurgy superalloys can meet the requirements of engines with high stress levels, and are the materials of choice for high-temperature components such as turbine disks, compressor disks and turbine baffles for high thrust-to-weight ratio engines. Powder preparation is the most important link in production. The quality of the powder directly affects the performance of the parts. The argon atomization (AA), rotating electrode (PREP) and dissolved hydrogen atomization (SHA) processes are mainly used. Russia and China use the PREP process, the United States Other countries use AA technology.
Intermetallic compounds are a new type of light specific gravity and high temperature materials. At present, basic research and development and application research on intermetallic compounds are mature, especially in the preparation and processing technology, toughening and strengthening, mechanical properties and application research of Ti-Al, Ni-Al and Fe-Al series materials. A remarkable achievement. Ti3Al-based alloy (TAC-1), TiAl-based alloy (TAC-2) and Ti2AlNb-based alloy have low density (3.8 ～ 5.8g / cm3), high temperature and high strength, high rigidity and excellent oxidation resistance, creep resistance, etc. Advantages, can reduce the weight of structural parts by 35 to 50%. Ni3Al-based alloy, MX-246 has good corrosion resistance, wear resistance and cavitation resistance, showing excellent application prospects. Fe3Al-based alloy has good resistance to oxidation and corrosion, has high strength at medium temperature (less than 600 ℃) and low cost. It is a new material that can partially replace stainless steel.
3 Classification by reinforcement
According to the strengthening method, it is divided into solid solution strengthening type, aging strengthening type, oxide dispersion strengthening type and grain boundary strengthening type.
The solid solution strengthened superalloy, adding some alloying elements to the base superalloy, forms a single-phase austenite structure, and the solute atoms distort the matrix of the solid solution matrix, so that the slip resistance in the solid solution increases and strengthens. The solute atoms can reduce the stacking fault energy of the alloy system and increase the tendency of dislocation decomposition, which makes cross-slip difficult to achieve and achieve the purpose of strengthening the superalloy.
Aging precipitation strengthening high temperature alloy is a heat treatment process where the alloy workpiece undergoes solution treatment and cold plastic deformation, and is placed at high temperature or room temperature to maintain its performance. For example, the GH4169 alloy has a maximum yield strength of 1000 MPa at 650 ° C, and the alloy temperature of the blade can reach 950 ° C.
The oxide dispersion-strengthened superalloy adopts a unique mechanical alloying (MA) process. The ultra-stable oxide dispersion-strengthened phase is evenly dispersed in the alloy matrix at high temperature to form a special superalloy. Its alloy strength can be maintained under the condition of close to the melting point of the alloy itself, and has excellent high temperature creep, high temperature oxidation resistance, carbon and sulfur corrosion resistance. At present, there are three main ODS alloys that have been commercially produced: MA956 alloy can be used in an oxidizing atmosphere at a temperature of up to 1350 ℃, ranking first in high-temperature alloys against oxidation, carbon, and sulfur corrosion. It can be used in the lining of aircraft engine combustion chambers; The MA754 alloy can be used in an oxidizing atmosphere at a temperature of up to 1250 ° C and maintains high-temperature strength and resistance to corrosion by medium-alkali glass. It has been used to make aero-engine guide gear rings and guide blades; MA6000 alloy has a tensile strength of 222MPa at 1100 ° C. The yield strength is 192MPa, the endurance strength at 1100 ℃ and 1000 hours is 127MPa, and it can be used for aeroengine blades.
Grain boundary strengthening superalloys utilize the effect of grain boundaries on the movement of dislocations. The finer the grains and the more the grain boundaries, the greater the blocking effect and the better the effect of strengthening. The grain boundary can limit the plastic deformation to a certain range to make the plastic deformation uniform, so refining the grain can improve the plasticity of the steel. The grain boundary is also an obstacle to crack propagation, so grain refinement can improve toughness, and grain boundary strengthening is the only way to increase strength without compromising its toughness.