Advanced high temperature alloy preparation process

(HY industry- Technical Center internal data)

  • In the world advanced engine development, the high temperature alloy material has accounted for 40%~60% of the total engine.Therefore, the high temperature alloy material is also known as “advanced engine cornerstone”.During this time, we will take you to a deep understanding of advanced high temperature alloy preparation, analysis and testing and application.

  • High temperature alloy, just as its name implies is at a high temperature (above 900 ℃) environment, and to a certain long time service of alloy under stress conditions.High temperature alloy is divided into three kinds of material: 760 ℃ high-temperature material, high temperature of 1200 ℃ and 1500 ℃ high temperature materials, the tensile strength of 800 mpa.Or refers to the 760-1500 ℃ above and the conditions of stress, the long-term work of the high temperature metal material, has excellent high temperature strength, good resistance to oxidation and thermal corrosion resistance, good fatigue properties, fracture toughness and other comprehensive performance, has become a military and civilian use of gas turbine engine hot end components an irreplaceable key materials

Aero – engine single crystal blade made of high – temperature alloy

  • In the broad sense, high-temperature alloy refers to a kind of alloy that can resist oxidation or corrosion at high temperature and can work for a long time under certain stress, including casting high-temperature metal materials such as high-temperature alloy and intermetallic compound.In a narrow sense of high temperature alloys based on iron, nickel, cobalt, can under the high temperature of about 600 ℃ or more oxidation or corrosion, and can work under certain stress for a long time of a kind of alloy.Since the beginning of the high temperature alloy from the old iron, nickel and cobalt as the base, the development and evolution, as well as the introduction of new processing technology, from the traditional deformation of casting high temperature alloy and high temperature alloy, develop high temperature alloy powder, the oxide dispersion strengthened (ODS) alloys, intermetallic compounds, such as new type of high temperature alloy, thus greatly extend the connotation of high temperature alloy.

  • High-temperature alloys can be roughly divided into the following categories:

Makeway classification characteristics Military applications
Cast superalloy Such as shaft polycrystalline High alloy degree, various strengthening means, good forming performance, higher working temperature than deformed high temperature alloy. Pan wheel blade, aerospace engine castings
Directional solidification of column crystals When used above 1000 degree, the performance is better than that of equiaxed polycrystalline Aero – engine blade, guide blade, etc
Single crystal Over 1200 degrees, with strong properties of high temperature alloy The next generation aero engine wainwheel blades, its nature largely determines the development of aero engine
Deformed superalloy Iron base deformation superalloy Used below 700 degrees, nickel content is less than 50%, weak antioxidant Turbine disc, combustor parts used in China in the 1950s
Nickel base deformation superalloy Use above 650-1000 degree, nickel content is higher than 50%, good thermal performance It is widely used in space engine plate, bar, plate forging and combustor etc.
Cobalt base deformation superalloy 730-1000 degree usage, upgrade version of nickel base alloy. Cobalt metal is very rare, belong to strategic resource, application is very few
New type superalloy Powder metallurgy high temperature alloy The temperature can be up to 1000 degrees, the structure is uniform, the thermal processing performance is good, the thermal fatigue is good Aerospace engine turbine disk, turbine baffle, drum shaft
ODS High temperature alloy High temperature, high yield strength and high temperature creep Space engine I wheel disc, seal plate, turbine baffle
Intermetallic compound superalloy High temperature has good oxidation resistance, high stiffness, low density and good elastic modulus Aerospace structural and engine components

 

  • The high temperature alloy mainly serves for the aerospace industry in the material industry.With the development of aerospace industry, China has established its own high temperature alloy system, thus forming a certain industrial scale.Due to its excellent properties such as high temperature resistance, corrosion resistance and fatigue resistance, high-temperature alloy has been gradually applied to the industrial fields such as electricity, automobile, metallurgy, glass manufacturing and atomic energy, thus greatly expanding the demand for high-temperature alloy.

  • High temperature alloy preparation process.

  • The properties of high temperature and corrosion resistance of high temperature alloy mainly depend on its chemical composition and microstructure.

  • The high temperature alloy material has complex composition, contains active elements such as chromium and aluminum, and presents chemical instability in the environment of oxidation or thermal corrosion. At the same time, defects such as machining hardening and residual stress are left on the surface of the machined parts, which bring adverse effects on the chemical and mechanical properties of the materials.Due to high alloying degree, composition segregation is very easy to occur in high temperature alloy. This segregation has great influence on the microstructure and properties of cast high temperature alloy and deformation high temperature alloy.These characteristics of high temperature alloy determine its processing technology different from ordinary metal materials

  • The development of high temperature alloy is a process of constant improvement and innovation of alloy theory and production technology.The strengthening of alloy includes solid solution strengthening of alloy and grain boundary strengthening of second phase fortifier.The process strengthening includes improving the structure of alloy, such as smelting, solidification crystallization, hot processing, heat treatment and surface treatment.

  • The production process of high temperature alloy mainly includes smelting, casting and heat treatment.The production process has a great impact on the mechanical properties of high-temperature alloy materials. The introduction of a new process often makes a leap in the performance of high-temperature alloy, and develops a batch of new high-temperature alloys, thus promoting the development of a generation of aero-engines and aircraft.Older alloys can also improve processes to improve material properties.

  • The preparation technology and technology of high temperature alloy material are still in progress and innovation.For example, the smelting process adopts the triple process of vacuum induction + electroslag remelting + vacuum proud smelting, and the vacuum self-consumption smelting adopts the advanced smelting control method.The high temperature strength of the material is improved by directional solidification column crystal alloy and single crystal alloy technology.The method of powder metallurgy is adopted to reduce the segregation of alloying elements and improve the strength of materials.In addition, oxide dispersion strengthened superalloy and intermetallic compound high temperature materials are also developing and innovating.

  • Powder metallurgy oxide dispersion strengthened (ODS) high temperature alloy preparation process

  • Powder metallurgy superalloy was developed in 1960 s, an advanced high temperature alloy preparation process due to the use of very fine metal powder as raw material, through thermal consolidation molding and subsequent thermal processing of uniform microstructure, grain fine, no macro segregation phenomenon, and the alloy of high temperature strength, creep properties and fatigue performance is excellent, so soon becomes the heat-resistant parts of aeroengine, the nuclear industry preferred material

  • High temperature oxide dispersion strengthened (ODS) alloy is a kind of high temperature alloy powder, its outstanding characteristic is under high temperature (1350 ℃ 1000 a) with high strength.For conventional superalloys and powder superalloys,Y ‘precipitated phase and carbon (nitrogen) compounds are the main strengthening methods.But at high temperature,Y’ precipitated phase and carbon (nitrogen) compounds become coarsened and dissolved in the matrix and lose the strengthening effect.

  • Oxide dispersion strengthened (ODS) high temperature alloy is a kind of alloy that disperses fine oxide particles (usually Y2O3) evenly in the matrix of high temperature alloy.

  • In the developed superalloy, precipitation reinforcement is often used to improve the strength of the material. When the service temperature of the material reaches a critical value, the precipitate phase will inevitably accumulate, grow up and dissolve, thus greatly reducing the high-temperature strength of the material.Therefore, the high temperature strength of the material is improved by adding fine oxides with high stability at high temperature into the alloy matrix through powder metallurgy.However, conventional smelting and metallurgical techniques make it impossible to uniformly add such fine oxides (d < 50nm) into the matrix, thus limiting the development of such oxide dispersion-reinforced alloys.Until the early 1970s, INCO pioneered a new mechanical alloying (MA) process, which solved the problem of uniform distribution of ODS alloy oxides and led to rapid development of alloys, some of which have reached the industrial production level.

HY-industry products grad:

  • inconel 600,inconel 601,inconel 625,inconel 825
  • incoloy 800,incoloy 800HT,incoloy 901,incoloy 926
  • monel 400,monel K500
  • nimonic 901, nonomic 80A,nimonic 90

Preparation of powder

  • There are three kinds of powder making processes: gas atomization, rotary electrode and vacuum atomization.However, the preparation method of ODS high-temperature alloy powder is different from the method mentioned above.The following four methods are commonly used:

  1. mechanical alloying (MA) method

  2. Mechanical alloying is the process of achieving solid alloying with high-energy grinding machines or ball mills. Developed by INCO in the late 1960s, mechanical alloying is the most effective method to realize micro mixing of heterogeneous materials.Currently,ODS high-temperature alloys mostly use MA technology to evenly disperse ultrafine oxide particles into the alloy matrix.The compacted alloy materials can be obtained by mechanical alloying powder containing dispersed oxide particles after consolidation treatment. Mechanical alloying is one of the key technologies to prepare ODS high temperature alloys.

  3. internal oxidation‍

  4. The internal oxidation method is to use the alloying element with a small content in the alloy and a strong affinity to oxygen to react with oxygen to form the oxide particle as the dispersed phase.

  5. chemical coprecipitation

  6. The principle of chemical coprecipitation method is to add appropriate precipitant in the prepared solution and control pH value within the appropriate range to prepare the precursor precipitate of ultrafine particles, and then through aging, filtration, washing, drying and thermal decomposition to obtain nano-scale composite oxide powder.

  7.  pre-alloy atomized powder

  8. The pre-configured alloy was melted under the protection of inert gases in the process of atomization. Oxygen was added to the atomized gas to oxidize and increase oxygen during the condensation process. The oxygen content in the atmosphere was controlled to obtain the atomized gas with different oxygen content.

thermosetting

  1. Loose superalloy powders can only be densified by consolidation process.The main methods of consolidation are hot isostatic pressure (HIP), hot extrusion, etc.

  2. Hot isostatic pressing (HIP)

  3. Hot isostatic pressure is a process of forming powder by high temperature and high pressure under vacuum condition.

  4. The key of hot isostatic pressure technology is the control of temperature, pressure and time. First of all, the temperature of hot isostatic pressure should not be too high, which can avoid the growth of dispersion phase.Secondly, the pressure selection of thermal isostatic pressure should be higher than the yield stress of the corresponding temperature alloy, so that the powder particles can effectively deform and undergo metallurgical bonding, eliminate the gap between materials and improve the density of the alloy.The choice of holding time is also critical. The microstructure of the densified alloy changes under high temperature and pressure for too long, and the compaction is not effective for too short time.

  5. hotextrusion (hotextrusion,HE)

  6. ODS high temperature alloy is usually consolidated by hot extrusion process, which can be either directly extruded by the powder jacket or compacted by hot isostatic pressing before secondary extrusion, as shown in the figure.

  7. process of preparation of ODS alloy by hot extrusion

  8. During hot extrusion, large shear force can effectively eliminate the original particle boundary and greatly increase the density of the alloy.High density dislocation is formed in the process of large plastic deformation, which increases the energy storage of the alloy, which is conducive to the formation of larger grains in the subsequent heat treatment process and improves the high-temperature performance of the alloy.Extrusion ratio, extrusion rate and the temperature are the main factors of microstructure and mechanical properties of ODS alloys, usually, in a larger extrusion ratio, low extrusion temperature and extrusion speed under thermal consolidation molding, alloy internal can form high dislocation density distribution and energy storage, conducive to the spread of the alloying elements and the formation of Y – Ti – zero phase, at the same time, after heat treatment can be formed along the extrusion direction of columnar grain structure, can effectively improve the high temperature creep properties of the alloy

  9. Compared with thermal isostatic pressure consolidation forming, hot extrusion can produce more deformation capacity and higher density compact body, and the structure and properties of alloy are quite different.

  10. Thermal mechanical treatment

  11. Through thermal mechanical treatment, the porosity of powder metallurgy alloy can be further reduced and the density can be increased. Meanwhile, the microstructure of the alloy can be more uniform, and the original powder particle boundary can be further formed into metallurgical bond.

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