WO2020189215A1 - Matériau d'alliage d'aluminure de titane pour forgeage à chaud, procédé de forgeage pour matériau d'alliage d'aluminure de titane, et corps forgé - Google Patents

Matériau d'alliage d'aluminure de titane pour forgeage à chaud, procédé de forgeage pour matériau d'alliage d'aluminure de titane, et corps forgé Download PDF

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WO2020189215A1
WO2020189215A1 PCT/JP2020/007922 JP2020007922W WO2020189215A1 WO 2020189215 A1 WO2020189215 A1 WO 2020189215A1 JP 2020007922 W JP2020007922 W JP 2020007922W WO 2020189215 A1 WO2020189215 A1 WO 2020189215A1
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forging
phase
alloy material
temperature
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PCT/JP2020/007922
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Japanese (ja)
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圭司 久布白
祐太朗 大田
聰 高橋
雅夫 竹山
広豊 中島
遼介 山形
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株式会社Ihi
国立大学法人東京工業大学
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Priority to EP20773214.0A priority Critical patent/EP3943627A4/fr
Priority to JP2021507142A priority patent/JP7233659B2/ja
Publication of WO2020189215A1 publication Critical patent/WO2020189215A1/fr
Priority to US17/447,479 priority patent/US20210404042A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18—High-melting or refractory metals or alloys based thereon
    • C22F1/183—High-melting or refractory metals or alloys based thereon of titanium or alloys based thereon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J5/00—Methods for forging, hammering, or pressing; Special equipment or accessories therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C14/00—Alloys based on titanium

Definitions

  • the present disclosure relates to a titanium aluminide alloy material for hot forging, a forging method of a titanium aluminide alloy material, and a forged body.
  • the TiAl (titanium aluminide) alloy is an alloy composed of an intermetallic compound of Ti (titanium) and Al (aluminum). TiAl alloys have excellent heat resistance, are lighter in weight and have higher specific strength than Ni-based alloys, and are therefore applied to aircraft engine parts such as turbine blades. However, since TiAl alloy is a difficult-to-process material due to its poor ductility, constant temperature forging is performed when hot forging is performed.
  • Patent Document 1 describes the effect of improving material properties by an additive element based on a titanium aluminized alloy. Further, Japanese Patent Application Laid-Open No.
  • Patent Document 2 proposes a TiAl alloy containing 40.0 to 42.8 atomic% of Al, which has excellent high-temperature strength and can be used as a hot forging material. It is stated that.
  • Patent Document 3 describes a method for processing a titanium aluminide alloy containing niobium, and teaches that it is used for manufacturing structural parts.
  • the processing of TiAl alloy by constant temperature forging is carried out at a low strain rate by keeping the mold and TiAl alloy material at almost the same temperature. Therefore, the forging material and the die are exposed to a high temperature, and the forging device including the peripheral parts thereof is also thermally affected. Therefore, if the forging temperature is high, the durability of the forging device or the like tends to decrease depending on the size of the heat load. .. For this reason, it is desired to realize forging at a lower temperature so that a general-purpose hot working method can be applied to the TiAl alloy material. For that purpose, it is necessary to improve the hot workability of the TiAl alloy material.
  • an object of the present disclosure is to provide a forging method of a titanium aluminide alloy material and a titanium aluminide alloy material for hot forging with improved workability during hot forging, and to provide a forged body of excellent quality. Is.
  • the titanium aluminide alloy material for hot forging is aluminum having an atomic number ratio of 43.0% or more and 45.0% or less, and 4.0% or more and 6.0%.
  • the gist is that it has a chemical composition consisting of the following niobium, 1.5% or more and 3.5% or less of chromium, and the remaining titanium and unavoidable impurities.
  • the titanium aluminide alloy material for hot forging includes aluminum having an atomic number ratio of 43.0% or more and 45.0% or less, and 4.0% or more and 6 Have a chemical composition consisting of 0.0% or less niobium, 1.5% or more and 3.5% or less chromium, 0% or more and 0.25% or less boron, and the balance of titanium and unavoidable impurities. Is the gist.
  • the hot forging method of the titanium aluminide alloy material includes the step of preparing the titanium aluminide alloy material for hot forging and the ⁇ phase in the state diagram of the titanium aluminide alloy material.
  • the forging temperature is set to a temperature within the phase equilibrium temperature region of either the ( ⁇ + ⁇ ) phase or the ( ⁇ + ⁇ + ⁇ ) phase, and the titanium aluminide alloy material is forged while being maintained at the forging temperature in a non-oxidizing atmosphere.
  • the gist is to have a hot forging process.
  • the forging temperature in the hot forging step can be 1200 ° C. or higher and 1300 ° C. or lower.
  • the hot forging method for the titanium aluminide alloy material further includes a first heat treatment for heating the titanium aluminide alloy forged product obtained by the hot forging step to a temperature of 1240 ° C. or higher and 1290 ° C. or lower, and the first heat treatment. It is preferable to have a second heat treatment for holding the titanium aluminide alloy forged product that has undergone the heat treatment at 900 ° C. or higher and 1100 ° C. or lower for 1 hour or longer. The temperature of the titanium aluminide alloy forged product that has undergone the first heat treatment may be lowered once before the second heat treatment.
  • the titanium aluminide alloy forged product contains aluminum having an atomic number ratio of 43.0% or more and 45.0% or less, and 4.0% or more and 6.0% or less. It has a chemical composition of niobium, 1.5% or more and 3.5% or less of chromium, the balance of titanium, and unavoidable impurities, and has a lamella structure crystal grain, a ⁇ phase crystal grain, and a ⁇ phase crystal grain. It has a metal structure including crystal grains, and the gist is that the volume ratio of the ⁇ phase in the metal structure is 80% or more.
  • the titanium aluminide alloy forged product contains 43.0% or more and 45.0% or less of aluminum and 4.0% or more and 6.0% or less in terms of atomic number ratio. It has a chemical composition of niobium, 1.5% or more and 3.5% or less of chromium, more than 0% and 0.25% or less of boron, and the balance of titanium and unavoidable impurities. It has a metal structure including particles, ⁇ phase particles, ⁇ phase particles, and boron particles, and the gist is that the volume ratio of the ⁇ phase in the metal structure is 80% or more.
  • hot forging of a TiAl alloy material is possible by constant temperature forging in which the forging temperature is set to a lower temperature. Therefore, the TiAl alloy material is forged by using a forging technique for a general metal. Is possible. Therefore, it is possible to contribute to the spread of TiAl alloy materials by improving economic efficiency in manufacturing processing costs, maintenance costs of manufacturing equipment, etc., and improving manufacturing efficiency of products.
  • SEM scanning electron microscope
  • Ti titanium
  • Ti titanium
  • ⁇ phase ⁇ -Ti
  • elements such as Mo (molybdenum), V (vanadium), Nb (niobium), Fe (iron), Cr (chromium), and Ni (nickel) are added, these elements become ⁇ phase ( ⁇ -Ti). It acts to stabilize the alloy and lowers the transformation temperature of the alloy.
  • the TiAl (titanium aluminide) alloy is an alloy material composed of TiAl ( ⁇ phase), Ti 3 Al ( ⁇ 2 phase), and the like, which are intermetallic compounds of Ti (titanium) and Al (aluminum). It is known that the TiAl alloy can be hot-worked by constant temperature forging at a forging speed with little strain. However, if the hot workability of the TiAl alloy is improved and constant temperature forging at a lower temperature becomes possible, the heat load of the forging equipment and the like will be reduced and the economic efficiency in manufacturing will be improved. Can be expanded.
  • a TiAl alloy material for hot forging (hereinafter, may be referred to as a TiAl alloy material for forging) having improved hot workability so that constant temperature forging at a lower temperature is possible is presented. ..
  • a method for producing a TiAl alloy material for hot forging and a method for forging a TiAl alloy material for hot forging will also be presented.
  • the hot workability of the TiAl alloy is improved by designing the chemical composition of the TiAl alloy so that the ⁇ -phase region in the phase diagram expands to the low temperature side.
  • the titanium aluminide alloy material (TiAl alloy material) for forging in the present disclosure is a molten material composed of a TiAl alloy containing an element that stabilizes the ⁇ phase, and the metal structure is ⁇ at the target forging temperature. It has a chemical composition designed to contain phases.
  • the TiAl alloy material for forging may contain B (boron) in addition to the above-mentioned constituent components, and the addition of boron is optional.
  • B boron
  • the addition of boron refines the crystal grains in the metallographic structure and enhances the ductility of the TiAl alloy material at high temperatures. Therefore, if necessary, boron can be added to the TiAl alloy material for forging within a suitable content range.
  • the metal structure thereof becomes a state in which a ⁇ phase is contained. Since the ⁇ phase has low high-temperature strength but is a soft phase, the TiAl alloy material containing the ⁇ phase in the metal structure can be easily forged.
  • the TiAl alloy forged product that has been forged and cooled to room temperature may contain a ⁇ phase in the metal structure, but the ⁇ phase can be modified in properties by heat treatment. That is, the properties of the alloy can be improved by heat-treating the forged body. Specifically, the high temperature strength can be increased by performing a heat treatment that produces a ⁇ phase.
  • Forging was cooled through a heat treatment is constituted by TiAl alloy material exhibiting a lamellar tissue (approximately 20 tissue volumes% of alpha 2 phase precipitated in layers in ⁇ phase) and ⁇ phases dispersed metal structure.
  • TiAl alloy material exhibiting a lamellar tissue (approximately 20 tissue volumes% of alpha 2 phase precipitated in layers in ⁇ phase) and ⁇ phases dispersed metal structure.
  • the TiAl alloy has a ⁇ phase in the metal structure at a high volume fraction of 80% or more, the forged product can exhibit high fracture ductility.
  • the TiAl alloy material for hot forging is composed of a TiAl alloy containing Ti and Al as main components, and contains a ⁇ -phase stabilizing element.
  • Nb (niobium) and Cr (chromium) are used as ⁇ -phase stabilizing elements.
  • the TiAl alloy material has an atomic number ratio of 43.0% or more and 45.0% or less of aluminum, 4.0% or more and 6.0% or less of niobium, and 1.5% or more.
  • the TiAl alloy material may further contain B (boron), if necessary.
  • the TiAl alloy material contains boron and has an atomic number ratio of 43.0% or more and 45.0% or less of aluminum, 4.0% or more and 6.0% or less of niobium, and 1. It has a chemical composition of 5% or more and 3.5% or less of chromium, 0% or more and 0.25% or less of boron, and the balance of titanium and unavoidable impurities.
  • the content of Al (aluminum) in the TiAl alloy constituting the TiAl alloy material for hot forging is preferably 43 atomic% or more and 45 atomic% or less.
  • the lower limit of the Al content is set to 43 atomic%.
  • the Al content in the alloy composition in which a lamellar structure having excellent high-temperature strength and toughness is formed is 47 to 48 atomic%, whereas the upper limit of the Al content in the TiAl alloy material for forging of the present disclosure is 45.
  • the metal structure of the TiAl alloy material may contain TiAl particles ( ⁇ phase) and Ti particles ( ⁇ phase) together with the crystal particles of the lamella structure. If the Al content is higher than 45.0 atomic%, the high temperature forging property of the TiAl alloy material is lowered, and a high forging temperature is required.
  • Nb (niobium) and Cr (chromium) are ⁇ -phase stabilizing elements having an action of stabilizing the ⁇ -phase in the metal structure.
  • Each of the ⁇ -phase stabilizing elements is effective in lowering the transformation temperature when used alone, and the region where the ⁇ -phase exists in the phase diagram can be expanded to the low temperature side.
  • Nb and Cr are used together in the present disclosure. As a result, the peak stress in the TiAl alloy is remarkably reduced, and the forgeability is remarkably improved.
  • Nb and Cr are elements that undergoes an eutectoid reaction and shows a ⁇ eutectoid phase diagram, but its ⁇ stabilizing performance is greater than that of Nb.
  • the ⁇ phase can be synergistically stabilized, so the Cr content can be kept low to avoid deterioration of workability due to precipitation of the ⁇ phase, and the high temperature deformability can be effectively enhanced. be able to. Therefore, hot forging of TiAl alloys at lower temperatures is possible.
  • the addition amounts of Nb and Cr may be set so as to be 5.5 atomic% or more and 9.5 atomic% or less in total.
  • the ratio of Nb content / Cr content is preferably about 1.7 to 2.6, preferably about 2.0. In such a range, the ⁇ phase can be suitably stabilized while preventing embrittlement due to the eutectoid reaction of Cr.
  • Nb is an element effective for improving oxidation resistance and strength.
  • the Nb content is preferably 4 atomic% or more and 6 atomic% or less.
  • the ⁇ phase can be satisfactorily formed in the heated state at the time of forging. If the Nb content is less than 4 atomic%, the ⁇ phase is not sufficiently stabilized, and it is difficult to obtain the effect of improving ductility by using it in combination with Cr, so that it is difficult to improve the forgeability of the TiAl alloy. If it exceeds 6 atomic%, segregation may occur and the specific gravity of the TiAl alloy increases.
  • the Cr is a ⁇ -phase stabilizing element having a high ⁇ -phase stabilizing effect, and its addition improves the forgeability and room temperature ductility of the TiAlTiAl alloy.
  • the Cr content may be set to 1.5 atomic% or more and 3.5 atomic% or less. If the Cr content is less than 1.5 atomic%, the ductility of the TiAl alloy is not sufficiently improved, and if it exceeds 3.5 atomic%, the TiAl alloy may become brittle and its strength may decrease.
  • B (boron) has a function of refining the crystal grains generated in the metal structure and increasing the ductility of the TiAl alloy.
  • the addition of B increases the ductility of the TiAl alloy in the temperature range of 1100 ° C. or higher, and the increase in ductility is particularly remarkable at 1200 ° C. or higher.
  • B has a function of increasing ductility at high temperature, and is therefore effective in improving hot forging property.
  • B has an effect of lowering the deformation resistance at the time of forging by adding it in combination with Nb and Cr which are ⁇ -phase stabilizing elements, and is also effective in improving the forging property in this respect.
  • the addition of B is optional, and when added, the content of B in the TiAl alloy is preferably more than 0 atomic% and 0.25 atomic% or less. As the content of B increases, the particle size of the crystal grains generated in the structure can be reduced to 200 ⁇ m or less, and the particle size can be suppressed to 100 ⁇ m or less.
  • the ductility of the TiAl alloy is improved by the refinement of the crystal grains. However, in the range where the B content exceeds 0.25 atomic%, the effect of further refinement of the crystal grains is hardly obtained, and the toughness is rather lowered. Therefore, the B content is 0.25 atomic% or less. It is good to set to.
  • boride having a size of more than 100 ⁇ m is likely to be formed during the preparation of the TiAl alloy material by casting, so that the ductility is rather lowered and the forgeability is lowered.
  • This boride is composed of TiB, TiB 2, etc., and precipitates in a needle-like shape.
  • the particle size of the crystal grains generated in the metal structure of the TiAl alloy material is 200 ⁇ m or less. .. Boride is contained in such crystal grains and occurs as particles having a particle size of 100 ⁇ m or less. By making such precipitated particles finer, the ductility of the TiAl alloy is increased, and the forgeability can be improved. Further, in the TiAl alloy that has been forged and heat-treated, the boride is finely precipitated as particles having a particle size of 100 ⁇ m or less in the crystal grains of the metal structure, thereby improving the mechanical strength of the TiAl alloy.
  • the grain size of the crystal grains shown in the present disclosure means the area average grain size converted from the area of the crystal grains by image analysis of the cross section of the metal structure.
  • Ti reacts with gas components in air and atmosphere at high temperature, and may contain impurities such as oxygen and nitrogen due to surface oxidation and internal diffusion of impurities.
  • Al can also contain oxygen by surface oxidation.
  • the TiAl alloy material for forging may contain such unavoidable impurities.
  • the method for producing a TiAl alloy material for forging includes a casting step of casting a TiAl alloy material by heating and melting a raw material whose overall composition is the chemical composition of the TiAl alloy material described above.
  • the raw material may be in any form of powder, metal pieces or metal ingots, or may be in a mixed form of two or more of these.
  • the powder, the metal piece, and the metal ingot may all be in the state of a simple metal as a component of the TiAl alloy material or an alloy of a plurality of components.
  • the raw material can be appropriately selected from the forms such as a mixture of simple metals, a mixture of simple metals and alloys, a simple substance of alloys, and a mixture of alloys and alloys.
  • the raw material can be prepared by blending each component so as to have the chemical composition of the above-mentioned TiAl alloy material as a whole.
  • a raw material prepared in advance to the above chemical composition may be obtained and used.
  • the boron content is 0.2 atomic% or more and 1.0 atomic% or less in consideration of loss during preparation, measurement error, and the like. It is preferable to mix them in such a manner as to be 0.5 atomic% or more and 1 atomic% or less.
  • a melting process of heating and melting the raw material prepared as described above and a molding process of cooling the melted raw material and casting it into an ingot (ingot) or the like are performed.
  • a molten TiAl alloy material having the above-mentioned chemical composition can be obtained, and this can be used as a TiAl alloy material for forging.
  • Casting may be performed by appropriately utilizing the melting technique and the casting technique generally used for casting a metal material. Examples thereof include a vacuum arc melting-centrifugal casting method, a melting-casting method (LEVICAST method), and a precision casting technique combining a face-coated crucible and centrifugal casting.
  • the apparatus used in the casting step may be any apparatus capable of preventing reactions such as contamination of impurities and oxidation, and a casting apparatus such as a vacuum induction furnace can be used.
  • HIP (hot hydrostatic pressure press) treatment may be performed on the molten material obtained by casting. Internal defects such as casting defects can be suppressed by HIP treatment.
  • a HIP apparatus used in the HIP treatment of a general metal material can be used.
  • the method for producing a TiAl alloy material for forging may further include a surface treatment for removing the casting surface (surface layer) on the surface of the molten TiAl alloy material obtained by the casting process.
  • a surface treatment for removing the casting surface (surface layer) on the surface of the molten TiAl alloy material obtained by the casting process.
  • Surface processing can be performed by cutting, grinding, or the like.
  • the TiAl alloy material for forging can be processed into a TiAl alloy forged body having a desired shape according to the following hot forging method. That is, the hot forging method of the TiAl alloy material includes a step of preparing a TiAl alloy material for hot forging having the above-mentioned chemical composition and a TiAl alloy material for hot forging at a forging temperature in a non-oxidizing atmosphere. It has a hot forging step of heating and forging while maintaining the forging temperature.
  • the above-mentioned surface processing can be included in the step of preparing the TiAl alloy material for hot forging.
  • the forging temperature is set in the phase equilibrium temperature region in which the ⁇ phase can exist in the phase diagram of the TiAl alloy, that is, the temperature within the phase equilibrium temperature region of any one of the ⁇ phase, the ( ⁇ + ⁇ ) phase and the ( ⁇ + ⁇ + ⁇ ) phase.
  • the forging temperature may be set as follows with reference to the phase diagram of the TiAl alloy.
  • FIG. 1 the relationship between the content of ⁇ -phase stabilizing elements (total of Nb and Cr contents [atomic%]) and the phase equilibrium state of the TiAl alloy was investigated with Ti-44 atomic% Al as the basic composition. It is a state diagram. For alloys with a ⁇ -phase stabilizing element content in the range of 5.5 to 9.5 atomic%, when the temperature is raised from room temperature by heating, the phase states of the alloy are ( ⁇ + ⁇ ) phase and ( ⁇ + ⁇ + ⁇ ) phase. , And changes to the ⁇ phase via the ( ⁇ + ⁇ ) phase.
  • the ( ⁇ + ⁇ ) phase and the ⁇ phase can be passed between the ( ⁇ + ⁇ + ⁇ ) phase and the ( ⁇ + ⁇ ) phase, but the ⁇ single phase The area is small. Therefore, it is easy to suppress the coarsening of ⁇ -phase particles in the process of temperature change.
  • the ⁇ phase is present in the alloy at a temperature of 1200 ° C. (1473 ° K.) or higher, preferably 1250 ° C. (1523 ° K.) or higher, and the forgeability is improved. Therefore, the forging temperature can be set to 1200 ° C. or higher, preferably 1250 ° C. or higher.
  • the upper limit of the forging temperature can be set within a range in which the ⁇ phase can exist, but the TiAl alloy material having the above-mentioned chemical composition can be suitably forged at a temperature of 1300 ° C. (1573 ° C.) or less. Therefore, this temperature may be set as an upper limit from the viewpoint of durability of the forging device or the like.
  • the forging temperature can be set in the range of about 1200 ° C. or higher and about 1300 ° C. or lower based on the phase diagram, and it is preferable to carry out constant temperature forging while maintaining the temperature of the TiAl alloy material in this range.
  • the hot forging process should be performed in a non-oxidizing atmosphere to prevent oxidation.
  • the non-oxidizing atmosphere include an atmosphere of an inert gas such as argon gas.
  • the forging method can be appropriately selected and applied from general metal material forging methods such as free forging, mold forging, rotary forging, and extrusion forging, and an appropriate forging device is appropriately selected according to the applied forging method. You can use it.
  • the TiAl alloy material for hot forging in the present disclosure can also be used in hot pressing and hot rolling.
  • the mold temperature is preferably about 700 ° C. or higher from the viewpoint of maintaining the temperature of the TiAl alloy material.
  • the processing by hot forging can be suitably carried out at a strain rate of about 0.1 / sec or more. Since the peak stress of the TiAl alloy material is small and the deformation resistance is low, it is possible to perform a good forging process without forging cracks even at a strain rate of about 1 to 10 / sec.
  • the TiAl alloy material heated to the forging temperature has improved high-temperature ductility due to the presence of the ⁇ phase in the metal structure, and the plastic deformation due to forging proceeds well.
  • Forging reduces casting defects in the TiAl alloy material and breaks the metallographic structure into fine crystalline granules. The larger the degree of processing in forging, the finer the metal structure can be. Forging processing with an effective strain of about 0.5 to 1 is possible.
  • the titanium aluminide alloy forged body (TiAl alloy forged body) obtained through the hot forging process is once cooled.
  • the cooling may be cooling inside the forging device or air cooling outside. Since the chemical composition of the TiAl alloy material for hot forging is designed to stabilize the ⁇ phase, coarsening of crystal grains due to the growth of the ⁇ phase in the metal structure is suppressed during cooling after forging. ..
  • the method for forging the TiAl alloy material may further include a heat treatment applied to the forged body obtained by the hot forging step.
  • the heat treatment may be performed in a non-oxidizing atmosphere to prevent oxidation.
  • the non-oxidizing atmosphere include an inert gas atmosphere such as argon gas, a vacuum atmosphere, and a reducing atmosphere such as hydrogen gas.
  • the heat treatment of the TiAl alloy forged product may include a first heat treatment step and a second heat treatment step.
  • the first heat treatment step the TiAl alloy forged product obtained by the forging step is heated to a temperature of 1240 ° C. or higher and 1290 ° C. or lower. This heating temperature is in the phase equilibrium temperature region of either the ( ⁇ + ⁇ ) phase or the ( ⁇ + ⁇ + ⁇ ) phase in the phase diagram, and the TiAl alloy constituting the forged product is in a state in which the ⁇ phase can exist.
  • the first heat treatment step may be performed so that the internal temperature of the TiAl alloy forged body reaches the above temperature range. Therefore, the processing time of the first heat treatment step can be generally set to about 15 minutes or more, and it is practical to set it in the range of about 1 to 5 hours.
  • the forged body that has undergone the first heat treatment should be cooled before the second heat treatment to temporarily lower the temperature.
  • the TiAl alloy forged product at room temperature that has undergone the first heat treatment step is held at a temperature of 900 ° C. or higher and 1100 ° C. or lower for 1 hour or longer.
  • the heating temperature is maintained for 1 hour or more and 5 hours or less.
  • the TiAl alloy forged product that has undergone the second heat treatment is then cooled to around room temperature.
  • the stress strain of the crystal grains due to forging is relaxed, and new crystal grains without strain are generated in place of the particles deformed by the strain.
  • the ⁇ phase generated in the TiAl alloy is dispersed and precipitated as fine crystal grains. That is, the first heat treatment acts as a recrystallization treatment.
  • the second heat treatment step has an effect as an aging treatment for alleviating strain at the grain boundaries.
  • the TiAl alloy constituting the forged product exhibits a metal structure having lamellar structure crystal grains, ⁇ phase crystal grains and ⁇ phase crystal grains (see FIG. 5 described later).
  • the ⁇ -phase stabilizing element dissolves in Ti.
  • the forged TiAl alloy is heat-treated to precipitate fine boride in the crystal grains in the form of needles. Therefore, the TiAl alloy constituting the forged body contains a metal structure containing fine boride particles having a particle size of about 0.1 ⁇ m or less, in addition to lamella structure crystal grains, ⁇ phase crystal grains and ⁇ phase crystal grains.
  • Boride particles are composed of TiB, TiB 2, and the like.
  • the TiAl alloy for forging is designed to have a chemical composition that easily suppresses coarsening of crystal grains in the process of temperature change, and high-temperature processability is improved by improving ductility. Therefore, hot forging can be performed at a larger strain rate while suppressing forging cracks.
  • hot forging is performed at a low strain rate of about 5 ⁇ 10 -5 / sec to 5 ⁇ 10 -1 / sec, but in the TiAl alloy for forging of the present disclosure, the peak is reached. Stress is kept low.
  • forging can be performed at a large strain rate of 1 / sec or more, and high-speed forging at a strain rate of 10 / sec or more is also possible, so that the productivity of parts such as turbine blades can be improved.
  • the forged TiAl alloy body that has undergone the forging process can be heat-treated to improve ductility and impart durability. Therefore, the TiAl alloy material for forging is useful as a forging material for manufacturing aircraft engine parts such as turbine blades by hot forging.
  • Sample 1 Ti-44.4Al-4.1Nb-5.2V
  • Sample 2 Ti-43.7Al-4.1Nb-5.1V-0.1C
  • Sample 3 Ti-43.9Al-4.1Nb-5.1V-0.2C
  • Sample 4 Ti-44.7Al-3.7Nb-3.5V
  • Sample 5 Ti-44.6Al-3.6Nb-3.8V-0.07B
  • Sample 6 Ti-45.9Al-5.3Nb-4.0V-0.15B
  • Sample 7 Ti-43.6Al-5.2Nb-2.6Cr-0.15B
  • Sample 8 Ti-43.0Al-4.0Nb-1.0Mo-0.15B
  • test piece for the compression test As a test piece for the compression test, a mold having a predetermined shape was used in the preparation of the above-mentioned sample, and samples (samples 1 to 8) of TiAl alloy material for forging corresponding to the shape of the mold were prepared. The following compression test was performed on each sample using the test piece.
  • the temperature was kept constant in the range of 1150 to 1300 ° C., and a load was applied to the test piece sandwiched between the two parallel plate surfaces of the test device to perform 0.01 / sec, 0.1 / sec, 1 / sec and so on.
  • a compression test was performed at each strain rate of 10 / sec to obtain a true stress-true strain curve up to true strain 1.2. The maximum stress in this curve was obtained as the peak stress.
  • the strain rate was taken as the true strain strain rate.
  • the relationship between the temperature and the peak stress was obtained by repeating the above-mentioned compression test while changing the temperature within the above range. The results are shown in FIG.
  • the peak stress in the TiAl alloy material is remarkably suppressed to be low in the sample 7, and it is clear that the forging property of the sample 7 at a low temperature is much higher than that of the other samples.
  • the peak stress of sample 7 corresponds to a value at a temperature higher than about 50 ° C. in other samples. Therefore, it can be considered that the forging can be performed at a temperature lower than that of other samples by about 50 ° C. or more, and the forging temperature can be set to about 1200 to 1300 ° C. It is considered that such improvement in forgeability is due to the composition in which both Nb and Cr are added.
  • Example 9 (Preparation of TiAl alloy material sample for forging: Sample 9) A sample (Sample 9) of a TiAl alloy material for forging having a chemical composition of Ti-44.0Al-5.0Nb-2.5Cr was prepared according to the same preparation method as in Example 1. In the preparation of the sample, a TiAl alloy sample for forging was formed into a predetermined shape using a mold.
  • the first heat treatment step and the second heat treatment step were carried out according to any of the following conditions C1 to C7.
  • the temperature of the test piece was once lowered to room temperature by furnace cooling.
  • the heat-treated test piece was subjected to a tensile test on the test piece using a gleeble tester, and the elongation at room temperature was measured.
  • a predetermined tensile force was applied to both ends of the test piece to gradually increase the tensile force until the test piece broke.
  • a stress strain diagram was created and the elongation was measured.
  • FIG. 3 shows a stress strain diagram of the test piece that has undergone the heat treatment under the conditions C6 or C7.
  • Second heat treatment Condition C1 1250 ° C x 1h, 900 ° C x 1h
  • Condition C2 1250 ° C x 1h, 900 ° C x 5h
  • Condition C3 1250 ° C x 1h, 950 ° C x 1h
  • Condition C4 1250 ° C x 1h, 950 ° C x 5h
  • Condition C5 1280 ° C x 1h, 1100 ° C x 1h
  • Condition C6 1300 ° C x 1h, None
  • Condition C7 1250 ° C x 1h, 1000 ° C x 1h
  • the elongation values of the test pieces after the heat treatment were 1.1% (condition C1), 1.2% (condition C2), 1.2% (condition C3), 1.0% (condition C4), and 1.8. % (Condition C5), 0.1% (Condition C6), 1.4% (Condition C7). Therefore, from the above results, it is understood that the fracture ductility (elongation value) of the TiAl alloy material differs depending on the heat treatment conditions.
  • condition C6 From the result of condition C6, it can be seen that the improvement in elongation is small only by the first heat treatment. That is, performing both the first heat treatment and the second heat treatment is remarkably effective in improving the elongation. Further, the first heat treatment functions effectively at a temperature of 1250 ° C. or higher, and the temperature setting of the first heat treatment in the range of 1250 to 1280 ° C. is appropriate. The second heat treatment is effective at a temperature of 900 ° C. or higher, and the temperature setting of the second heat treatment in the range of 900 to 1100 ° C. is appropriate.
  • Example 2 Using the TiAl alloy material sample of sample 9 that had been hot forged in Example 2, a test piece that had been heat-treated under various conditions was prepared. Each of the obtained test pieces was subjected to the same tensile test as in Example 2 to measure the elongation value [%].
  • the metallographic structure of the TiAl alloy was observed with a scanning electron microscope (SEM) for each of the test pieces.
  • SEM scanning electron microscope
  • the area ratio of the ⁇ phase (TiAl) in the image was calculated by image processing using the contrast information in the photographed image of the metal structure.
  • the obtained value was regarded as the volume fraction [%] of the ⁇ phase in the metal structure, and a graph showing the relationship between the volume fraction of the ⁇ phase and the elongation value obtained above was created. The obtained graph is shown in FIG.
  • Example 10 A sample (sample 10) of a TiAl alloy material for forging having a chemical composition of Ti-44.0Al-4.2Nb-3.3Cr was prepared according to the same preparation procedure as in Example 2. The sample of this TiAl alloy material was subjected to hot forging in the same manner as in Example 2, processed into a test piece having a predetermined size, and heat-treated under condition C3. For the obtained test piece, the elongation was measured by the tensile test and the volume fraction of the ⁇ phase was measured based on the photographed image of the metal structure in the same manner as described above.
  • the volume fraction of the ⁇ phase includes the volume fraction of the ⁇ phase crystal grains and the volume fraction of the ⁇ phase constituting the lamellar structure.
  • the graph of FIG. 4 there is a clear correlation between the volume ratio of the ⁇ phase in the metal structure and the ductility (elongation value) of the alloy material, and the ductility of the TiAl alloy is improved by increasing the ⁇ phase. Is understood.
  • the test piece shows an elongation of 1% or more. From this, it is clear that it is possible to provide a forged body of a TiAl alloy material exhibiting suitable ductility by performing heat treatment so that the volume fraction of the ⁇ phase is about 80% or more.
  • the measured value displayed as the sample 9 is the result of the test piece obtained by heat-treating the forged body under the conditions C3 or C6, and the measurement result of the above-mentioned sample 10 is also described. .. Since the sample 9 and the sample 10 heat-treated under the same condition C3 differ only in the ratio of Nb / Cr in the ⁇ -phase stabilizing element, the influence of the ratio of Nb / Cr can be known from these comparisons. According to this, the higher the ratio of Nb / Cr, the easier it is to impart ductility to the alloy material, and the higher the ductility is when the ratio of Nb content / Cr content (atomic number ratio) is about 1.7 or more. That is, it is considered that when the ratio of Nb content / Cr content is about 1.7 or more, embrittlement due to Cr eutectoid reaction is suppressed and good ductility is exhibited.
  • FIG. 5 is an image taken by a scanning electron microscope (SEM) of a metal structure in a test piece that has been heat-treated under condition C5 after forging the TiAl alloy material of sample 9.
  • the metal structure of the TiAl alloy forged product has lamellar structure ( ⁇ 2 / ⁇ ) crystal grains, ⁇ phase (Ti) crystal grains, and ⁇ phase (TiAl) crystal grains. These are generated from crystal grains that are finely broken by forging.
  • the lamellar structure has high temperature strength and a certain degree of ductility and toughness, and the ⁇ phase is excellent in high temperature strength.
  • the residual ⁇ -phase fine particles impart ductility at high temperatures.
  • the structure in which the lamellar tissue particles, the ⁇ -phase particles, and the ⁇ -phase particles are finely mixed and dispersed has improved high-temperature strength and excellent durability. Therefore, based on the same chemical composition, it is possible to improve the workability of the TiAl alloy material in hot forging and to maintain the high temperature strength of the TiAl alloy material after forging.
  • TiAl alloy forged body having excellent high-temperature strength and ductility at room temperature while lowering the temperature in hot forging of the TiAl alloy material, parts such as aircraft engines, moving blades and disks of gas turbines for power generation. It can be applied to manufacturing and contribute to the provision of excellent products. Further, by enhancing the economic efficiency, it can contribute to the expansion of the applicable range of hot forging of TiAl alloy materials.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
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  • Crystallography & Structural Chemistry (AREA)
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Abstract

La présente invention concerne un matériau d'alliage TiAl pour forgeage à chaud qui a une composition chimique comprenant, en termes de rapport atomique, 43,0 à 45,0 % de Al, 4,0 à 6,0 % de Nb, 1,5 à 3,5 % de Cr, et le reste étant Ti et des impuretés inévitables. En outre, le matériau d'alliage TiAl pour forgeage à chaud peut facultativement contenir du bore. Le matériau d'alliage TiAl pour forgeage à chaud est préparé, la température est maintenue dans une plage de température d'équilibre de phase pour l'une de la phase β, la phase (β+α) et la phase (β+α+γ) indiquée dans le diagramme de phase d'alliage TiAl, et le matériau d'alliage TiAl est forgé dans une atmosphère non oxydante. Des premier et deuxième traitements thermiques sont effectués après le forgeage. La présente invention améliore la forgeabilité isotherme dans un matériau TiAl et permet d'effectuer un forgeage à chaud à une température de forgeage plus basse.
PCT/JP2020/007922 2019-03-18 2020-02-27 Matériau d'alliage d'aluminure de titane pour forgeage à chaud, procédé de forgeage pour matériau d'alliage d'aluminure de titane, et corps forgé WO2020189215A1 (fr)

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EP20773214.0A EP3943627A4 (fr) 2019-03-18 2020-02-27 Matériau d'alliage d'aluminure de titane pour forgeage à chaud, procédé de forgeage pour matériau d'alliage d'aluminure de titane, et corps forgé
JP2021507142A JP7233659B2 (ja) 2019-03-18 2020-02-27 熱間鍛造用のチタンアルミナイド合金材及びチタンアルミナイド合金材の鍛造方法並びに鍛造体
US17/447,479 US20210404042A1 (en) 2019-03-18 2021-09-13 Titanium aluminide alloy material for hot forging, forging method for titanium aluminide alloy material, and forged body

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CN114951522B (zh) * 2022-06-28 2023-08-11 中南大学 一种单晶TiAl的等温锻造方法
CN116393928A (zh) * 2023-04-19 2023-07-07 北京科技大学 一种制备变形TiAl合金叶片的方法

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JPH06116691A (ja) * 1992-10-05 1994-04-26 Mitsubishi Materials Corp ＴｉＡｌ金属間化合物系Ｔｉ合金の熱処理法
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JP2015004092A (ja) 2013-06-19 2015-01-08 独立行政法人物質・材料研究機構 熱間鍛造型ＴｉＡｌ基合金
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US20210404042A1 (en) 2021-12-30

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