TiAl alloy castings, jet engine blades and turbine wheels

Abstract

This invention provides a highly versatile method for producing TiAl alloy castings that yields TiAl alloy castings with a sufficiently low oxygen content and allows the use of a variety of equipment and raw materials. [Solution] A TiAl alloy casting material characterized by containing 31.9% to 34.2% by mass of Al, 4.0% to 5.4% by mass of Nb, 2.3% to 3.0% by mass of Cr, 0.04% to 0.12% by mass of oxygen, and 0.01% to 0.07% by mass of Ca, with the remainder being Ti and impurities.

Description

[Technical Field]

[0001] This invention relates to TiAl alloy castings, jet engine blades, and turbine wheels. This application claims priority based on Japanese Patent Application No. 2022-050457, filed in Japan on March 25, 2022, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] Traditionally, nickel-based superalloys have been used as materials for jet engine blades and turbocharger wheels for passenger cars. In recent years, TiAl alloys have attracted attention as a new material for use in these components. TiAl alloys have a density of approximately half that of nickel-based superalloys. Therefore, even large components can be made with less weight, significantly contributing to improved engine efficiency through weight reduction, as well as to reductions in fuel consumption and carbon dioxide emissions.

[0003] In components made of TiAl alloy, which are used in practical applications as rotor blades and turbine wheels for jet engines, the concentration of impurities in the TiAl alloy forming the component is naturally specified. For oxygen, which is the most easily introduced impurity, the content in the TiAl alloy is specified to be, for example, 0.12 mass% or less. If the oxygen content in the TiAl alloy exceeds 0.12 mass%, the impact resistance of the component made of TiAl alloy deteriorates, and problems such as component failure during use are more likely to occur.

[0004] Typically, jet engine blades and turbine wheels made of TiAl alloy use TiAl alloy castings manufactured using casting methods. The raw materials used for casting include metallic element raw materials such as sponge titanium and Al grains, and / or master alloy ingots (cast ingots) made using these metallic element raw materials.

[0005] Currently, when casting TiAl alloy castings for jet engine blades and turbine wheels, the following manufacturing methods are used to obtain products with sufficiently low oxygen content that meet the compositional requirements for TiAl alloys. Specifically, a vacuum melting furnace is used to melt the raw materials in a vacuum or inert gas atmosphere, thereby preventing oxygen from entering the molten raw materials from the atmosphere. Furthermore, the raw materials are melted in a water-cooled copper crucible to prevent oxygen from entering the molten metal.

[0006] When melting metallic materials such as iron-based and nickel-based alloys, oxide ceramic crucibles are generally used. However, because TiAl alloys are reactive in their molten state, when melted in an oxide ceramic crucible, oxygen is introduced into the molten metal from the crucible, increasing the oxygen concentration in the casting material.

[0007] Furthermore, when casting TiAl alloy castings for jet engine blades and turbine wheels, raw materials with low oxygen content are used to obtain products with sufficiently low oxygen content that meet the compositional requirements for TiAl alloys. Specifically, raw materials of metal elements with low oxygen content, and / or master alloy ingots (castings) with low oxygen content made using raw materials of metal elements with low oxygen content are used.

[0008] Master alloy ingots with low oxygen content are typically manufactured using the following casting method: that is, the raw materials for the master alloy ingot are melted in a water-cooled copper crucible placed in a vacuum melting furnace under a vacuum or inert gas atmosphere.

[0009] Patent Document 1 describes a method for producing a TiAl alloy ingot by melting Ti and Al, which are the raw materials for melting, in a ceramic crucible using high-frequency induction melting, and then casting the resulting molten metal into a mold. Patent Document 1 also describes that by using yttria (Y2O3), the most chemically stable compound, as the material for the ceramic crucible, the amount of oxygen generated when the ceramic crucible decomposes during melting can be suppressed, and the concentration of oxygen mixed into the TiAl alloy can be suppressed.

[0010] Patent Document 2 describes a method for manufacturing a TiAl-based alloy ingot, wherein the oxygen content of the Ti raw material is 800 ppm or less, the oxygen content of the Al raw material is 100 ppm or less, and if the other alloying components are Cr, V, and Nb, their oxygen content is 2000 ppm or less, and if the other alloying components are Mn, their oxygen content is 3000 ppm or less. Patent Document 2 describes melting the alloying raw materials, solidifying them, and then melting the molten base material, which consists of a primary ingot whose components have been adjusted in advance, in a water-cooled copper crucible. Furthermore, Patent Document 2 describes storing the alloy material in an inert gas atmosphere so that it is not affected by surface oxidation or other factors.

[0011] Patent Document 3 describes a method for producing a high-purity TiAl-based intermetallic compound, using high-purity Ti with an oxygen content of 200 ppm or less and high-purity Al with a purity of 99.99% by weight or more as base materials, melting the mixture to reduce the oxygen content to 0.03% or less, casting it, and then annealing it. Patent Document 3 also describes repeating the melting and solidification process on a copper hearth multiple times.

[0012] Patent Document 4 describes a method for producing a TiAl-based intermetallic compound alloy by melting raw materials consisting of 48-70 atomic percent titanium and 30-52 atomic percent aluminum in a calcia crucible. Patent Document 4 also describes a method in which the titanium raw material is heated in a vacuum and degassed beforehand, and then the titanium and aluminum raw materials are charged into the crucible and melted by a vacuum induction melting method.

[0013] Non-patent document 1 describes a method of deoxidizing a Ti alloy by induction melting it in a water-cooled copper crucible and then adding a Ca alloy. Non-patent document 1 also describes an analysis of an ingot of a TiAl matrix alloy containing 0.16 mass% oxygen, deoxidized using an AlCa alloy as a deoxidizing agent, which showed that the oxygen content was reduced to 0.02% with Ca ≥ 0.3%. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Application Publication No. 2011-36877 (A) [Patent Document 2] Japanese Patent Application Publication No. 2009-113060 (A) [Patent Document 3] Japanese Patent Application Publication No. 3-193839 (A) [Patent Document 4] Japanese Patent Application Publication No. 3-199330 (A) [Non-patent literature]

[0015] [Non-Patent Document 1] Tomoki Shibata, Noboru Demukai, Deoxidation of TiAl, Electric Steelmaking, Vol. 64, No. 1, February 1993, pp. 32-39. [Overview of the project] [Problems that the invention aims to solve]

[0016] Conventional techniques required the use of special equipment to melt raw materials using a water-cooled copper crucible placed in a vacuum melting furnace under a vacuum or inert gas atmosphere, and / or to use special raw materials with low oxygen content. Therefore, there is a need to increase the options for equipment and raw materials that can be used when producing TiAl alloy castings with sufficiently low oxygen content.

[0017] The present invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a TiAl alloy casting material with a sufficiently low oxygen content, which can be obtained and which can use a variety of devices and raw materials, a TiAl alloy casting material having an oxygen content of 0.12 mass% or less, a rotor blade for a jet engine and a turbine wheel made of the TiAl alloy casting material having an oxygen content of 0.12 mass% or less.

Means for Solving the Problems

[0018] [1] A melting step of melting a raw material containing Ti and Al to obtain a molten metal, and a step of adding a deoxidizer containing Ca to either one or both of the raw material and the molten metal, wherein the deoxidizer is added so that the Ca concentration in the total mass of the raw material and the deoxidizer is 0.2 mass% to 1.0 mass%, and a deoxidizing step of heating the molten metal containing the deoxidizer to maintain a molten state, thereby generating fumes containing reaction products of oxygen and Ca in the molten metal to remove oxygen in the molten metal. A method for manufacturing a TiAl alloy casting material, characterized by including these steps.

[0019] [2] The method for manufacturing a TiAl alloy casting material according to [1], wherein the deoxidizer is an AlCa alloy.

[0020] [3] The melting step is a step of melting the raw material in an oxide ceramic crucible, and the deoxidizer addition step is either one or both of a step of putting the deoxidizer together with the raw material into the oxide ceramic crucible and a step of adding the deoxidizer to the molten metal placed in the oxide ceramic crucible. In the deoxidizing step, the method for manufacturing a TiAl alloy casting material according to [1] or [2], characterized by heating and melting the molten metal containing the deoxidizer placed in the oxide ceramic crucible.

[0021] [4] The method for producing a TiAl alloy casting material according to [1] or [2], characterized in that the deoxidizing agent addition step is a step of putting the deoxidizing agent together with the raw material into an oxide ceramic crucible installed in a vacuum melting furnace, the melting step is a step of melting the raw material in the oxide ceramic crucible installed in the vacuum melting furnace which is in an Ar atmosphere after the deoxidizing agent addition step, and in the deoxidizing step, the molten metal containing the deoxidizing agent is heated and melted in the oxide ceramic crucible installed in the vacuum melting furnace which is in an Ar atmosphere.

[0022] [5] The oxide ceramic crucible is placed in an atmospheric melting furnace, and the melting process comprises a mold setting step of setting the wider opening of a funnel-shaped mold toward the oxide ceramic crucible so as to cover the opening of the oxide ceramic crucible, an atmosphere replacement step of supplying Ar gas into the oxide ceramic crucible, and a heating step of heating the oxide ceramic crucible, and the deoxidizing agent addition step of adding the deoxidizing agent to the oxide ceramic crucible together with the raw materials, and deoxidizing the molten metal in the oxide ceramic crucible via the funnel-shaped mold A method for producing a TiAl alloy casting material according to [3], comprising one or both of the steps of adding a material, wherein in the deoxidation step, the molten metal containing the deoxidizing agent is heated and melted in the oxide ceramic crucible whose opening is covered by the funnel-shaped mold, the fumes in the oxide ceramic crucible are discharged through the funnel-shaped mold, and after the deoxidation step, the atmospheric melting furnace is inverted upside down with the oxide ceramic crucible and the funnel-shaped mold integrated together, and the molten metal is poured from the oxide ceramic crucible into the funnel-shaped mold and cooled in a casting step.

[0023] [6] A method for producing a TiAl alloy casting material according to any one of [1] to [5], characterized in that the raw materials include either or both of TiAl alloy cutting chips and TiAl alloy casting scrap.

[0024] [7] A TiAl alloy casting material characterized by containing 0.04% to 0.10% by mass of oxygen and 0.01% to 0.03% by mass of Ca. [8] A TiAl alloy casting material characterized by containing 31.9% to 34.2% by mass of Al, 4.0% to 5.4% by mass of Nb, 2.3% to 3.0% by mass of Cr, 0.04% to 0.12% by mass of oxygen, and 0.01% to 0.07% by mass of Ca, with the remainder being Ti and impurities.

[0025] A rotor blade for a jet engine, characterized by being made of the TiAl alloy casting material described in [9] [7] or [8]. A turbine wheel characterized by being made of the TiAl alloy casting material described in

[10] [7] or [8]. [Effects of the Invention]

[0026] The present invention provides a method for producing a TiAl alloy casting, comprising: a melting step of melting raw materials containing Ti and Al to form molten metal; a deoxidizing step of adding a deoxidizing agent containing Ca to either the raw materials or the molten metal, or both, wherein the Ca concentration in the total mass of the raw materials and the deoxidizing agent is 0.2% to 1.0% by mass; and a deoxidizing step of heating the molten metal containing the deoxidizing agent and maintaining the molten state to generate a fume containing reaction products of oxygen and Ca in the molten metal, thereby removing oxygen from the molten metal. As a result, a TiAl alloy casting with a sufficiently low oxygen content can be obtained by pouring the molten metal after the deoxidizing step into a mold and cooling it.

[0027] Therefore, according to the method for manufacturing TiAl alloy castings of the present invention, a TiAl alloy casting with a sufficiently low oxygen content can be obtained without using special equipment or special raw materials with low oxygen content, and a variety of equipment and raw materials can be used. For example, even if the raw materials contain poor quality raw materials with a high oxygen content, or if oxygen mixed in from the oxide ceramic crucible and / or atmosphere is present in the molten metal, a TiAl alloy casting with a sufficiently low oxygen content can be obtained by using the method for manufacturing TiAl alloy castings of the present invention. [Brief explanation of the drawing]

[0028] [Figure 1] This is a process diagram illustrating an example of a manufacturing method for the TiAl alloy casting material of this embodiment. [Figure 2] This is a process diagram illustrating an example of a manufacturing method for the TiAl alloy casting material of this embodiment. [Figure 3] This is a process diagram illustrating an example of a manufacturing method for the TiAl alloy casting material of this embodiment. [Figure 4] This is a process diagram illustrating an example of a manufacturing method for the TiAl alloy casting material of this embodiment. [Figure 5] This is a process diagram illustrating an example of a manufacturing method for the TiAl alloy casting material of this embodiment. [Figure 6] This is a process diagram illustrating an example of a manufacturing method for the TiAl alloy casting material of this embodiment. [Figure 7] This is a process diagram illustrating an example of a manufacturing method for the TiAl alloy casting material of this embodiment. [Modes for carrying out the invention]

[0029] In order to solve the above problems, the inventors of this invention conducted diligent research as described below. In other words, to obtain TiAl alloy castings with a sufficiently low oxygen content, a special apparatus is used that melts the raw materials using a water-cooled copper crucible installed in a vacuum melting furnace under a vacuum or inert gas atmosphere, resulting in high initial equipment investment and operating costs. Moreover, because a water-cooled copper crucible is used, the amount of molten metal that can be melted is small, resulting in a small number of castings that can be cast in one batch and insufficient productivity. Furthermore, when using a water-cooled copper crucible, the superheating temperature of the molten metal is low, which makes poor molten metal flow during casting more likely, leading to a low yield of good products.

[0030] To address the problems associated with using water-cooled copper crucibles, it is possible to use oxide ceramic crucibles, which are commonly used when melting metal materials such as iron-based and nickel-based alloys, as an alternative. When using oxide ceramic crucibles, it is possible to melt a larger volume of molten metal and to heat the molten metal to a higher temperature compared to using water-cooled copper crucibles.

[0031] However, molten TiAl alloy is highly reactive. Therefore, when raw materials containing Ti and Al are melted in an oxide ceramic crucible, oxygen originating from the material of the oxide ceramic crucible is mixed into the melted raw materials. As a result, the TiAl alloy casting obtained after casting has a high oxygen content. For this reason, conventionally, oxide ceramic crucibles could not be used to produce TiAl alloy castings with a sufficiently low oxygen content.

[0032] Furthermore, in order to reduce initial capital investment and operating costs, it is conceivable to use an atmospheric melting furnace instead of a vacuum melting furnace. However, when using an atmospheric melting furnace, oxygen from the atmosphere is mixed into the raw material to be melted. As a result, the TiAl alloy casting obtained after casting will have a high oxygen content.

[0033] Furthermore, in order to obtain TiAl alloy castings with a sufficiently low oxygen content, if special raw materials with low oxygen content are used, the raw materials are expensive, and special equipment is required for storing them. Also, when producing a master alloy ingot with a low oxygen content as a raw material, it is necessary to use special equipment that melts the raw materials using a water-cooled copper crucible installed in a vacuum melting furnace under a vacuum atmosphere or inert gas atmosphere.

[0034] On the other hand, the use of TiAl alloy scrap is required as a raw material for TiAl alloy castings. Possible TiAl alloy scraps include TiAl alloy cutting chips and / or TiAl alloy casting scrap. Examples of TiAl alloy cutting chips include those generated when manufacturing components such as jet engine blades from TiAl alloy castings. Examples of TiAl alloy casting scrap include casting scrap consisting of parts that do not become part of the TiAl alloy casting product, such as runners, generated during precision casting of TiAl alloys using lost-wax casting.

[0035] However, TiAl alloy scrap has a high oxygen content. Specifically, TiAl alloy cutting chips have organic substances such as coolant and cutting oil adhering to them. Because these organic substances are firmly attached to the TiAl alloy cutting chips, it is difficult to sufficiently reduce the oxygen content even by washing the chips with organic solvents. In addition, TiAl alloy casting scrap usually contains oxygen that has been introduced through the reaction between the mold, which is made of oxide ceramic, and the molten raw material. For this reason, TiAl alloy casting scrap also has a high oxygen content. For these reasons, it has been difficult to manufacture TiAl alloy castings with a sufficiently low oxygen content using raw materials containing TiAl alloy scrap with conventional technology.

[0036] In recent years, the production volume of components made from TiAl alloys has been rapidly expanding. In particular, the use of TiAl alloys for jet engine blades has been expanding globally, and their production volume is increasing. However, the current cost of jet engine blades made from TiAl alloys is several times that of jet engine blades made from Ni-based superalloys. For this reason, there is a strong demand to reduce the cost of TiAl alloy castings used for jet engine blades.

[0037] Therefore, in order to solve the above problems and realize a highly versatile method for producing TiAl alloy castings that yields TiAl alloy castings with a sufficiently low oxygen content, even when using a variety of devices, such as a special apparatus that melts raw materials using a water-cooled copper crucible installed in a vacuum melting furnace with a vacuum atmosphere or an inert gas atmosphere, as well as a variety of raw materials such as TiAl alloy scrap, the inventors focused on deoxidizing agents for melting raw materials and conducted diligent research.

[0038] As a result, it was found that the deoxidizing agent should be added to either the raw material or the molten metal, or both, such that the Ca concentration in the total mass of the raw material and the Ca-containing deoxidizing agent is 0.2% to 1.0% by mass, and then the molten metal containing the deoxidizing agent should be heated and maintained in a molten state. Ca is an element that readily combines with oxygen compared to Ti and Al. Therefore, by heating the molten metal and maintaining its molten state, the Ca in the molten metal reacts with the oxygen in the molten metal, producing reaction products such as CaO, CaTiO3, and CaAl2O4. These reaction products are discharged from the molten metal as fumes (steam). As a result, the oxygen in the molten metal is removed along with the Ca.

[0039] Furthermore, the inventors of the present invention have come up with the present invention after confirming that by adding a deoxidizing agent containing Ca such that the Ca concentration in the total mass of the raw material and the deoxidizing agent falls within the above range, a TiAl alloy casting material with a sufficiently low oxygen content and excellent impact resistance can be obtained without using special equipment or special raw materials with low oxygen concentration. Specifically, by using a method of adding a deoxidizing agent containing Ca to the above concentration, as shown in the examples described later, a TiAl alloy casting with a sufficiently low oxygen content can be obtained even when using a general-purpose melting furnace and an oxide ceramic crucible commonly used when melting metal materials, or when using raw materials containing TiAl alloy scrap with a high oxygen concentration.

[0040] The method for manufacturing the TiAl alloy casting material, the TiAl alloy casting material, the rotor blade for a jet engine, and the turbine wheel of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to the embodiments shown below.

[0041] [Manufacturing method for TiAl alloy castings] In this embodiment, as an example of a method for manufacturing a TiAl alloy casting, we will describe a case in which an apparatus equipped with an oxide ceramic crucible 2 installed in an atmospheric melting furnace 1 is used. Figures 1 to 7 are process diagrams illustrating an example of a method for manufacturing a TiAl alloy casting according to this embodiment. In Figures 1 to 6, reference numeral 1 indicates an atmospheric melting furnace, and reference numeral 2 indicates an oxide ceramic crucible.

[0042] A known atmospheric melting furnace 1 can be used. In this embodiment, a rollover furnace type atmospheric melting furnace 1 is used. As shown in Figure 1, the atmospheric melting furnace 1 has a substantially cylindrical housing section 1a with an open top. The atmospheric melting furnace 1 has a furnace wall 1b and a high-frequency coil 4 installed inside the furnace wall 1b for heating the oxide ceramic crucible 2. As shown in Figure 1, the oxide ceramic crucible 2 is installed inside the housing section 1a.

[0043] As the oxide ceramic crucible 2, known materials can be used. It is preferable to use a chemically stable oxide ceramic as the material for the oxide ceramic crucible 2, specifically calcia or yttria, and more preferably calcia because it is a material that is less prone to inclusion. By using an oxide ceramic crucible 2 made of calcia or yttria, the amount of oxygen mixed from the oxide ceramic crucible 2 into the molten raw material 3a can be suppressed. Therefore, even if the amount of deoxidizing agent containing Ca added to the raw material 3 or molten raw material 3a is small, the oxygen content in the TiAl alloy casting obtained after casting can be sufficiently reduced.

[0044] [Dissolution process] [Deoxidizer addition process] The method for manufacturing the TiAl alloy casting material of this embodiment includes a melting step. In the melting step, raw material 3 is melted to form molten raw material 3a. In this embodiment, raw material 3 is melted in an oxide ceramic crucible 2 installed in an atmospheric melting furnace 1 with an air atmosphere. As will be described later, the melting of raw material 3 is carried out after covering the opening of the oxide ceramic crucible 2 with a funnel-shaped mold 5 and creating an argon atmosphere inside the oxide ceramic crucible 2. The supply of argon into the oxide ceramic crucible 2 can be carried out, as will be described later, for example, by using a gas supply pipe 7 inserted into the oxide ceramic crucible 2 via the funnel-shaped mold 5.

[0045] In the dissolution process, as shown in Figure 1, a portion of the raw material 3 is placed into the oxide ceramic crucible 2. Furthermore, the entire amount of the deoxidizing agent containing Ca is added to the oxide ceramic crucible 2, and then the raw material 3 is dissolved.

[0046] (raw materials) Raw material 3 contains Ti and Al. In addition to Ti and Al, raw material 3 may also contain one or more additive elements selected from, for example, Nb, Cr, Mo, V, Mn, W, Fe, Si, C, and B. The composition of raw material 3 can be appropriately determined depending on the intended use of the TiAl alloy casting obtained after casting. As raw material 3, for example, a material containing 31.9% to 34.2% by mass of Al, 4.0% to 5.4% by mass of Nb, 2.3% to 3.0% by mass of Cr, and 0.1% to 0.5% by mass of oxygen, with the remainder being Ti and impurities, can be used.

[0047] Raw material 3 contains impurities at concentrations that do not impede the intended use of the manufactured TiAl alloy casting. When casting TiAl alloy castings for use as jet engine blades and turbine wheels, for example, it is preferable that the impurities contained in raw material 3 are within a range that satisfies the compositional specifications (material specifications for each product) of the manufactured TiAl alloy casting.

[0048] The composition of raw material 3 does not match the composition of the TiAl alloy casting obtained after casting. Specifically, this is because, in the manufacturing process of the TiAl alloy casting, there are elements that increase when mixed into the molten raw material 3a from the oxide ceramic crucible 2 that comes into contact with the molten raw material 3a, from the atmosphere, etc., elements that increase when a deoxidizing agent containing Ca is added, and elements that decrease when discharged from the molten raw material 3a as fumes.

[0049] In the manufacturing method of the TiAl alloy casting material of this embodiment, Ti and Al, which are the main elements of the TiAl alloy, are hardly mixed in from the equipment and atmosphere or discharged during the manufacturing process. Therefore, there is almost no increase or decrease in the amount of Ti associated with the manufacturing process of the TiAl alloy casting material. Thus, the mass of Ti used as raw material 3 and the mass of Ti contained in the TiAl alloy casting material obtained after casting can be considered to be the same. On the other hand, the amount of Al increases in the manufacturing process of the TiAl alloy casting material due to the use of AlCa alloy as a deoxidizing agent containing Ca, and decreases as it is discharged from the molten metal as a fume such as CaAl2O4 in the deoxidation process.

[0050] Furthermore, in the manufacturing method of the TiAl alloy casting material of this embodiment, Nb and Cr, which may be included in the raw material 3 as additive elements, are hardly introduced from the equipment and atmosphere or discharged during the manufacturing process, similar to Ti. Therefore, there is almost no increase or decrease in the amount of Nb and Cr associated with the manufacturing process of the TiAl alloy casting material. Thus, the mass of Nb and Cr used as raw material 3 can be considered to be the same as the mass of Nb and Cr contained in the TiAl alloy casting material obtained after casting.

[0051] If the composition of raw material 3 is, for example, 31.9% to 34.2% by mass of Al, 4.0% to 5.4% by mass of Nb, 2.3% to 3.0% by mass of Cr, and 0.1% to 0.5% by mass of oxygen, with the remainder being Ti and impurities, then after casting, a TiAl alloy casting material is easily obtained that contains 31.9% to 34.2% by mass of Al, 4.0% to 5.4% by mass of Nb, 2.3% to 3.0% by mass of Cr, 0.04% to 0.12% by mass of oxygen, and 0.01% to 0.07% by mass of Ca, with the remainder being Ti and impurities, which is preferable. A TiAl alloy casting material having such a composition has excellent impact resistance, and also has good machinability, tensile strength, and creep strength, making it suitable for use as a material for jet engine blades and turbine wheels.

[0052] The Al content in raw material 3 can be, for example, 31.9% to 34.2% by mass, and preferably 32.9% to 33.8% by mass. This is because the TiAl alloy casting obtained after casting will have better impact resistance, tensile strength, and creep strength.

[0053] The Nb content in raw material 3 can be, for example, 4.0% to 5.4% by mass, and preferably 4.4% to 5.0% by mass. This is because the TiAl alloy casting obtained after casting has good oxidation resistance. Furthermore, the Cr content in raw material 3 can be, for example, 2.3% to 3.0% by mass, and preferably 2.5% to 2.8% by mass. This is because it results in good ductility for the TiAl alloy casting material obtained after casting. When raw material 3 contains 4.4% to 5.0% by mass of Nb and 2.5% to 2.8% by mass of Cr in addition to Ti and Al, a TiAl alloy casting material is obtained that has superior impact resistance, as well as superior machinability, tensile strength, and creep strength.

[0054] The shape of raw material 3 is not particularly limited, and for example, metallic element raw materials such as sponge titanium, Al grains (pellets), Nb flakes, Cr grains, and / or master alloy ingots (castings) made using these metallic element raw materials can be used.

[0055] Raw material 3 may contain TiAl alloy scrap. Examples of TiAl alloy scrap include TiAl alloy cutting chips and TiAl alloy casting scrap. Examples of TiAl alloy cutting chips include cutting chips generated when manufacturing components such as rotor blades for jet engines from TiAl alloy castings. Examples of TiAl alloy casting scrap include casting scrap consisting of parts that do not become products of TiAl alloy castings, such as runners, generated when performing precision casting of TiAl alloys using lost-wax casting.

[0056] When TiAl alloy cutting chips are used as raw material 3, it is preferable to wash off any organic matter such as coolant and cutting oil adhering to the TiAl alloy cutting chips with an organic solvent such as acetone before use, in order to further reduce the oxygen content in the TiAl alloy casting material obtained after casting. As a method for washing TiAl alloy cutting chips with an organic solvent, known methods such as using an ultrasonic cleaner can be used. Furthermore, when TiAl alloy casting scrap is used as raw material 3, it is preferable to pickle the surface before use in order to further reduce the oxygen content in the TiAl alloy casting material obtained after casting.

[0057] (Ca-containing deoxidizing agent) As a deoxidizing agent containing Ca, for example, elemental Ca may be used, or Ca-containing compounds such as AlCa alloys, CaF2, and CaCl2 may be used. As a Ca-containing deoxidizing agent, AlCa alloys are preferred because they are solids, making them easy to handle, requiring no special care for storage, and not requiring any special safety considerations. As for the AlCa alloy, it is preferable to use one with a Ca content of 3% to 20% by mass, more preferably one with a Ca content of 10% or 5% by mass, and even more preferably one with a Ca content of 5% by mass, because the Ca content in the AlCa alloy fluctuates little during the manufacturing process and can be manufactured stably.

[0058] The deoxidizing agent containing Ca is added so that the Ca concentration in the total mass of raw material 3 and the deoxidizing agent is 0.2% to 1.0% by mass. The amount of deoxidizing agent containing Ca added can be appropriately determined within the above range depending on the composition of raw material 3, the composition range of the target TiAl alloy casting material, and conditions such as the atmosphere, temperature, and time used to heat the molten raw material 3a containing the deoxidizing agent. By adding the deoxidizing agent containing Ca so that the Ca concentration in the total mass of raw material 3 and the deoxidizing agent is within the above range, a TiAl alloy casting material with excellent impact resistance properties is obtained after casting, containing 0.04% to 0.12% by mass of oxygen and 0.01% to 0.07% by mass of Ca. In the method for producing the TiAl alloy casting material of this embodiment, the Ca concentration in the total mass of raw material 3 and the deoxidizing agent is 0.2% by mass or more, so the effect of adding the deoxidizing agent is fully obtained, and the oxygen content of the TiAl alloy casting material obtained after casting is 0.12% by mass or less. Furthermore, since the Ca concentration in the total mass of raw material 3 and the deoxidizing agent is set to 1.0% by mass or less, the residual Ca content in the TiAl alloy casting obtained after casting will be 0.07% by mass or less.

[0059] Furthermore, the deoxidizing agent containing Ca may be added such that the Ca concentration in the total mass of raw material 3 and the deoxidizing agent is 0.4% to 0.8% by mass. By setting the amount of deoxidizing agent containing Ca within the above range and appropriately adjusting conditions such as the composition of raw material 3, the atmosphere for heating the molten raw material 3a containing the deoxidizing agent, temperature, and time, a TiAl alloy casting material containing 0.04% to 0.10% by mass of oxygen and 0.01% to 0.03% by mass of Ca, and having superior impact resistance properties, can be obtained after casting. Ca-containing deoxidizing agents may be added such that the Ca concentration in the total mass of raw material 3 and the deoxidizing agent is 0.55% by mass to 0.65% by mass.

[0060] Next, as shown in Figure 2, the funnel-shaped mold 5 is placed on the furnace wall 1b of the atmospheric melting furnace 1 with its wider opening facing the oxide ceramic crucible 2 so as to cover the opening of the oxide ceramic crucible 2 (mold installation step). The wider opening of the funnel-shaped mold 5 functions as a sprue for pouring the molten raw material 3a into the funnel-shaped mold 5 in the casting step described later. It is preferable to use a funnel-shaped mold 5 whose internal volume is larger than the volume of the raw material 3.

[0061] As the funnel-shaped mold 5, one made of a known material used in the manufacture of TiAl alloy castings can be used. Specifically, as the funnel-shaped mold 5, a mold made of cast iron, carbon steel, etc., and having a two-part structure with a ceramic such as zircon coated on the inner surface to prevent reaction with the molten raw material 3a can be used. In this embodiment, the case in which a metal mold is used as the funnel-shaped mold 5 was described as an example, but lost-wax casting may also be performed using a ceramic mold made of alumina, silica, mullite, zirconia, etc. as the funnel-shaped mold 5. By performing lost-wax casting, a TiAl alloy casting material having a shape close to the final product can be obtained.

[0062] Furthermore, as shown in Figure 2, it is preferable to install a simple sealing material 6 made of cement or the like at the contact point between the funnel-shaped mold 5 and the furnace wall 1b of the atmospheric melting furnace 1. This prevents air from entering the oxide ceramic crucible 2 from the contact point between the funnel-shaped mold 5 and the furnace wall 1b of the atmospheric melting furnace 1.

[0063] Next, a gas supply pipe 7 is inserted through the narrower opening of the funnel-shaped mold 5, and Ar gas is supplied into the oxide ceramic crucible 2 via the gas supply pipe 7 (atmosphere replacement step). Ar gas is heavier than air. Therefore, when Ar gas is supplied into the oxide ceramic crucible 2, the Ar gas accumulates from the bottom of the oxide ceramic crucible 2, and the air is discharged through the funnel-shaped mold 5. As a result, the atmosphere inside the funnel-shaped mold 5 and the oxide ceramic crucible 2 is replaced with an Ar atmosphere, and contact between the molten raw material 3a, which is formed by dissolving the raw material 3, and air can be avoided.

[0064] Subsequently, the oxide ceramic crucible 2 is heated using a high-frequency coil 4 installed in the atmospheric melting furnace 1, and the raw material 3 is melted to form the molten raw material 3a, as shown in Figure 3 (heating step). In this embodiment, even after the inside of the funnel-shaped mold 5 and the inside of the oxide ceramic crucible 2 have been replaced with an Ar atmosphere, it is preferable to continue supplying Ar gas to the oxide ceramic crucible 2 until just before the lid 5a is installed on the narrower opening of the funnel-shaped mold 5 (see Figure 5). This effectively suppresses the mixing of oxygen from the air into the molten raw material 3a, and further reduces the oxygen content in the TiAl alloy casting material obtained after casting.

[0065] In the melting process of this embodiment, it is preferable to melt the raw material 3 while observing the inside of the oxide ceramic crucible 2 through the narrower opening of the funnel-shaped mold 5 using visual inspection or a camera. This allows confirmation of the melting status of the raw material 3 and whether or not all of the raw material 3 has melted.

[0066] Next, in the melting process of this embodiment, as shown in Figure 4, a funnel 8 is placed in the narrower opening of the funnel-shaped mold 5, and the remaining raw material 3 is added to the oxide ceramic crucible 2 in one or more batches through the funnel 8 and the funnel-shaped mold 5.

[0067] In the method for manufacturing TiAl alloy castings of this embodiment, the example given is that a portion of the raw material 3 is melted in the oxide ceramic crucible 2 to form molten metal, and then the remaining raw material 3 is added to the oxide ceramic crucible 2 in one or more batches. However, all of the raw material 3 may be melted in the oxide ceramic crucible 2 before melting, or a portion of the raw material 3 may be melted in the oxide ceramic crucible 2 while the remaining raw material 3 is added to the oxide ceramic crucible 2 in one or more batches. When raw material 3 is added to the oxide ceramic crucible 2 in multiple steps, different raw materials 3 may be added each time, some of the steps may be the same, or the same raw material may be added each time. This can be determined as appropriate depending on the composition and shape of raw material 3.

[0068] Furthermore, in the method for producing the TiAl alloy casting material of this embodiment, the entire amount of the deoxidizing agent containing Ca was placed in the oxide ceramic crucible 2 along with the raw material 3. However, the deoxidizing agent containing Ca may also be added to the molten raw material 3a (molten metal) placed in the oxide ceramic crucible 2 via a funnel-shaped mold 5. Furthermore, in the method for producing TiAl alloy castings according to this embodiment, the deoxidizing agent containing Ca may be added to the raw material 3 and / or molten raw material 3a in multiple steps. That is, a portion of the deoxidizing agent containing Ca may be placed in the oxide ceramic crucible 2 together with the raw material 3, and the remaining deoxidizing agent containing Ca may be added to the molten raw material 3a in the oxide ceramic crucible 2 in one or more steps via the funnel-shaped mold 5.

[0069] [Deoxidation process] In this embodiment, after confirming that all of the raw material 3 has dissolved, in the deoxidation step, the molten raw material 3a containing the deoxidizing agent is heated and melted in an oxide ceramic crucible 2 whose opening is covered by a funnel-shaped mold 5, and the molten state is maintained. This homogenizes the components contained in the molten raw material 3a. At the same time, a fume containing the reaction product of oxygen and Ca in the molten raw material 3a is generated and discharged through the funnel-shaped mold 5, thereby removing oxygen from the molten raw material 3a.

[0070] The time for heating and holding the molten raw material 3a containing the deoxidizing agent is preferably 2 to 10 minutes, and more preferably 3 to 5 minutes, after all of the raw material 3 has melted and become the molten raw material 3a containing the deoxidizing agent. If the time for holding the molten raw material 3a containing the deoxidizing agent in a molten state is 2 minutes or more, the reaction between oxygen and Ca in the molten raw material 3a proceeds sufficiently. As a result, the generation of fumes containing the reaction products of oxygen and Ca in the molten raw material 3a is promoted, and the effect of removing oxygen from the molten raw material 3a becomes even more pronounced. If the time for heating and holding the molten raw material 3a containing the deoxidizing agent in a molten state is 10 minutes or less, the oxygen content in the TiAl alloy casting material obtained after casting can be reduced without hindering the productivity of the TiAl alloy casting material.

[0071] The temperature at which the raw material 3a containing the deoxidizing agent is heated and held in a molten state is preferably 1650°C to 1750°C, and more preferably 1675°C to 1725°C. If the temperature at which the raw material 3a containing the deoxidizing agent is held in a molten state is 1650°C or higher, the reaction between oxygen and Ca in the raw material 3a is promoted, and the generation of fumes containing reaction products is promoted, so the effect of removing oxygen from the raw material 3a becomes even more pronounced. If the temperature at which the raw material 3a containing the deoxidizing agent is heated and held in a molten state is 1750°C or lower, the reaction between the oxide ceramic crucible 2 and the raw material 3a is suppressed, which is preferable.

[0072] In this embodiment, it is preferable to heat the raw material 3 in the oxide ceramic crucible 2 using a high-frequency coil 4, melt the raw material 3 in the oxide ceramic crucible 2 to obtain a molten raw material 3a containing a deoxidizing agent, and then continue heating the molten raw material 3a to maintain its molten state, thereby performing the deoxidation process. This allows for the efficient production of TiAl alloy castings.

[0073] In this embodiment, after the deoxidation process, a lid 5a is placed over the narrower opening of the funnel-shaped mold 5, as shown in Figure 5. The lid 5a can be made of, for example, cast iron or carbon steel, and may have a ceramic coating such as zircon applied to its inner surface to prevent reaction with the molten raw material 3a.

[0074] Subsequently, in this embodiment, as shown in Figure 6, the atmospheric melting furnace 1 is inverted upside down with the oxide ceramic crucible 2 and the funnel-shaped mold 5 integrated together, and the molten raw material 3a is poured from the oxide ceramic crucible 2 into the funnel-shaped mold 5 and cooled (casting process). This yields the TiAl alloy casting material 3b. Subsequently, as shown in Figure 7, the TiAl alloy casting material 3b is removed from the funnel-shaped mold 5 and cut, separating it into a product portion 3c consisting of the parts that will become the product, and a reusable portion 3e consisting of the parts that will not become the product due to the formation of shrinkage cavities 3d. The reusable portion 3e is TiAl alloy casting scrap and can be reused as raw material 3 for the TiAl alloy casting material 3b.

[0075] (Other examples) The method for manufacturing the TiAl alloy casting material according to this embodiment is not limited to the embodiment described above. For example, in the embodiments described above, an example of a method for manufacturing TiAl alloy castings was explained using an apparatus equipped with an oxide ceramic crucible 2 installed in an atmospheric melting furnace 1 as shown in Figure 1. However, a vacuum melting furnace may be used instead of an atmospheric melting furnace. As a vacuum melting furnace, a known type can be used; for example, a general vacuum induction melting furnace (VIM furnace) can be used.

[0076] When using a vacuum melting furnace, it is preferable to use the following method. Specifically, in the deoxidizing agent addition step, the entire amount of the deoxidizing agent is placed in an oxide ceramic crucible installed in the vacuum melting furnace along with the raw materials. Then, the inside of the vacuum melting furnace is evacuated and Ar gas is supplied to replace the atmosphere inside the vacuum melting furnace with an Ar gas atmosphere. Then, in the melting step, the entire amount of the raw materials is melted in the oxide ceramic crucible installed in the vacuum melting furnace, which is now under an Ar atmosphere, to obtain molten metal.

[0077] When using a vacuum melting furnace, it is preferable to melt the raw material 3 while observing the inside of the oxide ceramic crucible 2 through a quartz window installed in the vacuum induction melting furnace using a camera installed at the top of the furnace. This allows confirmation of the melting status of the raw material 3 and whether or not all of the raw material 3 has melted. Subsequently, in the deoxidation process, the molten metal containing the deoxidizing agent is heated in an oxide ceramic crucible placed in a vacuum melting furnace under an Ar atmosphere, and the molten state is maintained to remove oxygen from the molten metal.

[0078] The method for producing the TiAl alloy casting material of this embodiment includes a step of adding a deoxidizing agent containing Ca to either or both of the raw material 3 containing Ti and Al and various additive elements, and the molten raw material 3a obtained by melting the raw material 3, wherein the Ca concentration in the total mass of the raw material 3 and the deoxidizing agent is 0.2 mass% to 1.0 mass%, and a deoxidation step of heating the molten raw material 3a containing the deoxidizing agent and maintaining a molten state to generate a fume containing the reaction product of oxygen and Ca in the molten raw material 3a, thereby removing oxygen from the molten raw material 3a. As a result, the TiAl alloy casting material obtained by performing the casting step described above after the deoxidation step contains 0.04 mass% to 0.12 mass% of oxygen and 0.01 mass% to 0.07 mass% of Ca, and has excellent impact resistance properties.

[0079] Therefore, according to the method for manufacturing TiAl alloy castings of this embodiment, a TiAl alloy casting with a sufficiently low oxygen content can be obtained without using special equipment or special raw materials with low oxygen content. Specifically, the method for manufacturing TiAl alloy castings of this embodiment can use a variety of equipment, such as equipment equipped with an oxide ceramic crucible 2 installed in an atmospheric melting furnace 1 or a vacuum melting furnace, and a variety of raw materials, such as TiAl alloy cutting chips and TiAl alloy casting scrap, which have a high oxygen content, without limitation.

[0080] [TiAl alloy casting material] The TiAl alloy casting material of this embodiment contains 0.04% to 0.10% by mass of oxygen and 0.01% to 0.03% by mass of Ca. Because the oxygen content of the TiAl alloy casting material of this embodiment is 0.10% by mass or less and the Ca content is 0.03% by mass or less, it has excellent impact resistance. Furthermore, because the oxygen content is 0.04% by mass or more, the amount of Ca-containing deoxidizing agent used can be reduced when manufacturing using the manufacturing method of the TiAl alloy casting material of this embodiment. As a result, the Ca content in the TiAl alloy casting material can be reduced to 0.03% by mass or less. Also, because the Ca content is 0.01% by mass or more, a sufficient amount of Ca-containing deoxidizing agent can be secured when manufacturing using the manufacturing method of the TiAl alloy casting material of this embodiment, and the deoxidizing effect from the addition of the deoxidizing agent can be fully obtained. Therefore, various devices such as those equipped with an oxide ceramic crucible 2 installed in an atmospheric melting furnace 1 or a vacuum melting furnace, and various raw materials such as TiAl alloy cutting chips and TiAl alloy casting scrap can be used.

[0081] The TiAl alloy casting material of this embodiment may contain 31.9% to 34.2% by mass of Al, 4.0% to 5.4% by mass of Nb, 2.3% to 3.0% by mass of Cr, 0.04% to 0.12% by mass of oxygen, and 0.01% to 0.07% by mass of Ca, with the remainder being Ti and impurities. Such a TiAl alloy casting material has excellent impact resistance and good machinability, tensile strength, and creep strength, making it suitable for use as a material for jet engine blades and turbine wheels.

[0082] The TiAl alloy casting material of this embodiment may contain 32.9% to 33.8% by mass of Al, 4.4% to 5.0% by mass of Nb, 2.5% to 2.8% by mass of Cr, 0.04% to 0.12% by mass of oxygen, and 0.01% to 0.07% by mass of Ca, with the remainder being Ti and impurities. Such a TiAl alloy casting material has superior impact resistance, and also superior machinability, tensile strength, and creep strength, making it particularly suitable as a material for jet engine blades and turbine wheels.

[0083] The TiAl alloy castings of this embodiment can all be manufactured using the method for manufacturing TiAl alloy castings of this embodiment described above, by appropriately changing conditions such as the composition of raw material 3, the type and amount of deoxidizing agent containing Ca, and the atmosphere, temperature, and time used to heat the molten raw material 3a containing the deoxidizing agent.

[0084] [Motor blades for jet engines][Turbine wheels] The rotor blades and turbine wheels for the jet engine in this embodiment are made from the Al alloy casting material of this embodiment. Therefore, they have excellent impact resistance. The rotor blades and turbine wheels for the jet engine of this embodiment can be manufactured by machining the Al alloy casting of this embodiment, for example, using a known method. The TiAl alloy chips generated when machining the TiAl alloy casting are casting scrap and can be reused as raw material 3 for the TiAl alloy casting 3b.

[0085] Although embodiments of the present invention have been described in detail above, the configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications to the configurations are possible without departing from the spirit of the present invention. [Examples]

[0086] "Experimental Example 1" An air melting furnace 1 of the inversion furnace (rollover furnace) type, as shown in Figure 1, was used, and an oxide ceramic crucible 2 made of calcia was placed inside the air melting furnace 1. We prepared raw materials for each metal element, consisting of sponge titanium (product name: TST-1; manufactured by Toho Titanium Co., Ltd.), Al granules (pellets) (manufactured by Furuuchi Chemical Co., Ltd.), Nb flakes (manufactured by Rare Meta-Alic Co., Ltd.), and Cr granules (manufactured by Furuuchi Chemical Co., Ltd.). In addition, we prepared an AlCa alloy with a Ca content of 5% by mass as a deoxidizing agent containing Ca.

[0087] Each of the above metal element raw materials was weighed, and a raw material consisting of 33.4% by mass of Al, 4.8% by mass of Nb, 2.7% by mass of Cr, with the remainder being Ti and impurities was prepared. A deoxidizing agent containing Ca was added to the raw material to obtain the deoxidizing agent-containing raw material of Experimental Example 1, which contained 0.10% by mass of Ca. In other words, the Al content in the deoxidizing agent-containing raw material in Experimental Example 1 is the ratio of the total amount of Al grains contained in the deoxidizing agent-containing raw material to the amount of A1 in the AlCa alloy. Then, 500g of the deoxidizing agent-containing raw material from Experimental Example 1 was placed in the oxide ceramic crucible 2.

[0088] Next, as shown in Figure 2, the funnel-shaped mold 5 was placed on the furnace wall 1b of the atmospheric melting furnace 1 with its wider opening facing the oxide ceramic crucible 2 so as to cover the opening of the oxide ceramic crucible 2 (mold installation process). The funnel-shaped mold 5 used was a mold with a two-part structure made of carbon steel and coated on its inner surface with zircon paint (product name: Oka Paint 308; manufactured by Okazaki Mining Co., Ltd.). Next, as shown in Figure 2, a cement-based sealing material 6 was installed at the contact point between the funnel-shaped mold 5 and the furnace wall 1b of the atmospheric melting furnace 1.

[0089] Next, a gas supply pipe 7 was inserted through the narrower opening of the funnel-shaped mold 5, and Ar gas was supplied into the oxide ceramic crucible 2 via the gas supply pipe 7 (atmosphere replacement step). The supply of Ar gas into the oxide ceramic crucible 2 was continued until just before the lid 5a was placed over the narrower opening of the funnel-shaped mold 5 (see Figure 5). Subsequently, the oxide ceramic crucible 2 was heated using the high-frequency coil 4 installed in the atmospheric melting furnace 1, and the deoxidizing agent-containing raw material was dissolved to obtain the melting raw material 3a, as shown in Figure 3 (heating step).

[0090] The inside of the oxide ceramic crucible 2 was observed using a camera through the narrower opening of the funnel-shaped mold 5, and it was confirmed that all of the deoxidizing agent-containing raw material had dissolved. The oxide ceramic crucible 2 was then continuously heated to maintain the molten state of the molten raw material 3a containing the deoxidizing agent, after all of the deoxidizing agent-containing raw material had dissolved, at 1700°C for 3 minutes (deoxidation process). Subsequently, as shown in Figure 5, a lid 5a was placed over the narrower opening of the funnel-shaped mold 5. The lid 5a was made of carbon steel and had its inner surface coated with zircon paint (product name: Oka Paint 308; manufactured by Okazaki Mining Products Co., Ltd.).

[0091] Subsequently, as shown in Figure 6, the air melting furnace 1 was inverted while the funnel-shaped mold 5 and the air melting furnace 1 were integrated, and the molten raw material 3a was poured from the oxide ceramic crucible 2 into the funnel-shaped mold 5 and cooled (casting process). This yielded the TiAl alloy casting material 3b of Experimental Example 1, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0092] "Experimental Examples 2-5" The same raw materials as in Experimental Example 1 were weighed, and the same Ca-containing deoxidizing agent as in Experimental Example 1 was added to the raw materials to obtain a deoxidizing agent-containing raw material with the Ca content (amount added) shown in Table 1. Except for this, the process was the same as in Experimental Example 1 to obtain the TiAl alloy casting material 3b of Experimental Examples 2 to 5, which are roughly cylindrical ingots with a diameter of 40 mm and a length of 100 mm.

[0093] "Experimental Example 6" In Experimental Example 6, a TiAl alloy casting material 3b, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm, was obtained in the same manner as in Experimental Example 1, except that the raw material of Experimental Example 1 was used instead of the raw material containing the deoxidizing agent used in Experimental Example 1.

[0094] "Experimental Example 7" TiAl alloy cutting chips and TiAl alloy casting scrap were prepared using the same raw materials as in Experimental Example 1, with the same Ti, Al, Nb, and Cr content. The TiAl alloy cutting chips were ultrasonically cleaned with acetone before use. The TiAl alloy casting scrap was surface-pickled before use.

[0095] Then, of the metal element raw materials used in Experimental Example 1, 25% by mass was used as TiAl alloy cutting chips and 25% by mass was used as TiAl alloy casting scrap, and these were used as the raw materials for Experimental Example 7. Except for adding the same Ca-containing deoxidizing agent as in Experimental Example 1 to the raw materials for Experimental Example 7 to obtain the deoxidizing agent-containing raw material for Experimental Example 7 containing 0.10% by mass of Ca, the procedure was the same as in Experimental Example 1 to obtain the TiAl alloy casting material 3b of Experimental Example 7, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0096] "Experimental Examples 8-11" The same raw materials as in Experimental Example 7 were weighed, and a deoxidizing agent containing the same amount of Ca as in Experimental Example 1 was added to the raw materials to obtain a deoxidizing agent-containing raw material with the Ca content (amount added) shown in Table 1. Except for this, the process was the same as in Experimental Example 7 to obtain the TiAl alloy casting material 3b of Experimental Examples 8 to 11, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0097] "Experimental Example 12" Except for using the raw materials from Experimental Example 7 instead of the deoxidizing agent-containing raw materials from Experimental Example 7, the same procedure as in Experimental Example 7 was used to obtain the TiAl alloy casting material 3b of Experimental Example 12, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0098] "Experimental Example 13" Instead of the atmospheric melting furnace 1 shown in Figure 1, a vacuum induction melting furnace (VIM furnace) was used, and an oxide ceramic crucible 2 made of the same calcia as in Experimental Example 1 was placed inside the vacuum induction melting furnace. Then, in the same manner as in Experimental Example 1, 500g of the deoxidizing agent-containing raw material from Experimental Example 1 was placed into the oxide ceramic crucible 2.

[0099] Next, the vacuum melting furnace was evacuated and then Ar gas was supplied to replace the atmosphere inside the furnace with an Ar atmosphere. Subsequently, the deoxidizing agent-containing raw material was heated and melted in the oxide ceramic crucible 2 using an induction heating device installed in the vacuum induction melting furnace to obtain the melted raw material 3a (heating step). Then, using a camera installed at the top of the vacuum induction melting furnace, the inside of the oxide ceramic crucible 2 was observed through a quartz window installed in the vacuum induction melting furnace to confirm that all of the deoxidizing agent-containing raw material had melted. The oxide ceramic crucible 2 was then continuously heated to maintain the molten state of the melted raw material 3a containing the deoxidizing agent, after all of the deoxidizing agent-containing raw material had melted, at 1700°C for 3 minutes (deoxidation step).

[0100] Subsequently, the molten raw material 3a was poured from the oxide ceramic crucible 2 into a mold with a cylindrical inner surface placed inside a vacuum melting furnace and cooled (casting process). This yielded the TiAl alloy casting material 3b of Experimental Example 13, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0101] "Experimental Examples 14-17" The same raw materials as in Experimental Example 1 were weighed, and the same Ca-containing deoxidizing agent as in Experimental Example 1 was added to the raw materials to obtain a deoxidizing agent-containing raw material with the Ca content (amount added) shown in Table 2. Except for this, the process was the same as in Experimental Example 13 to obtain the TiAl alloy casting material 3b of Experimental Examples 14 to 17, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0102] "Experimental Example 18" Except for using the raw materials from Experimental Example 1 instead of the deoxidizing agent-containing raw materials from Experimental Example 1, the same procedure as in Experimental Example 13 was used to obtain the TiAl alloy casting material 3b of Experimental Example 18, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0103] "Experimental Example 19" Except for using the deoxidizing agent-containing raw material from Experimental Example 7, the same procedure as in Experimental Example 13 was used to obtain the TiAl alloy casting material 3b of Experimental Example 19, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0104] "Experimental Examples 20-23" The same raw materials as in Experimental Example 7 were weighed, and a deoxidizing agent containing the same amount of Ca as in Experimental Example 1 was added to the raw materials to obtain a deoxidizing agent-containing raw material with the Ca content (amount added) shown in Table 2. Except for this, the process was the same as in Experimental Example 13 to obtain the TiAl alloy casting material 3b of Experimental Examples 20 to 23, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0105] "Experimental Example 24" Except for using the raw materials from Experimental Example 7 instead of the deoxidizing agent-containing raw materials from Experimental Example 7, the same procedure as in Experimental Example 13 was used to obtain the TiAl alloy casting material 3b of Experimental Example 24, which is a roughly cylindrical ingot with a diameter of 40 mm and a length of 100 mm.

[0106] Tables 1 and 2 show the type of melting furnace used during manufacturing, the material of the crucible, the atmosphere inside the crucible while heating, the amount of Ca added (Ca concentration in the deoxidizing agent-containing raw material), the amount of TiAl alloy cutting chips added (content in the deoxidizing agent-containing raw material excluding the deoxidizing agent), and the amount of TiAl alloy casting scrap added (content in the deoxidizing agent-containing raw material excluding the deoxidizing agent) for the TiAl alloy casting materials of Experimental Examples 1 to 24. Furthermore, Tables 1 and 2 indicate the distinction between inventive examples and comparative examples for the TiAl alloy castings in Experimental Examples 1 to 24.

[0107] [Measurement of oxygen and calcium content] The TiAl alloy castings 3b obtained in Experimental Examples 1 to 24 were analyzed using an infrared absorption spectrometer (product name: EMGA-930; manufactured by HORIBA Corporation) to determine their oxygen content. Furthermore, the TiAl alloy castings 3b from Experimental Examples 1 to 24 were analyzed using a high-frequency inductively coupled plasma (ICP) emission spectrometer (product name: ICP-OES; manufactured by HORIBA Corporation) to determine their Ca content. The results are shown in Tables 1 and 2.

[0108] [Charpy impact test] The TiAl alloy castings 3b from Experimental Examples 1 to 24 were each subjected to a heat treatment by heating at 1200°C for 4 hours. These heat treatment conditions are the same as those typically used in hot isohydrostatic pressing (HIP) when manufacturing jet engine rotor blades made of TiAl alloy. Subsequently, a 55 mm long test specimen with a square cross-section of 10 mm x 10 mm was taken from the center of each TiAl alloy casting 3b, and a Charpy impact test was performed at room temperature. The results are shown in Tables 1 and 2.

[0109] In the Charpy impact test, a small 7.5J capacity tester (product name: impact Tester; manufactured by Toyo Seiki Co., Ltd.) was used to minimize measurement errors. Furthermore, notching the test specimens would result in extremely small impact values ​​for all experimental cases, making it difficult to clearly evaluate the differences between each case. Therefore, notching was not applied to the test specimens.

[0110] (Evaluation criteria) The Charpy impact value of the TiAl alloy casting material 3b in Experimental Examples 1 to 24 was 2.0 J / cm². 2 Items meeting the above (evaluation standard) will be considered good quality. The evaluation criteria for the Charpy impact value of TiAl alloy castings were determined based on the test results shown below.

[0111] A TiAl alloy casting material, which serves as a conventional jet engine rotor blade, was manufactured using the method described below. Specifically, a raw material consisting of 33.4 mass% Al, 4.8 mass% Nb, 2.7 mass% Cr, 0.08 mass% oxygen, with the remainder being Ti and impurities, was melted using a water-cooled copper crucible placed in a vacuum melting furnace under a vacuum atmosphere. The melted material was then poured into the same mold as in Experimental Example 13, which was also placed in the vacuum melting furnace, and cooled. This produced three evaluation TiAl alloy castings, which were approximately cylindrical ingots with a diameter of 40 mm and a length of 100 mm.

[0112] Three evaluation TiAl alloy castings were subjected to Charpy impact tests in the same manner as in Experimental Example 1. The result showed a Charpy impact value of 2.0 J / cm². 2 ~2.5J / cm 2 It was within the range. This indicates that the Charpy impact value of the TiAl alloy casting is 2.0 J / cm². 2 If the above is true, it can be evaluated that it has impact resistance properties equivalent to those of conventional TiAl alloy castings used for jet engine blades. Therefore, the evaluation standard value for the Charpy impact value of the TiAl alloy casting in this experimental example is 2.0 J / cm². 2 That concludes my explanation.

[0113] [Table 1]

[0114] [Table 2]

[0115] As shown in Tables 1 and 2, the TiAl alloy castings of the inventive examples, in which the deoxidizing agent was added so that the Ca concentration in the total mass of the raw material and the deoxidizing agent was 0.2% to 1.0%, all had an oxygen content of 0.12% or less (the specified (internal standard) value) and a Ca content within the range of 0.01% to 0.07%. Furthermore, all of the TiAl alloy castings of the inventive examples had a Charpy impact value of 2.0 J / cm², which was the evaluation standard value. 2 In conclusion, it was confirmed that the material possesses impact resistance properties equivalent to or better than those of conventional TiAl alloy castings used for jet engine blades.

[0116] From this, it was confirmed that by using raw materials in which the oxygen content of TiAl alloy castings produced without the addition of a deoxidizing agent (Experimental Examples 6, 12, 18, 24) is in the range of 0.175 mass% to 0.284 mass%, and by using a manufacturing method that differs only in that the Ca concentration in the total mass of the raw materials and the deoxidizing agent is 0.2 mass% to 1.0 mass%, it is possible to obtain TiAl alloy castings containing 0.04 mass% to 0.10 mass% of oxygen and 0.01 mass% to 0.03 mass% of Ca.

[0117] Furthermore, from the results of Experimental Examples 1 to 24, it was confirmed that by adding the deoxidizing agent so that the Ca concentration in the total mass of the raw material and the deoxidizing agent is 0.2% by mass to 1.0% by mass, a variety of apparatuses and raw materials can be used, such as a method using an apparatus equipped with an oxide ceramic crucible 2 installed in an atmospheric melting furnace 1, where the inside of the crucible is heated in an Ar reflux atmosphere; a method using an apparatus equipped with an oxide ceramic crucible 2 installed in a vacuum melting furnace, where the inside of the crucible is heated in an Ar atmosphere; and a method using raw materials including TiAl alloy cutting chips and TiAl alloy casting scrap.

[0118] More specifically, in Experimental Examples 1 and 13, the Ca concentration in the total mass of the raw material and deoxidizer was 0.1% by weight, resulting in insufficient deoxidation effect by Ca and an oxygen content exceeding the specified value. As a result, the Charpy impact value exceeded the evaluation standard value of 2.0 J / cm. 2 The value was less than [value]. In Experimental Examples 5 and 17, the Ca concentration in the total mass of the raw material and deoxidizer is 1.1% by weight, meaning that although the oxygen concentration is low, the Ca content is high. As a result, the Charpy impact value is 2.0 J / cm, which was the evaluation standard value. 2 The value was less than [value].

[0119] Also, in Experimental Example 7 and Experimental Example 19 using raw materials including TiAl alloy cutting chips and TiAl alloy casting scraps, similar to Example 1 and Experimental Example 13, since the Ca concentration in the total mass of the raw material and the deoxidizer was 0.1% by weight, the deoxidation effect by Ca was insufficient, and the oxygen content exceeded the specified value. As a result, the Charpy impact value was less than 2.0 J / cm 2 which was the evaluation criterion value.

[0120] Also, in Experimental Example 11 and Experimental Example 23 using raw materials including TiAl alloy cutting chips and TiAl alloy casting scraps, similar to Experimental Example 5 and Experimental Example 17, since the Ca concentration in the total mass of the raw material and the deoxidizer was 1.1% by weight, although the oxygen concentration was low, the Ca content was high. As a result, the Charpy impact value was less than 2.0 J / cm 2 which was the evaluation criterion value.

Industrial Applicability

[0121] It is possible to obtain a TiAl alloy casting material with a sufficiently low oxygen content without using special equipment, special materials, etc.

Explanation of Signs

[0122] 1 Atmosphere melting furnace 1a Accommodation part 1b Furnace wall 2 Oxide ceramic crucible 3 Raw material 3a Melting raw material 3b TiAl alloy casting material 3c Product part 3d Shrinkage cavity 3e Reuse part 4 High-frequency coil 5 Funnel-shaped mold 5a Lid 6 Sealing material 7 Gas supply pipe 8 Funnel

Claims

1. A TiAl alloy casting material characterized by containing 31.9% to 34.2% by mass of Al, 4.0% to 5.4% by mass of Nb, 2.3% to 3.0% by mass of Cr, 0.04% to 0.12% by mass of oxygen, and 0.01% to 0.07% by mass of Ca, with the remainder being Ti and impurities.

2. A rotor blade for a jet engine, characterized by being made of the TiAl alloy casting material described in claim 1.

3. A turbine wheel characterized by being made of the TiAl alloy casting material described in claim 1.

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