Tial alloy material, method for producing tial alloy material, component formed of tial alloy, and rotor blade for jet engine

Abstract

Disclosed is a method for producing a TiAl alloy material, the method including: a melting step in which a starting material is put into a calcia crucible and the starting material is melted in an atmosphere that has an oxygen concentration of 0.02 vol% to 0.5 vol% and a nitrogen concentration of 0.1 vol% to 2.5 vol% so as to form an alloy melt, the starting material being composed of alloy forming elements that include titanium and aluminum, calcium having a content of 0.1 mass% to 0.3 mass% in the starting material, oxygen having a content of 0.2 mass% or less in the starting material, nitrogen having a content of 0.02 mass% or less in the starting material, carbon having a content of 0.03 mass% or less in the starting material, and inevitable impurities; and a casting step in which the alloy melt is poured into a mold.

Description

TiAl alloy material, manufacturing method of TiAl alloy material, TiAl alloy part, and jet engine rotor blade

[0001] This disclosure relates to a TiAl alloy material, a method for manufacturing the TiAl alloy material, a TiAl alloy part, and a jet engine rotor blade. This application claims priority to Japanese Patent Application No. 2024-030547, filed on February 29, 2024, the contents of which are incorporated herein by reference.

[0002] Many applications of TiAl alloys have been explored. In the past, TiAl alloys have been put to practical use as materials for parts such as passenger car turbochargers and racing engine valves. Currently, most of the TiAl alloys produced are used as materials for the final stage turbine blades of jet engines.

[0003] Currently, among the jet engines that use jet engine blades made of TiAl alloy, the jet engine with the largest production volume is CFM International's LEAP (Leading Edge Aviation Propulsion). More than 100,000 LEAP jet engine blades are manufactured annually. LEAP jet engine blades use a TiAl alloy material made of TiAl4822 (Ti-48.0Al-2Nb-2Cr (atomic %)).

[0004] There are various methods for manufacturing TiAl alloy materials used for jet engine rotor blades, including casting, forging, additive manufacturing, etc. Currently, casting is the main method used for manufacturing TiAl alloy materials used for jet engine rotor blades.

[0005] Patent Document 1 discloses a method for producing a TiAl alloy ingot by melting Ti and Al by high-frequency induction melting in a ceramic crucible using yttria as a material, and pouring the resulting molten metal into a mold to produce a TiAl alloy ingot.

[0006] Patent Document 2 discloses a technique for producing an intermetallic compound TiAl-based alloy by vacuum induction melting. Patent Document 2 describes that a crucible made of calcia or a crucible lined with calcia is heated in a vacuum to perform a degassing treatment, and then raw materials are charged into the crucible and melted by vacuum induction melting. In the examples of Patent Document 2, the degree of vacuum in the melting furnace is set to 5×10 －４ It is described that the pressure was kept at Torr, and after the raw materials were dissolved, Ar gas was introduced.

[0007] Patent Document 3 discloses a method for producing a TiAl-based intermetallic compound alloy. Patent Document 3 describes that when raw materials consisting of titanium and aluminum are melted in a calcia crucible to produce a TiAl-based intermetallic compound alloy, the titanium raw material is heated in a vacuum and degassed in advance, and then the titanium and aluminum raw materials are charged into the crucible and melted by a vacuum induction melting method.

[0008] Patent Document 4 describes a method for producing a porous sintered body having interconnected pores suitable for molten metal filters, etc. Patent Document 4 also describes a method for producing a porous sintered body by filling the voids of a resin particle molded body formed by bonding resin particles with a slurry of inorganic powder. Examples of inorganic powders include oxides such as alumina, zirconia, zircon, cordierite, mullite, silica, aluminum titanate, and titania.

[0009] Patent Document 5 describes a porous filter for filtering inclusions contained in molten metal when the molten metal is cast and contains iron, nickel, and cobalt as its main components. Example 1 of Patent Document 5 describes that a flexible polyurethane foam (100 x 100 x 20 mm thick) having a three-dimensional skeleton is impregnated with a slurry, dried at 120°C, and then the organic matter is burned off at 600°C, followed by sintering.

[0010] Japanese Unexamined Patent Publication No. 2011-36877 (A) Japanese Unexamined Patent Publication No. 1983-223172 (A) Japanese Unexamined Patent Publication No. 3-199330 (A) Unexamined Japanese Patent Application No. 63-265880 (A) Unexamined Japanese Patent Application No. 2001-347364 (A)

[0011] In TiAl alloy parts currently in practical use, of course, upper limits are set for the concentrations of impurity elements contained in the TiAl alloy material. For example, for jet engine blades made of TiAl alloy material, oxygen, which is the most likely impurity element to be mixed into the TiAl alloy material, is specified to be 0.15% by mass or less. Furthermore, for jet engine blades made of TiAl alloy material, the upper limits for the nitrogen concentration, carbon concentration, and calcium concentration, which are impurity elements, are specified to be 0.03% by mass or less, 0.02% by mass or less, and 0.10% by mass or less.

[0012] When the oxygen concentration of a TiAl alloy material exceeds a specified value, its machinability deteriorates. Furthermore, when the oxygen concentration of a TiAl alloy material exceeds a specified value, its impact resistance also deteriorates. Therefore, for example, jet engine rotor blades made of a TiAl alloy material having an oxygen concentration exceeding the specified value may be susceptible to damage due to high-speed collisions with debris during operation.

[0013] Currently, when TiAl alloy materials are produced using a casting method, a method is used that takes into consideration the oxygen concentration in the molten alloy obtained by melting raw materials so that the oxygen concentration does not increase, so that the oxygen concentration is below a specified value. Specifically, a vacuum melting furnace is used to melt the raw materials in a high vacuum, or in an atmosphere that has been evacuated to a high vacuum and then partially replaced with an inert gas such as Ar, to produce a molten alloy. However, this method requires that the chamber of the vacuum melting furnace be evacuated to a high vacuum in order to melt the raw materials. This requires a significant amount of time and increases production costs.

[0014] Furthermore, a water-cooled copper crucible is usually used when melting raw materials. The use of a water-cooled copper crucible can suppress an increase in oxygen concentration due to oxygen being mixed into the molten alloy from the crucible. However, when melting raw materials using a water-cooled copper crucible, the following problems (1) to (4) arise. For this reason, TiAl alloy parts, such as jet engine blades, manufactured by the method of melting raw materials using a water-cooled copper crucible are very expensive.

[0015] (1) When raw materials are melted using a water-cooled copper crucible, unmelted material called skull adheres to the surface of the crucible because the crucible is water-cooled. The skull causes the TiAl alloy to have non-uniform compositions. Therefore, when melting raw materials using a water-cooled copper crucible, double melting is performed to homogenize the compositions of the TiAl alloy. That is, when melting raw materials using a water-cooled copper crucible, a master alloy ingot is produced using the molten alloy obtained by melting the raw materials in the first melting step. Then, the master alloy ingot is melted in the second melting step to produce the target TiAl alloy. Therefore, melting raw materials using a water-cooled copper crucible requires more time and effort than producing a TiAl alloy using a molten alloy obtained by a single melting step, which involves only one melting step.

[0016] (2) When melting raw materials using a water-cooled copper crucible, it is difficult to increase the amount of molten alloy that can be produced in one melting. As a result, the number of products that can be cast in one batch is small, resulting in insufficient productivity. (3) When melting raw materials using a water-cooled copper crucible, it is difficult to increase the superheat temperature of the molten alloy because the crucible is water-cooled. As a result, when casting the molten alloy obtained by melting the raw materials, poor melt flow is likely to occur, and the yield of good products is likely to be insufficient.

[0017] (4) A melting furnace using a water-cooled copper crucible is a special piece of equipment, and therefore requires a high initial investment.

[0018] In contrast, when producing casting materials made of general-purpose iron-based alloys and Ni-based alloys, for example, a method is generally used in which raw materials are melted in a low vacuum atmosphere using an oxide ceramic crucible. When melting raw materials in a low vacuum atmosphere, it is not necessary to evacuate the chamber to a high vacuum. Therefore, the time required to melt the raw materials can be significantly reduced compared to when evacuating the chamber to a high vacuum.

[0019] Furthermore, when melting raw materials using an oxide ceramic crucible, there is no need to cool the crucible as in the case of melting raw materials using a water-cooled copper crucible, and the surface temperature of the crucible can be increased. Therefore, unlike when melting raw materials using a water-cooled copper crucible, skulls do not adhere to the surface of the crucible. Therefore, a cast material having homogenized alloy components can be produced using a molten alloy obtained by a single melting process performed only once. Furthermore, when melting raw materials using an oxide ceramic crucible, there is no need to cool the crucible, so a large amount of molten alloy can be produced in one melting, resulting in excellent productivity. Furthermore, when melting raw materials using an oxide ceramic crucible, the surface temperature of the crucible can be increased, which reduces the risk of poor flow and improves castability. Furthermore, when melting raw materials using an oxide ceramic crucible, the initial capital investment and the amount of electricity required to melt the raw materials are significantly less than when melting raw materials using a water-cooled copper crucible.

[0020] As described above, when melting raw materials using an oxide ceramic crucible, the cost required to manufacture parts made of cast materials is significantly lower than when melting raw materials using a water-cooled copper crucible. Therefore, when manufacturing cast materials made of iron-based alloys, Ni-based alloys, etc., melting raw materials using a water-cooled copper crucible is rarely performed.

[0021] However, the molten alloy obtained by melting TiAl alloy raw materials is much more active than the molten alloy obtained by melting iron-based alloy raw materials and the molten alloy obtained by melting Ni-based alloy raw materials. Therefore, when TiAl alloy raw materials are melted in an oxide ceramic crucible in a low vacuum atmosphere, oxygen and nitrogen from the atmosphere are mixed into the molten alloy, and oxygen from the oxide ceramic crucible is mixed into the molten alloy. Therefore, in the past, TiAl alloy materials cast using a method of melting TiAl alloy raw materials in an oxide ceramic crucible in a low vacuum atmosphere did not have oxygen and nitrogen concentrations below the specified values. For these reasons, the method of melting raw materials in an oxide ceramic crucible in a low vacuum atmosphere has not been used to manufacture parts made of TiAl alloy materials.

[0022] The present disclosure has been made in consideration of the above circumstances, and aims to provide a method for producing a TiAl alloy material, which can produce a TiAl alloy material having an impurity element concentration equal to or lower than the specified value for jet engine blades made of TiAl alloy material, by using a method of melting raw materials using an oxide ceramic crucible without evacuating the inside of a chamber to a high vacuum.

[0023] Another object of the present disclosure is to provide a TiAl alloy material that can be manufactured by a method of melting raw materials using an oxide ceramic crucible without evacuating the chamber to a high vacuum, and that has an impurity element concentration that is equal to or lower than the specified value for jet engine blades made of TiAl alloy material.

[0024] Another object of the present disclosure is to provide a TiAl alloy part and a jet engine blade made of the TiAl alloy material of the present disclosure, in which the impurity element concentration is equal to or less than the specified value for a jet engine blade made of a TiAl alloy material.

[0025] The method for producing a TiAl alloy material according to the present disclosure includes: a melting step of charging raw materials into a calcia crucible and melting the raw materials in an atmosphere having an oxygen concentration of 0.02% by volume to 0.5% by volume and a nitrogen concentration of 0.1% by volume to 2.5% by volume to obtain a molten alloy; and a casting step of pouring the molten alloy into a mold, wherein the raw materials have a composition consisting of alloying element components including at least titanium and aluminum, 0.1 to 0.3% by mass of calcium, 0.2% by mass or less of oxygen, 0.02% by mass or less of nitrogen, 0.03% by mass or less of carbon, and inevitable impurities.

[0026] The method for producing a TiAl alloy material according to the present disclosure includes the steps of: charging raw materials into a calcia crucible and melting the raw materials in an atmosphere having an oxygen concentration of 0.02% to 0.5% by volume and a nitrogen concentration of 0.1% to 2.5% by volume to produce a molten alloy, the raw materials comprising alloying elements including titanium and aluminum, calcium in an amount of 0.1% to 0.3% by mass, oxygen in an amount of 0.2% by mass or less, nitrogen in an amount of 0.02% by mass or less, and carbon and inevitable impurities in an amount of 0.03% by mass or less; and casting the molten alloy into a mold. Therefore, the method for producing a TiAl alloy material according to the present disclosure can produce a TiAl alloy material containing the impurity elements calcium, oxygen, nitrogen, and carbon, with the impurity element contents being equal to or less than the specified values ​​for TiAl alloy blades for jet engines.

[0027] Furthermore, in the method for producing a TiAl alloy material according to the present disclosure, the raw materials are melted in an atmosphere with an oxygen concentration of 0.02% by volume to 0.5% by volume and a nitrogen concentration of 0.1% by volume to 2.5% by volume in the melting step, and there is no need to evacuate the chamber to a high vacuum. Therefore, according to the method for producing a TiAl alloy material according to the present disclosure, the time required to melt the raw materials can be significantly reduced compared to when the chamber is evacuated to a high vacuum.

[0028] Furthermore, in the method for producing a TiAl alloy material according to the present disclosure, the raw materials are melted using a calcia crucible, which is an oxide ceramic crucible, and therefore, castability and productivity are superior compared to the case where the raw materials are melted using a water-cooled copper crucible. Furthermore, a TiAl alloy material having homogenized alloy components can be produced using a molten alloy obtained by a single melting step performed only once before the casting step.

[0029] The TiAl alloy material of the present disclosure can be produced by melting raw materials in a calcia crucible without evacuating the chamber to a high vacuum, and contains impurity elements such as calcium, oxygen, nitrogen, and carbon, with the impurity element contents being equal to or less than the specified values ​​for jet engine blades made of TiAl alloy material. Therefore, the TiAl alloy material of the present disclosure can be suitably used as a material for TiAl alloy parts and jet engine blades.

[0030] Fig. 1 is a cross-sectional view illustrating the state in which the molten alloy passed through the woven fabric is being poured into a mold. Fig. 2 is a photograph of the appearance of a woven fabric made of a mixed oxide of alumina and silica with an average mesh size (gap spacing) of 1 mm. Fig. 3 is a cross-sectional view of the mold used in the examples.

[0031] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. Note that the numerical ranges in the present disclosure include upper and lower limit values. The same applies not only to the composition ranges shown below, but also to the pressure range, heat treatment temperature range, heat treatment time, and aperture range.

[0032] [1] A method for producing a TiAl alloy material according to the present disclosure includes: a melting step of charging raw materials into a calcia crucible and melting the raw materials in an atmosphere having an oxygen concentration of 0.02% by volume to 0.5% by volume and a nitrogen concentration of 0.1% by volume to 2.5% by volume to obtain a molten alloy, the raw materials comprising alloy-forming elements including titanium and aluminum, calcium in an amount of 0.1% by volume to 0.3% by volume, oxygen in an amount of 0.2% by mass or less, nitrogen in an amount of 0.02% by mass or less, and carbon and inevitable impurities in an amount of 0.03% by mass or less; and a casting step of pouring the molten alloy into a mold.

[0033] [2] According to the method for producing a TiAl alloy material according to the above [1], in the melting step, the calcia crucible containing the raw material is placed in a chamber of a vacuum melting furnace, and the chamber is made into a low vacuum state of 100 Pa to 2500 Pa, and then argon gas is introduced into the chamber to make the pressure therein 0.1 atm to 0.9 atm, thereby forming the atmosphere.

[0034] [3] According to the method for producing a TiAl alloy material according to the above item [1], it is preferable to carry out the melting step only once before carrying out the casting step. [4] According to the method for producing a TiAl alloy material according to the above item [1], it is preferable to produce a TiAl alloy material containing 0.10 mass % or less of calcium, 0.15 mass % or less of oxygen, 0.03 mass % or less of nitrogen, and 0.02 mass % or less of carbon.

[0035] [5] In the method for producing a TiAl alloy material according to the above item [1], the casting step may be a step of pouring the molten alloy that has been passed through a woven fabric into a mold, and the woven fabric may be made of a mixed oxide of alumina and silica, with a silica content of 10 mass% or less and an average mesh size of 0.5 mm to 2 mm. [6] In the method for producing a TiAl alloy material according to the above item [5], the TiAl alloy material may be produced that does not contain inclusions of 0.3 mm or more that have been mixed in from a crucible.

[0036] [7] According to the method for producing a TiAl alloy material according to the above [1], it is preferable to include a pretreatment step of heating cutting chips made of TiAl alloy in the atmosphere at 400°C to 800°C to form pretreated cutting chips before the melting step, and it is preferable to further charge the pretreated cutting chips into the calcia crucible in the melting step. [8] According to the method for producing a TiAl alloy material according to the above [7], it is preferable that the amount of the pretreated cutting chips charged into the calcia crucible is 40 mass% or less of the total mass of the raw material and the pretreated cutting chips.

[0037] [9] According to the method for producing a TiAl alloy material according to the above [1], the alloying elements may be composed of aluminum in an amount of 31.5 mass% to 34.0 mass%, niobium in an amount of 4.0 mass% to 5.5 mass%, chromium in an amount of 2.0 mass% to 3.0 mass%, and titanium in an amount of the remainder, in the raw material.

[0038]

[10] The TiAl alloy material according to the present disclosure is composed of alloying elements including titanium and aluminum, 0.02 to 0.10 mass% calcium, 0.04 to 0.15 mass% oxygen, 0.005 to 0.03 mass% nitrogen, 0.005 to 0.02 mass% carbon, and inevitable impurities.

[11] According to the TiAl alloy material according to the above

[10] , the alloying elements may be 31.5 to 34.0 mass% aluminum, 4.0 to 5.5 mass% niobium, 2.0 to 3.0 mass% chromium, and the balance titanium.

[0039]

[12] A TiAl alloy part according to the present disclosure is made of the TiAl alloy material described in

[10] or

[11] above.

[13] A jet engine blade according to the present disclosure is made of the TiAl alloy material described in

[10] or

[11] above.

[0040] [Summary of the Inventors' Development Process in the Present Disclosure] In order to solve the above-mentioned problems, the inventors conducted extensive research as described below. Specifically, the inventors focused on a method of adding calcium to the raw materials as a method for reducing the oxygen concentration in a molten alloy obtained by melting raw materials for a TiAl alloy. The calcium in the raw materials reacts with oxygen in the molten alloy to form CaO, which is evaporated and removed from the molten alloy. As a result, the TiAl alloy produced using this molten alloy has a low oxygen content.

[0041] Therefore, when the chamber is not evacuated to a high vacuum, oxygen that enters the molten alloy from the atmosphere and from the crucible can be removed by adding calcium to the raw materials, but nitrogen that enters the molten alloy from the atmosphere remains in the molten alloy.

[0042] Therefore, the inventors have conducted extensive research by adjusting the oxygen and nitrogen concentrations in the atmosphere by adjusting the degree of low vacuum, and by focusing on the relationship between the oxygen and nitrogen concentrations in the atmosphere and the concentration of nitrogen that is mixed into the molten alloy and remains in the TiAl alloy material. As a result, they have found that by melting raw materials containing 0.1 to 0.3 mass% of calcium, 0.2 mass% or less of oxygen, and 0.02 mass% or less of nitrogen in an atmosphere with an oxygen concentration of 0.02 to 0.5 volume% and a nitrogen concentration of 0.1 to 2.5 volume% to obtain a molten alloy, it is possible to obtain a TiAl alloy material with calcium, oxygen, and nitrogen concentrations below specified values, even if oxygen and nitrogen from the atmosphere are mixed into the molten alloy.

[0043] Furthermore, the present inventors have focused on oxide ceramic crucibles and conducted extensive research to solve the problems that arise when raw materials are melted using a water-cooled copper crucible. Among various oxide ceramics, calcia and yttria are chemically stable. Therefore, even when a crucible made of calcia and / or yttria is used to melt raw materials for a TiAl alloy and produce a highly active molten alloy, the oxygen concentration in the molten alloy does not increase significantly.

[0044] Furthermore, when the raw materials of the TiAl alloy material are melted using a calcia crucible, calcium is mixed into the molten alloy together with oxygen from the calcia crucible, unlike yttrium which is mixed into the molten alloy together with oxygen when an yttria crucible is used. In this case, calcium is evaporated and removed from the molten alloy in the form of calcium and / or reacts with oxygen in the molten alloy to become CaO.

[0045] For these reasons, the present inventors selected a calcia crucible as the crucible for melting the raw materials for the TiAl alloy material, and conducted extensive studies focusing on the relationships between the calcium concentration, oxygen concentration, and nitrogen concentration in the raw materials, the oxygen concentration and nitrogen concentration in the atmosphere in which the raw materials are melted to form the molten alloy, and the contents of impurity elements in the target TiAl alloy material.

[0046] As a result, they discovered that a method for producing a molten alloy involves placing raw materials in a calcia crucible and melting the raw materials in an atmosphere with an oxygen concentration of 0.02% to 0.5% by volume and a nitrogen concentration of 0.1% to 2.5% by volume, and using raw materials consisting of alloy-forming elements including titanium and aluminum, calcium contained in the raw materials in a content of 0.1% to 0.3% by mass, oxygen of 0.2% by mass or less, nitrogen of 0.02% by mass or less, and carbon and inevitable impurities of 0.03% by mass or less.

[0047] The inventors have confirmed that by using the above method, a TiAl alloy material containing the impurity elements of 0.02 mass% to 0.10 mass% calcium, 0.04 mass% to 0.15 mass% oxygen, 0.005 mass% to 0.03 mass% nitrogen, and 0.005 mass% to 0.02 mass% carbon can be produced by melting raw materials using an oxide ceramic crucible without evacuating the chamber to a high vacuum, and the contents of the impurity elements are equal to or less than the specified values ​​for jet engine blades made of TiAl alloy material, and have arrived at the present disclosure.

[0048] [Details of the embodiments of the present disclosure] The TiAl alloy material, the method for manufacturing the TiAl alloy material, the TiAl alloy part, and the jet engine blade of the present disclosure will be described in detail below.

[0049] [TiAl alloy material] The TiAl alloy material of this embodiment is a casting produced by a casting method, and is composed of alloying elements (alloying element components) including titanium and aluminum, 0.02 to 0.10 mass% calcium, 0.04 to 0.15 mass% oxygen, 0.005 to 0.03 mass% nitrogen, 0.005 to 0.02 mass% carbon, and inevitable impurities.

[0050] The inevitable impurities contained in the TiAl alloy material of this embodiment are not alloy-forming elements, nor are calcium, oxygen, nitrogen, or carbon, but are impurities that are mixed in the raw materials or during the manufacturing process.

[0051] The TiAl alloy material of this embodiment is manufactured by the manufacturing method of the TiAl alloy material of this embodiment described below. Therefore, the TiAl alloy material of this embodiment contains impurity elements such as calcium, oxygen, nitrogen, and carbon, as well as alloying elements including titanium and aluminum, and the contents of all of the impurity elements are equal to or less than the specified values ​​for jet engine blades made of TiAl alloy material.

[0052] "Aluminum (Al), Titanium (Ti)" Aluminum and titanium are basic alloying elements in TiAl alloys. Aluminum, together with titanium, forms the TiAl phase in TiAl alloy materials, Ti ３ It forms an Al phase and the like.

[0053] "Calcium (Ca)" The TiAl alloy material of this embodiment is manufactured using a method for removing oxygen from the molten alloy by using raw materials containing calcium. Therefore, the calcium contained in the TiAl alloy material of this embodiment remains without evaporating with oxygen during the manufacturing process. The TiAl alloy material of this embodiment has an oxygen content of 0.15 mass% or less and a calcium content of 0.02 mass% or more. Therefore, the TiAl alloy material of this embodiment has oxygen sufficiently removed from the molten alloy by the sufficient amount of calcium in the raw materials. Moreover, the cast TiAl alloy material of this embodiment has a calcium content of 0.10 mass% or less, which is below the specified value for jet engine blades. Therefore, the cast TiAl alloy material of this embodiment does not have its properties impaired by an excessive calcium content.

[0054] "Oxygen (O)" The TiAl alloy material of this embodiment is produced using oxygen-containing raw materials and a method of melting the raw materials in a calcia crucible without evacuating the chamber to a high vacuum. Therefore, the TiAl alloy material contains 0.04 mass% or more of oxygen derived from the oxygen in the raw materials and oxygen mixed in during the production process. Furthermore, the TiAl alloy material of this embodiment is produced using a method of removing oxygen from the molten alloy by using a calcium-containing raw material. As a result, the oxygen content of the TiAl alloy material of this embodiment is 0.15 mass% or less, which is below the specified value for jet engine blades. Therefore, the properties of the cast TiAl alloy material of this embodiment are not impaired by an excessive oxygen content.

[0055] "Nitrogen (N)" The TiAl alloy material of this embodiment is manufactured by using a method in which nitrogen-containing raw materials are melted in a calcia crucible without evacuating the chamber to a high vacuum. Therefore, the TiAl alloy material contains 0.005 mass % or more of nitrogen derived from the nitrogen in the raw materials and nitrogen mixed in during the manufacturing process.

[0056] In contrast, in conventional manufacturing methods of TiAl alloy materials, the chamber is evacuated to a high vacuum in order to make the nitrogen content in the TiAl alloy material equal to or less than the specified value for jet engine blades, and therefore the nitrogen content of the TiAl alloy material manufactured using the conventional method is less than 0.005 mass%.

[0057] The TiAl alloy material of this embodiment is produced by melting raw materials in an atmosphere with an oxygen concentration of 0.5% by volume or less and a nitrogen concentration of 2.5% by volume or less to obtain a molten alloy. As a result, the TiAl alloy material of this embodiment has a nitrogen content of 0.03% by mass or less, which is below the specified value for jet engine blades. Therefore, the TiAl alloy material of this embodiment does not suffer from impaired properties due to an excessive nitrogen content.

[0058] "Carbon (C)" The TiAl alloy material of this embodiment contains 0.005 mass % or more of carbon as an impurity element derived from raw materials, etc. However, the carbon content of the TiAl alloy material of this embodiment is 0.02 mass % or less, which is below the specified value for jet engine blades. Therefore, the TiAl alloy material of this embodiment does not have its properties impaired by a high carbon content.

[0059] The TiAl alloy material of this embodiment may contain, as alloying elements, titanium and aluminum, as well as one or more additive elements such as niobium (Nb), chromium (Cr), tungsten (W), manganese (Mn), silicon (Si), boron (B), molybdenum (Mo), etc. The type and content of the additive elements contained in the alloying elements can be appropriately determined depending on the performance required of the TiAl alloy material.

[0060] The TiAl alloy material of this embodiment preferably contains titanium and aluminum as alloying elements, as well as niobium and chromium as additive elements. Specifically, the alloying elements preferably have a composition consisting of 31.5 to 34.0 mass% aluminum, 4.0 to 5.5 mass% niobium, 2.0 to 3.0 mass% chromium, and the balance titanium. A TiAl alloy material having the above composition of alloying elements corresponds to a composition consisting of TiAl4822 (Ti-48.0Al-2Nb-2Cr (atomic %)). Therefore, a TiAl alloy material having the above composition of alloying elements can be preferably used for parts such as jet engine blades.

[0061] "Aluminum (Al)" The aluminum content in the TiAl alloy material is preferably 31.5% by mass or more, since it provides good impact resistance. The aluminum content is more preferably 32.0% by mass or more. Furthermore, the aluminum content in the TiAl alloy material is preferably 34.0% by mass or less, since it provides good creep strength and impact resistance. The aluminum content is more preferably 33.5% by mass or less.

[0062] "Niobium (Nb)" Niobium contributes to improving oxidation resistance when the Al content contained in the TiAl alloy material is within the above range. When the niobium content in the TiAl alloy material is 4.0 mass% or more, the effect of improving oxidation resistance becomes significant, so it is preferable. The niobium content is more preferably 4.5 mass% or more. Furthermore, when the niobium content in the TiAl alloy material is 5.5 mass% or less, it is preferable because the impact resistance becomes better. The niobium content is more preferably 5.2 mass% or less.

[0063] "Chromium (Cr)" Chromium improves impact resistance when the Al content in the TiAl alloy material is within the above range. A chromium content of 2.0 mass% or more is preferable because the effect of improving impact resistance is sufficiently obtained. The chromium content is more preferably 2.3 mass% or more. Furthermore, a chromium content of 3.0 mass% or less is preferable because it can suppress the decrease in fluidity of the molten alloy due to the inclusion of chromium and improve creep strength. The chromium content is more preferably 2.8 mass% or less.

[0064] [Method for Manufacturing TiAl Alloy Material] The method for manufacturing a TiAl alloy material of this embodiment includes a melting step of melting raw materials to form a molten alloy, and a casting step of pouring the molten alloy into a mold.

[0065] (Melting step) In the melting step of the manufacturing method of the TiAl alloy material of this embodiment, raw materials are used that consist of alloying elements (alloying elements) including titanium and aluminum, calcium contained in the raw materials in a content of 0.1 mass % to 0.3 mass %, oxygen of 0.2 mass % or less, nitrogen of 0.02 mass % or less, and carbon and inevitable impurities of 0.03 mass % or less.

[0066] "Alloying Elements (Alloying Elements)" The amounts of alloying elements in the raw materials are approximately the same as the amounts of alloying elements in the TiAl alloy material produced by the manufacturing method of this embodiment, except for the Al content, which evaporates to a certain extent during the melting process. Therefore, the amounts of alloying elements in the raw materials can be considered unchanged during the manufacturing process, except for the Al content. Furthermore, the amount of Al that decreases during the manufacturing process is predictable because it is reproducible depending on the melting conditions in the melting process. Therefore, by including excess Al in the raw materials in consideration of the amount of Al that decreases during the melting process, the types and contents of alloying elements in the raw materials can be adjusted to correspond to the alloy composition of the target TiAl alloy material.

[0067] The alloying elements in the raw materials preferably contain 31.5% to 34.0% by mass of aluminum, excluding the amount evaporated during the melting process, 4.0% to 5.5% by mass of niobium, 2.0% to 3.0% by mass of chromium, and the remainder titanium. By using the alloying elements in the raw materials with the above composition, a TiAl alloy material corresponding to a composition of TiAl4822 (Ti-48.0Al-2Nb-2Cr (atomic %)) can be produced. The aluminum content in the raw materials may be 32.0% to 33.5% by mass, or 32.3% to 33.2% by mass. The niobium content in the raw materials may be 4.5% to 5.2% by mass. The chromium content in the raw materials may be 2.3% to 2.8% by mass.

[0068] "Calcium (Ca)" In the manufacturing method of this embodiment, raw materials containing calcium are used. The calcium contained in the raw materials reduces the oxygen concentration in the molten alloy obtained by dissolving the raw materials. The calcium contained in the raw materials reacts with oxygen in the molten alloy to form CaO, which is evaporated and removed from the molten alloy. Since the calcium content in the raw materials is 0.1 mass% or more, the effect of removing oxygen from the molten alloy is sufficiently obtained. Therefore, in the manufacturing method of this embodiment, a TiAl alloy material having an oxygen content of 0.15 mass% or less can be manufactured. Furthermore, since the calcium content in the raw materials is 0.3 mass% or less, a TiAl alloy material having a calcium content of 0.10 mass% or less remaining in the TiAl alloy material can be manufactured.

[0069] In the manufacturing method of this embodiment, it is preferable to make the raw material contain calcium by adding an AlCa alloy to the raw material. As the AlCa alloy, it is preferable to use an alloy in which the calcium content in the AlCa alloy is 5 atomic % (Al-5Ca (atomic %)) or an alloy in which the calcium content in the AlCa alloy is 10 atomic % (Al-10Ca (atomic %)). This is because the target TiAl alloy material can be manufactured industrially stably and with high reproducibility.

[0070] When the AlCa alloy is contained in the raw material, the calcium content in the raw material is adjusted to 0.1 to 0.3 mass %. At the same time, the Al content in the raw material is adjusted according to the amount of the AlCa alloy used so that the target TiAl alloy material contains a predetermined amount of aluminum (Al).

[0071] "Nitrogen (N)" In the manufacturing method of this embodiment, the nitrogen content in the raw materials is set to 0.02 mass % or less, thereby making it possible to manufacture a TiAl alloy material having a nitrogen content of 0.03 mass % or less.

[0072] "Oxygen (O)" In the manufacturing method of this embodiment, the oxygen content in the raw materials is set to 0.2 mass% or less. Therefore, in the melting step, oxygen is removed from the molten alloy by calcium contained in the raw materials, thereby producing a TiAl alloy material having an oxygen content of 0.15 mass% or less and a calcium content of 0.10 mass% or less.

[0073] In the melting step of this embodiment, raw materials having a calcium content of 0.3 mass% or less and an oxygen content of 0.2 mass% or less are charged into a calcia crucible and melted to produce a molten alloy. Because the calcia crucible is chemically stable, an increase in oxygen concentration due to oxygen being mixed into the molten alloy from the calcia crucible can be suppressed. Furthermore, calcium mixed into the molten alloy from the calcia crucible together with oxygen is evaporated and removed from the molten alloy, either in the form of calcium or together with the oxygen in the molten alloy. Therefore, by melting raw materials in a calcia crucible to produce a molten alloy, even if calcium and / or oxygen are mixed into the molten alloy, a TiAl alloy material can be produced in which the calcium content remaining in the TiAl alloy material is 0.10 mass% or less and the oxygen content is 0.15 mass% or less.

[0074] "Carbon (C)" In the manufacturing method of this embodiment, the carbon content in the raw materials is set to 0.03 mass % or less. This makes it possible to manufacture a TiAl alloy material with a carbon content of 0.02 mass % or less. This is because, in the melting process, part of the carbon in the raw materials combines with oxygen in the molten alloy to produce CO or CO ２ This is because it evaporates as a gas.

[0075] The shape of each component contained in the raw material is not particularly limited. The shapes of the components in the raw material may be partially or entirely different. The shape of each component in the raw material may be, for example, pellet-like, flake-like, granular, sponge-like, powder-like, or the like. Furthermore, the raw material may contain raw materials in an alloy state.

[0076] In this embodiment, the raw material may be a master alloy ingot produced by melting the above-mentioned raw materials, or scrap made of a TiAl alloy. Examples of scrap made of a TiAl alloy include parts removed from a casting and not used as a TiAl alloy material, such as parts corresponding to runners for pouring molten alloy into a mold, and cutting chips made of a TiAl alloy. Examples of cutting chips made of a TiAl alloy include cutting chips generated when cutting a TiAl alloy material to manufacture TiAl alloy parts such as jet engine blades.

[0077] Conventionally, various scraps have been used as part of raw materials when producing cast materials made of iron-based alloys, Ni-based alloys, etc. However, when scrap is used as part of raw materials when producing TiAl alloy materials, the oxygen contained in the scrap can cause the oxygen content in the TiAl alloy material to exceed the specified value for TiAl alloy parts. For this reason, scrap has rarely been used as part of raw materials when producing TiAl alloy materials.

[0078] In contrast, in the manufacturing method of this embodiment, the raw material contains calcium in a content of 0.1 to 0.3 mass%, which removes oxygen from the molten alloy. Therefore, scrap can be used as it is as part of the raw material, as long as the raw material contains no more than 0.2 mass% oxygen, no more than 0.02 mass% nitrogen, and no more than 0.03 mass% carbon.

[0079] (Pretreatment Step) In the manufacturing method of the present embodiment, in the melting step, only the raw material may be charged into the calcia crucible, or the raw material may be charged into the calcia crucible and, further, cutting chips made of a TiAl alloy that have been pretreated in the pretreatment step (pretreated cutting chips) may be charged.

[0080] The cutting chips made of TiAl alloy contain the cutting lubricant (coolant) used when cutting the TiAl alloy material. Therefore, if the cutting chips are used as they are together with the raw material in the melting process, even if the content of impurity elements in the TiAl alloy forming the cutting chips is equal to or less than the specified value for jet engine blades made of TiAl alloy material, the oxygen and carbon originating from the cutting lubricant (coolant) adhering to the cutting chips may cause the oxygen and / or carbon content in the target TiAl alloy material to exceed the specified value for TiAl alloy parts.

[0081] In contrast, in the manufacturing method of this embodiment, when using cutting chips made of TiAl alloy, a pretreatment step is preferably performed before the melting step, in which the cutting chips made of TiAl alloy are heated in the atmosphere at 400°C to 800°C to produce pretreated cutting chips. By performing the pretreatment step, carbon in the cutting lubricant (coolant) adhering to the cutting chips made of TiAl alloy is burned and removed. Note that the pretreatment step does not remove oxygen originating from the cutting lubricant. However, as described above, oxygen originating from the cutting lubricant is removed from the molten alloy by reacting with calcium contained in the raw materials in the melting step.

[0082] Therefore, even if the pretreated cutting chips are put into the calcia crucible together with the raw materials in the melting step, oxygen and carbon originating from the cutting lubricant do not increase the oxygen and / or carbon content in the target TiAl alloy material. That is, in the manufacturing method of this embodiment, by performing the pretreatment step, the cutting chips made of TiAl alloy (pretreated cutting chips) can be used together with the raw materials of the TiAl alloy material to manufacture the TiAl alloy material of this embodiment, which has a carbon content below the specified value for jet engine blades.

[0083] In the manufacturing method of this embodiment, it is preferable to heat the cutting chips in the atmosphere at a temperature of 400°C or higher in the pretreatment step. This is because carbon in the cutting lubricant (coolant) adhering to the cutting chips made of TiAl alloy is burned and efficiently removed. Therefore, the carbon content remaining in the pretreated cutting chips made of TiAl alloy (pretreated cutting chips) is sufficiently low. The temperature at which the cutting chips are heated in the atmosphere in the pretreatment step is more preferably 450°C or higher, because this allows carbon in the cutting lubricant (coolant) to be burned more efficiently.

[0084] In addition, in the pretreatment step, it is preferable to heat the cutting chips in the atmosphere at a temperature of 800°C or less. This is because heating the cutting chips in the atmosphere can prevent the cutting chips from oxidizing and increasing the oxygen content in the cutting chips after pretreatment. As a result, in the melting step, oxygen is removed from the molten alloy using calcium contained in the raw materials, making it easier to obtain a TiAl alloy material whose oxygen content and calcium content are below the specified values ​​for jet engine blades made of TiAl alloy material. The temperature at which the cutting chips are heated in the atmosphere in the pretreatment step is more preferably 750°C or less, because this can effectively prevent the cutting chips from being oxidized.

[0085] The time for heating the cutting chips in the pretreatment step can be, for example, 20 to 60 minutes, and can be appropriately determined depending on the amount of cutting chips made of TiAl alloy and the amount of cutting lubricant (coolant) components adhering to the cutting chips.

[0086] In the manufacturing method of this embodiment, the cutting chips made of TiAl alloy may be washed with an organic solvent before being heated in the atmosphere in the pretreatment step. The organic solvent used to wash the cutting chips may be, for example, acetone, and can be appropriately selected depending on the cutting lubricant (coolant) components adhering to the cutting chips.

[0087] By cleaning the cutting chips made of TiAl alloy with an organic solvent, it is possible to remove some of the cutting lubricant (coolant) components adhering to the cutting chips. As a result, the amount of cutting lubricant (coolant) components that is burned by heating the cutting chips in the atmosphere can be reduced. This reduces the heating time of the cutting chips and / or further reduces the carbon content remaining in the cutting chips after pretreatment.

[0088] In the manufacturing method of this embodiment, the amount of pretreated cutting chips put into the calcia crucible is preferably 40 mass% or less of the total mass of the raw material and the pretreated cutting chips. When the amount of pretreated cutting chips is 40 mass% or less, a TiAl alloy material can be manufactured in which the content of impurity elements resulting from the use of pretreated cutting chips is sufficiently suppressed. As a result, it is easy to obtain the TiAl alloy material of this embodiment that is below the specified value for jet engine blades. Furthermore, the amount of pretreated cutting chips put into the calcia crucible is preferably 10 mass% or more of the total mass of the raw material and the pretreated cutting chips. This is because the cost reduction effect of using cutting chips can be sufficiently obtained.

[0089] The method for melting the raw materials in the melting step of this embodiment may be any method that can melt the raw materials to form a molten alloy, and any melting method can be used. For example, high-frequency melting can be used as the method for melting the raw materials.

[0090] "Atmosphere" In the melting step of this embodiment, raw materials are placed in a calcia crucible and melted in an atmosphere with an oxygen concentration of 0.02 vol% to 0.5 vol% and a nitrogen concentration of 0.1 vol% to 2.5 vol% to produce a molten alloy. The oxygen concentration in the atmosphere can be confirmed, for example, by measuring the atmosphere in the chamber using an oxygen concentration meter. The nitrogen concentration in the atmosphere can be confirmed, for example, by measuring the atmosphere in the chamber using a nitrogen concentration meter. When the atmosphere in the chamber is a gas obtained by partially evacuating air, the ratio of oxygen to nitrogen in the air is constant. Therefore, if the oxygen concentration in the atmosphere is 0.02 vol% to 0.5 vol%, the nitrogen concentration will be 0.1 vol% to 2.5 vol%. Therefore, by measuring the oxygen concentration in the atmosphere using an oxygen concentration meter, which is more versatile and cheaper than a nitrogen concentration meter, and calculating the nitrogen concentration in the atmosphere from the results, the measurement of the nitrogen concentration using a nitrogen concentration meter can be omitted.

[0091] In the melting process of this embodiment, the oxygen concentration in the atmosphere is 0.5 vol% or less, and the nitrogen concentration is 2.5 vol% or less, so the amounts of oxygen and nitrogen mixed into the molten alloy from the atmosphere are suppressed. Therefore, even if nitrogen is mixed into the molten alloy from the atmosphere, a TiAl alloy cast material with a nitrogen concentration below a specified value can be obtained. Furthermore, the oxygen mixed into the molten alloy from the atmosphere is removed from the molten alloy together with calcium in the raw materials, so that the oxygen and calcium concentrations in the TiAl alloy cast material are below the specified values.

[0092] Furthermore, since the oxygen concentration in the atmosphere is 0.02% by volume or more and the nitrogen concentration is 0.1% by volume or more, there is no need to evacuate the chamber to a high vacuum. Therefore, according to the manufacturing method of this embodiment, the time required to melt the raw material can be shortened compared to when the chamber is evacuated to a high vacuum.

[0093] In the melting step of this embodiment, a method for creating an atmosphere with an oxygen concentration of 0.02 vol % to 0.5 vol % and a nitrogen concentration of 0.1 vol % to 2.5 vol % can be, for example, by placing a calcia crucible containing the raw materials in a chamber of a vacuum melting furnace, creating a low vacuum of 100 Pa to 2500 Pa in the chamber, and then introducing argon gas to create a pressure of 0.1 atm to 0.9 atm. The reason why it is preferable to create the above atmosphere using this method is as follows.

[0094] If a calcia crucible containing raw materials is placed in a high vacuum atmosphere (i.e., under a low oxygen partial pressure), the durability (resistance to reactivity) of the calcia crucible against the molten alloy is significantly reduced. If the chamber is first evacuated to a low vacuum of 100 Pa to 2500 Pa and then argon gas is introduced to create an atmosphere with the above oxygen and nitrogen concentrations, the reduction in the durability (resistance to reactivity) of the calcia crucible against the molten alloy during the melting step can be alleviated.

[0095] In this embodiment, the calcia crucible containing the raw materials may be heated using a vacuum melting furnace or an atmospheric melting furnace, but it is preferable to heat it using a vacuum melting furnace. The reason for this is that when a low vacuum state of 100 Pa to 2500 Pa is created in the chamber using a vacuum melting furnace and then argon gas is introduced to create an atmosphere of 0.1 atm to 0.9 atm, the amount of argon gas used can be reduced compared to, for example, when argon gas is introduced into the chamber of an atmospheric melting furnace to create an atmosphere with the above oxygen and nitrogen concentrations.

[0096] In the above method, the chamber is evacuated to a low vacuum of 2500 Pa or less, so that an atmosphere with an oxygen concentration of 0.5% by volume or less and a nitrogen concentration of 2.5% by volume or less can be created. In addition, the chamber is evacuated to a low vacuum of 100 Pa or more, so the time required to melt the raw material can be significantly reduced compared to when the chamber is evacuated to a high vacuum.

[0097] Furthermore, in the above-described method, argon gas is introduced to create an atmosphere of 0.1 atmospheres or more, which sufficiently alleviates the decrease in the durability (reactivity resistance) of the calcia crucible against the molten alloy during the melting step. Therefore, the amount of oxygen mixed into the molten alloy from the calcia crucible can be more effectively suppressed. Furthermore, argon gas is introduced to create an atmosphere of 0.9 atmospheres or less, which can reduce the amount of argon gas used.

[0098] In this embodiment, raw materials are melted in a calcia crucible to produce a molten alloy. Therefore, unlike when a water-cooled copper crucible is used to melt raw materials, there is no need to cool the crucible, and the surface temperature of the crucible can be increased. Therefore, in this embodiment, unlike when a water-cooled copper crucible is used to melt raw materials, skulls do not adhere to the surface of the crucible. Therefore, a TiAl alloy material having homogenized alloy components can be produced using a molten alloy obtained by a single melting step performed only once before the casting step.

[0099] (Casting Step) In the casting step of the method for producing a TiAl alloy material according to this embodiment, the molten alloy produced in the melting step is poured into a mold. The mold used in this embodiment may be made of a known material and have a cavity with an inner shape similar to the shape of the part to be produced using the TiAl alloy material. For example, the mold may have a runner, which is a passageway for pouring the molten alloy into the cavity, connected to a gate of the mold.

[0100] As described above, in the melting step of this embodiment, raw materials are melted in a calcia crucible to produce a molten alloy. Ceramic crucibles, such as calcia crucibles, are generally made of porous materials obtained by sintering ceramic powder. Therefore, when raw materials are melted in the ceramic crucible, materials constituting the ceramic crucible may peel off from the surface in contact with the molten alloy and become mixed into the molten alloy as crucible inclusions. In particular, when the molten alloy is obtained by melting a TiAl alloy raw material, the molten alloy is highly active, and therefore peeling from the surface of the ceramic crucible is likely to occur, leading to the inclusion of crucible inclusions.

[0101] Conventionally, when crucible inclusions are mixed into a molten alloy obtained by melting raw materials of an iron-based alloy and / or a Ni-based alloy, the molten alloy is passed through a filter and then poured into a mold to remove the crucible inclusions. In this case, the filter used is a three-dimensional porous filter made of ceramic such as silica and having continuous pores.

[0102] However, it is difficult to remove crucible inclusions from a molten alloy obtained by melting raw materials for a TiAl alloy using a filter that is used to remove crucible inclusions from a molten alloy obtained by melting raw materials for an iron-based alloy and / or a Ni-based alloy, because the molten alloy obtained by melting raw materials for a TiAl alloy is highly active and has low fluidity.

[0103] Specifically, when a molten alloy obtained by melting raw materials for a TiAl alloy containing crucible inclusions is passed through the filter, the molten alloy reacts with the filter and dissolves, resulting in the inclusion of filter components in the molten alloy. This makes it impossible to obtain a TiAl alloy having the desired composition. Furthermore, because the molten alloy obtained by melting raw materials for a TiAl alloy has low fluidity, the open pores of the filter easily become clogged, making it impossible for the molten alloy to pass through.

[0104] Therefore, in order to remove crucible inclusions mixed into the molten alloy obtained by melting the raw materials of the TiAl alloy material, the inventors focused on a thin, flat woven fabric, which allows the molten alloy to pass through a shorter distance than a three-dimensional filter with continuous pores, and conducted extensive research as described below.

[0105] (Woven Fabric) The inventors first investigated the material of the woven fabric. First, they prepared a woven fabric made of tungsten, a woven fabric made of molybdenum, and a woven fabric made of carbon, and passed a molten alloy made by dissolving raw materials of a TiAl alloy through each of them. The temperature of the molten alloy passed through each woven fabric was in the range of 1600°C to 1650°C, which was below the melting points of tungsten, molybdenum, and carbon. However, all of the woven fabrics melted easily, and their durability against the molten alloy was insufficient. This is because the woven fabrics were formed by weaving thin wires, and therefore melted easily due to a solid-liquid reaction with the molten alloy.

[0106] Therefore, the present inventors have focused on ceramic materials as the material for the woven fabric, and have considered using a woven fabric made of a mixed oxide of alumina and silica, which is the most common, easily available, and relatively inexpensive among woven fabrics made of ceramic materials.The present inventors have considered that, among woven fabrics made of a mixed oxide of alumina and silica, a woven fabric that can be used to remove crucible inclusions mixed into a molten alloy obtained by melting raw materials of a TiAl alloy material must have the following characteristics (1) to (3).

[0107] (1) It does not melt in the molten alloy obtained by melting the raw materials of the TiAl alloy material. (2) It does not allow crucible inclusions of 0.3 mm or more, which are detectable in X-ray inspection of the TiAl alloy material, to pass through. (3) The woven fabric is less likely to cause poor running of the TiAl alloy material due to the obstruction of the flow of the molten alloy.

[0108] The present inventors investigated the above-mentioned property (1) by examining the silica content in a woven fabric made of a mixed oxide of alumina and silica. The main component of a woven fabric made of a mixed oxide of alumina and silica is alumina. The present inventors prepared woven fabrics with silica contents of 1 mass%, 5 mass%, 10 mass%, 15 mass%, and 28 mass%, and passed molten alloys made by dissolving raw materials of TiAl alloy material at the same temperature through each woven fabric.

[0109] As a result, the woven fabric having a silica content of 10% by mass or less in the mixed oxide did not melt in the molten alloy. This indicates that durability against the molten alloy can be ensured by using a woven fabric having a silica content of 10% by mass or less in the mixed oxide, and that the fabric can be used in this embodiment. This is because silica is chemically unstable compared to alumina. In other words, the woven fabric having a silica content of 10% by mass or less in the mixed oxide has high chemical stability.

[0110] Next, the present inventors investigated the above characteristics (2) and (3) by focusing on the mesh size of a woven fabric having a silica content of 10 mass% or less in the mixed oxide and the state of the molten alloy passing through the woven fabric, and found that it is preferable to use a method in which the molten alloy is passed through a woven fabric having a specific mesh size and then poured into a mold.

[0111] Figure 1 is a cross-sectional view illustrating the state in which molten alloy that has passed through a woven fabric is being poured into a mold. In Figure 1, reference numeral 10 denotes a runner for pouring the molten alloy into the mold. The runner 10 shown in Figure 1 is connected to a mold gate (not shown). A woven fabric 20 is installed between the upstream end (the upper end in Figure 1) and downstream end of the runner 10 shown in Figure 1, allowing molten alloy 30 to pass from top to bottom. As shown in Figure 1, a molten alloy layer 30b is formed on the woven fabric 20.

[0112] The molten metal layer 30b is formed by the molten alloy 30 supplied to the runner 10 remaining and accumulating on the woven fabric 20 for a certain period of time. That is, the molten alloy layer 30b is formed by dissolving the raw material TiAl alloy material into the molten alloy 30, which has low fluidity, and is formed by the woven fabric 20 having a specific mesh size that makes it difficult for the molten alloy 30 to pass through.

[0113] As shown in FIG. 1 , a plurality of crucible inclusions 31 mixed in the molten alloy 30 float on the liquid surface 30a of the molten alloy layer 30b. The crucible inclusions 31 are formed by peeling off the surface of the calcia crucible that is in contact with the molten alloy 30, and are lighter than the molten alloy 30. Therefore, the crucible inclusions 31 in the molten alloy layer 30b formed on the woven fabric 20 float up regardless of their size and are collected near the liquid surface 30a of the molten alloy 30. Therefore, the crucible inclusions 31 are unlikely to be present in the molten alloy 30 that passes from the molten alloy layer 30b through the woven fabric 20 and is poured into the mold. In other words, the formation of the molten alloy layer 30b on the woven fabric 20 removes the crucible inclusions 31 from the molten alloy 30 that is poured into the mold.

[0114] From this, it was found that the upper limit of the opening size of the woven fabric 20 through which the molten alloy 30 poured into the mold passes may be equal to or smaller than the size at which the molten alloy 30 accumulates and forms a molten metal layer 30b on the woven fabric 20. In other words, it was found that the upper limit of the opening size of the woven fabric 20 that can be used to remove the crucible inclusions 31 mixed into the molten alloy 30 obtained by melting the raw material of the TiAl alloy material is not determined by the size of the crucible inclusions 31, but may be determined based on the low fluidity of the molten alloy 30 obtained by melting the raw material of the TiAl alloy material.

[0115] Furthermore, in order to fully obtain the effect of removing crucible inclusions 31 from molten alloy 30 by molten metal layer 30b, it is preferable that molten alloy 30 be poured into runner 10 and molten metal layer 30b be formed immediately after molten alloy 30 reaches woven fabric 20. This is because crucible inclusions 31 can be more effectively removed from molten alloy 30 being poured into the mold.

[0116] Furthermore, after all of the molten alloy 30 has been poured into the runner 10, the temperature of the molten alloy 30, which contains a large amount of crucible inclusions 31 and remains on the woven fabric 20, preferably drops, causing a certain amount of the molten alloy layer 30b, while maintaining its layered shape, to solidify on the woven fabric 20. This is because crucible inclusions 31 concentrated in the molten alloy layer 30b can be prevented from passing through the woven fabric 20 and flowing into the mold until a certain amount of the molten alloy 30 has been poured into the runner 10. Furthermore, the molten alloy layer 30b solidified on the woven fabric 20 is a portion that will not be used as the TiAl alloy material. Therefore, in this embodiment, when the molten alloy 30 that has passed through the woven fabric 20 is poured into the mold, it is preferable to pour excess molten alloy (feed) that will not be used as the TiAl alloy material, taking into consideration the volume of the molten alloy layer 30b that remains and solidifies on the woven fabric 20.

[0117] Based on the above findings, the inventors have investigated the size of the openings in the woven fabric 20 through which the molten alloy 30, which has low fluidity and is obtained by melting the raw materials of the TiAl alloy material, passes when the molten alloy 30 is poured into a mold by gravity casting.

[0118] The smaller the mesh size of the woven fabric 20 through which the molten alloy 30 passes, the more reliable the removal of crucible inclusions 31 mixed in the molten alloy 30. However, if the mesh size of the woven fabric 20 is too small, the passage of the molten alloy 30 is hindered, which makes the TiAl alloy material more susceptible to poor molten flow and reduces castability. On the other hand, the larger the mesh size of the woven fabric 20, the easier it is for the molten alloy 30 to pass through, making the TiAl alloy material less susceptible to poor molten flow, thereby improving castability. However, if the mesh size is too large, the molten alloy 30 is less likely to remain on the woven fabric 20, preventing the formation of a molten metal layer 30b. As a result, the ability to remove crucible inclusions 31 mixed in the molten alloy 30 by passing the woven fabric 20 is reduced.

[0119] In order to study the size of the openings of the woven fabric 20, the inventors formed several types of woven fabric with different openings by the method described below, and passed a molten alloy made by dissolving raw materials of TiAl alloy through each of them. The woven fabric made of a mixed oxide of alumina and silica is made by weaving fiber bundles made of several thousand ceramic fibers with a wire diameter of about 10 μm into a plain weave, satin weave, or the like. A typical woven fabric made of a mixed oxide of alumina and silica has narrow openings and is dense, leaving almost no gaps for the molten alloy to pass through.

[0120] Therefore, the inventors prepared various commercially available woven fabrics made of a mixed oxide of alumina and silica, with a silica content of 1% to 10% by mass. They pulled fiber bundles from the woven fabric to create approximately equally spaced gaps. They then varied the ratio of the number of fiber bundles pulled from the woven fabric to the number of fiber bundles remaining in the woven fabric to create multiple types of woven fabrics with different mesh sizes. Figure 2 shows a photograph of the appearance of a woven fabric made of a mixed oxide of alumina and silica with an average mesh size (gap spacing) of 1 mm. The photograph shows non-uniform gaps because the mesh was created by manually pulling fiber bundles from a 10 cm x 10 cm existing woven fabric. The ratio of fiber bundles pulled from the woven fabric was such that one bundle was pulled out and three were left in a unit of four fiber bundles. The uneven gaps were due to uneven fiber distribution after the pulling. This existing woven fabric is commercially available.

[0121] As a result, it was found that it is preferable to use a woven fabric 20 having an average mesh size of 0.5 mm to 2 mm. Furthermore, the inventors installed a woven fabric 20 made of a mixed oxide of alumina and silica, in which the silica content in the mixed oxide was 10 mass % or less, and having an average mesh size of 0.5 mm to 2 mm, in a runner 10 shown in Figure 1. Then, a molten alloy 30 was passed through the woven fabric 20 and poured into a mold by gravity casting to produce a TiAl alloy material, and the maximum size of crucible inclusions 31 in the obtained TiAl alloy material was measured by the method described below.

[0122] In this specification, the size of the crucible inclusion 31 means the length of the longest diagonal line of the crucible inclusion 31 on a tomographic image generated using a CT (Computed Tomography) inspection device.

[0123] If the TiAl alloy material contains crucible inclusions 31 with a size of 0.3 mm or more, they can be detected by X-ray inspection of the TiAl alloy material. It was confirmed that the TiAl alloy material produced using the above method does not contain inclusions of 0.3 mm or more that are detectable by X-ray inspection, and a TiAl alloy material free of crucible inclusions 31 of 0.3 mm or more can be obtained. In other words, it was confirmed that the above method can remove not only crucible inclusions 31 larger than the average mesh size of the woven fabric 20, but also crucible inclusions 31 smaller than the average mesh size of the woven fabric 20.

[0124] As described above, in the casting step of the manufacturing method of this embodiment, in order to produce a TiAl alloy material that does not contain crucible inclusions 31 of 0.3 mm or more, it is preferable to pour the molten alloy 30 that has been passed through a woven fabric 20 made of a mixed oxide of alumina and silica, where the silica content in the mixed oxide is 10 mass % or less and the average mesh size is 0.5 mm to 2 mm, into a mold by gravity casting. The installation position of the woven fabric 20 through which the molten alloy 30 passes is not particularly limited, and may be any position between the upstream end and the downstream end of the runner 10.

[0125] Furthermore, in the casting process of this embodiment, the temperature of the molten alloy 30 when passing it through the woven fabric 20 is preferably 1550°C to 1700°C, and more preferably 1600°C to 1650°C. When the temperature of the molten alloy 30 is 1550°C or higher, the molten alloy 30 obtained by melting the raw materials of the TiAl alloy material has appropriate fluidity, making it even less likely that poor flow of the TiAl alloy material will occur. Furthermore, when the temperature of the molten alloy 30 is 1700°C or lower, a molten alloy layer 30b is quickly formed on the woven fabric 20, thereby more significantly removing crucible inclusions 31 from the molten alloy 30.

[0126] Furthermore, in this embodiment, by using gravity casting as a method for pouring the molten alloy 30 into the mold, there is no need to use special equipment as in the case of using, for example, suction casting and / or centrifugal casting, and TiAl alloy material can be easily produced using simple equipment.

[0127] In this embodiment, the molten alloy 30 is poured into a mold, and the mold is allowed to cool using a known method to produce a casting that is close to the shape of the desired TiAl alloy part. The mold is then removed from the casting, and machining is performed as necessary. The TiAl alloy material of this embodiment is obtained through the above steps.

[0128] The TiAl alloy material of this embodiment can be produced by melting raw materials in a calcia crucible without evacuating the chamber to a high vacuum, and contains impurity elements such as calcium, oxygen, nitrogen, and carbon, with the impurity element contents being equal to or less than the specified values ​​for jet engine blades made of TiAl alloy material. Therefore, the TiAl alloy material of this embodiment can be suitably used as a material for TiAl alloy parts and jet engine blades.

[0129] Furthermore, the method for producing a TiAl alloy material according to this embodiment can produce a TiAl alloy material containing the impurity elements calcium, oxygen, nitrogen, and carbon, with the impurity element content being equal to or less than the standard value for a jet engine blade made of a TiAl alloy material. Furthermore, the method for producing a TiAl alloy material according to this embodiment does not require the chamber to be evacuated to a high vacuum during the melting step. Therefore, the method for producing a TiAl alloy material according to this embodiment can significantly reduce the time required to melt the raw materials compared to when the chamber is evacuated to a high vacuum.

[0130] In addition, in the method for producing a TiAl alloy material according to the present embodiment, the raw materials are melted using a calcia crucible, which is an oxide ceramic crucible, and therefore, the method is superior in castability and productivity compared to the method for melting raw materials using a water-cooled copper crucible. Furthermore, a TiAl alloy material having homogenized alloy components can be produced using a molten alloy obtained by a single melting step performed only once before the casting step.

[0131] [TiAl alloy parts, jet engine rotor blades] Next, the TiAl alloy parts of this embodiment will be described using the jet engine rotor blades of this embodiment as an example. The TiAl alloy parts of this embodiment may be any parts made of the TiAl alloy material of this embodiment, such as turbine wheels of automotive turbochargers and rotor blades of power-generating gas turbines, but are not limited to jet engine rotor blades.

[0132] The jet engine blade of this embodiment is made of the TiAl alloy material of this embodiment, and therefore the content of impurity elements is equal to or less than the specified value for jet engine blades, making it suitable for use as a jet engine blade.

[0133] The shape of the jet engine rotor blade of this embodiment is not particularly limited. The jet engine rotor blade of this embodiment can be manufactured, for example, by using the TiAl alloy material of this embodiment, which is a cast product similar to the shape of the product, as a raw material and machining it using a known method as necessary. Therefore, compared to a manufacturing method in which the jet engine rotor blade is manufactured by cutting a large rectangular ingot made of TiAl alloy, for example, the amount of machining is small, and the number of processing steps and the amount of machining allowance can be reduced.

[0134] The above describes in detail the embodiments of the present disclosure, but the above embodiment is an example of the present disclosure, and additions, omissions, substitutions, and other modifications to the configuration are possible within the scope that does not deviate from the spirit of the present disclosure.

[0135] [Alloy No. 1 to Alloy No. 17] Cast TiAl alloy materials (Alloy No. 1 to Alloy No. 22) were produced using the production method described below.

[0136] The raw materials used were sponge Ti, Al pellets, granular Cr raw material, flake-shaped Nb raw material, and an AlCa alloy. The AlCa alloy used was an AlCa alloy containing 90 atomic % Al and 10 atomic % Ca, and the Ca content in the raw materials was weighed to be the content shown in Table 1 or Table 2. The amount of Al pellets in the raw materials was adjusted to the alloying element ratio shown below by subtracting the amount of Al contained in the AlCa alloy in the raw materials and the amount of Al evaporated during the manufacturing process. The raw materials were adjusted to a total mass of approximately 800 g.

[0137] The raw material contains alloying elements consisting of 33.3 mass% aluminum, 4.8 mass% niobium, 2.7 mass% chromium, and the balance titanium, as well as calcium, oxygen, nitrogen, carbon, and inevitable impurities contained in the raw material in the amounts shown in Table 1 or Table 2. This raw material composition corresponds to the composition of TiAl4822 (Ti-48.0Al-2Nb-2Cr (atomic %)).

[0138] Next, the raw materials were placed in a calcia (calcium oxide) crucible, and the calcia crucible containing the raw materials was placed in the chamber of a vacuum melting furnace, where the chamber was evacuated to a low vacuum of 100 Pa to 2500 Pa. Argon gas was then introduced into the chamber, and the pressure inside the chamber was adjusted to 0.1 atmospheres. This created an atmosphere with the oxygen and nitrogen concentrations shown in Table 1 or Table 2. In this atmosphere, the raw materials were melted using a high-frequency melting method, and after all the raw materials were melted, the high-frequency power supply was maintained at an output of 5 kW for 3 minutes, yielding a molten alloy.

[0139]

[0140]

[0141] Next, a mold shown in FIG. 3 was prepared. FIG. 3 is a cross-sectional view of the mold 1 used in the examples. The mold 1 shown in FIG. 3 is made of steel. The mold 1 has a two-split shape, and as shown in FIG. 3, it consists of a first mold 1a and a second mold 1b arranged opposite the first mold 1a. The first mold 1a and the second mold 1b are substantially identical. As shown in FIG. 3, a cavity 11 is provided within the mold 1, the cavity 11 having an inner surface shaped like a jet engine rotor blade with a large excess pad. The cavity 11 has a substantially plate-like shape sandwiched between the first mold 1a and the second mold 1b, and as shown in FIG. 3, the upper and lower portions are thicker.

[0142] Next, a conical runner 10 for pouring the molten alloy into the mold 1 was connected to a gate 1c opening on the top surface of the mold 1 shown in Figure 3, and a woven fabric 20 was placed between the gate 1c and the runner 10 so as to cover the gate 1c. The woven fabric 20 was made of a mixed oxide of alumina and silica, and commercially available woven fabrics with different silica contents shown below were prepared and used, with the average mesh size shown in Table 1 or Table 2, using the method described below.

[0143] As commercially available woven fabrics, woven fabrics were prepared which were formed by weaving fibers with a wire diameter of about 10 μm and had silica contents of 1 mass %, 5 mass %, 10 mass %, and 15 mass % in the mixed oxide.

[0144] The average mesh size of the woven fabric 20 was adjusted by pulling out fiber bundles from each woven fabric to provide gaps at approximately equal intervals and changing the ratio between the number of fiber bundles pulled out from the woven fabric and the number of fiber bundles left in the woven fabric. The average mesh size of the woven fabric was determined by enlarging a photograph of the appearance of the woven fabric, measuring the lengths of 10 or more gaps in each of two directions along the fiber bundles, and calculating the average value of these measurements.

[0145] The molten alloy was then passed through the woven fabric 20 via the runner 10 and poured into the mold 1 by gravity casting. The mass of the TiAl alloy cast material formed by the molten alloy filling the cavity 11 of the mold 1 shown in Figure 3 was approximately 450 g. Therefore, the molten alloy filling the runner 10 was a feeder that was not used as a TiAl alloy material. The poured molten alloy was then cooled to produce the TiAl alloy materials (Alloy No. 1 to Alloy No. 17), and the first mold 1a and the second mold 1b were separated, and the TiAl alloy materials were removed from the mold 1.

[0146] [Alloy No. 18 to Alloy No. 22] Cutting chips made of a TiAl alloy having a composition of TiAl4822 (Ti-48.0Al-2Nb-2Cr (atomic %)) were prepared. The cutting chips were then heated in the atmosphere for 1 hour at the heating temperature for the pretreatment step shown in Table 3 to obtain pretreated cutting chips. Next, the pretreated cutting chips were placed into a calcia crucible together with the raw materials so that the amount of pretreated cutting chips relative to the total mass of the raw materials and pretreated cutting chips was as shown in Table 3.

[0147]

[0148] Thereafter, the calcia crucible containing the raw materials and the pretreated cutting chips was placed in the chamber of a vacuum melting furnace, and molten alloys were produced in the same manner as in the above-mentioned Alloy No. 1 to Alloy No. 17. The molten alloys were poured into the mold 1 to produce TiAl alloy materials (Alloy No. 18 to Alloy No. 22), and the TiAl alloy materials were then removed from the mold 1.

[0149] The TiAl alloy materials of Alloy No. 1 to Alloy No. 22 obtained in this manner were evaluated for "molten metal circulation," "whether or not the woven fabric melted," "maximum size of crucible inclusions," and "contents of oxygen, nitrogen, carbon, and calcium in the TiAl alloy material" by the methods described below. The results are shown in Tables 4 to 6.

[0150] [Melting property] The TiAl alloy material removed from the mold 1 was visually observed to check for the presence or absence of a missing part. If a missing part was present, the molten metal running defect was evaluated as "present," and if no missing part was present, the molten metal running defect was evaluated as "absent."

[0151] [Whether or not the woven fabric melted] "Maximum size of crucible inclusion" The TiAl alloy material was processed using a CT (Computed Tomography) inspection device (manufactured by GE), which has higher sensitivity than a normal X-ray inspection device and can observe smaller inclusions, to generate a tomographic image (three-dimensional data) of the entire material. The obtained tomographic image was checked, and if it was confirmed that a portion of the woven fabric was missing, it was evaluated as "present" that the woven fabric had melted. If it was confirmed that the entire woven fabric remained without any missing parts, it was evaluated as "not present" that the woven fabric had melted.

[0152] All of the images obtained were checked, and the size of the largest crucible inclusion was measured. If there were no crucible inclusions of 0.3 mm or more that could be detected by an X-ray inspection device with lower sensitivity than a CT inspection device, the sample was evaluated as good. The size of the crucible inclusions was measured by measuring the length of the longest diagonal line of the crucible inclusion on the image. The size that could be detected by a CT inspection device was 0.1 mm or more. In Tables 4 to 6, crucible inclusions that could not be detected by a CT inspection device were listed as "undetectable."

[0153] "Contents of oxygen, nitrogen, carbon, and calcium in TiAl alloy material" A plurality of specimens measuring 3 mm in length, 3 mm in width, and 5 mm in length were cut out from the TiAl alloy material and washed with acetone. The contents of each element in the washed specimens were measured by the following method.

[0154] Using an analyzer (LECO, ONH836), the oxygen concentration of the test specimen was measured by the inert gas fusion-infrared absorption method, and the nitrogen concentration of the test specimen was measured by the inert gas fusion-thermal conductivity method. Furthermore, using an analyzer (LECO, CS844), the carbon concentration of the test specimen was measured by the combustion-infrared absorption method. Furthermore, using an ICP optical emission spectrometer (Agilent, 720-ES), the calcium concentration of the test specimen was measured by the hydrochloric acid-hydrofluoric acid decomposition method.

[0155] The specified values ​​for jet engine blades made of TiAl alloy material were an oxygen concentration of 0.15 mass% or less, a nitrogen concentration of 0.03 mass% or less, a carbon concentration of 0.02 mass% or less, and a calcium concentration of 0.10 mass% or less, and the blades were evaluated as being good.

[0156]

[0157]

[0158]

[0159] As shown in Tables 1 to 6, alloys Nos. 2, 3, 5 to 7, 9 to 17, and 19 to 21 (Examples) were prepared by melting raw materials containing alloying elements consisting of 33.3% by mass of aluminum, 4.8% by mass of niobium, 2.7% by mass of chromium, and the balance titanium, calcium in amounts of 0.1 to 0.3% by mass, oxygen in an amount of 0.2% by mass or less, nitrogen in an amount of 0.02% by mass or less, and carbon and inevitable impurities in an amount of 0.03% by mass or less, or raw materials and pretreated cutting chips in an atmosphere with an oxygen concentration of 0.02% by volume to 0.5% by volume and a nitrogen concentration of 0.1% by volume to 2.5% by volume. All of these alloys had calcium, oxygen, nitrogen, and carbon contents below the specified values ​​for jet engine blades made of TiAl alloy material.

[0160] Alloy Nos. 2, 3, 5 to 7, 9 to 17, and 19 to 21 (Examples) are TiAl alloy materials that contain alloying elements consisting of 33.3 mass% aluminum, 4.8 mass% niobium, 2.7 mass% chromium, and the balance titanium, as well as calcium, oxygen, nitrogen, carbon, and inevitable impurities, and correspond to the composition of TiAl4822 (Ti-48.0Al-2Nb-2Cr (atomic %)), with calcium, oxygen, nitrogen, and carbon contents within ranges not exceeding the specified values ​​for jet engine blades made of TiAl alloy materials.

[0161] In contrast, Alloy No. 1 (Comparative Example) had high oxygen and nitrogen concentrations in the atmosphere in the chamber, resulting in a nitrogen concentration in the TiAl alloy material exceeding the specified value. Alloy No. 4 (Comparative Example) had an oxygen concentration in the TiAl alloy material exceeding the specified value because the calcium concentration in the raw materials was too low. Furthermore, Alloy No. 8 (Comparative Example) had an calcium concentration in the raw materials that was too high, resulting in a calcium concentration in the TiAl alloy material exceeding the specified value.

[0162] In addition, in Alloy No. 18 (Comparative Example), the temperature at which the cutting chips were heated in the pretreatment step was less than 400°C, so carbon elements remained in the cutting chips after the pretreatment, and the carbon concentration in the TiAl alloy material exceeded the specified value. In addition, in Alloy No. 21 (Comparative Example), the temperature at which the cutting chips were heated in the pretreatment step was too high, so the cutting chips were oxidized, increasing the oxygen concentration in the cutting chips after the pretreatment, and the oxygen concentration in the TiAl alloy material exceeded the specified value.

[0163] Furthermore, in alloys Nos. 3 and 12, which used woven fabric with a silica content of 10% by mass or less, the woven fabric did not melt, and no crucible inclusions of 0.3 mm or larger were detected. In contrast, in alloy No. 9, which used woven fabric with a silica content of more than 10% by mass, the woven fabric melted, and a molten metal layer was not sufficiently formed on the woven fabric, resulting in the detection of crucible inclusions of up to 0.6 mm.

[0164] Furthermore, in alloys using a woven fabric with an average mesh size of 2.0 mm or less, such as alloy No. 2, no crucible inclusions of 0.3 mm or larger were detected. In contrast, in alloy No. 17, which used a woven fabric with an average mesh size of more than 2.0 mm, a molten metal layer was not sufficiently formed on the woven fabric, and crucible inclusions of up to 0.5 mm were detected.

[0165] Furthermore, poor molten metal running did not occur in alloys using woven fabric with an average mesh size of 0.5 mm or more, such as Alloy No. 14. In contrast, in Alloy No. 13, which used woven fabric with an average mesh size of less than 0.5 mm, the flow of the molten alloy was hindered by the woven fabric, resulting in poor molten metal running.

[0166] [Summary] As shown in Tables 1 to 6, by using a method in which raw materials are charged into a calcia crucible and the raw materials, which are composed of alloy-forming elements including titanium and aluminum, and predetermined contents of calcium, oxygen, nitrogen, carbon, and unavoidable impurities, are melted in an atmosphere of predetermined oxygen and nitrogen concentrations to obtain a molten alloy, TiAl alloy materials having calcium, oxygen, nitrogen, and carbon contents not exceeding the specified values ​​for jet engine rotor blades could be produced.

[0167] Furthermore, cutting chips made of TiAl alloy were heated in the atmosphere at 400 to 800°C to form pre-treated cutting chips, and in the melting process, raw materials were placed in a calcia crucible, and the pre-treated cutting chips were then placed therein. This enabled the production of a TiAl alloy material whose calcium, oxygen, nitrogen, and carbon contents were below the specified values ​​for jet engine blades.

[0168] Furthermore, in the casting process, the molten alloy was passed through a woven fabric made of a mixed oxide of alumina and silica, the mixed oxide having a silica content of 10 mass% or less and an average mesh size of 0.5 mm to 2 mm, and then poured into a mold, thereby producing a TiAl alloy material that did not contain crucible inclusions of 0.3 mm or more.

[0169] <Additional Notes> The manufacturing method of the TiAl alloy material, the TiAl alloy material, the TiAl alloy part, and the jet engine rotor blade described in each embodiment can be understood, for example, as follows.

[0170] [1] A method for producing a TiAl alloy material, comprising: a melting step of charging raw materials into a calcia crucible and melting the raw materials in an atmosphere having an oxygen concentration of 0.1% to 0.5% by volume and a nitrogen concentration of 0.5% to 2.5% by volume to obtain a molten alloy, wherein the raw materials are alloy-forming elements including titanium and aluminum, and the raw materials contain 0.1% to 0.3% by mass of calcium, 0.2% by mass or less of oxygen, 0.02% by mass or less of nitrogen, and 0.03% by mass or less of carbon and inevitable impurities; and a casting step of pouring the molten alloy into a mold.

[0171] [2] In the melting step, the calcia crucible containing the raw materials is placed in a chamber of a vacuum melting furnace, and the chamber is made into a low vacuum state of 500 Pa to 2500 Pa, and then argon gas is introduced into the chamber to make the atmosphere 0.1 atmosphere to 0.9 atmosphere. [3] The method for producing a TiAl alloy material according to [1].

[0172] [3] The method for producing a TiAl alloy material according to [1], wherein the melting step is performed only once before the casting step is performed. [4] The method for producing a TiAl alloy material according to [1], wherein the TiAl alloy material contains 0.06 mass% or less of calcium, 0.12 mass% or less of oxygen, 0.03 mass% or less of nitrogen, and 0.02 mass% or less of carbon.

[0173] [5] The method for producing a TiAl alloy material according to [1], wherein the casting step is a step of pouring the molten alloy that has been passed through a woven fabric into a mold, and the woven fabric is made of a mixed oxide of alumina and silica, the silica content is 10 mass% or less, and the average mesh size is 0.5 mm to 2 mm. [6] The method for producing a TiAl alloy material according to [5], wherein the TiAl alloy material is free from inclusions of 0.3 mm or more that have been mixed in from a crucible.

[0174] [7] The method for producing a TiAl alloy material according to [1], further comprising a pretreatment step of heating cutting chips made of TiAl alloy in the atmosphere at 400 to 800°C to form pretreated cutting chips before the melting step, wherein the pretreated cutting chips are further placed in the calcia crucible in the melting step. [8] The method for producing a TiAl alloy material according to [7], wherein the amount of the pretreated cutting chips placed in the calcia crucible is 40 mass% or less of the total mass of the raw material and the pretreated cutting chips.

[0175] [9] The manufacturing method of the TiAl alloy material according to [1], wherein the alloying elements are aluminum, niobium, chromium, and titanium, and the content of the alloying elements in the raw material is 31.5 mass% to 34.0 mass%.

[0176]

[10] A TiAl alloy material comprising alloying elements including titanium and aluminum, 0.02 mass% to 0.06 mass% calcium, 0.04 mass% to 0.12 mass% oxygen, 0.005 mass% to 0.03 mass% nitrogen, 0.005 mass% to 0.02 mass% carbon, and inevitable impurities.

[0177]

[11] The TiAl alloy material according to

[10] , wherein the alloying elements are 31.5% by mass to 34.0% by mass of aluminum, 4.0% by mass to 5.5% by mass of niobium, 2.0% by mass to 3.0% by mass of chromium, and the balance titanium.

[0178]

[12] A TiAl alloy part made of the TiAl alloy material according to

[10] or

[11] .

[13] A jet engine blade made of the TiAl alloy material according to

[10] or

[11] .

[0179]

[14] A method for producing a TiAl alloy material, comprising: a melting step of charging raw materials into a calcia crucible, and melting the raw materials in an atmosphere having an oxygen concentration of 0.1% by volume to 0.5% by volume and a nitrogen concentration of 0.5% by volume to 2.5% by volume to obtain a molten alloy; and a casting step of pouring the molten alloy into a mold, wherein the raw materials have a composition consisting of alloy-forming element components containing at least titanium and aluminum, 0.1 to 0.3% by mass of calcium, 0.2% by mass or less of oxygen, 0.02% by mass or less of nitrogen, 0.03% by mass or less of carbon, and inevitable impurities.

[0180]

[15] A method for producing a TiAl alloy material, comprising: a melting step of charging raw materials into a calcia crucible, and melting the raw materials in an atmosphere having an oxygen concentration of 0.02% by volume to 0.5% by volume and a nitrogen concentration of 0.1% by volume to 2.5% by volume to obtain a molten alloy; and a casting step of pouring the molten alloy into a mold, wherein the raw materials have a composition consisting of alloying element components containing at least titanium and aluminum, 0.1 to 0.3% by mass of calcium, 0.2% by mass or less of oxygen, 0.02% by mass or less of nitrogen, 0.03% by mass or less of carbon, and inevitable impurities.

[0181] The TiAl alloy material manufactured using the method for manufacturing a TiAl alloy material of the present disclosure can be produced at low cost, and has calcium, oxygen, nitrogen, and carbon contents below the specified values ​​for jet engine blades. Therefore, it can be suitably used as a material for TiAl alloy parts such as jet engine blades. In particular, the TiAl alloy material manufactured using the method for manufacturing a TiAl alloy material of the present disclosure, in which a molten alloy passed through a specific woven fabric is poured into a mold, does not contain crucible inclusions of 0.3 mm or more. Therefore, it can be more suitably used as a material for TiAl alloy parts.

[0182] REFERENCE SIGNS LIST 1 mold 1a first mold 1b second mold 1c sprue 10 runner 11 cavity 20 woven fabric 30 molten alloy 30a liquid surface 30b molten alloy layer 31 crucible inclusions

Claims

1. A method for producing a TiAl alloy material, comprising: a melting step of charging raw materials into a calcia crucible and melting the raw materials in an atmosphere with an oxygen concentration of 0.02% to 0.5% by volume and a nitrogen concentration of 0.1% to 2.5% by volume to produce a molten alloy, wherein the raw materials consist of alloy-forming elements including titanium and aluminum, and the raw materials contain 0.1% to 0.3% by mass of calcium, 0.2% by mass or less of oxygen, 0.02% by mass or less of nitrogen, and 0.03% by mass or less of carbon and inevitable impurities; and a casting step of pouring the molten alloy into a mold.

2. The method for producing a TiAl alloy material according to claim 1, wherein in the melting step, the calcia crucible containing the raw materials is placed in a chamber of a vacuum melting furnace, the chamber is made into a low vacuum state of 100 Pa to 2500 Pa, and then argon gas is introduced into the chamber to make the pressure in the range of 0.1 atmospheres to 0.9 atmospheres, thereby forming the atmosphere.

3. The method for producing a TiAl alloy material according to claim 1, wherein the melting step is carried out only once before the casting step is carried out.

4. A method for producing a TiAl alloy material according to claim 1, which produces a TiAl alloy material containing 0.1 mass% or less of calcium, 0.15 mass% or less of oxygen, 0.03 mass% or less of nitrogen, and 0.02 mass% or less of carbon.

5. A method for producing a TiAl alloy material according to claim 1, wherein the casting step is a step of pouring the molten alloy that has been passed through a woven fabric into a mold, and the woven fabric is made of a mixed oxide of alumina and silica, the silica content is 10 mass% or less, and the average mesh size is 0.5 mm to 2 mm.

6. The method for producing a TiAl alloy material according to claim 5, wherein the TiAl alloy material is free from inclusions of 0.3 mm or more that are mixed in from the crucible.

7. A method for producing a TiAl alloy material according to claim 1, further comprising a pretreatment step of heating cutting chips made of TiAl alloy in the atmosphere at 400°C to 800°C before the melting step to produce pretreated cutting chips, and further comprising putting the pretreated cutting chips into the calcia crucible in the melting step.

8. A method for producing a TiAl alloy material as described in claim 7, wherein the amount of the pre-treated cutting chips put into the calcia crucible is 40 mass % or less of the total mass of the raw material and the pre-treated cutting chips.

9. The method for producing a TiAl alloy material according to claim 1, wherein the alloying elements are aluminum in an amount of 31.5 to 34.0 mass % in the raw material, niobium in an amount of 4.0 to 5.5 mass % in the raw material, chromium in an amount of 2.0 to 3.0 mass % in the raw material, and titanium in an amount of the remainder.

10. A TiAl alloy material comprising alloying elements including titanium and aluminum, 0.02% by mass to 0.10% by mass of calcium, 0.04% by mass to 0.15% by mass of oxygen, 0.005% by mass to 0.03% by mass of nitrogen, 0.005% by mass to 0.02% by mass of carbon, and unavoidable impurities.

11. The TiAl alloy material of claim 10, wherein the alloying elements consist of: 31.5% to 34.0%, by weight, of aluminum; 4.0% to 5.5%, by weight, of niobium; 2.0% to 3.0%, by weight, of chromium; and the balance being titanium.

12. A TiAl alloy part made from the TiAl alloy material according to claim 10 or 11.

13. A jet engine rotor blade made of the TiAl alloy material according to claim 10 or 11.

Images