TiAl casting alloy

Abstract

To provide a TiAl casting alloy that is excellent in castability, machinability, and strength at high temperature and impact resistance at room temperature.SOLUTION: A TiAl casting alloy comprises aluminum (Al): 44.5-46.5 atom%, nickel (Ni): 0.3-1.0 atom%, niobium (Nb): 1.0-5.0 atom%, with the balance being titanium (Ti) and unavoidable impurities. Preferably, in addition to these components, one or more of chromium (Cr), manganese (Mn), vanadium (V), tungsten (W) are contained in a total of 0.5-2.0 atom%.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a TiAl casting alloy that is suitable for use in jet engine rotor blades, turbine wheels of passenger car turbochargers, and the like, and that has excellent castability, machinability, and high-temperature strength. [Background technology]

[0002] In recent years, TiAl alloys have been used in jet engine rotor blades and turbine wheels for passenger car turbochargers. The density of TiAl alloys is about half that of the Ni-based and iron-based superalloys that have traditionally been used in these products, so they have the advantage of not increasing weight even when the size is increased, and they contribute greatly to reducing fuel consumption by improving engine efficiency.

[0003] Currently, jet engine blades are cut out entirely from simple rectangular ingots using cutting processes. This requires a large amount of processing, which creates a current challenge: high processing costs. Therefore, it is thought that a method will be needed in the future to produce material with a shape similar to that of the blade using precision casting, and then machine it into a finished product. Precision casting is a method of producing a casting of the desired shape using a ceramic mold with a cavity of the same shape as the product, filling this cavity with molten metal during casting and allowing it to solidify. The ceramic mold that adheres to the outside of the casting is destroyed and removed.

[0004] Meanwhile, in the case of the turbine wheels of passenger car turbochargers, another part for which TiAl alloys are currently used, they are significantly smaller in size than jet engine blades, so it is possible to manufacture the entire product using precision casting. Most parts of the product, such as the impeller on the top, remain in the shape that would be produced by precision casting, but for the joint with the shaft, the back of the turbine wheel is machined to form a convex joint surface about 15 mm in diameter.

[0005] When casting turbine wheels, the current method involves introducing molten metal from the back of the turbine wheel. This leaves a channel for introducing the molten metal (called a gate) on the back. As will be discussed later, TiAl alloys have poor castability, so to prevent defects, this gate must be made thicker. Specifically, a diameter of approximately 30 mm is required. When machining the joining surface, this thick gate must be machined to form a joining part with a diameter of approximately 15 mm, which requires a significant amount of machining. In other words, both jet engine rotor blades and passenger car turbocharger turbine wheels require extensive machining even after the parts are manufactured by precision casting. Generally, TiAl alloys are harder and more brittle than other practical metallic materials, resulting in poor machinability. Specifically, when cut under the same conditions as other metallic materials, the product can develop surface peeling or chipping, known as "pick-out," and the tool wear is also significant, necessitating frequent tool replacement. Therefore, machining must be performed under low-load conditions, with extremely low rotation speeds and cutting depths, which increases machining time and increases costs, creating an issue.

[0006] On the other hand, the biggest issue currently facing precision casting of TiAl alloys is the low yield of non-defective products. This low yield results in extremely high product unit prices. The main reason for the low yield of non-defective products is the poor castability of conventional TiAl alloys. There are many reasons for the poor castability of TiAl alloys, but the main reason is the low fluidity of the molten metal. This often results in the molten metal not filling the narrow cavity of the mold all the way to the tip, and shrinkage cavities forming inside the thick parts. These defects result in defective products, lowering the yield of non-defective products. In other words, based on the current situation described above, a TiAl alloy suitable for jet engine rotor blades and turbine wheels for passenger car turbochargers must have good castability (fluidity of the molten metal) to improve the yield of good products, and at the same time, have excellent machinability to reduce processing costs. It goes without saying that the alloy must also have good high-temperature strength required for product use, and a certain level of impact resistance at room temperature to prevent breakage during manufacturing and use.

[0007] In the precision casting of TiAl alloys, methods such as suction casting and centrifugal casting have been used to forcibly improve the running properties of the molten metal by pressurizing the molten metal (see, for example, Patent Documents 1, 2, and 3). Patent Document 1 discloses the production of precision castings by suction casting, and Patent Document 2 discloses the production of precision castings by centrifugal casting. Furthermore, Patent Document 3 discloses the production of precision castings by centrifugal casting in a suction casting device. However, even with these measures, it was not possible to completely compensate for the poor castability of TiAl alloys, and there was a problem that defects such as poor molten metal flow were likely to occur in the products.

[0008] Meanwhile, TiAl alloys are known that have improved machinability by intentionally forming a third phase called the β phase (see, for example, Patent Document 4). Patent Document 4 discloses a TiAl alloy having a microstructure in which lamellar grains with an average grain size of 1 to 65 μm are arranged, in which α2 phases and γ phases are alternately stacked, and the gaps between the lamellar grains are filled with a matrix containing β phases and γ phases, the area fraction of the lamellar grains is 30 to 70%, the spacing between the α2 phases within the lamellar grains, i.e., the lamellar spacing, is 0.4 to 1.5 μm, and the area fraction of the β phase is 5 to 15%, and one of its properties is excellent machinability. However, the problem is that the area ratio of the β phase must be at least 5%. The β phase is characterized by its softness at high temperatures, and is typically used to improve deformability during hot forging, as in this prior art. Being soft at high temperatures means low strength at high temperatures, which reduces the excellent high-temperature strength, particularly creep strength, that is the greatest feature of TiAl alloys. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 4-22562 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-78067 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-254052 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-356729 Summary of the Invention [Problem to be solved by the invention]

[0010] In view of the above, an object of the present invention is to provide a TiAl casting alloy suitable for use in jet engine rotor blades, turbine wheels of passenger car turbochargers, etc., and more particularly to provide a TiAl casting alloy that is excellent in castability, machinability, high-temperature strength, and room-temperature impact resistance. [Means for solving the problem]

[0011] The present inventors have found that within a relatively narrow range of Al content, there is no undue deterioration in the castability, machinability, high-temperature strength, and room-temperature impact resistance targeted in this application. They have also found that the addition of Ni improves castability and machinability, and the addition of Nb improves high-temperature strength. They have also found that the addition of Cr and Mn further improves castability and machinability, and the addition of V and W further improves high-temperature strength. They have also found that, in order to ensure a certain level of room-temperature impact resistance, it is best to keep the amounts of the above-mentioned additive elements, excluding Nb, as small as possible. As a result of the above, the inventors have invented a TiAl casting alloy having the following composition, which will be explained in detail below.

[0012] The TiAl casting alloy of the present invention is composed of 44.5-46.5 atomic % aluminum (Al), 0.3-1.0 atomic % nickel (Ni), 1.0-5.0 atomic % niobium (Nb), the balance being titanium (Ti) and unavoidable impurities, and more preferably contains, in addition to the above components, one or more of chromium (Cr), manganese (Mn), vanadium (V), and tungsten (W) in a total amount of 0.5-2.0 atomic % to solve the above problems.

[0013] Aluminum (Al): Together with Ti, it is a basic element of TiAl alloys, and constitutes TiAl phase, Ti3Al phase, etc. If the Al content is 44.5 atomic % or less, impact resistance and machinability at room temperature decrease, and if it is 46.5 atomic % or more, high-temperature strength decreases, so the Al content is preferably 44.5 to 46.5 atomic %.

[0014] Nickel (Ni) improves castability and machinability at the above Al content, but the effect of adding it is small at 0.3 atomic % or less, and adding it at 1.0 atomic % or more is undesirable because it reduces high-temperature strength and room-temperature impact resistance below the required values. Therefore, the Ni content is preferably 0.3 to 1.0 atomic %.

[0015] Niobium (Nb) improves high-temperature strength through solid solution strengthening, but the effect of adding less than 0.5 atomic percent is small, and adding more than 5.0 atomic percent is undesirable because it reduces machinability and room temperature impact resistance below the required level. Therefore, the amount of Nb added should be 0.5 to 5.0 atomic percent.

[0016] Adding chromium (Cr) and manganese (Mn) to the above alloy further improves the castability and machinability, but adding 0.5 atomic % or less of these elements alone or in combination is not desirable as the effect of the addition is small. The addition of vanadium (V) and tungsten (W) further improves high-temperature strength, but adding them alone or in combination at less than 0.5 atomic percent is undesirable because the effect is minimal. Also, adding Cr, Mn, V, and W alone or in combination at more than 2.0 atomic percent reduces room-temperature impact resistance below the required level, which is undesirable. Therefore, the preferred amounts of Cr, Mn, V, and W, either alone or in combination, are 0.5 to 2.0 atomic percent.

[0017] As described above, the TiAl casting alloy of the present invention has excellent castability, machinability, high-temperature strength, and room-temperature impact resistance, making it advantageous for precision castings and suitable for use in jet engine rotor blades, turbine wheels for passenger car turbochargers, and the like.

[0018] Next, the TiAl casting method of the present invention will be described. First, the raw materials are melted. The raw materials are then cast to a composition of 44.5-46.5 atomic percent aluminum (Al), 0.3-1.0 atomic percent nickel (Ni), 1.0-5.0 atomic percent niobium (Nb), with the remainder consisting of titanium (Ti) and unavoidable impurities. More preferably, the raw materials are adjusted to contain, in addition to the above components, one or more of chromium (Cr), manganese (Mn), vanadium (V), and tungsten (W) in a total amount of 0.5-2.0 atomic percent. There are no particular limitations on the shape of the raw materials, and they can be pellets, granules, sponge, powder, or any other suitable form. Alternatively, a master alloy ingot of the same composition that has been previously melted can be remelted and used.

[0019] The crucible used for melting may be a water-cooled copper crucible, which is normally used for melting TiAl alloys, or a ceramic crucible. For example, an yttria crucible or a calcia crucible may be used. Furthermore, any melting method may be used as long as the raw materials are melted to form a molten metal, and for example, high-frequency melting may be used. For example, when high-frequency melting is used, the crucible containing the raw materials may be placed in a chamber, the chamber may be evacuated, and an inert gas such as argon gas may be introduced to melt the raw materials.

[0020] In the next step, the resulting molten metal is poured into a mold. While there are no particular restrictions on the material of the mold, in the case of industrial precision casting, it is desirable to use a zirconia-based ceramic mold, which is commonly used for Ti-based alloys, as this reduces surface defects. Similarly, in the case of industrial precision casting, in order to prevent defects by filling the molten metal up to the tip of the thin product and improve the yield of good products, it is desirable to use a method of forcibly pressurizing the molten metal, such as suction casting or centrifugal casting. [Effects of the Invention]

[0021] The TiAl casting alloy of the present invention contains 44.5-46.5 atomic percent Al without excessively deteriorating castability, machinability, high-temperature strength, or room-temperature impact resistance. Furthermore, the addition of 0.3-1.0 atomic percent Ni improves castability and machinability, while the addition of 1.0-5.0 atomic percent Nb improves high-temperature strength. Furthermore, the addition of 0.5-2.0 atomic percent of one or more of chromium (Cr), manganese (Mn), vanadium (V), and tungsten (W) further improves castability, machinability, and high-temperature strength. Although the addition of these elements reduces room-temperature impact resistance to some extent, a certain level of impact resistance can be maintained as long as the addition amounts are within the above ranges. [Brief explanation of the drawings]

[0022] [Figure 1] Schematic diagram of the molds used in Examples 1 to 25. [Figure 2] Appearance of Alloy 8 [Figure 3A] Appearance of molten alloy 8 after it has been poured out of a mold [Figure 3B] Appearance of molten alloy 6 poured from a mold DETAILED DESCRIPTION OF THE INVENTION [Example]

[0023] The present invention will be described below with reference to the drawings. [Example 1 to Example 25] The Ti sponge granular raw material, Al pellets, Ni granular raw material, Nb flake raw material, Cr granular raw material, Mn flake raw material, AlV master alloy granular raw material, and W powder were weighed to meet the composition shown in Table 1. The raw materials were mixed to a total weight of approximately 500 g, placed in an yttria crucible, and melted by high-frequency melting. Specifically, the crucible containing the raw materials was placed in the chamber of the melting furnace, and evacuation of the chamber was initiated. After the specified vacuum level was reached, argon gas was introduced. After the argon gas pressure reached the specified value, the high-frequency power supply was gradually increased in power to heat the raw materials and melt them. The maximum power output was 5 kW. After all the raw materials were melted, the power was reduced to 3.5 kW and held for 3 minutes. The molten metal was then poured into a mold.

[0024] [Table 1A]

[0025] [Table 1B]

[0026] [Table 1C]

[0027] The three Tables 1A, 1B, and 1C above are one table divided into three sections. Information about each sample is listed in separate rows across the three Tables 1A, 1B, and 1C. For example, for "Alloy No. 1," the classification is "Comparative Alloy," the composition is 44.3% Al, 0.7% Ni, and 2.0% Nb in atomic percent, the melt flow rate (g) is 26, the number of pull marks (number of pull marks) is 8, the tensile strength at 800°C (MPa) is 480, the Charpy absorbed energy at room temperature (J) is 4.0, the castability is "Good," the machinability is "Poor," the high-temperature strength is "Good," and the room-temperature impact resistance is "Poor." The other samples are similarly described above.

[0028] In Table 3, the castability was evaluated as "×" when the amount of molten metal flowed out was less than 20 g, "○" when it was 20 g or more, and "◎" when it was 40 g or more. 2 After processing, if the number of ripped cracks was 5 or more, it was rated as "×", if it was 5 or less, it was rated as "○", and if it was 2 or less, it was rated as "◎". For high-temperature strength, if the tensile strength at 800°C was 400MPa or less, it was rated as "×", if it was 400MPa or more, it was rated as "○", and if it was 500MPa or more, it was rated as "◎". For impact resistance at room temperature, if the Charpy absorbed energy at room temperature was less than 5J, it was rated as "×", and if it was 5J or more, it was rated as "○".

[0029] FIG. 1 is a diagram schematically showing the molds used in casting the alloys of Examples 1 to 25. In the figure, the mold of this embodiment comprises a mold body 10, a cavity 20, and a spacer 30. The mold body 10 is composed of a right block 12 and a left block 14. It is essentially a two-piece mold, secured by clamping the outside with a clamping rod or similar. Therefore, by removing the clamping rod or similar, the mold body 10 can be easily separated into the right block 12 and the left block 14. The mold is made of cast iron, but to simulate the conditions of an actual precision casting, a zirconia-based paint is applied to the inner surface of the mold that comes into contact with the molten metal. Furthermore, the mold was not preheated to improve castability. Before pouring, an alumina funnel was placed on top of the mold, and the entire cavity inside the mold and the funnel were filled with molten metal up to the middle.

[0030] The cavity 20 has the shape of the article to be produced from the casting alloy; for example, in the case of a turbine blade, it has a thick base and a thin tip. To evaluate the castability of each alloy, the size of the cavity 20 was 80 mm long, and the widths were gradually reduced from top to bottom: cavity 21 (30 mm), cavity 22 (20 mm), cavity 23 (15 mm), cavity 24 (3 mm), and cavity 25 (1 mm). A cavity was also provided in the lowest cavity 25. A spacer 30 was placed at the bottom of the mold to provide space below this lowest cavity 25. During casting, some of the molten metal leaks out from a 1 mm wide gap provided in the lowest cavity 25 before solidification. Naturally, the state of this leakage is closely related to the fluidity of the molten metal, so the weight of this leaked molten metal was measured, and the more the weight, the better the alloy was considered to be in terms of castability.

[0031] After pouring, the mold was allowed to cool to a certain temperature, and the clamp was removed to separate the mold at the location shown in Figure 1, and the TiAl alloy casting material was taken out. The samples obtained in Examples 1 to 25 are referred to as Alloy 1 to Alloy 25, respectively. The compositions of Alloy 1 to Alloy 25 obtained were exactly as targeted. The methods for evaluating the castability, machinability, high-temperature strength, and room-temperature impact resistance of Alloy 1 to Alloy 25, as well as the criteria for judging the relative merits based on the results, are as follows:

[0032] (1) Castability When pouring Alloy 1 to Alloy 25, the weight of the molten metal leaking from a 1 mm gap at the bottom of the mold was measured. Castability was judged to be poor when the weight of the leaked molten metal was 20 g or less, excellent when it was 20 g or more, and even better when it was 40 g or more.

[0033] (2) Machinability Cylinders measuring 20 mm in diameter and 80 mm in length were machined from 30 mm wide sections of the cast alloys 1 to 25, and turning tests were conducted using a general-purpose lathe with a carbide tip. The machining conditions were a rotation speed of 500 rpm, a cutting depth of 0.2 mm, and a feed rate of 0.1 mm / rpm, and a length of 50 mm was machined. The machined area was therefore 157 cm2. The entire surface after machining was visually inspected to count the number of ripped sections (surface peeling). Machinability was assessed as poor when there were five or more ripped sections, excellent when there were five or fewer sections, and even better when there were two or fewer sections.

[0034] (3) High temperature strength Tensile test specimens with a total length of 60 mm were machined from a 15 mm wide section of the cast alloy 1-25. The parallel section had a diameter of 4 mm, a length of 20 mm, and a gripping section with an M10 x P1.5 screw. The tensile test was performed at 800°C, and the tensile strength at break, which is the maximum load, was measured. Tensile strengths of 400 MPa or less were considered to have poor high-temperature strength, those of 400 MPa or more were considered to have excellent high-temperature strength, and those of 500 MPa or more were considered to have even better high-temperature strength.

[0035] (4) Impact resistance at room temperature Charpy impact test specimens measuring 10 mm in length, 10 mm in width, and 55 mm in length were machined from 20 mm wide sections of the cast alloys 1 through 25. Charpy impact tests were conducted at room temperature to measure absorbed energy. Note that TiAl alloys are generally brittle materials, and if a standard 2 mm V-notch were introduced in a Charpy impact test, the absorbed energy would be too low to adequately compare the differences between the alloys. Therefore, for this evaluation, smooth specimens without notches were used. Obtained absorbed energy of 5 J or less was considered poor for impact resistance at room temperature, and 5 J or more was considered excellent.

[0036] The measurement results of the various properties mentioned above and the performance evaluation results of each alloy based on these are summarized in Table 1. Figure 2 shows an example of the appearance of the cast material, which is Alloy 3. Figure 3 shows an example of the appearance of the leaked part from the bottom of the mold. Figure 3A shows the appearance of the leaked part for Alloy 8, and Figure 3B shows the appearance of the leaked part for Alloy 6, photographed from the back side of the mold.

[0037] The results of the casting experiments and evaluation of various properties shown above indicate that Alloys 2 to 4, Alloys 7 to 9, and Alloys 12 to 14, which contain 44.5-46.5 atomic percent aluminum (Al), 0.3-1.0 atomic percent nickel (Ni), 1.0-5.0 atomic percent niobium (Nb), with the remainder consisting of Ti and unavoidable impurities, are excellent TiAl casting alloys for the purposes of this application. Furthermore, Alloys 17 to 19 and Alloys 22 to 24, which contain, in addition to the above components, 0.5-2.0 atomic percent of one or more of chromium (Cr), manganese (Mn), vanadium (V), and tungsten (W), are even more excellent TiAl casting alloys for the purposes of this application.

[0038] This will be described in more detail below. (1) Suitable concentration of Al Alloys 1 to 5 represent a group in which the Al concentration was varied. In this group, the components excluding Al, Ti, and irreversible impurities were within the ranges of 0.3-1.0 atomic percent nickel (Ni) and 1.0-5.0 atomic percent niobium (Nb). When the Al content was 44.7%, 45.5%, and 46.3% (Alloys 2, 3, and 4, respectively), the castability, machinability, high-temperature strength, and room-temperature impact resistance were all good. However, when the Al content was relatively low at 44.3% (Alloy 1, comparative alloy), the machinability and room-temperature impact resistance were poor. Furthermore, when the Al content was relatively high at 46.7% (Alloy 5, comparative alloy), the high-temperature strength was poor.

[0039] (2) Suitable concentration of Ni Alloys 6 to 10 represent a group in which the Ni concentration was significantly varied. In this group, the components excluding Ni, Ti, and irreversible impurities were aluminum (Al) 44.5–46.5 at.% and niobium (Nb) 1.0–5.0 at.%. When Ni was 0.4%, 0.7%, or 0.9% (Alloys 7, 8, and 9, respectively), the castability, machinability, high-temperature strength, and room-temperature impact resistance were all good. However, when Ni was relatively low at 0.2% (Alloy 6, comparative alloy), the castability and machinability were poor. Furthermore, when Ni was relatively high at 1.2% (Alloy 10, comparative alloy), the castability and machinability were even better, but the high-temperature strength and room-temperature impact resistance were poor.

[0040] (3) Suitable concentration of Nb Alloys 11 to 15 represent a group in which the Cr concentration was significantly varied. In this group, the components, excluding Nb, Ti, and irreversible impurities, were within the ranges of aluminum (Al) 44.5–46.5 at. % and nickel (Ni) 0.3–1.0 at. When Nb was 1.2%, 3.0%, or 4.8% (Alloys 12, 13, and 14, respectively), the castability, machinability, high-temperature strength, and room-temperature impact resistance were all good. However, when Nb was relatively low at 0.8% (Alloy 11, comparative alloy), high-temperature strength was poor. Furthermore, when Nb was relatively high at 5.2% (Alloy 15, comparative alloy), high-temperature strength was even better, but machinability and room-temperature impact resistance were poor.

[0041] (4) Effects of adding Cr and Mn Alloys 16–20 are alloys containing Cr and Mn in addition to the invention alloys. This group contains 44.5–46.5 atomic percent aluminum (Al), 0.3–1.0 atomic percent nickel (Ni), and 1.0–5.0 atomic percent niobium (Nb). When the Cr+Mn content is 0.4% (Alloy 16), castability, machinability, high-temperature strength, and room-temperature impact resistance are all good, but not significantly different from the alloys containing no Cr+Mn. On the other hand, when the Cr+Mn content is 1.0, 1.2, or 1.5% (Alloys 17, 18, and 19, respectively), castability and machinability are even better than the alloys containing no Cr+Mn. Furthermore, when the Cr+Mn content is relatively high at 2.6% (Alloy 20, comparative alloy), high-temperature strength and room-temperature impact resistance are poor.

[0042] (5) Effects of adding V and W Alloys 21 to 25 are alloys containing V and W in addition to the invention alloys. The contents of these alloys are within the ranges of 44.5-46.5 atomic percent aluminum (Al), 0.3-1.0 atomic percent nickel (Ni), and 1.0-5.0 atomic percent niobium (Nb). When the V+W content is 0.4% (Alloy 21), castability, machinability, high-temperature strength, and room-temperature impact resistance are all good, but not significantly different from the alloys containing no V+W. On the other hand, when the V+W content is 1.3%, 0.9%, or 1.7% (Alloys 22, 23, and 24, respectively), the high-temperature strength is even better than the alloys containing no V+W. It can also be seen that when the V+W content is relatively high at 2.3% (Alloy 25, comparative alloy), the machinability and room-temperature impact resistance are poor.

[0043] (6) Summary As described above, the measurement and evaluation results in Table 1 indicate that TiAl casting alloys with concentrations excluding Ti and irreversible impurities within the ranges of aluminum (Al): 44.5-46.5 at.%, nickel (Ni): 0.3-1.0 at.%, and niobium (Nb): 1.0-5.0 at.% exhibit superior properties for the purposes of this application compared to alloys outside these composition ratios. Furthermore, it has been shown that alloys containing, in addition to the above components, one or more of chromium (Cr), manganese (Mn), vanadium (V), and tungsten (W) in a total amount of 0.5-2.0 at.% exhibit even superior properties for the purposes of this application. [Industrial Applicability]

[0044] As explained in detail above, the TiAl casting alloy of the present invention has excellent castability, so when used in precision castings, the occurrence of defects due to poor molten metal flow and the like is suppressed. Furthermore, because of its excellent machinability, it is possible to reduce the cost of cutting the castings. Furthermore, because of its excellent high-temperature strength and room-temperature impact resistance, it is suitable for use in turbine wheels of turbochargers used in gas turbines and jet engines for power generation, and in land transportation engines such as passenger cars and marine engines. [Explanation of symbols]

[0045] 10 Mold body 12 Right Block 14 Left Block 20 Cavity 21, 22, 23, 24, 25 Hollow parts 30 spacer

Claims

1. A TiAl casting alloy consisting of aluminum (Al): 44.5-46.5 atomic %, nickel (Ni): 0.3-1.0 atomic %, niobium (Nb): 1.0-5.0 atomic %, the balance being titanium (Ti) and unavoidable impurities.

2. 2. The TiAl casting alloy of claim 1, further comprising at least one of vanadium (V) and tungsten (W), the total of which is 0.5-2.0 atomic %.

3. Further, it contains vanadium (V) and manganese (Mn), and the total of manganese (Mn) and vanadium (V) is 0.5-2.0 atomic %; Alternatively, the material further contains tungsten (W) and chromium (Cr), and the total amount of chromium (Cr) and tungsten (W) is 0.5-2.0 atomic %.

2. The TiAl casting alloy of claim 1.

4. 2. The TiAl casting alloy of claim 1, further comprising one of chromium (Cr) or manganese (Mn), and containing 0.5-2.0 atomic percent of chromium (Cr) or manganese (Mn).

5. A turbine wheel for a turbocharger, which is a precision casting made of the TiAl casting alloy according to any one of claims 1 to 4.

6. 5. A precision cast product, comprising a jet engine blade and a power generation gas turbine blade, the precision cast product being made of the TiAl casting alloy according to claim 1.

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