HOT-FORGED TIAL-BASED ALLOY, METHOD FOR PRODUCING SAME, AND USES FOR SAME

Abstract

The present invention provides a TiAl-based alloy, including: Al: 41 to 43 at %; Fe: 0 to 2.5 at %; Ni: 0 to 2.5 at %; Mo: 0 to 2.0 at %; W: 0 to 2.0 at %; Cr: 0 to 4.5 at %; Mn: 0 to 5.5 at %; V: 0 to 10 at %; Nb: 0 to 10 at %; C: 0.3 to 0.7 at %; and a remainder consisting of Ti and inevitable impurities, in which an alloy element parameter “P=(41.5−Al)/3+Fe+Ni+Mo+W+0.5 Cr+0.4 Mn+0.2 V+0.2 Nb—C” is in a composition range of 1.1 to 1.9, and the TiAl-based alloy has a microstructure consisting of a γ phase of 5 to 30 area %, a β phase of 0.5 to 5 area %, and a lamellar structure occupying a remaining part.

Claims

1. A TiAl-based alloy, comprising: Al: 41 to 43 at %; Fe: 0 to 2.5 at %; Ni: 0 to 2.5 at %; Mo: 0 to 2.0 at %; W: 0 to 2.0 at %; Cr: 0 to 4.5 at %; Mn: 0 to 5.5 at %; V: 0 to 10 at %; Nb: 0 to 10 at %; C: 0.3 to 0.7 at %; and a remainder consisting of Ti and inevitable impurities, wherein an alloy element parameter P obtained by Equation (1) below is in a composition range of 1.1 to 1.9, and the TiAl-based alloy has a microstructure consisting of a γ phase of 5 to 30 area %, a β phase of 0.5 to 5 area %, and a lamellar structure occupying a remaining part,
P=(41.5−Al)/3+Fe+Ni+Mo+W+0.5 Cr+0.4 Mn+0.2 V+0.2 Nb—C  (1).

2. The TiAl-based alloy according to claim 1, comprising: Al: 41.2 to 42.8 at %; Fe: 0 to 2.0 at %; Ni: 0 to 2.0 at %; Mo: 0 to 1.7 at %; W: 0 to 1.7 at %; Cr: 0 to 4.0 at %; Mn: 0 to 5.0 at %; V: 0 to 8 at %; Nb: 0 to 8 at %; C: 0.35 to 0.65 at %; and a remainder consisting of Ti and inevitable impurities, wherein the alloy element parameter P is in a composition range of 1.2 to 1.8, and the TiAl-based alloy has a microstructure consisting of a γ phase of 7 to 25 area %, a β phase of 0.5 to 4.5 area %, and a lamellar structure occupying a remaining part.

3. The TiAl-based alloy according to claim 1, comprising: Al: 41.4 to 42.6 at %, Fe: 0 to 1.5 at %; Ni: 0 to 1.5 at %; Mo: 0 to 1.5 at %; W: 0 to 1.5 at %; Cr: 0 to 3.5 at %; Mn: 0 to 4.5 at %; V: 0 to 6 at %; Nb: 0 to 6 at %; C: 0.4 to 0.6 at %; and a remainder consisting of Ti and inevitable impurities, wherein the alloy element parameter P is in a composition range of 1.3 to 1.7, and the TiAl-based alloy has a microstructure consisting of a γ phase of 10 to 20 area %, a β phase of 0.5 to 4 area %, and a lamellar structure occupying a remaining part.

4. A method for producing a TiAl-based alloy, comprising: a step of hot-forging a TiAl-based alloy base material that has the composition and the microstructure according to claim 1 as the temperature of the TiAl-based alloy base material is held in a coexistence temperature range of an α phase and a β phase; and a step of holding a TiAl-based alloy material obtained by hot-forging in a temperature range of 1200 to 1250° C. for 0.5 to 5 hours and then heat treating the TiAl-based alloy material at a cooling rate of 1 to 10° C./min.

5. The method for producing a TiAl-based alloy according to claim 4, wherein in a cooling process in the step of heat treating the TiAl-based alloy material, a γ phase is precipitated from the β phase and an amount of the β phase is reduced.

6. A blade for a turbine using a TiAl-based alloy material that has the composition and the microstructure according to claim 1.

7. A gas turbine for power generation, a jet engine for an aircraft, a supercharger for a ship, or a gas turbine or a steam turbine for various industrial machines, which uses the blade for a turbine according to claim 6.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0092] FIG. 1 is an appearance photograph explaining a TiAl alloy ingot used in examples of the present invention.

[0093] FIG. 2 is an explanatory diagram of a hot-forging test conducted to evaluate hot forgeability, where (A) shows a sample shape before the hot forging and (B) shows a sample shape after the hot forging.

[0094] FIG. 3 is a dimensional diagram of a tensile test piece in accordance with JISZ2241.

[0095] FIG. 4A shows a comparative alloy (alloy number 28) of the present invention.

[0096] FIG. 4B shows an example alloy (alloy number 32) of the present invention.

[0097] FIG. 5A shows a comparative alloy (alloy number 37) of the present invention.

[0098] FIG. 5B shows an example alloy (alloy number 33) of the present invention.

[0099] FIG. 6 shows a flowchart of area rate measurement.

[0100] FIG. 7A shows a SEM image of an alloy structure in the surface contact rate measurement in S104 in FIG. 8.

[0101] FIG. 7B shows a SEM image of the alloy structure in the surface contact rate measurement in S104 in FIG. 8.

DESCRIPTION OF EMBODIMENTS

Examples

[0102] Hereinafter, the present invention will be described using the drawings. First, details of a procedure for creating a TiAl-based hot-forged alloy according to the present invention and an evaluation test procedure will be described in order.

[0103] Procedure 1: Creation of Ingot

[0104] FIG. 1 is a representative example of appearances of ingots created to have alloy compositions (alloys 1 to 49) shown in Tables 1 and 2. All the ingots have substantially the same appearance (photograph). The method of manufacturing the ingot is high-frequency melting using an yttria crucible.

[0105] Raw materials of the ingot were sponge Ti and particulate raw materials of Al, Fe, Ni, Mo, W, Cr, Mn, V, and Nb. C was added in a state contained in TiC powder, and a total weight of the ingot was about 850 g. The dissolution atmosphere was in argon gas. Casting was performed using a casting mold made of casting iron with an inner diameter of Φ50 mm, feeding head was cut, and the lower side (a portion with a uniform thickness) was used for a hot-forging test. The height of the ingot material during the hot-forging test was about 100 mm.

[0106] Procedure 2: Hot-Forging Test

[0107] The hot-forging test was conducted as in the explanatory diagram shown in FIG. 2. FIG. 2 is an explanatory diagram of the hot-forging test conducted to evaluate hot forgeability, where (A) shows a sample shape before the hot forging and (B) shows a sample shape after the hot forging. In other words, the forging was conducted by setting the heating temperature to 1350° C., taking the ingot out of the furnace, placing the ingot in a press, and then lowering the press. The lowering speed of the press was 50 mm/second or more, and the forging direction was an upset direction. The number of times the forging was performed was once, and the ingot material with a height t of 100 mm at the first forging was compressed to 20 mm (see (A) and (B) of FIG. 2).

[0108] FIGS. 6A and 6B are appearance photographs in a case in which the TiAl alloys used in the examples of the present invention were heated to 1350° C. and were hot forged. FIG. 6A shows a comparative alloy (alloy number 28), and FIG. 6B shows an example alloy (alloy number 32).

[0109] Procedure 3: Investigation of Suitable Heat Treatment Conditions

[0110] A heat treatment test was conducted on the hot-forged material after the aforementioned procedure 2 with the holding temperature, the holding time, and the cooling (temperature dropping) speed changed, and suitable heat treatment conditions were investigated through structure observation.

[0111] As a result, for the alloy according to the present invention, that is, the TiAl hot-forged alloy with the alloy element parameter P represented by Equation (1) described above to fall within a range of 1.1 to 1.9 at %, the holding temperature was preferably 1200 to 1250° C. was ascertained. Also, a preferable holding time of 0.5 to 5 hours and a preferable cooling rate of 1 to 10 [° C./min] was ascertained.

[0112] Note that the structure determined to be suitable in the investigation of the heat treatment conditions was a structure in which the area rate of the γ phase was 5 to 30%, the area rate of the β phase was 0.5 to 5 area %, and the remainder was a lamellar structure.

[0113] FIGS. 5A and 5B show reflected electron images of the microstructures after the heat treatment of the TiAl hot-forged alloy used in the example of the present invention, where FIG. 5A shows a comparative alloy (alloy number 37) and FIG. 5B shows an example alloy (alloy number 33).

[0114] FIG. 6 shows a flowchart of measurement of an area rate. FIGS. 7A and 7B are explanatory diagrams of a treatment process performed on an SEM image of an alloy structure in measurement of an area rate, where FIG. 7A shows S104 in FIG. 6 and FIG. 7B shows S108 in FIG. 6.

[0115] In the flowchart of the measurement of the area rate, a statistically meaningful number, for example, three reflected electron image photographs were taken for one sample using a scanning electron microscope first (S100). Next, the three reflected electron image photographs imaged were then printed out on paper (S102). Then, γ phases and β phases in the microstructure of the TiAl hot-forged alloys in the reflected electron image photographs were outlined with pens of different colors (S104). The outlined reflected electron image photographs were read by a scanner and were converted into image files such as PEG files, for example (S106). Then, image processing was performed on the image files using image software such as, for example, Adobe Photoshop (registered trademark) manufactured by Adobe Systems Incorporated to color the inside of the outlines with the same colors as the pens used for the outlines (S108). Then, the numbers of pixels of the colors were measured and were then compared with the numbers of pixels of the entire photographs, thereby obtaining the area rates (S110). Finally, average values of the three photographs were obtained and regarded as results of the area rates of the γ phase and the β phase (S112).

[0116] Note that although the measurement of the area rate was conducted by printing out the images of the scanning electron microscope on paper once, manually converting the printed images into the image files, and performing the image processing thereon in the aforementioned area rate measurement, such image-processing arithmetic operations may be performed by an image-processing system using a computer program to perform image processing.

[0117] Procedure 4: Room Temperature Tensile Test.

[0118] Next, heat treatment under suitable conditions was performed on the hot-forged material, and a tensile test was conducted. The tensile test was conducted in accordance with JISZ2241, and in regard to the shape of the tensile test piece, a cylindrical rod test piece with an entire length of 40 mm, with a length of 8 mm at gripped portions at both ends, with a length of 16 mm at the center portion, and with a diameter of Φ4 mm, as shown in FIGS. 4A and 4B, was used. The tested material was worked into the shape of a cylindrical rod test piece, and a tensile test at room temperature was conducted thereon to measure elongation and strength. As criteria for determining results as being good or bad in regard to the elongation at room temperature, results of less than 0.5% were determined to be bad while results of 0.5% or more were determined to be good. Also, in regard to the strength at room temperature, strength of less than 550 MPa was determined to be bad while strength of 550 MPa or more was determined to be good.

[0119] In the examples of the invention of the present application as described above, targeted properties were as follows. In other words, the targeted property of the hot forgeability was that no cracking occurred in the material even if the ingot with the height of 100 mm was forged to 20 mm in one compression as shown in FIG. 2. As for material properties after the heat treatment, a target ductility at room temperature was 0.5% or more, and a target strength at room temperature was 550 MPa or more.

[0120] Hereinafter, results of performing hot forging and heat treatment on ingots created to have the compositions in Tables 1 and 2 and evaluating the products in the aforementioned procedure will be described for each of the alloys 1 to 48.

TABLE-US-00001 TABLE 1 Alloy index Component (at %) P (Predetermined Alloy Category Al Fe Ni Mo W Cr Mn V Nb C equation) Alloy 1 Comparative alloy 40.5 0.8 2.0 0.5 1.43 Alloy 2 Example alloy 41.0 0.2 0.2 1.0 2.0 0.5 1.37 Alloy 3 Example alloy 42.0 0.3 0.3 3.0 5.0 0.5 1.53 Alloy 4 Example alloy 43.0 1.0 5.0 0.5 1.50 Alloy 5 Comparative alloy 43.5 0.5 0.5 1.0 2.0 4.0 0.5 1.53 Alloy 6 Example alloy 42.0 2.4 0.5 1.73 Alloy 7 Comparative alloy 42.0 2.6 0.5 1.93 Alloy 8 Example alloy 42.0 2.4 0.5 1.73 Alloy 9 Comparative alloy 42.0 2.6 0.5 1.93 Alloy 10 Example alloy 42.0 1.9 0.5 1.23 Alloy 11 Comparative alloy 42.0 2.1 0.5 1.43 Alloy 12 Example alloy 42.0 1.9 0.5 1.23 Alloy 13 Comparative alloy 42.0 2.1 0.5 1.43 Alloy 14 Example alloy 42.0 4.0 0.5 1.33 Alloy 15 Comparative alloy 42.0 5.0 0.5 1.83 Alloy 16 Example alloy 42.0 5.0 0.5 1.33 Alloy 17 Comparative alloy 42.0 6.0 0.5 1.73 Alloy 18 Example alloy 42.0 9.0 0.5 1.13 Alloy 19 Comparative alloy 42.0 11.0 0.5 1.53 Alloy 21 Example alloy 42.0 9.0 0.5 1.13 Alloy 22 Comparative alloy 42.0 11.0 0.5 1.53 Alloy 23 Comparative alloy 42.0 1.0 4.0 0.2 1.73 Alloy 24 Example alloy 42.0 1.0 4.0 0.3 1.63 Alloy 25 Example alloy 42.0 1.0 4.0 0.5 1.43 Heat treatment conditions Area rate of Result of tensile test for forged material each phase after at room temperature Result of forging Temperature Time Cooling rate heat treatment (%) Elongation Strength Alloy test at 1350° C.) (° C.) (h) (° C./min) γ phase β phase (%) (MPa) Alloy 1 No Cracking 1220 2.0 2.5 13.3 3.3 0.4 643 Alloy 2 No Cracking 1220 2.0 2.5 14.3 3.2 0.6 605 Alloy 3 No Cracking 1220 2.0 2.5 17.5 4.2 1.0 584 Alloy 4 No Cracking 1220 2.0 2.5 15.7 4.3 0.8 561 Alloy 5 Cracking occurred Alloy 6 No Cracking 1220 2.0 2.5 21.3 3.8 0.5 578 Alloy 7 No Cracking 1220 2.0 2.5 27.6 4.8 0.4 603 Alloy 8 No Cracking 1220 2.0 2.5 19.5 3.5 0.6 574 Alloy 9 No Cracking 1220 2.0 2.5 23.1 4.7 0.3 602 Alloy 10 No Cracking 1220 2.0 2.5 10.0 4.0 0.5 587 Alloy 11 No Cracking 1220 2.0 2.5 14.4 4.5 0.4 624 Alloy 12 No Cracking 1220 2.0 2.5 9.6 2.7 0.6 589 Alloy 13 No Cracking 1220 2.0 2.5 17.5 4.3 0.3 641 Alloy 14 No Cracking 1220 2.0 2.5 12.4 2.5 0.6 565 Alloy 15 No Cracking 1220 2.0 2.5 26.1 4.8 0.4 572 Alloy 16 No Cracking 1220 2.0 2.5 10.4 2.5 0.5 557 Alloy 17 No Cracking 1220 2.0 2.5 21.4 3.8 0.4 578 Alloy 18 No Cracking 1220 2.0 2.5 9.5 1.5 0.6 601 Alloy 19 No Cracking 1220 2.0 2.5 17.8 3.8 0.3 643 Alloy 21 No Cracking 1220 2.0 2.5 13.5 1.0 0.7 623 Alloy 22 No Cracking 1220 2.0 2.5 18.7 3.0 0.3 656 Alloy 23 No Cracking 1220 2.0 2.5 25.8 5.8 0.4 576 Alloy 24 No Cracking 1220 2.0 2.5 22.0 4.7 0.6 567 Alloy 25 No Cracking 1220 2.0 2.5 13.2 3.5 1.1 590

TABLE-US-00002 TABLE 2 Alloy index Component (at %) P (Predetermined Alloy Category Al Fe Ni Mo W Cr Mn V Nb C equation) Alloy 26 Example alloy 42.0 1.5 4.0 0.7 1.48 Alloy 27 Comparative alloy 42.0 2.0 4.0 0.8 1.63 Alloy 28 Comparative alloy 42.0 0.5 3.0 0.5 1.03 Alloy 29 Example alloy 42.0 0.3 0.3 1.0 1.7 0.5 1.11 Alloy 30 Example alloy 41.5 0.4 3.0 6.0 0.4 1.80 Alloy 31 Example alloy 42.0 0.6 0.5 2.0 2.0 0.5 1.38 Alloy 32 Example alloy 42.5 0.6 2.0 5.0 0.6 1.47 Alloy 33 Example alloy 43.0 0.5 0.4 1.0 3.0 0.7 1.40 Alloy 34 Example alloy 42.5 0.5 0.4 3.0 5.0 0.4 1.77 Alloy 35 Example alloy 41.5 2.0 2.0 0.3 1.50 Alloy 36 Example alloy 42.0 0.4 0.4 1.0 2.0 2.0 0.5 1.83 Alloy 37 Comparative alloy 42.0 2.0 4.0 0.5 1.93 Alloy 38 Comparative alloy 42.0 1.0 4.0 0.5 1.43 Alloy 39 Example alloy 42.0 1.0 4.0 0.5 1.43 Alloy 40 Example alloy 42.0 1.0 4.0 0.5 1.43 Alloy 41 Comparative alloy 42.0 1.0 4.0 0.5 1.43 Alloy 42 Comparative alloy 42.0 1.0 4.0 0.5 1.43 Alloy 43 Example alloy 42.0 1.0 4.0 0.5 1.43 Alloy 44 Example alloy 42.0 1.0 4.0 0.5 1.43 Alloy 45 Comparative alloy 42.0 1.0 4.0 0.5 1.43 Alloy 46 Example alloy 42.0 1.0 4.0 0.5 1.43 Alloy 47 Example alloy 42.0 1.0 4.0 0.5 1.43 Alloy 48 Comparative alloy 42.0 1.0 4.0 0.5 1.43 Heat treatment conditions Area rate of Result of tensile test for forged material each phase after at room temperature Result of forging Temperature Time Cooling rate heat treatment (%) Elongation Strength Alloy test at 1350° C.) (° C.) (h) (° C./min) γ phase β phase (%) (MPa) Alloy 26 No cracking 1220 2.0 2.5 16.2 3.0 0.6 630 Alloy 27 No cracking 1220 2.0 2.5 25.0 1.7 0.3 664 Alloy 28 Cracking occurred Alloy 29 No cracking 1220 2.0 2.5 5.5 1.0 0.7 670 Alloy 30 No cracking 1220 2.0 2.5 25.4 4.7 0.9 579 Alloy 31 No cracking 1220 2.0 2.5 12.7 1.5 1.3 612 Alloy 32 No cracking 1220 2.0 2.5 15.7 2.7 1.2 590 Alloy 33 No cracking 1220 2.0 2.5 8.1 3.3 0.9 624 Alloy 34 No cracking 1220 2.0 2.5 26.4 4.3 1.1 567 Alloy 35 No cracking 1220 2.0 2.5 16.8 3.2 0.8 597 Alloy 36 No cracking 1220 2.0 2.5 24.9 4.8 0.5 585 Alloy 37 No cracking 1220 2.0 2.5 27.9 5.5 0.4 569 Alloy 38 No cracking 1190 2.0 2.5 32.6 3.5 1.6 530 Alloy 39 No cracking 1200 2.0 2.5 14.8 1.8 1.4 578 Alloy 40 No cracking 1250 2.0 2.5 12.0 4.7 0.6 606 Alloy 41 No cracking 1260 2.0 2.5 10.8 5.8 0.4 642 Alloy 42 No cracking 1220 0.4 2.5 10.7 6.0 0.4 597 Alloy 43 No cracking 1220 0.5 2.5 11.8 4.8 0.6 620 Alloy 44 No cracking 1220 5.0 2.5 15.7 1.0 0.5 612 Alloy 45 No cracking 1220 6.0 2.5 16.3 0.3 0.3 634 Alloy 46 No cracking 1220 2.0 1.0 15.7 1.0 1.4 589 Alloy 47 No cracking 1220 2.0 10.0 12.2 4.5 0.6 623 Alloy 48 No cracking 1220 2.0 12.0 11.0 5.7 0.4 634 [0121] Alloy 1 (comparative alloy): Al was less than the composition range of the examples. Since the amount of the α2 phase was excessively large, elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0122] Alloys 2, 3, and 4 (example alloys): Al fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0123] Alloy 5 (comparative alloy): Al exceeded the composition range of the examples. The amount of β phase during the forging was small, hot forgeability was bad, and for example, cracking occurred during the hot forging. Note that the following evaluation was not conducted on this sample. [0124] Alloy 6 (example alloy): Fe fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0125] Alloy 7 (comparative alloy): Fe exceeded the composition range of the examples. The elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0126] Alloy 8 (example alloy): Ni fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0127] Alloy 9 (comparative alloy): Ni exceeded the composition range of the examples. Elongation at room temperature was 0.3%, which was below the determination criteria and was determined to be bad. [0128] Alloy 10 (example alloy): Mo fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0129] Alloy 11 (comparative alloy): Mo exceeded the composition range of the examples. The elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0130] Alloy 12 (example alloy): W fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0131] Alloy 13 (comparative alloy): W exceeded the composition range of the examples. Elongation at room temperature was 0.3%, which was below the determination criteria and was determined to be bad. [0132] Alloy 14 (example alloy): Cr fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0133] Alloy 15 (comparative alloy): Cr exceeded the composition range of the examples. The elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0134] Alloy 16 (example alloy): Mn fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0135] Alloy 17 (comparative alloy): Mn exceeded the composition range of the examples. The elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0136] Alloy 18 (example alloy) V fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0137] Alloy 19 (comparative alloy): V exceeded the composition range of the examples. Elongation at room temperature was 0.3%, which was below the determination criteria and was determined to be bad. Note that the alloy 20 was a missing number. [0138] Alloy 21 (example alloy): Nb fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0139] Alloy 22 (comparative alloy): Nb exceeded the composition range of the examples. Elongation at room temperature was 0.3%, which was below the determination criteria and was determined to be bad. [0140] Alloy 23 (comparative alloy): C was less than the composition range of the examples. Since the amount of γ phase precipitated from the β phase in the cooling process was small and more β phase remained than the target amount, elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0141] Alloys 24, 25, and 26 (example alloys): C fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0142] Alloy 27 (comparative alloy): C exceeded the composition range of the examples. Elongation at room temperature was 0.3%, which was below the determination criteria and was determined to be bad. [0143] Alloy 28 (comparative alloy): The alloy index was smaller than the composition range of the examples. The amount of β phase during the forging was small, hot forgeability was bad, and for example, cracking occurred during the hot forging. Note that the following evaluation was not conducted on this sample. [0144] Alloys 29, 30, 31, 32, 33, 34, 35, and 36 (example alloys): The alloy indexes fell within the composition range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0145] Alloy 37 (comparative alloy): The alloy index exceeded the composition range of the examples. Since more β phase remained than the target amount, elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0146] Alloy 38 (comparative alloy): The heat treatment temperature was lower than the specified range of the examples. Since the amount of γ phase was larger than the target amount, strength at room temperature was 530 MPa which was below the determination criteria and was determined to be bad. [0147] Alloys 39 and 40 (example alloys): The heat treatment temperatures fell within the specified range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0148] Alloy 41 (comparative alloy): The heat treatment temperature was higher than the specified range of the examples. Since more β phase remained than the target amount, elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0149] Alloy 42 (comparative alloy): The heat treatment time was shorter than the specified range of the examples. Since the β phase in the forged material did not decrease to the amount by which the β phase was equilibrated at the temperature and more β phase after the heat treatment remained than the target amount, elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad. [0150] Alloys 43 and 44 (example alloys): The heat treatment times fell within the specified range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0151] Alloy 45 (comparative alloy): The heat treatment time was longer than the specified range of the examples. Since the lamellar structure became coarse after long-term holding, elongation at room temperature was 0.3%, which was below the determination criteria and was determined to be bad. [0152] Alloys 46 and 47 (example alloys): The cooling rates fell within the specified range of the examples. Satisfactory hot forgeability and elongation and strength at room temperature were achieved. [0153] Alloy 48 (comparative alloy): The cooling rate fell faster than the specified range of the examples. Since the cooling rate was too fast, the amount of γ phase precipitated from the β phase was small, and more β phase remained than the target amount, elongation at room temperature was 0.4%, which was below the determination criteria and was determined to be bad.

INDUSTRIAL APPLICABILITY

[0154] As described in detail above, the TiAl-based alloy according to the present invention has excellent hot forgeability and ductility and strength at room temperature and is thus suitable for TiAl-based alloy material as a blade for a turbine, for example.

[0155] Also, the blade for a turbine is suitably used as a gas turbine for power generation, a jet engine for an aircraft, a supercharger for a ship, or a gas turbine or a steam turbine for various industrial machines.