WO2022260026A1

WO2022260026A1 - Tial alloy, tial alloy powder, tial alloy component, and method for producing same

Info

Publication number: WO2022260026A1
Application number: PCT/JP2022/022883
Authority: WO
Inventors: 祐太朗大田; 優斗宮澤; 圭司久布白
Original assignee: 株式会社Ihi
Priority date: 2021-06-09
Filing date: 2022-06-07
Publication date: 2022-12-15
Also published as: US20240110261A1; EP4353855A1; JPWO2022260026A1

Abstract

This TiAl alloy contains 47–50 at% of Al, 1–2 at% of Nb, 2–5 at% of Zr, and 0.05–0.3 at% of B, with the remainder comprising Ti and unavoidable impurities.

Description

TiAl alloy, TiAl alloy powder, TiAl alloy part and method for producing the same

The present disclosure relates to TiAl alloys, TiAl alloy powders, TiAl alloy parts, and methods of manufacturing the same.

A TiAl (titanium aluminide) alloy is an alloy formed of an intermetallic compound of Ti and Al. TiAl alloys have excellent heat resistance, are lighter in weight and have a higher specific strength than Ni-based alloys, and are therefore applied to aircraft engine parts such as turbine blades. A TiAl alloy containing Cr and Nb is used as such a TiAl alloy (see Patent Document 1).

JP 2013-209750 A

By the way, in order to reduce the weight of TiAl alloy parts such as turbine blades, it is required to increase the strength of the TiAl alloy to increase the specific strength. However, with conventional TiAl alloys, it is difficult to improve mechanical strength and ductility in a well-balanced manner to increase strength, and increasing ductility may reduce mechanical strength.

Therefore, an object of the present disclosure is to provide a TiAl alloy, a TiAl alloy powder, a TiAl alloy part, and a method for manufacturing the same that can improve the mechanical strength and ductility of the TiAl alloy in a well-balanced manner.

The TiAl alloy according to the present disclosure contains 47 atomic % to 50 atomic % Al, 1 atomic % to 2 atomic % Nb, 2 atomic % to 5 atomic % Zr, and 0.05 atomic % or more 0.3 atomic % or less of B, and the balance consists of Ti and unavoidable impurities.

In the TiAl alloy according to the present disclosure, the Al content may be 47 atomic % or more and 49 atomic % or less.

In the TiAl alloy according to the present disclosure, the Nb content is 1 atomic%, the Al content is 47 atomic% or more and 48 atomic% or less, and the Zr content is 2 atomic% or more and 4 atomic%. It may be below.

In the TiAl alloy according to the present disclosure, the Nb content is 1 atomic%, the Al content is 47 atomic% or more and 48 atomic% or less, and the Zr content is 2 atomic% or more and 3 atomic%. It may be below.

In the TiAl alloy according to the present disclosure, the Nb content is 2 atomic%, the Al content is 47 atomic% or more and 49 atomic% or less, and the Zr content is 2 atomic% or more and 3 atomic%. It may be below.

In the TiAl alloy according to the present disclosure, the Nb content is 2 atomic%, the Al content is 47 atomic% or more and 48 atomic% or less, and the Zr content is 2 atomic% or more and 4 atomic%. It may be below.

In the TiAl alloy according to the present disclosure, the Al content may be 47 atomic % or more and 48 atomic % or less, and the Zr content may be 2 atomic % or more and 4 atomic % or less.

In the TiAl alloy according to the present disclosure, the Al content may be 47 atomic % or more and 48 atomic % or less, and the Zr content may be 2 atomic % or more and 3 atomic % or less.

The TiAl alloy according to the present disclosure preferably has a room temperature tensile strength at break of 600 MPa or more and a room temperature tensile strain at break of 1.2% or more.

The TiAl alloy powder according to the present disclosure is made of the TiAl alloy described above.

A TiAl alloy component according to the present disclosure is formed of the TiAl alloy described above.

A method for manufacturing a TiAl alloy component according to the present disclosure includes a sealing step of filling a metal sheath with the TiAl alloy powder formed of the TiAl alloy described above and sealing the TiAl alloy powder sealed with the metal sheath, and a hot isostatic pressing step of performing hot isostatic pressing at 1200° C. or higher and 1300° C. or lower and 150 MPa or higher.

According to the above configuration, it is possible to improve the mechanical strength and ductility of the TiAl alloy in a well-balanced manner.

FIG. 4 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 1 atomic % in the embodiment of the present disclosure; FIG. 4 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 1 atomic % in the embodiment of the present disclosure; FIG. 4 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 2 atomic % in the embodiment of the present disclosure; FIG. 4 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 2 atomic % in the embodiment of the present disclosure; FIG. 4 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 1 atomic % or more and 2 atomic % or less in the embodiment of the present disclosure. FIG. 4 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 1 atomic % or more and 2 atomic % or less in the embodiment of the present disclosure. 1 is a diagram showing the configuration of a TiAl alloy component made up of a turbine blade in an embodiment of the present disclosure; FIG. 1 is a flow chart showing the configuration of a method for manufacturing a TiAl alloy component in an embodiment of the present disclosure; 4 is a photograph showing the results of metallographic observation of TiAl alloys of Examples 1 to 9 in an embodiment of the present disclosure. FIG. 10 is a photograph showing the results of observing the metallographic structure of TiAl alloys of Examples 10 to 18 in an embodiment of the present disclosure; FIG. 2 is a graph showing the solidification morphology of TiAl alloys of Examples 1 to 9, in an embodiment of the present disclosure; FIG. 4 is a graph showing the solidification morphology of TiAl alloys of Examples 10 to 18, in embodiments of the present disclosure; FIG. 4 is a photograph showing the results of metallographic observation by an optical microscope of the specimens of Examples A and B in the embodiment of the present disclosure. 4 is a graph showing tensile test results in an embodiment of the present disclosure; 4 is a graph showing creep test results in an embodiment of the present disclosure;

The embodiments of the present disclosure will be described in detail below with reference to the drawings. The TiAl (titanium aluminide) alloy according to the embodiment of the present disclosure includes 47 atomic % to 50 atomic % Al (aluminum), 1 atomic % to 2 atomic % Nb (niobium), and 2 atomic % to 5 Zr (zirconium) of atomic % or less and B (boron) of 0.05 atomic % or more and 0.3 atomic % or less are contained, and the balance is composed of Ti (titanium) and unavoidable impurities . Next, the reason why the composition range of each alloy component constituting the TiAl alloy is limited will be explained.

Al (aluminum) has the function of improving mechanical strength and ductility such as room temperature ductility. The content of Al is 47 atomic % or more and 50 atomic % or less. When the content of Al is less than 47 atomic %, the content of Ti or the like, which has a higher density than that of Al, increases, resulting in a decrease in specific strength. If the Al content is greater than 50 atomic %, the ductility is lowered. The Al content may be 47 atomic % or more and 49 atomic % or less. This can further improve the mechanical strength and ductility of the TiAl alloy.

Nb (niobium) has the function of improving oxidation resistance and mechanical strength. The content of Nb is 1 atomic % or more and 2 atomic % or less. If the Nb content is less than 1 atomic %, the oxidation resistance and high-temperature strength may deteriorate. When the Nb content is more than 2 atomic %, the density of Nb is higher than the densities of Al and Ti, so the specific strength is lowered.

Zr (zirconium) has the function of improving oxidation resistance and mechanical strength. Zr is an element that stabilizes the γ phase and contributes to improving ductility such as room temperature ductility. Zr also contributes to the improvement of creep strength by reducing the diffusion rate. The content of Zr is 2 atomic % or more and 5 atomic % or less. If the Zr content is less than 2 atomic %, oxidation resistance, ductility such as room-temperature ductility, and mechanical strength such as high-temperature strength may decrease. If the Zr content is greater than 5 atomic %, segregation may occur. The occurrence of Zr segregation may reduce the mechanical strength and ductility.

B (boron) has the function of increasing ductility such as room temperature ductility by refining crystal grains. The content of B is 0.05 atomic % or more and 0.3 atomic % or less. If the B content is less than 0.05 atomic %, crystal grains may become coarse and ductility may decrease. If the B content exceeds 0.3 atomic %, the impact resistance may deteriorate. By setting the B content to 0.05 atomic % or more and 0.3 atomic % or less, the steel is composed of fine crystal grains having a crystal grain size of 100 μm or less, so that ductility can be improved.

B has the function of precipitating fine borides in crystal grains by heat treatment or the like to improve the mechanical strength. Fine borides are formed including those having a particle size of 0.1 μm or less. Fine borides consist of TiB, TiB2, and so _on . Precipitation of fine borides in crystal grains can improve mechanical strength such as tensile strength, fatigue strength, and creep strength.

The balance of the TiAl alloy is composed of Ti and unavoidable impurities. An unavoidable impurity is an impurity that may be mixed even if it is not added intentionally. Since the TiAl alloy does not contain Cr (chromium), it is possible to suppress a decrease in mechanical strength. Since the TiAl alloy does not contain V (vanadium), it is possible to suppress deterioration in mechanical strength and oxidation resistance. Since the TiAl alloy does not contain Mo (molybdenum), a decrease in specific strength can be suppressed.

Next, the solidification morphology of the TiAl alloy will be explained. The solidification morphology of TiAl alloys is related to the Al, Zr and Nb contents. By changing the contents of Al, Zr and Nb, the solidification mode of the TiAl alloy changes to α solidification, β solidification, γ solidification, and α solidification + γ solidification. Alpha solidification is a solidification morphology in which the solidification process of a TiAl alloy passes through the alpha single phase region. β-solidification is a solidification morphology in which the solidification process of TiAl alloys passes through the β-single-phase region. γ solidification is a form of solidification in which the solidification process of TiAl alloys passes through a γ single phase region. α-solidification + γ-solidification is a solidification mode in which the solidification process of the TiAl alloy passes through the α+γ two-phase region. In the case of γ solidification, columnar coarse crystal grains are formed, so the anisotropy of the metal structure becomes stronger. On the other hand, in the case of α solidification or β solidification, since equiaxed crystal grains are formed, the isotropy of the metal structure becomes stronger and the anisotropy of the metal structure becomes weaker. In the case of α solidification + γ solidification, equiaxed crystal grains and columnar crystal grains are formed. Become. Since B precipitates fine borides in crystal grains, it hardly affects the solidification morphology of the TiAl alloy.

As the Al content increases, the solidification mode of the TiAl alloy tends to be γ-solidification. As the Al content becomes smaller, the solidification mode of the TiAl alloy tends to be α-solidification+γ-solidification, α-solidification or β-solidification. As the Zr content increases, the solidification morphology of the TiAl alloy tends to be gamma solidification. As the Zr content becomes smaller, the solidification morphology of the TiAl alloy tends to be α-solidification+γ-solidification, α-solidification or β-solidification. As the Nb content increases, the solidification mode of the TiAl alloy tends to be α-solidification+γ-solidification, α-solidification or β-solidification. As the Nb content becomes smaller, the solidification morphology of the TiAl alloy tends to be gamma solidification.

FIG. 1 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 1 atomic %. The TiAl alloy has a Nb content of 1 atomic %, and an Al and Zr content of R1 point (Al: 47 atomic %, Zr: 2 atomic %) and R2 point (Al: 48 atomic %) shown in FIG. %, Zr: 2 atomic %), R3 point (Al: 48 atomic %, Zr: 4 atomic %), R4 point (Al: 47 atomic %, Zr: 5 atomic %). may be configured. That is, the TiAl alloy is surrounded by 1 atomic % of Nb, 0.05 atomic % or more and 0.3 atomic % or less of B, and the four points R1, R2, R3, and R4 shown in FIG. Al and Zr having a composition range may be contained, and the balance may be composed of Ti and unavoidable impurities. When the TiAl alloy is composed of this alloy composition, the solidification mode can be α-solidification only or α-solidification + γ-solidification. As a result, the anisotropy of the metal structure is suppressed more than when the solidification mode consists only of γ solidification. By suppressing the anisotropy of the metal structure, the mechanical properties and the like of the TiAl alloy become more isotropic. For example, such a TiAl alloy contains 1 atomic percent Nb, 0.05 atomic percent to 0.3 atomic percent B, 47 atomic percent to 48 atomic percent Al, and 2 atomic percent to 4 atomic percent % or less Zr, and the balance may be composed of Ti and unavoidable impurities.

FIG. 2 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 1 atomic %. The TiAl alloy has a Nb content of 1 atomic %, and an Al and Zr content of point S1 (Al: 47 atomic %, Zr: 2 atomic %) and point S2 (Al: 48 atomic %) shown in FIG. %, Zr: 2 atomic %), S3 point (Al: 48 atomic %, Zr: 3 atomic %), S4 point (Al: 47 atomic %, Zr: 5 atomic %). may be configured. That is, the TiAl alloy is surrounded by 1 atomic % of Nb, 0.05 atomic % or more and 0.3 atomic % or less of B, and the four points S1, S2, S3, and S4 shown in FIG. Al and Zr having a composition range may be contained, and the balance may be composed of Ti and unavoidable impurities. When the TiAl alloy is composed of this alloy composition, the solidification mode can be alpha solidification only. This further suppresses the anisotropy of the metal structure because the solidification morphology does not include gamma solidification. By further suppressing the anisotropy of the metal structure, the mechanical properties of the TiAl alloy become more isotropic. For example, such a TiAl alloy contains 1 atomic percent Nb, 0.05 atomic percent to 0.3 atomic percent B, 47 atomic percent to 48 atomic percent Al, and 2 atomic percent to 3 atomic percent % or less Zr, and the balance may be composed of Ti and unavoidable impurities.

FIG. 3 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 2 atomic %. The TiAl alloy has a Nb content of 2 atomic %, and an Al and Zr content of T1 point (Al: 47 atomic %, Zr: 2 atomic %) and T2 point (Al: 49 atomic %) shown in FIG. %, Zr: 2 atomic %), T3 point (Al: 49 atomic %, Zr: 3 atomic %), T4 point (Al: 48 atomic %, Zr: 4 atomic %), T5 point (Al: 47 atomic %, Zr: 4 atomic %). That is, the TiAl alloy has 2 atomic % of Nb, 0.05 atomic % or more and 0.3 atomic % or less of B, and five points of T1 point, T2 point, T3 point, T4 point, and T5 point shown in FIG. Al and Zr from the enclosed composition range may be contained, and the balance may be composed of Ti and unavoidable impurities. When the TiAl alloy is composed of this alloy composition, the solidification mode can be α-solidification only or α-solidification + γ-solidification. As a result, the anisotropy of the metal structure is suppressed more than when the solidification mode consists only of γ solidification. By suppressing the anisotropy of the metal structure, the mechanical properties and the like of the TiAl alloy become more isotropic. For example, such a TiAl alloy contains 2 atomic percent Nb, 0.05 atomic percent to 0.3 atomic percent B, 47 atomic percent to 49 atomic percent Al, and 2 atomic percent to 3 atomic percent % or less Zr, and the balance may be composed of Ti and unavoidable impurities. In addition, such a TiAl alloy contains 2 atomic % Nb, 0.05 atomic % to 0.3 atomic % B, 47 atomic % to 48 atomic % Al, and 2 atomic % to 4 atomic % % or less Zr, and the balance may be composed of Ti and unavoidable impurities.

FIG. 4 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 2 atomic %. The TiAl alloy has a Nb content of 2 atomic %, and an Al and Zr content of W1 point (Al: 47 atomic %, Zr: 2 atomic %) and W2 point (Al: 49 atomic %) shown in FIG. %, Zr: 2 atomic %), W3 point (Al: 48 atomic %, Zr: 4 atomic %), W4 point (Al: 47 atomic %, Zr: 4 atomic %). may be configured. That is, the TiAl alloy is surrounded by 2 atomic % Nb, 0.05 atomic % or more and 0.3 atomic % or less B, and four points W1, W2, W3, and W4 shown in FIG. Al and Zr having a composition range may be contained, and the balance may be composed of Ti and unavoidable impurities. When the TiAl alloy is composed of this alloy composition, the solidification mode can be alpha solidification only. This further suppresses the anisotropy of the metal structure because the solidification morphology does not include gamma solidification. By further suppressing the anisotropy of the metal structure, the mechanical properties of the TiAl alloy become more isotropic. For example, such a TiAl alloy contains 2 atomic percent Nb, 0.05 atomic percent to 0.3 atomic percent B, 47 atomic percent to 48 atomic percent Al, and 2 atomic percent to 4 atomic percent % or less Zr, and the balance may be composed of Ti and unavoidable impurities.

FIG. 5 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 1 atomic % or more and 2 atomic % or less. In the TiAl alloy, when the Nb content is 1 atomic % or more and 2 atomic % or less, the Al and Zr contents are X1 point (Al: 47 atomic %, Zr: 2 atomic %) and X2 shown in FIG. At four points: point (Al: 48 atomic %, Zr: 2 atomic %), X3 point (Al: 48 atomic %, Zr: 4 atomic %), X4 point (Al: 47 atomic %, Zr: 4 atomic %) It may consist of the enclosed composition range. That is, the TiAl alloy contains 1 atomic % or more and 2 atomic % or less of Nb, 0.05 atomic % or more and 0.3 atomic % or less of B, and 4 points of X1 point, X2 point, X3 point, and X4 point shown in FIG. Al and Zr in the composition range enclosed by dots may be contained, and the balance may be composed of Ti and unavoidable impurities.

The composition range surrounded by the four points X1, X2, X3, and X4 shown in FIG. 5 is surrounded by the four points R1, R2, R3, and R4 shown in FIG. The composition range overlaps with the composition range surrounded by five points T1, T2, T3, T4, and T5 shown in FIG. When the TiAl alloy is composed of this alloy composition, the solidification mode can be α-solidification only or α-solidification + γ-solidification. As a result, the anisotropy of the metal structure is suppressed more than when the solidification mode consists only of γ solidification. By suppressing the anisotropy of the metal structure, the mechanical properties and the like of the TiAl alloy become more isotropic. For example, such a TiAl alloy contains 1 atomic % to 2 atomic % Nb, 0.05 atomic % to 0.3 atomic % B, 47 atomic % to 48 atomic % Al, 2 and Zr in an amount of atomic % to 4 atomic %, and the balance may be composed of Ti and unavoidable impurities.

FIG. 6 is a diagram showing the relationship between the Al and Zr contents when the Nb content is 1 atomic % or more and 2 atomic % or less. In the TiAl alloy, when the Nb content is 1 atomic % or more and 2 atomic % or less, the Al and Zr contents are Y1 point (Al: 47 atomic %, Zr: 2 atomic %), Y2 Point (Al: 48 atomic %, Zr: 2 atomic %), Y3 point (Al: 48 atomic %, Zr: 3 atomic %), Y4 point (Al: 47.5 atomic %, Zr: 4 atomic %), Y5 It may be configured in a composition range surrounded by five points (Al: 47 atomic %, Zr: 4 atomic %). That is, the TiAl alloy contains Nb of 1 atomic % or more and 2 atomic % or less, B of 0.05 atomic % or more and 0.3 atomic % or less, and Y1 point, Y2 point, Y3 point, Y4 point, Y5 point shown in FIG. It may contain Al and Zr in a composition range surrounded by five points, and the balance may be composed of Ti and unavoidable impurities.

The composition range surrounded by the five points Y1, Y2, Y3, Y4, and Y5 shown in FIG. 6 is the four points S1, S2, S3, and S4 shown in FIG. The enclosed composition range and the composition range enclosed by four points of W1 point, W2 point, W3 point, and W4 point shown in FIG. 4 overlap each other. When the TiAl alloy is composed of this alloy composition, the solidification mode can be alpha solidification only. This further suppresses the anisotropy of the metal structure because the solidification morphology does not include gamma solidification. By further suppressing the anisotropy of the metal structure, the mechanical properties of the TiAl alloy become more isotropic. For example, such a TiAl alloy contains 1 atomic % to 2 atomic % Nb, 0.05 atomic % to 0.3 atomic % B, 47 atomic % to 48 atomic % Al, 2 and Zr in an amount of atomic % or more and 3 atomic % or less, and the balance may be composed of Ti and unavoidable impurities.

Next, the metallographic structure of the TiAl alloy will be described. The metal structure of the TiAl alloy is composed of fine crystal grains with a crystal grain size of 100 μm or less. This can improve the ductility of the TiAl alloy. Moreover, the metal structure of the TiAl alloy is composed of lamellar grains and γ grains, and there is no segregation of Zr. Lamellar grains are formed by regularly arranging an α ₂ phase composed of Ti ₃ Al and a γ phase composed of TiAl in layers. The γ grains are made of TiAl. The γ-grains are, for example, equiaxed γ-grains. The grains of the γ grains contain borides with a grain size of 0.1 μm or less. The boride is composed of TiB, TiB2, etc., and is needle _- like.

Lamellar grains can improve mechanical strength such as tensile strength, fatigue strength, and creep strength. γ grains can improve ductility and high temperature strength. Fine borides having a particle size of 0.1 μm or less can improve mechanical strength. In the metal structure of the TiAl alloy, when the total volume ratio of lamellar grains and γ grains is 100% by volume, the volume ratio of γ grains is preferably 80% by volume or more, and the remainder is lamellar grains. Since the metal structure of the TiAl alloy is mainly composed of γ grains, it is possible to improve mechanical strength and ductility in a well-balanced manner. In addition, since the metal structure of the TiAl alloy does not have Zr segregation, it is possible to suppress deterioration in mechanical strength and ductility.

Next, the mechanical properties of the TiAl alloy according to the embodiment of the present disclosure will be explained. As for the mechanical properties at room temperature of the TiAl alloy, when a tensile test is performed in accordance with JIS, ASTM, etc., the room temperature tensile breaking strength is 600 MPa or more, and the room temperature tensile breaking strain is 1.2% or more. . Thus, according to the TiAl alloy according to the embodiment of the present disclosure, it is possible to improve mechanical strength and ductility in a well-balanced manner.

Next, a TiAl alloy part using a TiAl alloy according to an embodiment of the present disclosure will be described. TiAl alloy parts can be applied to aircraft engine parts, turbine blades of gas turbines for power generation, and the like. FIG. 7 is a diagram showing the configuration of a TiAl alloy component 10 that is a turbine blade. Since the TiAl alloy described above has high mechanical strength such as high-temperature strength, the heat resistance of the TiAl alloy component 10 can be improved. In addition, since the TiAl alloy described above is excellent in ductility such as room temperature ductility, even when the TiAl alloy component 10 is assembled or assembled, damage to the TiAl alloy component 10 can be suppressed. The TiAl alloy parts are not limited to aircraft engine parts, and may be, for example, turbocharger parts such as turbocharger turbine wheels, vehicle parts such as automobile engine valves, and the like.

TiAl alloy parts can be cast by melting the above TiAl alloy. TiAl alloy parts can be cast by melting the above TiAl alloy in a vacuum induction furnace or the like. For casting, a casting apparatus used for casting general metal materials can be used.

The TiAl alloy parts are formed by powder compacting by metal powder injection molding (MIM method), hot isostatic pressing (HIP method), or the like, using TiAl alloy powder formed from the above TiAl alloy as raw material powder. good too. The TiAl alloy powder is formed of the TiAl alloy described above, and can be produced by a firing synthesis method, a mechanical alloying method, a plasma rotating electrode method, an atomizing method (water atomizing method, gas atomizing method), or the like. The TiAl alloy powder is preferably a rapidly solidified powder. Since the rapidly solidified powder is produced by rapidly solidifying alloy droplets, segregation of Zr contained in the TiAl alloy can be further suppressed.

Next, as an example, a method for manufacturing a TiAl alloy part by hot isostatic pressing (HIP method) will be described. FIG. 8 is a flow chart showing the configuration of a method for manufacturing a TiAl alloy component. The method for manufacturing a TiAl alloy component includes a sealing step (S10) and a hot isostatic pressing step (S12).

The sealing step (S10) is a step of filling the metal sheath with the TiAl alloy powder formed of the TiAl alloy described above and sealing. TiAl alloy powder made of the TiAl alloy described above is used as the raw material powder. As the TiAl alloy powder, it is preferable to use a rapidly solidified powder produced by a gas atomization method or the like. The TiAl alloy powder is packed in a metal sheath and sealed. A titanium sheath made of pure titanium is preferably used as the metal sheath. The thickness of the titanium sheath is preferably 1 mm, for example. The TiAl alloy powder filled in the metal sheath is sealed by electron beam welding or the like after vacuum degassing.

The hot isostatic pressing step (S12) is a step of hot isostatic pressing the TiAl alloy powder filled in the metal sheath at 1200°C or higher and 1300°C or lower and 150 MPa or higher. A TiAl alloy component is molded by subjecting the TiAl alloy powder filled in the metal sheath to hot isostatic pressing. The hot isostatic pressure treatment can be performed at a heating temperature of 1200° C. or higher and 1300° C. or lower and a pressure of 150 MPa or higher. The pressure may be, for example, 150 MPa or more and 200 MPa or less. The holding time at the heating temperature can be 3 hours or more. The holding time at the heating temperature may be, for example, 3 hours or more and 5 hours or less. After the hot isostatic pressurization, the pressure is released, the furnace is cooled to 900° C., and then quenched at 900° C. or less. By performing such a cooling method, cracking of the TiAl alloy component can be suppressed. Rapid cooling from 900° C. should be performed at a cooling rate faster than air cooling, and can be performed by gas fan cooling or the like.

The method for manufacturing a TiAl alloy component may include a stress relief step of holding at 800° C. or more and 950° C. or less for 1 hour or more and 5 hours or less to relieve stress after the hot isostatic pressing step (S12). . As a result, residual stress and the like in the TiAl alloy parts are removed, so that the ductility of the TiAl alloy parts can be improved.

　The hot isostatic pressure treatment and stress removal should be performed in a vacuum atmosphere or in an inert gas atmosphere such as argon gas to prevent oxidation. For the hot isostatic pressing treatment, a HIP apparatus or the like used for hot isostatic pressing of general metal materials can be used. For stress relief, an atmosphere furnace or the like used for stress relief annealing of general metal materials can be used. A heat treatment step for adjusting the metal structure may be provided after the hot isostatic pressing step (S12) and the stress removing step.

As described above, the TiAl alloy having the above configuration includes Al of 47 atomic % or more and 50 atomic % or less, Nb of 1 atomic % or more and 2 atomic % or less, Zr of 2 atomic % or more and 5 atomic % or less, and 0.05 atomic %. and 0.3 atomic % or less of B, and the balance is composed of Ti and unavoidable impurities. Thereby, the mechanical strength and ductility of the TiAl alloy can be improved in a well-balanced manner.

The solidification morphology of the TiAl alloy was evaluated. The TiAl alloys of Examples 1 to 18 are described. The TiAl alloys of Examples 1 to 18 contain Al, Nb, Zr, and B, and the balance is Ti and unavoidable impurities. Table 1 shows the alloy composition of each TiAl alloy.

The TiAl alloys of Examples 1 to 9 had a Nb content of 1 atomic %, a B content of 0.2 atomic %, an Al content of 47 atomic % to 50 atomic %, and a Zr content of 3 atomic %. It was changed in the range of atomic % to 5 atomic %. The TiAl alloys of Examples 10 to 18 had a Nb content of 2 atomic %, a B content of 0.2 atomic %, an Al content of 48 atomic % to 50 atomic %, and a Zr content of 2 atomic %. It was changed in the range of atomic % to 4 atomic %.

Each TiAl alloy raw material having the alloy composition shown in Table 1 was melted and cast in a high-frequency vacuum melting furnace to form a TiAl alloy ingot having each alloy composition. Then, the metal structure of the TiAl alloy was observed to evaluate the solidification morphology. FIG. 9 is a photograph showing the observation results of the metal structures of the TiAl alloys of Examples 1-9. FIG. 10 is a photograph showing the observation results of the metal structures of the TiAl alloys of Examples 10-18.

The solidification form of the TiAl alloys of Examples 1 and 2 was only α-solidification. The TiAl alloy of Example 3 had a solidification mode of α solidification + γ solidification. In the TiAl alloys of Examples 4 to 9, the only solidification mode was gamma solidification. The solidification morphology of the TiAl alloys of Examples 10 to 13 was alpha solidification only. The TiAl alloy of Example 14 had a solidification mode of α-solidification + γ-solidification. In the TiAl alloys of Examples 15 to 18, the only solidification mode was gamma solidification.

FIG. 11 is a graph showing the solidification morphology of the TiAl alloys of Examples 1 to 9. FIG. 12 is a graph showing the solidification morphology of the TiAl alloys of Examples 10-18. In the graphs of FIGS. 11 and 12, the horizontal axis represents the amount of Zr (atomic %), and the vertical axis represents the amount of Al (atomic %). are indicated by triangles, and only γ coagulation is indicated by squares. FIG. 11 shows the four points R1, R2, R3, and R4 shown in FIG. 1 and the four points S1, S2, S3, and S4 shown in FIG. were described together. In FIG. 12, five points T1, T2, T3, T4, and T5 shown in FIG. 3 and four points W1, W2, W3, and W4 shown in FIG. was described together with

It became clear that when the Al content increases, the solidification morphology of the TiAl alloy tends to change from α-solidification or α-solidification + γ-solidification to γ-solidification. For example, as shown in FIG. 11, when the Nb content is 1 atomic %, when the Zr content is 3 atomic % to 5 atomic %, the Al content is 49 atomic % or more and the solidified form is γ Only coagulation occurred. As shown in FIG. 12, when the Nb content is 2 atomic %, when the Zr content is 2 atomic % to 4 atomic %, the Al content is 50 atomic % or more and the solidification form is γ Only coagulation occurred.

It became clear that when the Zr content increases, the solidification morphology of the TiAl alloy tends to change from α-solidification or α-solidification + γ-solidification to γ-solidification. For example, when the Nb content is 1 atomic % and the Al content is 48 atomic % as shown in FIG. When the Zr content was 5 atomic %, α solidification + γ solidification occurred, and when the Zr content was 5 atomic %, only γ solidification occurred. Further, as shown in FIG. 12, when the Nb content is 2 atomic % and the Al content is 49 atomic %, only α solidification is performed when the Zr content is 2 atomic %, and the Zr content is 3 atomic %. When the content of Zr was 4 atomic %, only γ solidification occurred.

It became clear that when the Nb content increases, the solidification morphology of the TiAl alloy tends to change from γ-solidification to α-solidification + γ-solidification or α-solidification. For example, when the Al content is 49 atomic % and the Zr content is 3 atomic %, only γ solidification occurs when the Nb content is 1 atomic % as shown in FIG. Furthermore, when the Nb content was 2 atomic %, α-solidification + γ-solidification occurred.

From the graph of FIG. 11, the Nb content is 1 atomic %, and the Al and Zr contents are R1 point (Al: 47 atomic %, Zr: 2 atomic %), R2 point ( Al: 48 atomic %, Zr: 2 atomic %), R3 point (Al: 48 atomic %, Zr: 4 atomic %), R4 point (Al: 47 atomic %, Zr: 5 atomic %) It was found that the coagulation morphology was α-coagulation only or α-coagulation + γ-coagulation when the composition range was defined as follows.

Next, I will explain the reason for this. First, from FIG. 11, R3 point (Al: 48 atomic %, Zr: 4 atomic %) is α solidification + γ solidification, and R4 point (Al: 47 atomic %, Zr: 5 atomic %) is α solidification only. is clear. Since the R1 point (Al: 47 atomic %, Zr: 2 atomic %) has a smaller Zr content than the R4 point (Al: 47 atomic %, Zr: 5 atomic %), only α solidification occurs. Point R2 (Al: 48 atomic %, Zr: 2 atomic %) has a lower Zr content than the point (Al: 48 atomic %, Zr: 3 atomic %) in FIG. Therefore, when the Al and Zr contents are in the composition range surrounded by the four points R1, R2, R3, and R4 shown in FIG. Or it becomes α coagulation + γ coagulation.

From the graph of FIG. 11, the Nb content is 1 atomic %, and the Al and Zr contents are S1 point (Al: 47 atomic %, Zr: 2 atomic %), S2 point ( Al: 48 atomic %, Zr: 2 atomic %), S3 point (Al: 48 atomic %, Zr: 3 atomic %), S4 point (Al: 47 atomic %, Zr: 5 atomic %) It was found that the coagulation form was only α coagulation when it was composed in the composition range.

Next, I will explain the reason for this. First, it is clear from FIG. 11 that only α solidification occurs at points S3 (Al: 48 atomic %, Zr: 3 atomic %) and S4 points (Al: 47 atomic %, Zr: 5 atomic %). At point S1 (Al: 47 atomic %, Zr: 2 atomic %), the Zr content is smaller than at point S4 (Al: 47 atomic %, Zr: 5 atomic %), so only α solidification occurs. Also, since the S2 point (Al: 48 atomic %, Zr: 2 atomic %) has a smaller Zr content than the S3 point (Al: 48 atomic %, Zr: 3 atomic %), only α solidification occurs. Therefore, when the Al and Zr contents are in the composition range surrounded by the four points S1, S2, S3, and S4 shown in FIG. become.

From the graph of FIG. 12, the content of Nb is 2 atomic %, and the content of Al and Zr is T1 point (Al: 47 atomic %, Zr: 2 atomic %), T2 point ( Al: 49 atomic %, Zr: 2 atomic %), T3 point (Al: 49 atomic %, Zr: 3 atomic %), T4 point (Al: 48 atomic %, Zr: 4 atomic %), T5 point (Al: 47 atomic %, Zr: 4 atomic %), it was found that the solidification mode is α solidification only or α solidification + γ solidification.

Next, I will explain the reason for this. First, from FIG. 12, T2 point (Al: 49 atomic %, Zr: 2 atomic %) and T4 point (Al: 48 atomic %, Zr: 4 atomic %) are only α solidification, T3 point (Al: 49 atomic % , Zr: 3 atomic %) are α-coagulation + γ-coagulation. At point T1 (Al: 47 atomic %, Zr: 2 atomic %), the Al content is smaller than at point T2 (Al: 49 atomic %, Zr: 2 atomic %), so only α-solidification occurs. Also, since the T5 point (Al: 47 atomic %, Zr: 4 atomic %) has a smaller Al content than the T4 point (Al: 48 atomic %, Zr: 4 atomic %), only α solidification occurs. Therefore, when the Al and Zr contents are in the composition range surrounded by the five points T1, T2, T3, T4, and T5 shown in FIG. α coagulation only or α coagulation + γ coagulation.

From the graph of FIG. 12, the content of Nb is 2 atomic %, and the content of Al and Zr is W1 point (Al: 47 atomic %, Zr: 2 atomic %), W2 point ( Al: 49 atomic %, Zr: 2 atomic %), W3 point (Al: 48 atomic %, Zr: 4 atomic %), W4 point (Al: 47 atomic %, Zr: 4 atomic %) It was found that the coagulation form was only α coagulation when it was composed in the composition range.

Next, I will explain the reason for this. First, it is clear from FIG. 12 that the W2 point (Al: 49 atomic %, Zr: 2 atomic %) and the W3 point (Al: 48 atomic %, Zr: 4 atomic %) are α solidification only. Since the W1 point (Al: 47 atomic %, Zr: 2 atomic %) has a smaller Al content than the W2 point (Al: 49 atomic %, Zr: 2 atomic %), only α solidification occurs. Since the W4 point (Al: 47 atomic %, Zr: 4 atomic %) has a smaller Al content than the W3 point (Al: 48 atomic %, Zr: 4 atomic %), only α solidification occurs. Therefore, when the Al and Zr contents are in the composition range surrounded by the four points W1, W2, W3, and W4 shown in FIG. become.

From the graphs of FIGS. 11 and 12, when the Nb content is 1 atomic % or more and 2 atomic % or less, the Al and Zr contents are the X1 point (Al: 47 atomic %, Zr : 2 atomic %), X2 point (Al: 48 atomic %, Zr: 2 atomic %), X3 point (Al: 48 atomic %, Zr: 4 atomic %), X4 point (Al: 47 atomic %, Zr: 4 atomic %), it was found that the solidification mode is α-coagulation only or α-coagulation + γ-coagulation.

From the graphs of FIGS. 11 and 12, when the Nb content is 1 atomic % or more and 2 atomic % or less, the Al and Zr contents are the Y1 point (Al: 47 atomic %, Zr : 2 atomic %), Y2 point (Al: 48 atomic %, Zr: 2 atomic %), Y3 point (Al: 48 atomic %, Zr: 3 atomic %), Y4 point (Al: 47.5 atomic %, Zr : 4 atomic %), Y 5 points (Al: 47 atomic %, Zr: 4 atomic %), when the composition range is surrounded by 5 points, the solidification mode may be only α solidification. all right.

Next, using the TiAl alloy powders formed from the TiAl alloys of Examples 1 and 11, specimens of Examples A and B were produced, and their mechanical properties and the like were evaluated. First, the method of manufacturing the specimens of Examples A and B will be described. The specimens of Examples A and B were prepared by powder molding by hot isostatic pressing.

First, the pure titanium sheath was filled with TiAl alloy powder and sealed. For the specimen of Example A, the TiAl alloy powder formed from the TiAl alloy of Example 1 was used. The TiAl alloy powder formed from the TiAl alloy of Example 11 was used for the specimen of Example B. As the TiAl alloy powder formed from the TiAl alloy in Examples 1 and 11, a rapidly solidified powder produced by a gas atomization method was used. The TiAl alloy powder filled in the pure titanium sheath was sealed by electron beam welding after vacuum degassing.

The TiAl alloy powder filled in the pure titanium sheath was hot isostatically pressed at 1250°C and 172 MPa for 3 hours. After the hot isostatic pressurization, the pressure was released and the furnace was cooled to 900°C, followed by quenching below 900°C. Rapid cooling from 900° C. was performed by gas fan cooling. In this manner, specimens of Examples A and B were produced.

For the specimens of Examples A and B, metallographic observation was performed. Metal structure observation was performed with an optical microscope and an electron microscope. FIG. 13 is a photograph showing the results of metallographic observation of the specimens of Examples A and B with an optical microscope, FIG. 13(a) is a photograph of the specimen of Example A, and FIG. , and a photograph of a test piece of Example B. FIG.

The metal structures of the specimens of Examples A and B were composed of fine crystal grains with a crystal grain size of 100 μm or less. The metal structures of the specimens of Examples A and B are composed of lamellar grains and equiaxed γ grains, and borides having a grain size of 0.1 μm or less are contained within the equiaxed γ grains. included. In the metal structures of Examples 1 and 11, the volume ratio of the equiaxed γ grains was 80% by volume or more when the total volume ratio of the lamellar grains and the equiaxed γ grains was 100% by volume. , and the remainder consisted of lamellar grains. Regarding the volume ratio of each grain, the area ratio of each grain was calculated by image processing from information on the contrast of each grain in the metal structure photograph obtained by an electron microscope, and this was used as the volume ratio of each grain. In addition, no segregation of Zr was observed in the metal structures of the specimens of Examples A and B.

Next, the room temperature mechanical properties of the specimens of Examples A and B were evaluated. The specimens of Examples A and B were subjected to a room temperature tensile test. Similarly, the specimen of Comparative Example A was subjected to a room temperature tensile test. The specimen of Comparative Example A was made of a TiAl alloy containing 48 atomic % Al, 2 atomic % Nb, 2 atomic % Cr, and the balance consisting of Ti and unavoidable impurities.

The tensile test was performed according to ASTM E8. FIG. 14 is a graph showing tensile test results. In FIG. 14, the strain is plotted on the horizontal axis and the stress is plotted on the vertical axis, showing the stress-strain curve of each specimen. The specimens of Examples A and B were larger than the specimen of Comparative Example A in room temperature tensile breaking strength and room temperature tensile breaking strain. The specimens of Examples A and B had a room temperature tensile breaking strength of 600 MPa or more and a room temperature tensile breaking strain of 1.2% or more. Further, the specimen of Example A had a room temperature tensile breaking strength of 700 MPa or more, and the specimen of Example B had a room temperature tensile breaking strain of 1.4% or more. From these results, it became clear that the specimens of Examples A and B were excellent in mechanical strength and ductility, and that the mechanical strength and ductility were improved in a well-balanced manner.

The specimens of Example A and Comparative Example A were subjected to a creep test. A creep test was performed in accordance with JIS Z 2271. FIG. 15 is a graph showing creep test results. In the graph of FIG. 15, the horizontal axis is the Larson-Miller parameter P, the vertical axis is the specific strength, the specimen of Example A is indicated by a square, and the specimen of Comparative Example A is indicated by x. there is Note that the Larson-Miller parameter P is a parameter represented by P=T×log(t _r +C). T is the absolute temperature (K), _tr is the time to rupture (h), and C is a material constant. The material constant C was set to 20. As shown in FIG. 15, the specimen of Example A was superior to the specimen of Comparative Example A in creep properties. From these results, it was found that the specimen of Example A was superior to the specimen of Comparative Example A in high-temperature strength characteristics.

The present disclosure can improve the mechanical strength and ductility of the TiAl alloy in a well-balanced manner, and is therefore useful for aircraft engine parts, turbine blades of gas turbines for power generation, and the like.

Claims

47 atomic % or more and 50 atomic % or less of Al;
1 atomic % or more and 2 atomic % or less of Nb;
2 atomic % or more and 5 atomic % or less of Zr;
0.05 atomic % or more and 0.3 atomic % or less of B,
A TiAl alloy with the balance being Ti and unavoidable impurities.
A TiAl alloy according to claim 1,
A TiAl alloy having an Al content of 47 atomic % or more and 49 atomic % or less.
A TiAl alloy according to claim 1,
The content of Nb is 1 atomic %,
Al content is 47 atomic % or more and 48 atomic % or less,
A TiAl alloy having a Zr content of 2 atomic % or more and 4 atomic % or less.
A TiAl alloy according to claim 1,
The content of Nb is 1 atomic %,
Al content is 47 atomic % or more and 48 atomic % or less,
A TiAl alloy having a Zr content of 2 atomic % or more and 3 atomic % or less.
A TiAl alloy according to claim 1,
The content of Nb is 2 atomic %,
Al content is 47 atomic % or more and 49 atomic % or less,
A TiAl alloy having a Zr content of 2 atomic % or more and 3 atomic % or less.
A TiAl alloy according to claim 1,
The content of Nb is 2 atomic %,
Al content is 47 atomic % or more and 48 atomic % or less,
A TiAl alloy having a Zr content of 2 atomic % or more and 4 atomic % or less.
A TiAl alloy according to claim 1,
Al content is 47 atomic % or more and 48 atomic % or less,
A TiAl alloy having a Zr content of 2 atomic % or more and 4 atomic % or less.
A TiAl alloy according to claim 1,
Al content is 47 atomic % or more and 48 atomic % or less,
A TiAl alloy having a Zr content of 2 atomic % or more and 3 atomic % or less.
A TiAl alloy according to any one of claims 1 to 8,
A TiAl alloy having a room temperature tensile strength at break of 600 MPa or more and a room temperature tensile strain at break of 1.2% or more.
A TiAl alloy powder formed from the TiAl alloy according to any one of claims 1 to 8.
A TiAl alloy part formed of the TiAl alloy according to any one of claims 1 to 8.
A method for manufacturing a TiAl alloy part, comprising:
a sealing step of filling a metal sheath with TiAl alloy powder formed of the TiAl alloy according to any one of claims 1 to 8 and sealing the metal sheath;
A hot isostatic pressing step of subjecting the TiAl alloy powder sealed with the metal sheath to hot isostatic pressing at 1200° C. or higher and 1300° C. or lower and 150 MPa or higher;
A method for manufacturing a TiAl alloy component, comprising: