TiAl-based alloy, preparation method and application thereof

Abstract

The application relates to the alloy processing technical field, in particular to a TiAl-based alloy and a preparation method and application thereof. The alloy improves the room-temperature elongation, the room-temperature strength and the high-temperature strength of the TiAl alloy by comprehensively considering the relationship between the proportioning of various elements, the addition of trace elements and the alloy organization and mechanical properties, and provides a basic guarantee for the subsequent processing of the rod and the preparation of the parts. A second purpose of the application is to provide the preparation method of the TiAl-based alloy, the arrangement of the primary vacuum self-consumption smelting, the secondary vacuum condensation shell smelting, the preheating treatment and the last vacuum self-consumption smelting can solve the problem that the high-melting-point elements in the alloy are easy to segregate, and the uniformity of the alloy material is improved.

Description

Technical Field

[0001] This invention relates to the field of alloy processing technology, and more specifically, to a TiAl-based alloy, its preparation method, and its applications. Background Technology

[0002] TiAl-based intermetallic compound alloys possess excellent properties such as low density, high specific strength, high specific modulus, high creep resistance, oxidation resistance, and combustion resistance, making them highly promising lightweight and high-temperature resistant structural materials. They have become key materials for the next generation of high thrust-to-weight ratio aero-engines and spacecraft applications.

[0003] Looking at the current development of TiAl alloys, cast TiAl alloys have developed more rapidly. For example, blade parts made of cast Ti-48-2Cr-2Nb alloy have begun to be mass-produced and applied in aero-engines. However, due to the larger grain size of cast TiAl alloys, it is difficult to achieve a room temperature elongation of more than 3%. According to current literature reports, only cast single-crystal TiAl alloys can achieve a room temperature elongation of more than 6%. However, due to limitations in the manufacturing process, cast single-crystal TiAl alloys cannot currently be made into larger-sized bars.

[0004] Furthermore, the smelting of large-size titanium-aluminum alloy ingots currently mostly employs a 2-3 cycle vacuum consumable arc (VAR) melting method. This method primarily involves melting and solidifying sponge titanium and various intermediate alloys or elemental materials to produce ingots. Because the VAR melting process itself places extremely high demands on the airtightness of the crucible and the stability of the molten pool, it is difficult to control the uniformity of the alloy composition through stirring during actual melting. Therefore, sponge titanium and various alloying elements must undergo processes such as mixing, pressing, and welding to prepare consumable electrodes with relatively uniform composition before VAR melting. However, this method still cannot overcome the elemental segregation problem that occurs during the solidification process of the molten pool, resulting in inconsistent quality of the produced alloy ingots.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a TiAl-based alloy that completely or partially solves the technical problems of large grain size and low room temperature elongation in the casting of single-crystal TiAl-based alloys in the prior art. This alloy comprehensively improves the room temperature elongation, room temperature strength, and high temperature strength of TiAl alloys by taking into account the relationship between the proportion of each element, the addition of trace elements, and the alloy structure and mechanical properties, thus providing a fundamental guarantee for the subsequent processing of bars and the preparation of parts.

[0007] The second objective of this invention is to provide a method for preparing the TiAl-based alloy as described above. By combining a first vacuum consumable melting, a second vacuum solidification melting, preheating treatment, and a final vacuum consumable melting, the problem of easy segregation of high-melting-point elements in the alloy can be solved, thereby improving the uniformity of the alloy material.

[0008] A third objective of this invention is to provide applications of the TiAl-based alloys as described above.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] This invention provides a TiAl-based alloy, mainly composed of the following components by mass percentage:

[0011] Al 45%–47%, Nb 3%–6%, Mo 0.4%–0.6%, B 0.05%–0.09%, balance Ti and unavoidable impurities.

[0012] Preferably, the TiAl-based alloy is mainly composed of the following components by mass percentage:

[0013] Al 46%–46.5%, Nb 4%–5%, Mo 0.45%–0.5%, B 0.06%–0.08%, balance Ti and unavoidable impurities.

[0014] Preferably, the TiAl-based alloy is mainly composed of γ phase, α2 phase and B2.

[0015] Preferably, the volume fraction of (α2+γ) lamellar clusters is 90% to 96%, and the size of the (α2+γ) lamellar clusters is 80 to 200 μm.

[0016] Preferably, the volume fraction of the B2 phase is between 4% and 10%.

[0017] Preferably, the room temperature elongation of the bar prepared from the TiAl-based alloy ingot is greater than 4%.

[0018] Preferably, the bar made from the TiAl-based alloy ingot has a tensile strength greater than 500 MPa at 900°C.

[0019] This invention provides a method for preparing the TiAl-based alloy, comprising the following steps:

[0020] After the ingredients are proportioned, TiAl-based alloy ingots are prepared by a process of primary vacuum arc remelting, secondary vacuum solidification melting, preheating treatment, and final vacuum arc remelting.

[0021] Preferably, the preheating treatment is performed at a temperature of 400–600°C for 2–4 hours.

[0022] This invention provides an application of the aforementioned TiAl-based alloy in the manufacture of aerospace equipment.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The TiAl-based alloy provided by the present invention can improve the grain size of the alloy by reasonably adding and balancing elements, especially the contents of Al, Mo and B, and comprehensively improve the room temperature elongation, room temperature strength and high temperature strength of the TiAl alloy, thus providing a basic guarantee for the subsequent processing of bars and the preparation of parts.

[0025] (2) The method for preparing TiAl-based alloys provided by the present invention can solve the problem of easy segregation of high-melting-point elements in the alloy and improve the uniformity of the alloy material by combining a first vacuum self-consumption melting, a second vacuum solidification melting, preheating treatment and a final vacuum self-consumption melting.

[0026] (3) The method for preparing TiAl-based alloys provided by the present invention solves the brittleness problem of solidified titanium-aluminum alloy ingots by preheating treatment. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 This is a low-magnification photograph of the TiAl-based alloy ingot proposed in Embodiment 1 of the present invention;

[0029] Figure 2 This is a high-magnification optical metallographic photograph of the core of the TiAl-based alloy ingot proposed in Example 1 of the present invention;

[0030] Figure 3 This is a high-magnification optical metallographic photograph of the TiAl-based alloy ingot at 1 / 2R as described in Example 1 of this invention;

[0031] Figure 4 This is a high-magnification optical metallographic photograph of the edge of the TiAl-based alloy ingot proposed in Embodiment 1 of the present invention. Detailed Implementation

[0032] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0033] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0034] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0035] Unless otherwise specified, in this invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. "Several" refers to any two or more.

[0036] Unless otherwise specified, in this invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, terms such as "first," "second," "third," and "fourth" serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0037] In a first aspect, the present invention provides a TiAl-based alloy based on the technical problem of improving the room temperature elongation of TiAl-based alloys, which is mainly composed of the following components by mass percentage:

[0038] Al 45%–47%, Nb 3%–6%, Mo 0.4%–0.6%, B 0.05%–0.09%, balance Ti and unavoidable impurities.

[0039] In some implementations, the mass percentage of Al, typically but not limitingly, can be any single value or a range of any two of the following: 45%, 45.1%, 45.2%, 45.5%, 45.8%, 46%, 46.2%, 46.6%, 46.7%, 46.8%, 46.9%, and 47%.

[0040] In some implementations, the mass percentage of Nb, typically but not limitingly, can be any one value or a range of any two of the following: 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%.

[0041] In some implementations, the mass percentage of Mo, typically but not limitingly, can be any one value or a range of any two of the following: 0.4%, 0.42%, 0.45%, 0.48%, 0.5%, 0.54%, 0.56%, 0.58%, 0.6%.

[0042] In some implementations, the mass percentage of B, typically but not limitingly, can be any one value or a range of any two of 0.05%, 0.06%, 0.07%, 0.08%, 0.09%.

[0043] The TiAl-based alloying elements provided by this invention are simple in type but rationally combined. The addition of Nb and Mo can improve the oxidation resistance of TiAl-based alloys and have a solid solution strengthening effect. Specifically, the Mo content can improve the plasticity and strength of the alloy and improve its oxidation resistance. The Nb content improves the oxidation resistance of the alloy, increases its high-temperature strength and creep resistance, and reduces its plasticity. The B content of 0.07%-0.09% can refine the grains, improve strength and hot workability, and improve the casting performance of the product after alloying. Overall, it improves the room temperature elongation, room temperature strength and high-temperature strength of TiAl alloys, providing a basic guarantee for subsequent bar processing and part preparation.

[0044] To obtain TiAl-based alloys with superior casting properties, the content of each component was optimized.

[0045] In some embodiments, the TiAl-based alloy is primarily composed of the following components by mass percentage:

[0046] Al 46%–46.5%, Nb 4%–5%, Mo 0.45%–0.5%, B 0.06%–0.08%, balance Ti and unavoidable impurities.

[0047] In some embodiments, the TiAl-based alloy is mainly composed of γ phase, α2 phase, and B2 phase.

[0048] In some embodiments, the volume fraction of (α2+γ) lamellar clusters is above 99%, and the B2 phase content is ≤1%.

[0049] In some embodiments, the grain size of the TiAl-based alloy is between 150 and 400 μm.

[0050] In some embodiments, the room temperature elongation of the TiAl-based alloy rods is greater than 4%, for example greater than 4.1%, greater than 4.2%, greater than 4.3%, greater than 4.4%, greater than 4.5%, or an elongation range of 4.1% to 5.0%.

[0051] In some embodiments, the tensile strength of the TiAl-based alloy at 900°C is greater than 500 MPa, for example, greater than 505 MPa, greater than 510 MPa, greater than 515 MPa, greater than 520 MPa, greater than 525 MPa, greater than 530 MPa, or a range of tensile strength values ​​such as 505 MPa to 530 MPa.

[0052] In some implementations, the room temperature tensile strength of the TiAl-based alloy can also be improved, with a room temperature tensile strength greater than 850 MPa.

[0053] Secondly, since the addition of high-melting-point elements Mo and Nb can cause segregation problems during the smelting process, this invention provides a method for preparing a TiAl-based alloy, comprising the following steps:

[0054] After the ingredients are proportioned, TiAl-based alloy ingots are prepared by a process of primary vacuum arc remelting, secondary vacuum solidification melting, preheating treatment, and final vacuum arc remelting.

[0055] This invention solves the problem of segregation of high-melting-point elements in alloys and improves the uniformity of alloy materials by combining a primary vacuum self-consumption melting process, a secondary vacuum solidification melting process, a preheating treatment, and a final vacuum self-consumption melting process.

[0056] In some implementations, the vacuum degree of a single vacuum self-consuming melting process is less than 5 Pa, the size of the single crystallizer is Φ300 mm, the melting current is controlled in the range of 5 to 8 kA, and the melting voltage is 25 to 30 V.

[0057] In some embodiments, the homogenization of alloying elements is improved by introducing secondary vacuum solidification melting, and a Φ220mm secondary solidification ingot is obtained by casting after solidification melting. Preferably, the secondary vacuum solidification melting current is 25-30kA, and the voltage during the stable melting stage is 40-45V.

[0058] In some implementations, during the final vacuum consumable melting process, the melting current is controlled at 3 to 4.5 kA, the melting voltage is controlled at 20 to 25 V, and the melting vacuum degree is lower than 5 Pa.

[0059] In some embodiments, the method provided by the present invention is suitable for preparing large-sized alloy ingots, for example, ingots with a diameter greater than 200 mm; preferably, greater than or equal to 200 mm.

[0060] In some embodiments, a preheating treatment is performed before the final vacuum arc remelting to avoid electrode breakage caused by a large temperature gradient during electrode melting as the ingot diameter increases due to the intrinsic brittleness of the titanium-aluminum alloy solidified ingot. Preferably, the preheating temperature is 400–600°C, for example, any one or a range of any two values ​​from 400°C, 450°C, 500°C, 550°C, and 600°C, and the preheating time is 2–4 hours, for example, any one or a range of any two values ​​from 2 hours, 3 hours, and 4 hours.

[0061] Thirdly, this invention provides an application of a TiAl-based alloy in the manufacture of aerospace equipment.

[0062] Examples 1-4 and Comparative Examples 1-3

[0063] The elemental composition and mass fraction of the TiAl-based alloys provided in Examples 1-4 and Comparative Examples 1-3 of this invention are shown in Table 1:

[0064] Table 1. Elemental composition and mass ratio in TiAl-based alloys

[0065] Example 1 46 4 0.5 0.08 margin Example 2 45 3 0.4 0.06 margin Example 3 47 6 0.45 0.05 margin Example 4 46.5 4 0.6 0.09 margin Comparative Example 1 46 4 1.0 0.08 margin Comparative Example 2 46 4 0.5 0.1 margin Comparative Example 3 44 4 0.5 0.08 margin

[0066] The methods for preparing TiAl-based alloys provided in Examples 1-4 and Comparative Examples 1-3 of this invention include the following steps:

[0067] (1) Using grade 0 or higher sponge titanium, AlNb master alloy, AlMo master alloy and AlB3 alloy as raw materials, the raw materials are mixed evenly according to the composition ratio in Table 1 and then pressed into electrode blocks on a press.

[0068] (2) The electrode blocks are welded to form an electrode for primary vacuum self-consumption melting. Primary vacuum self-consumption melting is carried out in a vacuum self-consumption melting furnace. The melting vacuum degree is less than 5Pa, the primary crystallizer size is Φ300mm, the melting current is controlled at 7kA, and the melting voltage is 26V.

[0069] (3) The ingot riser of the first vacuum self-consumption melting was flattened and then welded outside the furnace to form a solidified electrode. After a second vacuum solidified melting, it was cast to obtain a Φ220mm secondary solidified ingot. The solidified melting current was 28kA and the voltage during the stable melting stage was 42V.

[0070] (4) After flattening both ends of the solidified ingot, the electrodes are welded in the furnace to obtain electrodes that have undergone three vacuum consumable melting processes. A preheating treatment is performed between the final vacuum consumable melting processes at a temperature of 400℃ for 4 hours. After the preheating is completed, the hot material is loaded into the vacuum consumable furnace of a Φ300mm crystallizer for the final vacuum consumable melting. The final consumable melting process requires controlled melting with a small current: the melting current is controlled at 4.0kA, the melting voltage at 25V, and the melting vacuum degree is below 5Pa.

[0071] Example 5

[0072] Compared with Example 1, Example 5 has the same composition. In the method, only the preheating step (4) is different. The preheating temperature is 600℃ and the time is 2h.

[0073] Comparative Example 4

[0074] Compared with Example 1, Comparative Example 4 has the same composition. In the method, in step (4), Comparative Example 4 does not undergo preheating treatment and directly performs the final vacuum self-consumption melting.

[0075] Experimental Example 1

[0076] The TiAl-based alloys provided in Examples 1-5 and Comparative Examples 1-4 were subjected to metallographic microscopy tests, and the grain size was obtained by the truncation method. The scanning electron microscope images were analyzed using Image-Pro Plus 6.0 image processing software, and the volume fraction of each phase was statistically analyzed according to the different color contrasts of different phases.

[0077] The results are shown in Table 2.

[0078] Table 2

[0079]

[0080] Figure 1 Low-magnification photograph of the TiAl-based alloy ingot proposed in Example 1 of this invention. Figure 2 This is a high-magnification optical metallographic photograph of the core of the TiAl-based alloy ingot proposed in Example 1 of the present invention. Figure 3 This is a high-magnification optical metallographic photograph of the TiAl-based alloy ingot at 1 / 2R as described in Example 1 of this invention. Figure 4 This is a high-magnification optical metallographic photograph of the edge of the TiAl-based alloy ingot proposed in Embodiment 1 of the present invention. As can be seen from the figure, the metallographic distribution of the ingot is uniform from the edge to the center.

[0081] Experiment Example 2 Mechanical Property Testing

[0082] The tensile strength and yield strength of the TiAl-based alloy bars prepared in Examples 1-4 and Comparative Examples 1-3 were tested at room temperature and high temperature. The room temperature elongation was also tested. The results are shown in Table 3.

[0083] The room temperature tensile properties were tested according to GB / T 228.1 standard, and the high temperature tensile properties were tested according to GB / T228.2 standard.

[0084] The room temperature elongation was measured manually by measuring the gauge length after fracture and then calculating the elongation.

[0085] Table 3 Mechanical property test results

[0086]

[0087]

[0088] Experimental results show that the room temperature tensile plasticity of the extruded bars prepared from the alloy ingots prepared by this invention is increased by more than 4%, and the tensile strength at 900℃ reaches more than 500MPa. This comprehensively improves the room temperature elongation, room temperature strength and high temperature strength of TiAl alloy, providing a basic guarantee for the subsequent processing of bars and the preparation of parts.

[0089] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A TiAl-based alloy, characterized in that, It mainly consists of the following components by mass percentage: composition: Al 45%~47%, Nb 3%~6%, Mo 0.4%~0.6%, B 0.05%~0.09%, balance Ti and unavoidable impurities; The TiAl-based alloy is mainly composed of γ phase, α2 phase and B2 phase; The volume fraction of (α2+γ) lamellar clusters is above 99%, and the size of the (α2+γ) lamellar clusters is 150~400μm; The volume fraction of the B2 phase is ≤1%.

2. The TiAl-based alloy according to claim 1, characterized in that, It mainly consists of the following components by mass percentage: composition: Al 46%~46.5%, Nb 4%~5%, Mo 0.45%~0.5%, B 0.06%~0.08%, balance Ti and unavoidable impurities.

3. The TiAl-based alloy according to claim 1 or 2, characterized in that, The bars prepared from the TiAl-based alloy ingots have a room temperature elongation greater than 4%.

4. The TiAl-based alloy according to claim 1 or 2, characterized in that, The bar stock prepared from the TiAl-based alloy ingot has a tensile strength greater than 500 MPa at 900°C.

5. The method for preparing the TiAl-based alloy according to any one of claims 1-4, characterized in that, Includes the following steps: After the ingredients are proportioned, TiAl-based alloy ingots are prepared by a process of one vacuum self-consumption melting, two vacuum solidification melting, preheating treatment and a final vacuum self-consumption melting. The preheating treatment is performed at a temperature of 400~600℃ for 2~4 hours.

6. The application of the TiAl-based alloy according to any one of claims 1-4 in the manufacture of aerospace equipment.

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