Postweld heat treatment method for Ti2AlNb-based alloy joint

Abstract

The invention relates to the technical field of material heat treatment, in particular to a post-weld heat treatment method for a Ti2AlNb-based alloy joint, which comprises the following steps: performing diffusion welding on a Ti2AlNb alloy material to obtain a Ti2AlNb alloy diffusion welding joint; the Ti2AlNb alloy diffusion welding joint is subjected to solution treatment in an alpha < 2 + > B2 two-phase region, and a solid-solution-state diffusion welding joint is obtained; and the diffusion welding joint is subjected to aging treatment in a B2 + O two-phase region, after heat preservation is finished, the diffusion welding joint is cooled to the room temperature, and the Ti2AlNb-based alloy joint is obtained. The post-weld heat treatment method for the Ti2AlNb-based alloy joint aims at solving the problem that the design index cannot be met after the performance of the post-weld joint and the parent metal of the Ti2AlNb-based alloy diffusion welding joint is lost.

Description

Technical Field

[0001] The invention relates to the technical field of material heat treatment, and in particular to a post-weld heat treatment method for a Ti2AlNb-based alloy joint. Background Art

[0002] New aircraft have the characteristics of faster flight speed and longer range. The greatly increased flight speed and distance will inevitably lead to a harsher service environment for components, making the long-term service temperature of parts reach above 700℃ and the short-term working temperature reach above 1000℃. Therefore, higher requirements are put forward for aviation structural materials. At present, nickel-based high-temperature alloys have good high-temperature resistance, but the material itself has a high density. The increase in mass will directly affect the comprehensive performance of the aircraft, so it is difficult to meet the needs of future aircraft. Ti2AlNb alloy has the advantages of low density, high specific strength, good high-temperature oxidation resistance and good processing performance. The increase in Nb content significantly improves its high-temperature performance, and the long-term working temperature is increased to 600-800℃, and it can reach above 1000℃ in a short time. At the same time, the density of Ti2AlNb-based alloy is reduced by more than 40% compared with nickel-based high-temperature alloy, making Ti2AlNb alloy expected to replace nickel-based high-temperature alloy in the aerospace field. Widely used, so Ti2AlNb alloy has become a hot spot in new material research.

[0003] At present, Ti2AlNb alloy structural parts in the aviation and aerospace fields are mostly manufactured by welding processes, mainly including electron beam welding, laser welding, diffusion welding, friction welding, brazing and other methods. However, traditional fusion welding is prone to thermal crack defects for thin-walled multi-ribbed hollow structures, and wide and thick plates cannot be welded through. Friction welding will form flash inside the cavity, which cannot be removed. Therefore, hollow structures can only be manufactured by brazing or diffusion welding.

[0004] The hollow structure of Ti2AlNb alloy needs to have good high temperature resistance. Vacuum brazing is easy to form intermetallic compounds at the interface, resulting in a low brazed joint. Therefore, direct diffusion welding is currently mainly used. Diffusion welding is a joint obtained by mutual diffusion of atoms on both sides of the interface under certain temperature and pressure conditions. The joint strength is usually equivalent to that of the parent materials on both sides. However, the diffusion welding temperature is high and the insulation time is long, which causes a certain degree of loss of parent material performance after welding. After experimental verification, it was found that its room temperature and high temperature mechanical properties were reduced (the room temperature strength of Ti2AlNb alloy parent material after welding was reduced by about 10%, and the high temperature tensile strength at 700℃ was reduced by 10-15%). The strength of Ti2AlNb alloy welded joints directly affects the comprehensive performance of the aircraft during on-orbit flight.

[0005] Therefore, the inventor provides a post-weld heat treatment method for a Ti2AlNb-based alloy joint. Summary of the invention

[0006] (1) Technical issues to be solved

[0007] The embodiment of the present invention provides a post-weld heat treatment method for a Ti2AlNb-based alloy joint, which solves the technical problem that the joint and the base material performance of the Ti2AlNb alloy diffusion welded joint cannot meet the design indicators after the performance loss.

[0008] (2) Technical solution

[0009] The present invention provides a post-weld heat treatment method for a Ti2AlNb-based alloy joint, comprising the steps of:

[0010] Diffusion welding is performed on the Ti2AlNb alloy material to obtain a Ti2AlNb alloy diffusion welding joint;

[0011] The Ti2AlNb alloy diffusion welded joint is subjected to a solid solution treatment in the α2+B2 two-phase region to obtain a solid solution state diffusion welded joint;

[0012] The diffusion welded joint is subjected to aging treatment in a B2+O two-phase region, and after heat preservation, is cooled to room temperature to obtain a Ti2AlNb-based alloy joint.

[0013] Furthermore, the process parameters of the solution treatment are: the solution temperature T1 is 1000-1050°C, and the holding time t1 is 2-4h.

[0014] Furthermore, the solution temperature T1 is 1020°C.

[0015] Furthermore, the insulation time t1 is 2h.

[0016] Furthermore, the process parameters of the aging treatment are: after the aging temperature T2 is 780-820°C, the insulation time t2 is 20-24h.

[0017] Furthermore, the aging temperature T2 is 800°C.

[0018] Furthermore, the insulation time t2 is 24h.

[0019] Furthermore, the vacuum degree during diffusion welding is less than 8×10 -3 Pa.

[0020] Furthermore, the room temperature tensile strength of the Ti2AlNb-based alloy joint is greater than 1000 MPa.

[0021] Furthermore, the high temperature tensile strength of the Ti2AlNb-based alloy joint is greater than 800 MPa.

[0022] (3) Beneficial effects

[0023] In summary, after two heat treatments, the microstructure of the Ti2AlNb alloy diffusion welding joint of the present invention is transformed from a primary O phase with a higher volume fraction and larger size to a lamellar O phase structure with smaller size, and the lamellar structure is dispersed inside the grains, thereby significantly improving the room temperature and high temperature strength of the joint, especially the high temperature performance above 700°C, to meet the requirements of future aircraft for lightweight and high-strength materials above 700°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0025] Figure 1 It is a schematic flow chart of a post-weld heat treatment method for a Ti2AlNb-based alloy joint provided in an embodiment of the present invention;

[0026] Figure 2 This is a microstructure morphology diagram of a Ti2AlNb-based alloy diffusion welded joint provided in Example 1 of the present invention;

[0027] Figure 3 This is a joint microstructure morphology diagram of a Ti2AlNb-based alloy joint provided in Example 1 of the present invention after solid solution treatment;

[0028] Figure 4 This is a joint microstructure morphology diagram of a Ti2AlNb-based alloy joint provided in Example 1 of the present invention after secondary heat treatment. DETAILED DESCRIPTION

[0029] The following detailed description of the embodiments of the present invention is provided in conjunction with the accompanying drawings and examples. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present invention, but cannot be used to limit the scope of the present invention, that is, the present invention is not limited to the described embodiments.

[0030] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0031] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the products of the present invention are conventionally placed when in use, or are the orientations or positional relationships conventionally understood by those skilled in the art. These are merely for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0032] Figure 1 is a schematic diagram of a post-weld heat treatment method for a Ti2AlNb-based alloy joint provided in an embodiment of the present invention, see Figure 1 , the method may include the following steps:

[0033] S100, performing diffusion welding on the Ti2AlNb alloy material to obtain a Ti2AlNb alloy diffusion welding joint.

[0034] Specifically, the vacuum degree during diffusion welding is less than 8×10 -3 Pa.

[0035] S200, subjecting the Ti2AlNb alloy diffusion welding joint to solid solution treatment in the α2+B2 two-phase region to obtain a diffusion welding joint in a solid solution state.

[0036] Specifically, the process parameters of the solution treatment are: the solution temperature T1 is 1000-1050°C, and the holding time t1 is 2-4 hours. Furthermore, the solution temperature T1 is 1020°C, and the holding time t1 is 2 hours. After the insulation is completed, quenching is carried out in oil (or water) immediately to obtain a diffusion welded joint in a solid solution state; the Ti2AlNb alloy binary phase diagram and DSC obtained that the transformation temperature of the Ti2AlNb alloy from the B2+O two-phase region to the B2+O+α2 three-phase region is about 960°C, and the transformation temperature from the B2+O+α2 three-phase region to the B2+α2 two-phase region is about 1060°C. Usually, the diffusion welding temperature of Ti2AlNb alloy is about 940-980°C. The obtained joint structure is mainly composed of primary O phase, and the secondary O phase is dissolved in the matrix during the welding process. When the welding temperature is low, it is mainly composed of O phase. When the welding temperature is high, a small amount of α2 phase will precipitate in the O phase. The growth of O phase will increase the plasticity of the material, but the tensile strength will be reduced to a certain extent. In this embodiment, the Ti2AlNb alloy joint is solution treated at 1000-1050°C, with the aim of completely dissolving the O phase in the matrix at a relatively high temperature in the B2+α2 two-phase region. Under the condition of fast cooling, since the Nb element is a stabilizing element of the β phase, a single-phase microstructure dominated by a metastable B2 phase is formed in the joint region. At the same time, the B2 phase is a body-centered cubic structure with more slip systems. At the same time, the grains grow significantly at a high solution temperature, and the tensile properties are significantly reduced. Therefore, a secondary heat treatment is required to precipitate the strengthening phase.

[0037] S300, subjecting the diffusion welded joint to aging treatment in the B2+O two-phase region, cooling it to room temperature after the insulation is completed to obtain a Ti2AlNb-based alloy joint.

[0038] Specifically, the process parameters of the aging treatment are: after the aging temperature T2 is 780-820°C, the holding time t2 is 20-24h. Furthermore, the aging temperature T2 is 800°C, and the holding time t2 is 24h. The room temperature tensile strength of the Ti2AlNb-based alloy joint finally obtained is greater than 1000MPa, and the high temperature tensile strength is greater than 800MPa. After the insulation is completed, air cooling or argon cooling to room temperature is carried out. 780-820°C is in the B2+O two-phase region. During the secondary heat treatment process, the metastable phase begins to decompose, and a smaller primary O phase is precipitated in the joint area. At the same time, the secondary O phase is precipitated inside the grain, thereby significantly improving the mechanical properties of the joint. The aging temperature cannot be too high, otherwise the O phase will grow and coarsen.

[0039] Example 1

[0040] This embodiment uses the second generation Ti2AlNb alloy, whose nominal chemical composition is Ti-22Al-25Al, and its specific processing process includes the following steps:

[0041] Step 1: Vacuum diffusion welding: After the Ti2AlNb alloy is processed to the diffusion welding requirements, vacuum diffusion welding is performed using the optimized diffusion welding process parameters to obtain a Ti2AlNb alloy diffusion welding joint. Figure 2 , Ti2AlNb alloy diffusion welding joint microstructure, lath-like O phase and equiaxed α2 phase precipitate at the grain boundary, and smaller lath-like O phase and lamellar O phase precipitate inside the grain.

[0042] Step 2: Primary heat treatment: Place the diffusion welded joint obtained in step 1 in a heat treatment furnace for solution treatment, that is, heat the part to a temperature of 1020°C, keep the temperature for 120 minutes, and immediately cool it to room temperature with oil after the end of the heat treatment to obtain a diffusion welded joint after solution treatment. Figure 3 After solid solution, metastable B2 phase grains are formed with larger grain size, and only a small amount of smaller equiaxed α2 phase precipitates at the grain boundary.

[0043] Step 3: Secondary heat treatment: Place the solid solution diffusion welded joint obtained in step 2 in a vacuum heat treatment furnace, heat it to 800°C, keep it warm for 24 hours, and then cool it to room temperature by blowing argon gas. Figure 4 After aging, lamellar O phase precipitates at the grain boundary, and fine needle-shaped O phase precipitates inside the grain. From the tensile performance results, it can be concluded that the size and distribution state of the O phase have a great influence on the mechanical properties of the joint. The dispersed lamellar O phase can significantly improve its room temperature and high temperature tensile properties.

[0044] The room temperature and high temperature tensile properties of the Ti2AlNb alloy diffusion welded joint prepared by this embodiment are shown in Table 1 below. It can be seen that after heat treatment, the room temperature tensile strength of the joint is increased by more than 10%, and the high temperature tensile strength is increased by more than 40%.

[0045] Table 1 Comparison of room temperature and high temperature tensile strength of welded unheat treated / heat treated

[0046]

[0047] It should be clear that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. The present invention is not limited to the specific steps and structures described above and shown in the figures. In addition, for the sake of brevity, a detailed description of known methods and technologies is omitted here.

[0048] The above are only embodiments of the present application and are not limited to the present application. For those skilled in the art, the present application may have various changes and variations without departing from the scope of the present invention. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A post-weld heat treatment method for a Ti2AlNb-based alloy joint, characterized in that: The method comprises the following steps: Diffusion welding is performed on the Ti2AlNb alloy material to obtain a Ti2AlNb alloy diffusion welding joint; The Ti2AlNb alloy diffusion welded joint is subjected to a solid solution treatment in the α2+B2 two-phase region to obtain a solid solution state diffusion welded joint; The diffusion welded joint is subjected to aging treatment in a B2+O two-phase region, and after heat preservation, is cooled to room temperature to obtain a Ti2AlNb-based alloy joint.

2. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 1, characterized in that: The process parameters of the solution treatment are: solution temperature T1 is 1000-1050°C, and holding time t1 is 2-4h.

3. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 2, characterized in that: The solution temperature T1 is 1020°C.

4. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 2, characterized in that: The insulation time t1 is 2h.

5. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 1, characterized in that: The process parameters of the aging treatment are: the aging temperature T2 is 780-820°C, and the holding time t2 is 20-24h.

6. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 5, characterized in that: The aging temperature T2 is 800°C.

7. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 5, characterized in that: The insulation time t2 is 24h.

8. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 1, characterized in that: The vacuum degree during diffusion welding is less than 8×10 -3 Pa.

9. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 1, characterized in that: The room temperature tensile strength of the Ti2AlNb-based alloy joint is greater than 1000 MPa.

10. The post-weld heat treatment method for Ti2AlNb-based alloy joints according to claim 1, characterized in that: The high temperature tensile strength of the Ti2AlNb-based alloy joint is greater than 800 MPa.

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