Method for strengthening liquid phase diffusion welding joint and welding system using same

Abstract

The invention relates to the technical field of high-temperature alloy welding, and provides a method for strengthening a liquid phase diffusion welding head and a welding system using the same. The method comprises the steps that S1, the to-be-welded faces of the two Ni3Al-based alloy blocks are ground and then carburized; and S2, attachments on the carburized surface are removed, and BNi-2 is selected as a middle layer for liquid-phase diffusion welding. The method has the beneficial effects that a welding influence area is removed through a heat preservation program at the first specified temperature T1, and uniformization of components and structures of a connector is achieved. Cooling to a second specified temperature T2 at a cooling speed of not less than 5 DEG C / min after heat preservation, increasing the nucleation rate of a gamma '-Ni3Al phase in the crystal, inhibiting coarsening of the gamma'-Ni3Al phase, and generating a cubic or nearly cubic precipitated phase with uniform size; and then cooling to a third specified temperature T3 at the cooling speed of not more than 5 DEG C / min to promote precipitation and growth of M23C6 type carbides at the joint and the parent metal grain boundary so as to generate granular / rod-shaped / strip-shaped strengthening phases which are uniformly distributed along the grain boundary.

Description

Technical Field

[0001] The invention relates to the technical field of high temperature alloy welding, and in particular to a method for strengthening a liquid phase diffusion welding joint and a welding system using the same. Background Art

[0002] Ni3Al-based high-temperature alloys have broad application prospects in the fields of hot end components of aerospace engines due to their advantages such as easy manufacturing, low density, high-temperature strength and excellent oxidation resistance. Since the alloy is composed of a variety of alloying elements, thermal cracking is prone to occur during the fusion welding process. Liquid phase diffusion welding is currently usually used to achieve reliable connection. Liquid phase diffusion welding is also called diffusion brazing and transient liquid phase connection. The Ni3Al-based alloy joints produced by this process usually have room temperature tensile and shear properties close to those of the parent material. However, under creep conditions close to the service temperature, the performance is poor and the life is short.

[0003] At present, the main method to improve the mechanical properties of liquid phase diffusion welding joints is post-weld heat treatment. This process can achieve the homogenization of the joint composition and structure, and eliminate harmful phases in the affected area. This method is simple and effective, but has a certain upper limit. Since the intermediate layer used in liquid phase diffusion welding has a certain composition difference with the base material and often does not contain carbon, even if an appropriate heat treatment process is used, it is impossible to precipitate sufficient carbides at the grain boundaries of the joint. This results in a relatively large cracking tendency at the joint, often showing the characteristics of brittle intergranular fracture.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The object of the present invention is to provide a method for strengthening a liquid phase diffusion welding joint and a welding system using the same, so as to solve the technical problems existing in the prior art.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a method for strengthening a liquid phase diffusion welding joint, comprising:

[0007] S1: grinding and carburizing the surfaces to be welded of the two Ni3Al-based alloy blocks;

[0008] S2: Remove the attachments on the carburized surface and use BNi-2 as the intermediate layer for liquid phase diffusion welding;

[0009] S3: After the welding is completed, the sample is kept at the first designated temperature T1, and then quickly cooled to the second designated temperature T2, and then slowly cooled to the third designated temperature T3.

[0010] In an optional embodiment, in S1,

[0011] Use a wire electrical discharge cutting machine to cut the Ni3Al-based alloy ingot into two cubes. After grinding the welding surface to 400-2000 mesh, place it in a vacuum carburizing system for surface carburizing;

[0012] The carburizing method is pulse carburizing, and the carburizing medium is acetylene.

[0013] In an alternative embodiment,

[0014] The mass fraction of carbon on the carburized surface is 0.3-0.5%, the carburizing temperature is 800-950°C, the pre-carburizing holding time is 0.5-1 hour, the total carburizing time is 1.5-2.5 hours, the strong carburizing time for each cycle is 30-60 seconds, and the diffusion time is 60-120 seconds.

[0015] In an alternative embodiment,

[0016] The mass fraction of carbon on the carburized surface is 0.4%, the carburizing temperature is 950°C, the holding time is 30 minutes, the total carburizing time is 2 hours, the strong carburizing time for each cycle is 60 seconds, and the diffusion time is 120 seconds.

[0017] In an alternative embodiment, in S2,

[0018] After grinding and removing the carbon black and oxide attachments on the carburized surface, perform liquid-phase diffusion welding in a vacuum diffusion bonding system.

[0019] In an alternative embodiment, the welding temperature is 1080-1150°C, and the holding time is 1.5-3 hours.

[0020] In an alternative embodiment, the welding temperature is 1100°C, and the holding time is 2 hours.

[0021] In an alternative embodiment, in S3,

[0022] The temperature range of T1 is 1150°C ≤ T1 < 1300°C, the holding time at T1 is not less than 4 hours, the temperature range of T2 is 950°C ≤ T2 ≤ 1050°C, and the rapid cooling rate is not less than 5°C / min;

[0023] The temperature range of T3 is 750°C ≤ T3 ≤ 850°C, and the slow cooling rate is not greater than 5°C / min.

[0024] In an alternative embodiment,

[0025] The temperature of T1 is 1200°C, the holding time at T1 is 4 hours, the temperature of T2 is 1000°C, and the rapid cooling rate is 20°C / min;

[0026] The temperature of T3 is 800 °C, and the rate of slow cooling is 0.25 °C / min.

[0027] On the other hand, the present invention also provides a welding system, including: a method of using the strengthened liquid-phase diffusion welding head as described above.

[0028] The beneficial effects of the present invention are as follows:

[0029] (1) In the method of the strengthened liquid-phase diffusion welding head of the present invention, the carbon content of the surface to be welded is increased by pre-welding carburization, providing a composition basis for regulating the precipitation behavior of grain boundary carbides in the subsequent joint. During the liquid-phase diffusion welding process, an interlayer with a composition similar to that of the base material is selected, and appropriate holding temperature and holding time are used to ensure that the joint achieves complete isothermal solidification.

[0030] (2) During the post-weld heat treatment process of the present invention, the welding affected zone is removed through the holding procedure at the first specified temperature T1 to achieve the homogenization of the joint composition and microstructure. After holding, it is cooled to the second specified temperature T2 at a cooling rate of not less than 5 °C / min to increase the nucleation rate of intragranular γ′-Ni3Al phase and inhibit its coarsening, generating uniformly sized cubic or near-cubic precipitates; then it is cooled to the third specified temperature T3 at a cooling rate of not more than 5 °C / min to promote the precipitation and growth of M 23 C6-type carbides at the grain boundaries of the joint and the base material, generating granular / rod-shaped / strip-shaped strengthening phases uniformly distributed along the grain boundaries; the two-step post-weld cooling solution heat treatment can achieve a more diverse grain boundary precipitation effect. This method can enhance the precipitation strengthening effect in the grains and at the grain boundaries of the joint, thereby improving the mechanical properties of the welded sample, and has the advantages of simple operation, low energy consumption, and low cost, and has good application prospects. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1 It is a process flow schematic diagram of the strengthened liquid-phase diffusion welding head method provided by the embodiment of the present invention.

[0033] Figure 2 It is a microstructural diagram after pre-weld carburization treatment and liquid-phase diffusion welding provided by the embodiment of the present invention ( Figure 2 a is the macroscopic morphology of the joint area; Figure 2 b is the γ+γ′ duplex structure in the isothermal solidification zone; Figure 2 c is the precipitate at the interface between the joint and the base material; Figure 2d is the diffusion influence zone; Figure 2 e is the dendritic structure near the joint area; Figure 2 f is the γ+γ′ duplex structure far from the joint area).

[0034] Figure 3 is the microstructural diagram after pre-welding carburizing treatment, liquid-phase diffusion welding and two-stage cooling solution heat treatment provided by the embodiment of the present invention ( Figure 3 a is the macroscopic morphology of the joint area, Figure 3 b is the γ+γ′ duplex structure in the isothermal solidification zone, Figure 3 c is the precipitated phase at the grain boundary of the joint, Figure 3 d is the interdendritic structure in the base metal area, Figure 3 e is the γ+γ′ duplex structure in the base metal area, Figure 3 f is the grain boundary structure in the base metal area).

[0035] Figure 4 is the microstructural diagram of the joint of the comparative example provided by the present invention.

[0036] Figure 5 is the creep curve and creep rate curve diagram in the embodiment and comparative example of the present invention ( Figure 5 a is the creep curve; Figure 5 b is the creep rate curve). Specific embodiments

[0037] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] It should be noted that when a component is referred to as "fixed to" or "adhered to" another component, it can be directly or indirectly located on that other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to that other component. The orientations or positions indicated by the terms "upper", "lower", "left", "right", "front", "rear", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientations or positions shown in the drawings, and are only for convenience of description and cannot be construed as limitations on the technical solutions of the present application. The terms "first" and "second" are only used for convenience of description and cannot be construed as indicating or implying relative importance or implicitly indicating the quantity of technical features. The meaning of "a plurality" is two or more, and the meaning of "several" is any quantity including one, unless otherwise specifically defined.

[0039] Please refer to the attached Figures 1-5 , the purpose of this embodiment is to provide a method for strengthening the liquid-phase diffusion welded joint, including:

[0040] S1: Grind the surfaces to be welded of two Ni3Al-based alloy blocks and then carburize them. Optionally, use a wire electrical discharge cutting machine to cut a Ni3Al-based alloy ingot into two cubes, grind the surfaces to be welded to 400 - 2000 mesh, and then place them in a vacuum carburizing system for surface carburization. Among them, the carburizing method is pulse carburizing, and the carburizing medium is acetylene. In this embodiment, the carbon mass fraction on the carburized surface is 0.3 - 0.5%, the carburizing temperature is 800 - 950 °C, the holding time before carburizing is 0.5 - 1 hour, the total carburizing time is 1.5 - 2.5 hours, the strong carburizing time for each cycle is 30 - 60 seconds, and the diffusion time is 60 - 120 seconds. By controlling the carburizing parameters, surfaces to be welded with different carburizing effects can be obtained.

[0041] S2: Remove the attachments on the carburized surface, and select BNi-2 as the intermediate layer for liquid phase diffusion welding. Optionally, after grinding and removing the carbon black and oxide attachments on the carburized surface, perform liquid phase diffusion welding in a vacuum diffusion bonding system. The welding temperature is 1080 - 1150 °C, and the holding time is 1.5 - 3 hours.

[0042] S3: Keep the welded sample at a first specified temperature T1 for heat preservation and then quickly cool it to a second specified temperature T2, and then slowly cool it to a third specified temperature T3. The temperature range of T1 is 1150 °C ≤ T1 < 1300 °C, the holding time at T1 is not less than 4 h, the temperature range of T2 is 950 °C ≤ T2 ≤ 1050 °C, and the rapid cooling rate is not less than 5 °C / min; the temperature range of T3 is 750 °C ≤ T3 ≤ 850 °C, and the slow cooling rate is not greater than 5 °C / min. By regulating the nodal temperatures and cooling rates in the two stages, Ni3Al-based alloy joints with various intragranular / grain boundary precipitation effects can be obtained. The intragranular precipitates are cubic or near-cubic, with uniform size and uniformly distributed within the grains; the grain boundary precipitates in the joint are short rod-shaped or long strip-shaped and uniformly distributed along the grain boundaries. The types of precipitates include intragranular γ'-Ni3Al phase and grain boundary M 23 C6-type carbides.

[0043] In the preferred embodiment,

[0044] S1: Use a wire electrical discharge cutting machine to cut a Ni3Al-based alloy ingot into two cubes of 20 × 20 × 40 mm 3 with the surfaces to be welded (20 × 20 mm 2Grind to 2000 mesh; place the processed sample in a vacuum carburizing system for surface carburizing; select acetylene as the carburizing medium, with a carbon mass fraction of 0.4% on the carburized surface, a carburizing temperature of 950 °C, and a pre-carburizing holding time of 30 minutes; use the pulse carburizing method, with a total carburizing time of 2 hours, a strong carburizing time of 60 seconds and a diffusion time of 120 seconds for each cycle; after carburizing, use 2000-mesh sandpaper to grind off the carbon black and a small amount of oxides attached to the carburized surface.

[0045] S2: Place the sample in a vacuum diffusion bonding system for TLP bonding; select BNi-2 as the intermediate layer, with a welding temperature of 1100 °C and a holding time of 2 hours.

[0046] S3: Place the welded sample in a muffle furnace, heat it to T1 (1200 °C) and hold for 4 hours, then cool the sample to T2 (1000 °C) at a cooling rate of 20 °C / min to increase the nucleation rate of the γ′ phase and inhibit its coarsening; then cool it to T3 (800 °C) at a cooling rate of 0.25 °C / min to promote the 23 precipitation and growth of M

[0047] In the comparative example,

[0048] S1: Use a wire electrical discharge machine to cut the Ni3Al-based alloy ingot into two 20×20×40 mm 3 cubes, grind the welding surface (20×20 mm 2 ) to 2000 mesh, and place the sample in a vacuum diffusion bonding system for TLP bonding. Select BNi-2 as the intermediate layer, with a welding temperature of 1100 °C and a holding time of 2 hours.

[0049] S2: Place the welded sample in a muffle furnace, heat it to 1160 °C and hold for 4 hours, then cool it to room temperature in the furnace.

[0050] After completing the regulation of the precipitation behavior of the Ni3Al-based alloy liquid-phase diffusion welded joint structure, observe the microstructure of the treated nickel aluminide alloy through a scanning electron microscope JSM-7800F.

[0051] In the preferred embodiment, as Figure 3 shown, near-cubic γ′-Ni3Al phases are precipitated within the grains. Strip-shaped M 23 C6-type carbides are precipitated at the grain boundaries. In the comparative example, as Figure 4 shown, near-cubic γ′-Ni3Al phases are precipitated within the grains, and small-sized particulate carbides are precipitated at the grain boundaries. By comparing the preferred embodiment and the comparative example, it can be seen that the strengthened liquid-phase diffusion welded joint combining pre-welding carburizing and post-welding heat treatment processes can promote the precipitation of grain boundary carbides while maintaining the near-cubic shape of the γ′-Ni3Al phases within the grains of the joint.

[0052] Creep performance test:

[0053] Referring to the requirements in GB / T 2039-2012 "Test Method for Uniaxial Tensile Creep of Metallic Materials", the samples in the preferred embodiments and the comparative examples were respectively made into round cross-section specimens, and a CRIMS RDL50 high-temperature creep testing machine was used for creep testing. The test temperature was 800 °C and the stress was 160 MPa.

[0054] The test results are as follows:

[0055] As Figure 5 shown in a, the creep life of the sample in the preferred embodiment was 808 hours, which was increased by 120% compared with the sample in the comparative example. The creep rate curve ( Figure 5 b) shows that the sample in the preferred embodiment exhibits typical "three-stage" characteristics, namely, the first stage with a rapid decrease in creep rate (work hardening, a large number of dislocations proliferating), the second stage with a relatively stable creep rate (dynamic balance between work hardening and dynamic softening), and the third stage with a rapid increase in creep rate (crack propagation). This is similar to the creep behavior of the Ni3Al-based superalloy base material. While the sample in the comparative example only exhibits the first two creep stages and lacks the third stage reflecting the crack propagation process. The sample in the comparative example fractured at the joint, with poor resistance to crack propagation and macroscopic fracture occurring in a very short time. In addition, the steady-state creep rate of the sample in the preferred embodiment is lower, indicating that it has higher creep deformation resistance.

[0056] It should be noted that in the method for strengthening the liquid-phase diffusion welded joint of the present invention, by controlling the carburizing parameters, a weld surface with different carburizing effects can be obtained; by regulating the node temperature and cooling rate in two stages, a Ni3Al-based alloy joint with various intragranular / grain boundary precipitation effects can be obtained. Compared with the traditional liquid-phase diffusion welding process, pre-weld carburizing provides a composition basis for subsequent regulation of the grain boundary carbide precipitation behavior of the joint; two-step post-weld cooling and solution heat treatment can achieve more diverse grain boundary precipitation effects. This method can improve the intragranular and grain boundary precipitation strengthening effects of the joint, thereby improving the mechanical properties of the welded sample, and has the advantages of simple operation, low energy consumption, and low cost, and has good application prospects.

[0057] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for strengthening a liquid phase diffusion welding joint, characterized in that: include: S1: grinding and carburizing the surfaces to be welded of the two Ni3Al-based alloy blocks; S2: Remove the attachments on the carburized surface and use BNi-2 as the intermediate layer for liquid phase diffusion welding; S3: After the welding is completed, the sample is kept at the first designated temperature T1, and then quickly cooled to the second designated temperature T2, and then slowly cooled to the third designated temperature T3.

2. The method for strengthening a liquid phase diffusion welding joint according to claim 1, characterized in that: In S1, The Ni3Al-based alloy ingot is cut into two cubes using an electric spark cutting machine, and the surface to be welded is polished to 400-2000 mesh, and then placed in a vacuum carburizing system for surface carburizing; The carburizing method is a pulse carburizing method, and the carburizing medium is acetylene.

3. The method for strengthening a liquid phase diffusion welding joint according to claim 2, characterized in that: The carbon mass fraction of the carburized surface is 0.3-0.5%, the carburizing temperature is 800-950°C, the pre-carburizing holding time is 0.5-1 hour, the total carburizing time is 1.5-2.5 hours, the intensive carburizing time of each cycle is 30-60 seconds, and the diffusion time is 60-120 seconds.

4. The method for strengthening a liquid phase diffusion welding joint according to claim 3, characterized in that: The carbon mass fraction of the carburized surface is 0.4%, the carburizing temperature is 950° C., the holding time is 30 minutes, the total carburizing time is 2 hours, the intensive carburizing time in each cycle is 60 seconds, and the diffusion time is 120 seconds.

5. The method for strengthening a liquid phase diffusion welding joint according to claim 1, characterized in that: In S2, After the carbon black and oxide attachments on the carburized surface are removed by grinding, liquid phase diffusion welding is performed in a vacuum diffusion bonding system.

6. The method for strengthening a liquid phase diffusion welding joint according to claim 5, characterized in that: The welding temperature is 1080-1150° C., and the heat preservation time is 1.5-3 hours.

7. The method for strengthening a liquid phase diffusion welding joint according to claim 6, characterized in that: The welding temperature is 1100° C. and the holding time is 2 hours.

8. The method for strengthening a liquid phase diffusion welding joint according to claim 1, characterized in that: In S3, The temperature range of T1 is 1150°C≤T1<1300°C, the holding time at T1 is not less than 4h, the temperature range of T2 is 950°C≤T2≤1050°C, and the rapid cooling rate is not less than 5°C / min; The temperature range of T3 is 750°C≤T3≤850°C, and the slow cooling rate is no more than 5°C / min.

9. The method for strengthening a liquid phase diffusion welding joint according to claim 8, characterized in that: The temperature of T1 is 1200°C, the holding time at T1 is 4 hours, the temperature of T2 is 1000°C, and the rapid cooling rate is 20°C / min; The temperature of T3 is 800° C., and the slow cooling rate is 0.25° C. / min.

10. A welding system, characterized in that: include: A method for strengthening a liquid phase diffusion welding joint as claimed in any one of claims 1 to 9.

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