A method of strengthening a liquid phase diffusion welded joint and a welding system using the same

Abstract

The application relates to the technical field of high-temperature alloy welding, and provides a method for strengthening a liquid-phase diffusion welded joint and a welding system using the same.S1: after the welding surfaces of two Ni3Al-based alloy blocks are polished, the surfaces are carburized;S2: the attachments on the carburized surfaces are removed, and BNi-2 is selected as an intermediate layer to perform liquid-phase diffusion welding.The beneficial effects are that the welding affected zone is removed through the holding procedure at a first specified temperature T1, and the uniformity of the joint composition and structure is realized.The cooling speed is not less than 5 DEG C / min after the holding to a second specified temperature T2, the nucleation rate of intracrystalline gamma'-Ni3Al phase is increased, and the coarsening thereof is inhibited, and the cubic or near-cubic precipitated phase with uniform size is generated;then the cooling speed is not more than 5 DEG C / min to a third specified temperature T3, the joint and the base material grain boundary M 23 The precipitation and growth of C6 type carbides generate the granular / rod-shaped / strip-shaped strengthening phase which is uniformly distributed along the grain boundaries.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy welding technology, specifically to a method for strengthening liquid phase diffusion welded joints and a welding system using the same. Background Technology

[0002] Ni3Al-based superalloys have broad application prospects in aerospace engine hot-end components and other fields due to their advantages such as ease of manufacturing, low density, high-temperature strength, and excellent oxidation resistance. Because this alloy is composed of multiple alloying elements, it is prone to hot cracking during fusion welding. Currently, liquid phase diffusion welding is commonly used to achieve reliable connections. Liquid phase diffusion welding is also known as diffusion brazing or transient liquid phase joining. Ni3Al-based alloy joints produced by this process typically have room temperature tensile and shear properties close to those of the base material; however, their performance is poor and their lifespan is short under creep conditions close to service temperatures.

[0003] Currently, the main method for improving the mechanical properties of liquid phase diffusion welded joints is post-weld heat treatment. This process can achieve homogenization of the joint composition and microstructure, and eliminate harmful phases in the affected zone. This method is simple and effective, but it has certain limitations. Because the intermediate layer used in liquid phase diffusion welding has a certain compositional difference from the base material and often does not contain carbon, even with appropriate heat treatment processes, it is impossible to precipitate sufficient carbides at the grain boundaries of the joint. This results in a relatively high tendency for cracking at the joint, often exhibiting characteristics of brittle intergranular fracture.

[0004] Therefore, this invention is proposed. Summary of the Invention

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

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

[0007] S1: Grind the surfaces of the two Ni3Al-based alloy blocks to be welded and then carburize them;

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

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

[0010] In an optional embodiment, in S1,

[0011] The Ni3Al-based alloy ingot was cut into two cubes using an electrical discharge machine. The surfaces to be welded were then ground to 400-2000 grit and placed in a vacuum carburizing system for surface carburizing.

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

[0013] In an optional embodiment,

[0014] The carbon mass fraction on the carburized surface is 0.3-0.5%, the carburizing temperature is 800-950℃, 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 optional embodiment,

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

[0017] In an optional embodiment, in S2,

[0018] After grinding to remove carbon black and oxide deposits from the carburized surface, liquid phase diffusion welding is performed in a vacuum diffusion bonding system.

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

[0020] In an optional embodiment, the welding temperature is 1100℃ and the holding time is 2 hours.

[0021] In an optional embodiment, in S3,

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

[0023] The temperature range of T3 is 750℃≤T3≤850℃, and the slow cooling rate is no more than 5℃ / min.

[0024] In an optional embodiment,

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

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

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

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

[0029] (1) The enhanced liquid-phase diffusion welding method of the present invention increases the carbon content of the surface to be welded by pre-welding carburizing, providing a compositional basis for subsequent control of the grain boundary carbide precipitation behavior of the joint. During the liquid-phase diffusion welding process, an intermediate layer with a composition similar to that of the base material is selected, and appropriate heat preservation temperature and heat preservation time are used to ensure that the joint achieves complete isothermal solidification.

[0030] (2) In the post-weld heat treatment process of this invention, the weld-affected zone is removed and the composition and microstructure of the joint are homogenized by holding at a first specified temperature T1. After holding, the temperature is cooled to a second specified temperature T2 at a cooling rate of not less than 5℃ / min to increase the nucleation rate of the intragranular γ′-Ni3Al phase and suppress its coarsening, generating cubic or near-cubic precipitates with uniform size; then, the temperature is cooled to a third specified temperature T3 at a cooling rate of not more than 5℃ / min to promote the growth of M-type precipitates at the joint and the base material grain boundaries. 23 The precipitation and growth of C6-type carbides generate granular / rod-shaped / strip-shaped reinforcing phases uniformly distributed along grain boundaries; a two-step cooling solution heat treatment after welding can achieve more diverse grain boundary precipitation effects. This method can improve the intragranular and grain boundary precipitation strengthening effect of the joint, thereby improving the mechanical properties of the welded sample. It is simple to operate, low in energy consumption, and low in cost, and has good application prospects. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the process flow for the enhanced liquid phase diffusion welding joint method provided in an embodiment of the present invention.

[0033] Figure 2 Microstructure diagrams of the pre-weld carburizing treatment and liquid phase diffusion welding provided in embodiments of the present invention ( Figure 2 a represents the macroscopic morphology of the joint area; Figure 2 b represents the isothermal solidification region γ+γ′ biphase structure; Figure 2 c represents the precipitated phase at the interface between the joint and the base material; Figure 2d represents the diffusion influence zone; Figure 2 e represents dendritic structure near the joint region; Figure 2 f represents the γ+γ′ biphasic tissue located far from the junction region.

[0034] Figure 3 Microstructure diagrams of the product after pre-weld carburizing, liquid phase diffusion welding, and post-weld two-stage cooling solution heat treatment provided in embodiments of the present invention. Figure 3 a represents the macroscopic morphology of the joint area. Figure 3 b represents the isothermal solidification region γ+γ′ two-phase structure. Figure 3 c represents the precipitate at the grain boundary of the joint. Figure 3 d represents the interdendritic structure of the parent material region. Figure 3 e represents the γ+γ′ two-phase structure of the parent material region. Figure 3 f represents the grain boundary structure of the parent material region.

[0035] Figure 4 The microstructure diagram of the comparative joint provided by the present invention.

[0036] Figure 5 The creep curves and creep rate curves in the embodiments and comparative examples of the present invention are shown in the figure. Figure 5 a represents the creep curve; Figure 5 b is the creep rate curve. Detailed Implementation

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

[0038] It should be noted that when a component is referred to as being "fixed to" or "attached" to another component, it can be located directly or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly or indirectly connected to that other component. The terms "upper," "lower," "left," "right," "front," "rear," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate orientations or positions based on the accompanying drawings, and are for ease of description only, and should not be construed as limiting the technical solution. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. "Multiple" means two or more, and "several" means any number including one, unless otherwise explicitly specified.

[0039] Please see the appendix Figure 1-5 The purpose of this embodiment is to provide a method for strengthening liquid phase diffusion welded joints, including:

[0040] S1: The surfaces to be welded on two Ni3Al-based alloy blocks are ground and then carburized. Optionally, the Ni3Al-based alloy ingot is cut into two cubes using an EDM machine, and the surfaces to be welded are ground to 400-2000 grit before being placed in a vacuum carburizing system for surface carburizing. 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℃, the pre-carburizing holding time is 0.5-1 hour, the total carburizing time is 1.5-2.5 hours, and each cycle of strong carburizing lasts 30-60 seconds, with a diffusion time of 60-120 seconds. By controlling the carburizing parameters, surfaces to be welded with different carburizing effects can be obtained.

[0041] S2: Remove the deposits on the carburized surface and use BNi-2 as an intermediate layer for liquid phase diffusion welding; alternatively, after grinding to remove the carbon black and oxide deposits on the carburized surface, perform liquid phase diffusion welding in a vacuum diffusion bonding system. The welding temperature is 1080–1150℃, and the holding time is 1.5–3 hours.

[0042] S3: After welding, the sample is held at a first specified temperature T1 and then rapidly cooled to a second specified temperature T2, followed by slow cooling to a third specified temperature T3. The temperature range of T1 is 1150℃ ≤ T1 < 1300℃, and the holding time at T1 is no less than 4 hours. The temperature range of T2 is 950℃ ≤ T2 ≤ 1050℃, and the rapid cooling rate is no less than 5℃ / min. The temperature range of T3 is 750℃ ≤ T3 ≤ 850℃, and the slow cooling rate is no greater than 5℃ / min. By controlling the node temperature and cooling rate in both stages, Ni3Al-based alloy joints with various intragranular / grain boundary precipitation effects can be obtained. The intragranular precipitates are cubic or near-cubic, uniform in size, and evenly distributed within the grains; the joint grain boundary precipitates are short rod-shaped or long strip-shaped and evenly 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 an electrical discharge machine to cut the Ni3Al-based alloy ingot into two 20×20×40mm pieces. 3 The cube, the surface to be welded (20×20mm) 2Grind to 2000 grit; place the treated sample in a vacuum carburizing system for surface carburizing; use acetylene as the carburizing medium, the carbon mass fraction of the carburized surface is 0.4%, the carburizing temperature is 950℃, and the pre-carburizing holding time is 30 minutes; use pulse carburizing method, the total carburizing time is 2 hours, the strong carburizing time of each cycle is 60 seconds, and the diffusion time is 120 seconds; after carburizing, use 2000 grit sandpaper to polish away the carbon black and a small amount of oxides adhering to the carburized surface;

[0045] S2: Place the sample in a vacuum diffusion bonding system for TLP bonding; use BNi-2 as the intermediate layer, the welding temperature is 1100℃, and the holding time is 2 hours;

[0046] S3: The welded sample was placed in a muffle furnace and heated to T1 (1200℃) and held for 4 hours. Then, the sample was cooled to T2 (1000℃) at a rate of 20℃ / min to increase the nucleation rate of the γ′ phase and inhibit its coarsening. Finally, it was cooled to T3 (800℃) at a rate of 0.25℃ / min to promote the formation of the M phase. 23 C6 precipitation and growth.

[0047] In the comparative example,

[0048] S1: Use an electrical discharge machine to cut the Ni3Al-based alloy ingot into two 20×20×40mm pieces. 3 The cube, the surface to be welded (20×20mm) 2 Grind to 2000 grit, then place the sample in a vacuum diffusion bonding system for TLP bonding. BNi-2 was selected as the intermediate layer, the welding temperature was 1100℃, and the holding time was 2 hours.

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

[0050] After controlling the precipitation behavior of the liquid phase diffusion welded joint of Ni3Al-based alloy, the microstructure of the treated Ni3Al alloy was observed using a scanning electron microscope JSM-7800F.

[0051] In a preferred embodiment, such as Figure 3 As shown, a near-cubic γ′-Ni3Al phase precipitated within the crystal. Strip-shaped M phases precipitated at the grain boundaries. 23 C6 type carbides. In the comparative examples, such as... Figure 4 As shown, a near-cubic γ′-Ni3Al phase precipitated within the grains, while small-sized granular carbides precipitated at the grain boundaries. Comparison of the preferred embodiment and the comparative example reveals that the enhanced liquid phase diffusion weld joint, combining pre-weld carburizing with post-weld heat treatment, can promote the precipitation of grain boundary carbides while maintaining the near-cubic γ′-Ni3Al phase within the joint grains.

[0052] Creep performance test:

[0053] In accordance with the requirements of GB / T 2039-2012 "Metallic Materials - Uniaxial Tensile Creep Test Method", the samples from the preferred embodiment and the comparative example were prepared into circular cross-section specimens, and creep tests were conducted using a CRIMS RDL50 high-temperature creep testing machine. The test temperature was 800℃, and the stress was 160MPa.

[0054] The test results are as follows:

[0055] like Figure 5 As shown in Figure a, the creep life of the sample in the preferred case was 808 hours, which was 120% higher than that of the sample in the comparative example. Creep rate curve ( Figure 5 (b) indicates that the sample in the preferred embodiment exhibits a typical "three-stage" characteristic: a first stage of rapid decrease in creep rate (work hardening, massive dislocation proliferation), a second stage of relatively stable creep rate (dynamic equilibrium between work hardening and dynamic softening), and a third stage of rapid increase in creep rate (crack propagation). This is similar to the creep behavior of Ni3Al-based superalloy base materials. The sample in the comparative example, however, only exhibits the first two creep stages, lacking the third stage of reactive crack propagation. The fracture of the sample in the comparative example occurred at the joint, demonstrating poor resistance to crack propagation and macroscopic fracture occurring within a very short time. Furthermore, the sample in the preferred embodiment exhibits a lower steady-state creep rate, indicating a higher resistance to creep deformation.

[0056] It should be noted that the enhanced liquid phase diffusion welding joint method of this invention can obtain weld surfaces with different carburizing effects by controlling the carburizing parameters; and by adjusting the node temperature and cooling rate in two stages, Ni3Al-based alloy joints with various intragranular / grain boundary precipitation effects can be obtained. Compared with the traditional liquid phase diffusion welding process, pre-weld carburizing provides a compositional basis for subsequent control of joint grain boundary carbide precipitation behavior; the two-step cooling solution heat treatment after welding can achieve more diverse grain boundary precipitation effects. This method can improve the intragranular and grain boundary precipitation strengthening effect of the joint, thereby improving the mechanical properties of the welded sample. It is also simple to operate, low in energy consumption, and low in cost, showing good application prospects.

[0057] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for strengthening liquid phase diffusion welded joints, characterized in that, include: S1: Grind the surfaces of the two Ni3Al-based alloy blocks to be welded and then carburize them; In S1, the Ni3Al-based alloy ingot is cut into two cubes using an electrical discharge machine. The surface to be welded is then ground to 400-2000 mesh and placed in a vacuum carburizing system for surface carburizing. The carburizing method is pulse carburizing, the carburizing medium is acetylene; the carbon mass fraction of the carburized surface is 0.3~0.5%, the carburizing temperature is 800~950℃, the pre-carburizing holding time is 0.5~1 hour, the total carburizing time is 1.5~2.5 hours, the strong carburizing time of each cycle is 30~60 seconds, and the diffusion time is 60~120 seconds. S2: Remove the deposits on the carburized surface and use BNi-2 as an intermediate layer for liquid phase diffusion welding; S3: After welding, the sample is kept at the first specified temperature T1 and then rapidly cooled to the second specified temperature T2, and then slowly cooled to the third specified temperature T3. In S3, the temperature range of T1 is 1150°C≤T1<1300°C, and 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; the temperature range of T3 is 750°C≤T3≤850°C, and the slow cooling rate is not greater than 5°C / min.

2. The method for strengthening liquid phase diffusion welded joints as described in claim 1, characterized in that, The carbon mass fraction of the carburized surface is 0.4%, the carburizing temperature is 950℃, the pre-carburizing holding time is 30 minutes, the total carburizing time is 2 hours, and the strong carburizing time and diffusion time for each cycle are 60 seconds and 120 seconds respectively.

3. The method for strengthening liquid phase diffusion welded joints as described in claim 1, characterized in that, In S2, After grinding to remove carbon black and oxide deposits from the carburized surface, liquid phase diffusion welding is performed in a vacuum diffusion bonding system.

4. The method for strengthening liquid phase diffusion welded joints as described in claim 3, characterized in that, The welding temperature is 1080~1150℃, and the holding time is 1.5~3 hours.

5. The method for strengthening liquid phase diffusion welded joints as described in claim 4, characterized in that, The welding temperature is 1100℃, and the holding time is 2 hours.

6. The method for strengthening liquid phase diffusion welded joints as described in claim 1, characterized in that, The temperature of T1 is 1200°C, and 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.

7. A welding system, characterized in that, include: The method for strengthening liquid phase diffusion welded joints as described in any one of claims 1-6.

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