Laser cladding assisted instantaneous liquid phase diffusion bonding method for nickel-based alloy and austenitic steel

Abstract

The invention discloses a laser cladding assisted instantaneous liquid phase diffusion bonding method for nickel-based alloy and austenitic steel, and belongs to the technical field of metal material welding. The method comprises the following steps: (1) preparing a nickel-based alloy cladding layer on a to-be-connected surface of base metal austenitic steel by adopting a laser cladding technology; (2) carrying out mechanical grinding and cleaning treatment on the nickel-based alloy block and the austenitic steel with the cladding layer; (3) the to-be-welded faces of the nickel-based alloy block and the austenitic steel are bonded together through nickel-based welding paste and clamped through a clamp, and a sandwich assembly structure is obtained; and (4) putting the sandwich assembly structure into a vacuum diffusion furnace for instantaneous liquid phase diffusion bonding. According to the method, the nickel-based alloy cladding layer is firstly cladded on the surface of the austenitic steel, so that the component gradient of a middle layer and austenitic steel base metal is relieved, generation of a harmful second phase on an interface is prevented during instantaneous liquid phase connection, and the technical problem that an existing nickel-based alloy and austenitic steel joint is low in strength is solved.

Description

Technical Field

[0001] This invention relates to the field of metal welding technology, specifically to a laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel. Background Technology

[0002] To achieve the "dual-carbon" strategic goals, ensure national energy security, and build a clean, low-carbon, safe, and efficient energy system, advanced nuclear energy—safe, reliable, sustainable, economical, and multi-purpose—has become the trend of future energy development. Currently, pressurized water reactors (PWRs) dominate the global commercial nuclear power plant reactor market, accounting for 65%-70% of all commercial reactors. my country's operating and under-construction nuclear power plants also primarily use PWR reactors, whose main architecture consists of a nuclear reactor, a reactor coolant system (primary loop), a steam power conversion system (secondary loop), and auxiliary systems. In these two loops, the safe and reliable operation of the coolant system is crucial for the stable operation of the nuclear power plant. As the main pressure-bearing equipment of the reactor coolant system, the loop piping must withstand extreme operating conditions during service, including the combined effects of high temperature, high pressure, high radiation environments, complex corrosive media, and alternating loads. These stringent service conditions place extremely high demands on piping materials: they must not only possess excellent corrosion resistance, high-temperature mechanical properties, and radiation resistance, but also good formability and weldability. In order to optimize cost-effectiveness while ensuring safety, engineering practice usually selects different materials according to the actual working conditions of different parts of the pipeline, which inevitably involves dissimilar metal welding technology.

[0003] Bimetallic joints made of IN718 nickel-based alloy and 316LN austenitic steel are currently widely used in circuit piping due to their excellent mechanical properties, oxidation resistance, and corrosion resistance at both room and high temperatures. However, during welding, the alloying elements in IN718 nickel-based alloy segregate, reducing the weldability of the precipitation-strengthened alloy and affecting the mechanical properties of the welded structure. On the other hand, although austenitic stainless steel exhibits better weldability than other types of stainless steel, its high coefficient of thermal expansion and low thermal conductivity can lead to deformation and residual stress in the welded joints. Among various welding methods, transient liquid phase diffusion bonding (TLP) has the advantages of low connection pressure, low residual stress, and minimal deformation, and has been widely used in the welding of high-temperature alloys, ceramics, and heat-resistant steels. However, during dissimilar metal TLP bonding, the diffusion of melting point degrading elements in the interlayer into the base metal and the dissolution of high-melting-point elements in the base metal into the liquid phase can cause elements such as boron (B) and silicon (Si) to combine with base metal elements to form harmful phases. The presence of these phases can severely impair the mechanical properties of the joint. Therefore, exploring new methods to improve interfacial bonding has become a key research focus in addressing the technical bottlenecks faced by TLP (Transient Liquid Phase Diffusion) bonding of dissimilar metals. Among numerous surface modification technologies, laser cladding has become one of the most widely used surface modification methods due to its advantages such as rapid cooling, significant microstructure refinement, narrow heat-affected zone, and good metallurgical bonding with the matrix. Therefore, combining laser cladding with transient liquid phase diffusion bonding provides an innovative technical solution for improving the performance of dissimilar metal joints. Summary of the Invention

[0004] The purpose of this invention is to provide a laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel. This method utilizes a paste-like intermediate layer of specific composition and designs a composite process of laser cladding and instantaneous liquid phase diffusion bonding to bond dissimilar metals, thereby obtaining a reliable joint between IN718 nickel-based alloy and 316LN steel with uniform structure and good mechanical properties.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A laser cladding-assisted transient liquid phase diffusion bonding method for joining nickel-based alloys and austenitic steel is disclosed. This method employs a combined laser cladding and transient liquid phase diffusion bonding process to join the nickel-based alloys and austenitic steel, specifically including the following steps:

[0007] (1) A nickel-based alloy cladding layer with a thickness of 730 μm was prepared on the surface of the austenitic steel base material to be joined by laser cladding technology.

[0008] (2) Mechanical grinding and cleaning were performed on the base material nickel-based alloy block and the austenitic steel with cladding layer.

[0009] (3) Joint assembly: The nickel-based alloy block and the austenitic steel surfaces to be welded after step (2) are bonded together with nickel-based solder paste and clamped with a fixture to obtain a "sandwich" assembly structure.

[0010] (4) Diffusion bonding: The “sandwich” assembly structure (including the fixture) obtained in step (3) is placed in a vacuum diffusion furnace for instantaneous liquid phase diffusion bonding.

[0011] Furthermore, the austenitic steel is 316LN steel, and the nickel-based alloy is IN718 superalloy.

[0012] Further, in step (1), the austenitic steel surface is pretreated before the cladding layer is prepared. The pretreatment is to first polish it with 80#, 240#, 320# and 400# sandpaper in sequence, and then use anhydrous ethanol as a medium for ultrasonic cleaning for 10 to 30 minutes to remove oil stains and then blow it dry for later use.

[0013] Further, in step (1), the cladding powder used in the laser cladding process is 150-mesh IN718 powder, and the laser cladding process parameters are: laser power of 1450-1520W, powder feeding amount of 3.0-4.5g / min, spot diameter of 2.5-3.5mm, scanning speed of 12-18mm / s, overlap rate of 25-35%, and the laser cladding process is carried out in a nitrogen atmosphere.

[0014] Further, in step (2), the mechanical grinding process of the austenitic steel and nickel-based alloy surfaces to be joined with the cladding layer is as follows: grinding is performed sequentially with 80#, 240#, 320#, and 400# sandpaper; the cleaning process is as follows: first ultrasonic cleaning with acetone for 15-25 minutes, then ultrasonic cleaning with anhydrous ethanol for 3-6 minutes; the specific method of acid washing is as follows: the sample surface is first cleaned with acid washing solution I for 2-5 minutes, then cleaned with acid washing solution II for 1-2 minutes. The composition of acid washing solution I is: HNO3 is 18-23 vol.%, HF is 6-8 vol.%, and water is the balance. Acid washing solution II is a mixture of CuCl2, HCl and C2H5OH in a weight ratio of 1:(15-25):(15-25).

[0015] Further, in step (3), the nickel-based solder paste is BNi-2 nickel-based solder paste (its chemical composition is: Cr 7.16wt.%, Fe 3.22wt.%, Si 4.96wt.%, B 3.00wt.%, with the remainder being Ni). The amount of the nickel-based solder paste used on the surfaces to be joined is (1.0-1.5)×10. -3 g / mm 2 (Calculated based on single-sided area).

[0016] Furthermore, in step (3), the pressure applied when the clamp is clamped is 0.8-1.5 MPa.

[0017] Further, in step (4) of the diffusion bonding process, the temperature is first raised to 550-650℃ and held for 25-35 minutes to allow the binder in the solder paste to completely evaporate; then the temperature is raised to 1050-1150℃ and held for 10-80 minutes; finally, the temperature is cooled to room temperature with the furnace (or cooled to room temperature of 20-25℃ at a cooling rate of 5-30℃ / min) to complete the entire welding process and realize the connection between the nickel-based alloy and the austenitic steel.

[0018] Furthermore, in step (4) of the diffusion bonding process, the heating rate is 3-8℃ / min; the entire diffusion bonding process is carried out under vacuum conditions, with a welding vacuum degree of (3~5)×10 -3 Pa.

[0019] Furthermore, the joint obtained by this method has no obvious microcracks at the interface, and its tensile strength at room temperature is 688.5-748.8 MPa, with an elongation greater than 35%.

[0020] The advantages and beneficial effects of this invention are as follows:

[0021] 1. This invention differs from the traditional instantaneous liquid phase diffusion bonding process. First, a nickel-based alloy cladding layer is clad onto the surface of austenitic steel using laser cladding technology. This cladding layer not only alleviates the compositional gradient between the intermediate layer (solder paste) and the austenitic steel base material, but also hinders the generation of harmful second phases at the interface during instantaneous liquid phase bonding at 1100℃, thus solving the technical problem of low joint strength between existing nickel-based alloys and austenitic steel.

[0022] 2. This invention uses laser cladding-assisted instantaneous liquid phase diffusion connection and heat preservation for 15-60 minutes to obtain a reliable dissimilar joint. The joint interface has no obvious microcracks and has good mechanical properties. The tensile strength at room temperature can reach 688.5-748.8 MPa. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the laser cladding process on the surface of 316LN.

[0024] Figure 2 It is a sandwich assembly structure consisting of base metal IN718, base metal 316LN, and intermediate layer BNi-2 nickel-based solder paste.

[0025] Figure 3 Scanning electron microscope (SEM) image of the instantaneous liquid phase diffusion connection joint of 316LN and IN718 after laser cladding treatment and holding at 1100℃ for 15 min.

[0026] Figure 4Scanning electron microscope (SEM) image of the instantaneous liquid phase diffusion connection joint of 316LN and IN718 after laser cladding treatment and heat treatment at 1100℃ for 60 min.

[0027] Figure 5 Scanning electron microscope (SEM) image of the instantaneous liquid phase diffusion connection joint of 316LN and IN718 after laser cladding treatment and holding at 1100℃ for 5 min.

[0028] Figure 6 Scanning electron microscope (SEM) image of the transient liquid phase diffusion joint of 316LN and IN718 without laser cladding treatment after holding at 1100℃ for 15 min.

[0029] Figure 7 Scanning electron microscope (SEM) image of the transient liquid phase diffusion joint of 316LN and IN718 without laser cladding treatment after holding at 1100℃ for 60 min.

[0030] Figure 8 Energy dispersive spectroscopy (EDS) of the intermediate layer and the second phase at the interface between the intermediate layer and the 316LN of the instantaneous liquid-phase diffusion joint after holding at 1100℃ for 15 min for 316LN and IN718 without laser cladding treatment. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0032] Example 1:

[0033] This embodiment describes a laser cladding-assisted instantaneous liquid phase diffusion bonding method for IN718 nickel-based alloy and 316LN austenitic steel. The specific process is as follows:

[0034] 1. Pre-treatment of 316LN stainless steel before laser cladding: Use a wire EDM machine to cut 20mm×20mm×10mm block samples from the 316LN sample. 2 The surfaces to be joined are sanded sequentially with 80#, 240#, 320#, and 400# sandpaper, then ultrasonically cleaned with anhydrous ethanol for 15 minutes to remove oil stains and then dried for later use.

[0035] 2. For the 316LN surface to be connected (20×20mm) 2 Laser cladding is performed, and the laser cladding process is as follows: Figure 1As shown. The cladding powder used in the laser cladding was 150-mesh IN718 powder. The process parameters were: laser power of 1500W, powder feed rate of 3.742g / min, spot diameter of 3mm, scanning speed of 15mm / s, and overlap rate of 30%. The laser cladding process was carried out in a nitrogen atmosphere. A cladding layer with a thickness of approximately 730μm was prepared on the 316LN surface to be joined by laser cladding.

[0036] 3. Use a wire EDM machine to cut 20mm×20mm×10mm block samples from the large IN718 sample. Before diffusion bonding, pre-treat the IN718 nickel-based alloy and 316LN steel (with cladding layer) samples as follows: Prepare the surfaces of the two samples to be bonded (20×20mm). 2 The sample was mechanically polished sequentially with 80#, 240#, 320#, and 400# sandpaper. Then, it was ultrasonically cleaned with acetone for 20 minutes, followed by ultrasonic cleaning with anhydrous ethanol for 5 minutes. After drying, the sample surface to be joined was acid-washed. The specific acid-washing method was as follows: the sample surface was immersed in acid-washing solution I (20 vol.% HNO3, 5 vol.% HF, and water as the balance) for 3 minutes, and then immersed in acid-washing solution II (a mixture of CuCl2, HCl, and C2H5OH in a weight ratio of 1:20:20) for 1 minute.

[0037] 4. Apply 0.5g of BNi-2 solder paste to the surfaces of the two samples to be welded, bond the two samples together, and clamp them with a fixture. Apply 1MPa pressure to the fixture to obtain a "sandwich" assembly structure, as shown below. Figure 2 As shown.

[0038] 5. Place the "sandwich" assembly structure (with fixtures) in a vacuum diffusion welding furnace and evacuate to a vacuum level of 5×10⁻⁶. -3 Heating begins at Pa. The temperature is first increased from room temperature to 600°C at a rate of 5°C / min and held for 30 minutes to ensure complete evaporation of the binder in the solder paste. Then, the temperature is increased to 1100°C at a rate of 5°C / min and held for 15 minutes. The sample is then cooled to room temperature in the furnace to obtain a well-connected sample with a reliable dissimilar joint.

[0039] Example 2:

[0040] This embodiment describes a laser cladding-assisted instantaneous liquid phase diffusion bonding method for IN718 nickel-based alloy and 316LN austenitic steel. The specific process is as follows:

[0041] 1. Pre-treatment of 316LN stainless steel before laser cladding: Use a wire EDM machine to cut 20mm×20mm×10mm block samples from the 316LN sample. (The 20×20mm block sample...) 2The surfaces to be joined are sanded sequentially with 80#, 240#, 320#, and 400# sandpaper, then ultrasonically cleaned with anhydrous ethanol for 15 minutes to remove oil stains and then dried for later use.

[0042] 2. For the 316LN surface to be connected (20×20mm) 2 Laser cladding was performed using 150-mesh IN718 powder. The process parameters were: laser power of 1500W, powder feed rate of 3.742g / min, spot diameter of 3mm, scanning speed of 15mm / s, and overlap rate of 30%. The laser cladding process was carried out in a nitrogen atmosphere. A cladding layer with a thickness of 730μm was prepared on the 316LN surface to be joined by laser cladding.

[0043] 3. Use a wire EDM machine to cut 20mm×20mm×10mm block samples from the large IN718 sample. Before diffusion bonding, pre-treat the IN718 nickel-based alloy and 316LN steel (with cladding layer) samples as follows: Prepare the two samples with surfaces to be bonded (20×20mm). 2 The sample was mechanically ground sequentially using 80#, 240#, 320#, and 400# sandpaper. Then, it was ultrasonically cleaned with acetone for 20 minutes, followed by ultrasonic cleaning with anhydrous ethanol for 5 minutes. After drying, the sample surface to be joined was acid-washed. The specific acid-washing method was as follows: the sample surface was immersed in acid-washing solution I (20 vol.% HNO3, 5 vol.% HF, and water as the balance) for 3 minutes, followed by immersion in acid-washing solution II (a mixture of CuCl2, HCl, and C2H5OH in a weight ratio of 1:20:20) for 1 minute.

[0044] 4. Apply 0.5g of BNi-2 solder paste to the two surfaces of the samples to be welded, bond the two samples together, and clamp them with a fixture. Apply 1MPa pressure to the fixture to obtain a "sandwich" assembly structure.

[0045] 5. Place the "sandwich" assembly structure (with fixture) in a vacuum diffusion soldering furnace. Evacuate the furnace to a vacuum level of 5 × 10⁻³ Pa, then begin heating. Increase the temperature from room temperature to 600℃ at a rate of 5℃ / min and hold for 30 minutes to ensure complete evaporation of the binder in the solder paste. Then, increase the temperature to 1100℃ at a rate of 5℃ / min and hold for 60 minutes. Finally, cool the furnace to room temperature to obtain the bonded sample.

[0046] Comparative Example 1:

[0047] The only difference between this example and Example 1 is that the heat preservation time is 5 minutes.

[0048] Comparative Example 2:

[0049] The only difference between this example and Example 1 is that the laser cladding process is not performed.

[0050] Comparative Example 3:

[0051] The only difference between this example and Example 2 is that the laser cladding process is not performed.

[0052] The microstructure of the weld samples from the above embodiments and comparative examples was characterized by microscopy. The weld seam of each sample was centered and cut into cuboids of 3mm × 5mm × 10mm. The cross-sections perpendicular to the weld surface were mechanically ground sequentially with 240#, 320#, 500#, 1200#, and 3000# sandpaper, and then polished. The resulting samples were etched with aqua regia for 30 seconds. The microstructure was observed using a scanning electron microscope (SEM, JSM-7800), and the phase composition was analyzed using an energy dispersive spectroscopy (EDS, EDAX) system. Figure 3-4 The SEM images of laser cladding-assisted instantaneous liquid phase bonding joints from Examples 1-2, after holding at 1100℃ for 15 min and 60 min, show that the joints have completed the isothermal solidification process, with a uniform microstructure in the weld area, forming a single γ(Ni) solid solution. The average tensile strength of the joints after holding at 15 min reaches 748.8 MPa, and the average tensile strength of the joints after holding at 60 min reaches 688.5 MPa. Figure 5-7 For comparative test results: Figure 5 Although laser cladding was performed before welding, the microstructure of the joint under short welding holding time was analyzed using scanning images. A non-isothermal solidification zone was found in the weld center, containing a large number of hard and brittle intermetallic compounds (such as CrB, Ni3Si, and Ni-Si-B precipitates), which would compromise the joint's performance. Tensile analysis showed that the average tensile strength of the joint under these conditions was only 320 MPa. Figure 6-7 To avoid laser cladding before welding, SEM images of the transient liquid phase joints were obtained after holding at 1100℃ for 15 and 60 min, respectively. The scanned images revealed large voids at the interface between the intermediate layer (solder paste) and the 316LN steel. These voids were suspected to be caused by the corrosion and sloughing off of the second phase during metallographic preparation. Therefore, an uncorroded joint sample without the cladding layer, held at 1100℃ for 15 min, was observed using SEM, and EDS analysis was performed on this phase. Figure 8EDS spectral analysis showed that boron and nitrogen were relatively enriched in this phase compared to the matrix. Furthermore, the average tensile strength of the joint without the cladding layer after 15 minutes of heat treatment was only 395 MPa, and the average tensile strength of the joint without the cladding layer after 60 minutes of heat treatment was only 373 MPa. Comparative analysis shows that the presence of this phase severely impairs the mechanical properties of the joint. Meanwhile, laser cladding can suppress the formation of this phase, greatly improving the mechanical properties of the joint. The mechanical properties of the joints in the above embodiments and comparative examples are shown in Table 1.

[0053] Table 1 Comparison of tensile properties of instantaneous liquid phase joints before and after laser cladding at room temperature.

[0054]

[0055]

[0056] By appropriately adjusting the process parameters according to the present invention, the connection performance of IN718 nickel-based alloy and 316LN steel can be improved. The present invention has been described above as exemplary. It should be noted that any simple modifications, alterations, or equivalent substitutions that can be made by those skilled in the art without creative effort, without departing from the core of the present invention, fall within the protection scope of the present invention.

Claims

1. A method for laser cladding-assisted instantaneous liquid-phase diffusion bonding of nickel-based alloys and austenitic steel, characterized in that: This method employs a combined process of laser cladding and transient liquid-phase diffusion bonding to join nickel-based alloys with austenitic steel, specifically including the following steps: (1) A nickel-based alloy cladding layer with a thickness of 700-750 μm was prepared on the surface of the austenitic steel base material to be joined by laser cladding technology; (2) Mechanical grinding and cleaning were performed on the base material nickel-based alloy block and the austenitic steel with cladding layer. (3) Joint assembly: The nickel-based alloy block and the austenitic steel surfaces to be welded after step (2) are bonded together with nickel-based solder paste and clamped with a fixture to obtain a "sandwich" assembly structure. (4) Diffusion bonding: The "sandwich" assembly structure obtained in step (3) is placed in a vacuum diffusion furnace for instantaneous liquid phase diffusion bonding.

2. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 1, characterized in that: The austenitic steel is 316LN steel, and the nickel-based alloy is IN718 superalloy.

3. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 1, characterized in that: In step (1), a pretreatment is performed on the surface of austenitic steel before preparing the cladding layer. The pretreatment is to first polish the surface with 80#, 240#, 320# and 400# sandpaper in sequence, and then perform ultrasonic cleaning for 10 to 30 minutes with anhydrous ethanol as the medium to remove oil stains and then blow dry for later use.

4. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 1, characterized in that: In step (1), the cladding powder used in the laser cladding process is 150-mesh IN718 powder. The laser cladding process parameters are: laser power of 1450-1520W, powder feeding amount of 3.0-4.5g / min, spot diameter of 2.5-3.5mm, scanning speed of 12-18mm / s, overlap rate of 25-35%, and the laser cladding process is carried out in a nitrogen atmosphere.

5. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 1, characterized in that: In step (2), the mechanical grinding process of the austenitic steel and nickel-based alloy surfaces to be joined with the cladding layer is as follows: grinding is performed sequentially with 80#, 240#, 320#, and 400# sandpaper; the cleaning process is as follows: first ultrasonic cleaning with acetone for 15-25 minutes, then ultrasonic cleaning with anhydrous ethanol for 3-6 minutes; the specific method of acid washing is as follows: the sample surface is first cleaned with acid washing solution I for 2-5 minutes, then cleaned with acid washing solution II for 1-2 minutes. The composition of acid washing solution I is: HNO3 is 18-23 vol.%, HF is 6-8 vol.%, and water is the balance. Acid washing solution II is a mixture of CuCl2, HCl and C2H5OH in a weight ratio of 1:(15-25):(15-25).

6. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 1, characterized in that: In step (3), the nickel-based solder paste is BNi-2 nickel-based solder paste; the amount of nickel-based solder paste used on the surfaces to be joined is (1.0-1.5)×10. -3 g / mm 2 (Calculated based on single-sided area).

7. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 1, characterized in that: In step (3), the pressure applied when the clamp is clamped is 0.8-1.5 MPa.

8. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 1, characterized in that: In step (4) of diffusion bonding, the temperature is first raised to 550-650℃ and held for 25-35 minutes to allow the binder in the solder paste to completely evaporate; then the temperature is raised to 1050-1150℃ and held for 10-80 minutes; finally, the temperature is cooled to room temperature with the furnace to complete the entire welding process and achieve the bonding between the nickel-based alloy and the austenitic steel.

9. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 8, characterized in that: In step (4), the heating rate during diffusion bonding is 3-8℃ / min; the entire diffusion bonding process is carried out under vacuum conditions, with a welding vacuum degree of (3-5)×10⁻⁶. -3 Pa.

10. The laser cladding-assisted instantaneous liquid phase diffusion bonding method for nickel-based alloys and austenitic steel according to claim 1, characterized in that: The joint obtained by this method has no obvious microcracks at the interface, and its tensile strength at room temperature is 688.5-748.8 MPa, with an elongation of more than 35%.

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