A laser welding method for a lap joint of a niobium alloy and a nickel-based superalloy

Abstract

A laser welding method of Nb alloy and nickel-based superalloy lap joint, in the method, the to-be-welded regions of the Nb alloy, titanium interlayer, rhenium interlayer and nickel-based superalloy are respectively subjected to fine grinding with sandpaper, polishing, distilled water cleaning, acetone immersion ultrasonic cleaning and drying; the Nb alloy, titanium interlayer, rhenium interlayer and nickel-based superalloy are sequentially stacked together in order to form a to-be-welded workpiece; the to-be-welded workpiece is placed in a low vacuum environment protected by inert gas, the stacked to-be-welded workpiece is tightly pressed by a pressing plate, and the vacuum degree of the low vacuum environment is 100 Pa to 500 Pa; laser lap welding of the to-be-welded workpiece is completed, and in the welding process, laser is vertically incident on the surface of the Nb alloy, sequentially passes through the Nb alloy, titanium interlayer, rhenium interlayer and nickel-based superalloy, so that the metals of the titanium interlayer and the rhenium interlayer are mutually fused with the Nb alloy and the nickel-based superalloy on both sides to form a lap joint.

Description

Technical Field

[0001] This invention belongs to the field of dissimilar metal laser welding technology, and in particular, a laser welding method for lap joints of niobium alloy and nickel-based high-temperature alloy. Background Technology

[0002] Alkali metal cooling stack power heat exchangers need to have good resistance to alkali metal corrosion. At the same time, the high heat dissipation requirements of radiant heat sinks result in high workpiece temperatures, which in turn requires a corresponding increase in the operating temperature of the heat source. This necessitates that the materials have good high-temperature creep strength and good formability.

[0003] Niobium alloys possess good room-temperature plasticity, excellent machinability, good thermal conductivity, resistance to alkali metal corrosion, and high high-temperature strength, making them suitable for alkali metal-side components of heat exchangers in lithium-cooled nuclear reactors. Nickel-based superalloys exhibit good room-temperature strength and plasticity, high creep strength, and good oxidation resistance, impact resistance, and weldability, making them suitable for manufacturing gas-cooled side components of heat exchangers in nuclear reactor generators. In other words, it is necessary to use both niobium alloys and nickel-based alloys in a complex, sealed structure. Therefore, there is an urgent need to achieve a reliable connection between niobium alloys and nickel-based superalloys.

[0004] Welding niobium alloys with nickel-based superalloys presents several challenges. First, the formation of brittle intermetallic compounds easily leads to immediate post-weld cracking. The Nb-Ni system contains three low-melting-point compounds: Ni8Nb, Ni3Nb, and Ni6Nb7. Ni3Nb, also known as the initial δ phase, is a hard and brittle phase with an incoherent interface to the matrix. During plastic deformation under stress, the unreinforcing phase precipitation zone becomes a strain concentration area, making the interface between the δ phase and the matrix prone to cracking due to strain differences. Second, the probability of porosity defects is high during the welding of refractory metals, and the gaps between the laminated materials further increase this probability. Furthermore, the joining of dissimilar materials presents significant stress-deformation problems.

[0005] Currently, brazing can be used to join niobium alloys and nickel-based superalloys, producing joints with good wettability, dense structure, and no defects. However, the brazing filler metal has a low melting point and poor high-temperature performance, making it difficult to meet the high-temperature service requirements of niobium alloys and nickel-based superalloys. Diffusion welding and explosive welding are excellent methods for joining dissimilar metal materials, and can produce defect-free niobium alloy and nickel-based superalloy joints. However, explosive welding is difficult to use for joining niobium alloys and nickel-based superalloys of different sizes and complex curved shapes, while diffusion welding has high requirements for assembly clearance and the pressure applied during welding, making it difficult to join large-size and large-format niobium alloys and nickel-based superalloys.

[0006] Therefore, this invention designs a double-intermediate-layer metallurgical transition scheme based on "metallurgical compatibility," employing low-vacuum welding to suppress porosity defects, and using a low-heat-input laser welding method and a low-expansion-coefficient intermediate layer to control deformation. The technology described in this invention has the advantages of fewer brittle phases, fewer defects, smaller deformation, and excellent high-temperature joint performance. Furthermore, it requires lower assembly clearances and offers higher welding efficiency.

[0007] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention proposes a laser welding method for lap joints of niobium alloy and nickel-based superalloys, aiming to solve the cracking problem caused by brittle intermetallic compounds during the welding of dissimilar metal materials such as niobium-based alloys and nickel-based superalloys. This method can achieve effective connection of niobium alloy and nickel-based superalloys, successfully solving the cracking problem after laser welding of dissimilar joints of niobium alloy and nickel-based superalloys, and improving the mechanical properties of the niobium alloy and nickel-based superalloy joints.

[0009] The objective of this invention is achieved through the following technical solution: a laser welding method for lap joints of niobium alloy and nickel-based superalloy includes the following steps.

[0010] Step 1: The areas to be welded, including the niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based high-temperature alloy, are respectively subjected to fine sanding, polishing, distilled water cleaning, acetone immersion ultrasonic cleaning, and drying.

[0011] Step 2: Stack the niobium alloy, titanium intermediate layer, rhenium intermediate layer and nickel-based high-temperature alloy in sequence to form the workpiece to be welded. Place the workpiece to be welded in a low vacuum environment protected by inert gas. Use a pressure plate to press the stacked workpieces to be welded together. The vacuum degree of the low vacuum environment is 100Pa to 500Pa.

[0012] Step 3: Complete the laser lap welding of the workpiece to be welded. During the welding process, the laser is incident perpendicularly on the surface of the niobium alloy and passes through the niobium alloy, titanium intermediate layer, rhenium intermediate layer and nickel-based high temperature alloy in sequence, so that the metal of the titanium intermediate layer and rhenium intermediate layer fuses with the niobium alloy and nickel-based high temperature alloy on both sides to form a lap joint.

[0013] In the method described, in step 1, the niobium alloy includes Nb521 and Nb1Zr, and the nickel-based high-temperature alloy includes GH3128 and K447A.

[0014] In the method described, the niobium alloy has a thickness of 2mm to 4mm, the nickel-based high-temperature alloy has a thickness of 2mm to 4mm, the titanium interlayer has a thickness of 0.5mm to 1mm and a width of 5mm to 10mm, and the rhenium interlayer has a thickness of 0.3mm to 1mm and a width of 5mm to 10mm.

[0015] In the method described, the overlap gap between each pair of niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy ranges from 0 mm to 0.2 mm.

[0016] In the method described above, in step 2, during the clamping process, a shim is placed on each of the non-overlapping areas on both sides of the niobium alloy and the nickel-based superalloy to ensure that the workpiece is clamped tightly.

[0017] In the method described, in step 3, the laser welding power is 3500W to 4500W, the welding speed is 35mm / s to 45mm / s, the laser defocusing amount is -2mm to +2mm, the laser spot diameter is 0.2mm, and the laser incident direction is perpendicular to the material surface.

[0018] In the method described, the niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy exhibit a narrow-wide-narrow-wide variable diameter riveted weld from top to bottom.

[0019] In the method described, in step 3, the Nb-Ti system has no intermetallic compounds, the solid solubility of Re in titanium in the Ti-Re system reaches 40 wt.%, and the Re-Ni system has no intermetallic compounds, meaning that there is good metallurgical compatibility between any two adjacent metal layers.

[0020] In the method described, in step 3, the sum of the thicknesses of the niobium alloy and the titanium interlayer does not exceed the thickness of the nickel-based superalloy, and the Re melting width is not greater than 40% of the average weld width.

[0021] In the method described, in step 3, the Ni content in the upper niobium alloy molten pool is less than 20%, and the Nb content in the lower nickel-based superalloy molten pool is less than 20%.

[0022] Compared with existing technologies, this invention has the following advantages: The laser welding method for lap joints of niobium alloy and nickel-based superalloy uses Ti and Re as intermediate layer elements. Ti and Nb are infinitely miscible without intermetallic compounds, as are Ni and Re. Re has a high solid solubility in Ti, reaching 40 wt.%, and due to its high melting point, its melting amount in the lap joint is low, thus reducing the likelihood of brittle intermetallic compounds forming at the joint. This avoids the formation of brittle intermetallic compounds of Nb and Ni, suppressing weld cracking.

[0023] The intermediate layer element Re used in this invention has a high melting point, while Ti has a low melting point. Therefore, in the laser-cut four-way lap joint, the narrow Re element molten pool acts as a barrier, hindering the miscibility of Nb and Ni elements in the upper and lower molten pools. Simultaneously, Re and Ti elements in the molten pool exert a solid solution strengthening effect on the weld metal, increasing the microhardness of the weld zone. Furthermore, since the coefficient of thermal expansion of Re is lower than that of Nb and Ni, it is beneficial for reducing deformation and improving the mechanical properties of the joint.

[0024] Experiments showed that the strength and toughness of the laser lap joint of niobium alloy and nickel-based superalloy were significantly improved after adopting the present invention. The room temperature tensile shear strength at the narrowest point of the weld joint reached 391 MPa. The tensile shear fracture location was located at the niobium-zirconium side weld. The microstructure of the tensile fracture surface of the weld was mainly characterized by cleavage fracture. Attached Figure Description

[0025] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0026] In the attached diagram:

[0027] Figure 1 The diagrams show the Nb-Ti binary phase diagram, the Ti-Re binary phase diagram, and the Re-Ni binary phase diagram.

[0028] Figure 2 A schematic diagram of laser lap welding of niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy;

[0029] Figure 3 This is a diagram showing the element distribution of the cross-section of the lap joint;

[0030] Figures 4(a) and 4(b) are schematic diagrams of the tensile shear specimens of the lap joint and stress-displacement curves of the tensile shear test.

[0031] Figure 5 The cross-sectional morphology of the joint after fracture in the tensile-shear test;

[0032] Figure 6 Longitudinal micro Vickers hardness curve of the weld zone of the lap joint;

[0033] Figure 7 The micro Vickers hardness of the niobium alloy side, titanium intermediate layer, and rhenium intermediate layer of the lap joint;

[0034] Figure 8 The cross-sectional morphology of the joint after it has undergone one thermal cycle at 850℃ following a tensile-shear fracture.

[0035] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0036] Specific embodiments of the invention will now be described in more detail with reference to the accompanying drawings. While specific embodiments of the invention are shown in the drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0037] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0038] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0039] For better understanding, in one embodiment, such as Figures 1 to 8 As shown, the laser welding method for lap joints of niobium alloy and nickel-based superalloy includes the following steps:

[0040] Step 1: The areas to be welded, including the niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based high-temperature alloy, are respectively subjected to fine sanding, polishing, distilled water cleaning, acetone immersion ultrasonic cleaning, and drying.

[0041] Step 2: Stack the niobium alloy, titanium intermediate layer, rhenium intermediate layer and nickel-based high-temperature alloy in sequence to form the workpiece to be welded. Place the workpiece to be welded in a low vacuum environment protected by inert gas. Use a pressure plate to press the stacked workpieces to be welded together. The vacuum degree of the low vacuum environment is 100Pa to 500Pa.

[0042] Step 3: Complete the laser lap welding of the workpiece to be welded. During the welding process, the laser is incident perpendicularly on the surface of the niobium alloy and passes through the niobium alloy, titanium intermediate layer, rhenium intermediate layer and nickel-based high temperature alloy in sequence, so that the metal of the titanium intermediate layer and rhenium intermediate layer fuses with the niobium alloy and nickel-based high temperature alloy on both sides to form a lap joint.

[0043] The laser welding method for lap joints of niobium alloy and nickel-based superalloy of the present invention can form a very narrow melting zone in the Re layer, which significantly reduces the exchange and mixing of metals between the upper and lower molten pools. This not only solves the problem of cracking after laser welding of niobium alloy and nickel-based superalloy joints, but also achieves good shear strength.

[0044] In a preferred embodiment of the method, in step 1, the niobium alloy includes Nb521 and Nb1Zr, and the nickel-based superalloy includes GH3128 and K447A.

[0045] In a preferred embodiment of the method, the niobium alloy has a thickness of 2mm to 4mm, the nickel-based superalloy has a thickness of 2mm to 4mm, the titanium interlayer has a thickness of 0.5mm to 1mm and a width of 5mm to 10mm, and the rhenium interlayer has a thickness of 0.3mm to 1mm and a width of 5mm to 10mm. When the thicknesses of the titanium and rhenium interlayers are below the above ranges, the isolation effect of the interlayers deteriorates. When the thicknesses of the titanium and rhenium interlayers are above the above ranges, the stress mismatch caused by the difference in the coefficients of thermal expansion during thermal cycling is aggravated, leading to a deterioration in the service performance of the joint.

[0046] In a preferred embodiment of the method, the overlap gap between each pair of niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy ranges from 0 mm to 0.2 mm.

[0047] In a preferred embodiment of the method, in step 2, a shim is placed on each of the non-overlapping areas on both sides of the niobium alloy and the nickel-based superalloy during the clamping process to make the workpiece clamped tightly.

[0048] In a preferred embodiment of the method, in step 3, the laser welding power is 3500W to 4500W, the welding speed is 35mm / s to 45mm / s, the laser defocusing amount is -2mm to +2mm, the laser spot diameter is 0.2mm, and the laser incident direction is perpendicular to the material surface.

[0049] In a preferred embodiment of the method, the niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy exhibit a narrow-wide-narrow-wide variable diameter riveted weld from top to bottom.

[0050] In a preferred embodiment of the method, in step 3, the Nb-Ti system contains no intermetallic compounds, the solid solubility of Re in titanium in the Ti-Re system reaches 40 wt.%, and the Re-Ni system contains no intermetallic compounds.

[0051] In a preferred embodiment of the method, in step 3, the sum of the thicknesses of the niobium alloy and the titanium interlayer does not exceed the thickness of the nickel-based superalloy, and the Re melting width is not greater than 40% of the average weld width, meaning that any two adjacent metal layers have good metallurgical compatibility.

[0052] In a preferred embodiment of the method, in step 3, the Ni content in the upper niobium alloy molten pool is less than 20%, and the Nb content in the lower nickel-based superalloy molten pool is less than 20%.

[0053] In one embodiment, a laser welding method for a lap joint of niobium alloy and nickel-based superalloy includes:

[0054] Step 1: The areas to be welded, including the niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based high-temperature alloy, are respectively subjected to fine sanding, polishing, distilled water cleaning, acetone immersion ultrasonic cleaning, and drying.

[0055] Step 2: Stack the niobium alloy, titanium intermediate layer, rhenium intermediate layer, and nickel-based high-temperature alloy together in sequence. Place the workpiece to be welded in a low-vacuum environment protected by inert gas and use a pressure plate to press the four layers of materials together.

[0056] Step 3: Complete the laser lap welding of the workpiece to be welded. During the welding process, the laser is incident vertically and passes through the niobium alloy, titanium intermediate layer, rhenium intermediate layer and nickel-based high temperature alloy in sequence, so that the two intermediate layer metals are fused with the base materials on both sides to form a lap joint.

[0057] In step 1, the niobium alloy includes Nb521 and Nb1Zr, and the nickel-based high-temperature alloy includes GH3128 and K447A.

[0058] In step 1, the thickness of the niobium alloy is 2mm to 4mm, and the thickness of the nickel-based high-temperature alloy is 2mm to 4mm.

[0059] In step 1, the thickness of the titanium interlayer is 0.5mm to 1mm and the width is 5mm to 10mm, and the thickness of the rhenium interlayer is 0.3mm to 1mm and the width is 5mm to 10mm.

[0060] In step 1, the purity of the titanium interlayer is ≥99.99%, and the purity of the rhenium interlayer is ≥99.99%.

[0061] In step 1, a relatively large overlap gap is allowed between each layer to prevent incomplete welding due to excessive gaps. After fine grinding and polishing with sandpaper, the overlap gap between each pair of the four layers—niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy—ranges from 0mm to 0.2mm.

[0062] In step 2, preferably, during the stacking of the four layers of materials—niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy—the overlap area between the niobium alloy and the nickel-based superalloy is 1mm to 3mm wide during single-pass welding. Multiple welds can be performed in parallel to obtain a wider overlap area.

[0063] In step 2, during the clamping process, a shim is placed on each of the non-overlapping areas on both sides of the niobium alloy and the nickel-based superalloy to ensure that the workpiece is clamped tightly.

[0064] In step 2, preferably, the inert gas is argon with a purity of ≥99.99%. Argon gas is repeatedly purged and vacuumed before laser welding to ensure a low-vacuum inert gas environment.

[0065] In step 3, the laser welding power is 3500W to 4500W, the welding speed is 35mm / s to 45mm / s, the laser defocusing amount is -2mm to +2mm, the laser spot diameter is 0.2mm, and the laser incident direction is perpendicular to the material surface.

[0066] In step 3, due to the large differences in physical properties such as melting point and thermal conductivity of each material, the melting width of each layer of material varies greatly, resulting in a narrow-wide-narrow-wide "variable diameter riveting" weld from top to bottom.

[0067] In step 3, a transition layer design based on metallurgical compatibility was adopted. Specifically, the Nb-Ti system has no intermetallic compounds, the solid solubility of Re in titanium in the Ti-Re system reaches 40 wt.%, and the Re-Ni system has no intermetallic compounds. That is, there is good metallurgical compatibility between any two adjacent metal layers.

[0068] In step 3, the Re melting width is ≤ 40% of the average weld width, which effectively suppresses the element exchange between the upper and lower Re molten pools. The Marangoni convection in the upper and lower parts of the molten pool is relatively independent, which effectively avoids the formation of Nb-Ni intermetallic compounds.

[0069] In step 3, the various elements in the upper weld of the rhenium intermediate layer are uniformly mixed, and the various elements in the lower weld of the rhenium intermediate layer are uniformly mixed. The weld also contains Re elements, which can improve high-temperature strength and high-temperature creep performance. Furthermore, the higher concentration of Re elements in the upper weld can compensate for the decrease in creep performance caused by Ti elements, while the nickel-based superalloy in the lower weld itself possesses good high-temperature creep performance.

[0070] In step 3, Re has high high-temperature strength and a lower coefficient of thermal expansion than niobium alloys and nickel-based high-temperature alloys, resulting in a small expansion and contraction of the rhenium interlayer during thermal cycling.

[0071] In step 3, the Ni content in the upper niobium alloy molten pool is less than 20%, and the Nb content in the lower nickel-based superalloy molten pool is less than 20%.

[0072] Figure 2 The diagram illustrates the welding process of laser-laid joints with niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy. Figure 3 The morphology of the cross-section of the lap joint after welding is shown. It can be seen that the Re melting width is ≤ 40% of the average weld width, effectively suppressing the element exchange between the upper and lower Re molten pools. The various elements in the upper weld of the rhenium interlayer are uniformly mixed, and the various elements in the lower weld of the rhenium interlayer are also uniformly mixed, with Re elements mixed in to improve high-temperature strength and high-temperature creep performance. The Ni content in the upper niobium alloy molten pool is 9 wt.%, and the Nb content in the lower nickel-based superalloy molten pool is less than 10 wt.%. Figures 4(a) and 4(b) show the tensile-shear test results of the laser-laid joints of niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based superalloy. The shear strength at the narrowest point of the lap joint reached 391 MPa. Figure 5 The fracture location of the tensile-shear test is shown. It can be seen that the joint cracks at the fusion line of the weld zone on the niobium side. The hardness of the weld centers in the niobium alloy area, the titanium interlayer, and the rhenium interlayer is higher than that of the base material. Figure 8 It can be seen that after the tensile shear fracture, the specimen underwent one thermal cycle at 850℃ and no new cracks appeared.

[0073] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A laser welding method of a Nb alloy to a nickel-based superalloy lap joint, characterized by, It includes the following steps, Step 1: The areas to be welded, including the niobium alloy, titanium interlayer, rhenium interlayer, and nickel-based high-temperature alloy, are respectively subjected to fine sanding, polishing, distilled water cleaning, acetone immersion ultrasonic cleaning, and drying. Step 2: Stack the niobium alloy, titanium intermediate layer, rhenium intermediate layer and nickel-based high-temperature alloy in sequence to form the workpiece to be welded. Place the workpiece to be welded in a low vacuum environment protected by inert gas. Use a pressure plate to press the stacked workpieces to be welded together. The vacuum degree of the low vacuum environment is 100Pa ~ 500Pa. Step 3: Complete the laser lap welding of the workpiece to be welded. During the welding process, the laser is incident perpendicularly on the surface of the niobium alloy and passes through the niobium alloy, titanium intermediate layer, rhenium intermediate layer and nickel-based high temperature alloy in sequence, so that the metal of the titanium intermediate layer and rhenium intermediate layer fuses with the niobium alloy and nickel-based high temperature alloy on both sides to form a lap joint.

2. The method of claim 1, wherein, In step 1, the niobium alloy includes Nb521 and Nb1Zr, and the nickel-based superalloy includes GH3128 and K447A.

3. The method of claim 1, wherein, In step 2, during the clamping process, a shim is placed on each of the non-overlapping areas on both sides of the niobium alloy and the nickel-based superalloy to ensure that the workpiece is clamped tightly.

4. The method of claim 1, wherein, In step 3, the Nb-Ti system contains no intermetallic compounds, the solid solubility of Re in titanium in the Ti-Re system reaches 40 wt.%, and the Re-Ni system contains no intermetallic compounds.

5. The method of claim 1, wherein, In step 3, the sum of the thicknesses of the niobium alloy and the titanium interlayer does not exceed the thickness of the nickel-based superalloy, and the Re melting width is not greater than 40% of the average weld width.

6. The method of claim 1, wherein, In step 3, the Ni content in the upper niobium alloy molten pool is less than 20%, and the Nb content in the lower nickel-based superalloy molten pool is less than 20%.

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