A welding method for nickel-based superalloy double-wire indirect electric arc additive repair

Abstract

The present application belongs to the technical field of metal material welding and additive manufacturing, and discloses a welding method for nickel-based high-temperature alloy double-wire indirect electric arc additive repair, which comprises the following steps: welding and repairing the nickel-based high-temperature alloy by using double-wire indirect electric arc welding, wherein the welding wire used comprises crack suppression type welding wire and grain boundary repair type welding wire, and the welding wire is all flux-cored wire; the flux core of the crack suppression type welding wire comprises the following components in parts by mass: IN738 master alloy powder 90-95 parts, TiB2 powder 2-4 parts, CeO2 powder 1-2 parts, hafnium metal powder 0.5-1.5 parts, and calcium fluoride powder 1-3 parts; the flux core of the grain boundary repair type welding wire comprises the following components in parts by mass: Ni-Cr-B-Si alloy powder 10-20 parts, IN738 master alloy powder 75-85 parts, manganese metal powder 2-3 parts, magnesium metal powder 0.2-0.8 parts, and silicon dioxide powder 1-3 parts; during the welding and repairing, the switching frequency of the positive and negative electrodes of the welding power source between the two welding wires is 50-100 Hz. The present application is suitable for low-crack and high-efficiency additive repair welding of heat-sensitive nickel-based high-temperature alloys such as IN738.

Description

Technical Field

[0001] This invention belongs to the field of metal material welding and additive manufacturing technology, and relates to a welding method for double-wire indirect arc additive repair of nickel-based superalloys, which is suitable for low-crack, high-efficiency additive repair welding of heat-sensitive nickel-based superalloys such as IN738. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] IN738 nickel-based superalloys are widely used in critical hot-end components operating in extreme environments, such as turbine blades for aero-engines and guide vanes for gas turbines, due to their excellent high-temperature strength, creep resistance, and oxidation resistance. These high-value components inevitably suffer wear, ablation, and other damage during long-term service. Repairing them using welding additive manufacturing technology is a key approach to extending their service life and reducing operating costs.

[0004] However, IN738 alloy contains a high content of strengthening elements such as Al and Ti, has a wide solidification temperature range, and is extremely heat sensitive. In conventional welding processes (such as TIG and MIG welding), more than half of the heat is applied to the base material, and the heat input is generally high, which will exacerbate the tendency of IN738 alloy to liquefy and solidification crack.

[0005] Twin-wire indirect arc welding ignites an arc between two welding wires, using most of the arc heat to melt the welding wires. A small amount of arc heat and molten droplet heat is used to heat the base metal to form a molten pool, significantly reducing heat input to the base metal and thus largely suppressing liquefaction cracking in the heat-affected zone. However, the droplet transfer patterns of the two rows of welding wires in this welding method are inconsistent (often manifesting as one row of large droplets and one row of small droplets), and these droplets diverge outwards under electromagnetic repulsion, causing severe metal spatter, reducing material utilization and the quality of the weld bead formation.

[0006] Moreover, traditional single-component welding wires cannot simultaneously achieve multiple functions such as crack suppression, grain boundary repair, and molten pool purification. If a single flux-cored welding wire is used to combine multiple functional phases, problems such as agglomeration, uneven distribution, or mutual interference of functional components are likely to occur, resulting in unstable and poor crack control effects.

[0007] Furthermore, existing repair mechanisms are mostly "single-condition passive response" types, such as relying solely on stress or temperature to trigger a phase transition or reaction. This type of repair behavior lacks precision and initiative, often leading to the ineffective release and waste of repair materials in non-critical areas, resulting in insufficient reliability and economy of the overall repair process. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the purpose of this invention is to provide a welding method for the dual-wire indirect arc additive repair of nickel-based superalloys. This method enables low-crack, high-efficiency, and high-quality additive repair of heat-sensitive nickel-based superalloys such as IN738.

[0009] To achieve the above objectives, the present invention employs the following technical solution:

[0010] This invention provides a welding method for repairing nickel-based superalloys using a dual-wire indirect arc additive manufacturing process, comprising the following steps:

[0011] Nickel-based superalloys were repaired by twin-wire indirect arc welding. The welding wires used included two types: crack-inhibiting welding wire and grain boundary repair welding wire. Both welding wires were flux-cored welding wires.

[0012] The flux core of the crack-inhibiting welding wire, by weight, includes the following components: 90-95 parts of IN738 master alloy powder, 2-4 parts of TiB2 powder, 1-2 parts of CeO2 powder, 0.5-1.5 parts of metallic hafnium powder, and 1-3 parts of calcium fluoride powder.

[0013] The flux core of the grain boundary repair welding wire comprises, by weight, the following components: 10-20 parts Ni-Cr-B-Si alloy powder, 75-85 parts IN738 master alloy powder, 2-3 parts metallic manganese powder, 0.2-0.8 parts metallic magnesium powder, and 1-3 parts silicon dioxide powder; wherein the Ni-Cr-B-Si alloy powder has Ni as the matrix component and contains 5-20% Cr, 0.8-4% B, and 1.6-5% Si, where % is by weight.

[0014] During welding repair, the switching frequency of the positive and negative poles of the welding power source between the two welding wires is 50-100Hz.

[0015] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows:

[0016] This invention achieves multi-scale active intervention throughout the entire welding process, from crack initiation suppression to microcrack self-repair, through the synergistic function of dual wires. Laboratory verification shows that using the method of this invention to repair IN738 alloy can reduce the crack rate of the weld and heat-affected zone from over 18% in the traditional process to below 3%.

[0017] This invention combines the low heat input characteristics of twin-wire indirect arc welding with the high stability of composite control technology, reducing the heat-affected zone width by more than 30% compared to traditional MIG welding. Simultaneously, due to effective spatter suppression, material utilization is high, and the deposition rate can stably reach over 4.2 kg / h, meeting the needs of industrial-scale batch repair.

[0018] This invention introduces a coaxial swirling shielding gas design. By utilizing the speed and shape differences between the inner and outer airflow layers, a centripetal pressure gradient is formed around the arc zone, applying aerodynamic constraint to the molten droplets about to leave the arc zone. This supplements the physical field control, improving the droplet collection effect and the molten pool protection effect. Through the periodic current switching generated by a high-frequency alternating polarity power supply, the melting speed and droplet size of the two welding wires are actively controlled. Furthermore, an externally applied alternating electromagnetic field of the same frequency is used to change the direction of force on the droplets, fundamentally solving the problems of welding instability, droplet dispersion, and spatter. Through the combined control of the electromagnetic field and the airflow field, the droplet transition is smooth and concentrated, spatter is reduced by more than 70%, and the cladding layer is aesthetically pleasing, dense, and free of obvious defects such as porosity and slag inclusions. The cladding width concentration is increased by 40%.

[0019] The two electrodes of this invention use conventional micron-sized powder, eliminating the need for expensive nanomaterials or complex microcapsule preparation processes. They are compatible with existing flux-cored welding wire production lines, reducing production costs by more than 30%. Functional components are released on demand, achieving an effective utilization rate of over 95%, thus avoiding material waste. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of the welding method according to an embodiment of the present invention;

[0022] Figure 2 This is a schematic diagram of the internal and external airflow field setup in the welding method of this invention embodiment;

[0023] Figure 3 These are cross-sectional views and microstructure diagrams of the additive repair layers obtained in two embodiments of the present invention;

[0024] Figure 4 This is a photograph of the additive repair layer with poor surface forming obtained in Comparative Example 2.

[0025] In the figure, 1-crack suppression welding wire; 2-grain boundary repair welding wire; 3-transverse alternating electromagnetic field; 4-dual-wire indirect arc; 5-positive electrode droplet; 6-negative electrode droplet; 7-Lorentz force; 8-molten pool; 9-workpiece; 10-outer gas inlet; 11-inner gas inlet; 12-inner swirling gas; 13-gas protective curtain. Detailed Implementation

[0026] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] Terminology Explanation:

[0028] IN738 nickel-based superalloy: is a precipitation-hardening nickel-based cast superalloy with excellent high-temperature strength and creep resistance.

[0029] Twin-wire indirect arc welding is a welding method in which the electric arc burns between the ends of two welding wires without directly forming a main circuit with the workpiece (base material). Its characteristic is that the heat is primarily used to melt the welding wires, resulting in lower heat input to the base material.

[0030] Flux-cored arc welding wire (FCAW) is a tubular welding wire made of a metal strip encasing a powdered core.

[0031] Low-carbon ferrochrome is a ferrochrome alloy with a carbon content of 0.15-0.5%, where % is a mass percentage.

[0032] Solidification cracking is a crack formed when the residual low-melting-point liquid film in the dendritic intergranular space of the solid-liquid two-phase region is pulled apart during the solidification process of weld metal.

[0033] Liquation cracking: Under the action of welding thermal cycling, low-melting-point eutectic phases at grain boundaries or between dendrites in the heat-affected zone of the base metal or previous weld are remelted (liquefied) and pulled apart.

[0034] Heat-affected zone (HAZ): The area in which the base metal undergoes changes in its metallographic structure and mechanical properties due to the influence of the welding heat source during the welding process.

[0035] Lorentz force: The force exerted on a moving electric charge in a magnetic field.

[0036] To address the technical problems mentioned in the background section, this invention provides a welding method for double-wire indirect arc additive repair of nickel-based superalloys, comprising the following steps:

[0037] Nickel-based superalloys were repaired by twin-wire indirect arc welding. The welding wires used included crack-inhibiting welding wire and grain boundary repair welding wire, both of which were flux-cored welding wires.

[0038] The flux core of the crack-inhibiting welding wire, by weight, includes the following components: 90-95 parts of IN738 master alloy powder, 2-4 parts of TiB2 powder, 1-2 parts of CeO2 powder, 0.5-1.5 parts of metallic hafnium powder, and 1-3 parts of calcium fluoride powder.

[0039] The flux core of the grain boundary repair welding wire comprises, by weight, the following components: 10-20 parts Ni-Cr-B-Si alloy powder, 75-85 parts IN738 master alloy powder, 2-3 parts metallic manganese powder, 0.2-0.8 parts metallic magnesium powder, and 1-3 parts silicon dioxide powder; wherein the Ni-Cr-B-Si alloy powder has Ni as the matrix component and contains 5-20% Cr, 0.8-4% B, and 1.6-5% Si, where % is by weight.

[0040] During welding repair, the switching frequency of the positive and negative poles of the welding power source between the two welding wires is 50-100Hz.

[0041] Under the influence of welding current, TiB2 and Hf form high-melting-point (Ti,Hf)B2 composite boride dispersed particles in situ within the molten pool. These particles are pinned to the interdendritic gaps during solidification, effectively hindering the extension and separation of the liquid film and inhibiting the initiation of solidification cracks from the source. CeO2, as a surface-active element, accumulates at the solidification front, reducing the solid / liquid interface energy, significantly promoting heterogeneous nucleation, and refining the solidification structure. CaF2, as a slag-forming agent, reduces the viscosity of the molten slag, improves its fluidity, facilitates the escape of gases from the molten pool, and reduces the risk of stress concentration and crack induction caused by porosity.

[0042] During the final stage of solidification of the molten pool, the low-melting-point Ni-Cr-B-Si eutectic liquid phase remains in a flowing state, capable of actively penetrating and backfilling. Microcracks (≤10μm in width) caused by solidification shrinkage stress are self-repaired at the grain boundaries. Boron (B) can also react with carbides in IN738 to form more stable boron carbides, blocking the propagation path of cracks along the carbide chains. Mn and Mg are used to purify the grain boundaries. Mn reacts with harmful impurity sulfur (S) to form high-melting-point MnS particles, eliminating sulfur embrittlement; Mg acts as a strong deoxidizer, inhibiting grain boundary oxidation.

[0043] In dual-wire indirect arc welding, a key challenge is that the melting rate of the negative electrode wire is typically faster than that of the positive electrode wire. Due to the difference in polarity spot pressure and electromagnetic contraction force, a larger droplet forms at the tip of the negative electrode wire, disrupting arc stability and force balance. To address this issue, a high-frequency variable polarity welding power source is employed. By frequently switching and precisely controlling the duty cycle (the time ratio of each wire as the negative and positive electrode), the heat input applied to the two wires is actively and independently adjusted. This effectively compensates for the difference in melting rates between the two electrodes, bringing them closer together and resulting in uniformly sized droplets. Ultimately, under a more symmetrical and stable force field, a smooth droplet transfer is achieved.

[0044] In some embodiments, the Ni-Cr-B-Si alloy powder has a matrix composition of Ni and contains 14-16% Cr, 3.0-4.0% B and 3.5-4.5% Si, where % is a mass percentage.

[0045] The TiB2 powder has a particle size of 5-10 μm.

[0046] In some embodiments, the melting point of the Ni-Cr-B-Si alloy powder is 950-1050℃.

[0047] Preferably, the preparation method of the Ni-Cr-B-Si alloy powder is as follows: after drying nickel, chromium, low-carbon ferrochrome, ferrosilicon and ferroboron alloy, they are mixed according to the stoichiometric ratio and smelted at a temperature of 1300-1450℃ for 20-40 minutes.

[0048] After the molten liquid is formed into a liquid stream, it is pulverized by atomizing gas to obtain atomized metal droplets;

[0049] The atomized molten metal droplets are cooled and solidified to obtain the product.

[0050] During vacuum melting, hold the temperature for 20-40 minutes to ensure the alloy liquid composition is homogenized and fully degassed.

[0051] More preferably, the drying temperature is 100-150℃ and the drying time is 2-4 hours.

[0052] More preferably, the nickel is electrolytic nickel.

[0053] In a further preferred embodiment, during smelting, the furnace is evacuated to below 5 Pa, then filled with argon gas to a positive pressure of 20-50 kPa, and then induction heating is performed.

[0054] More preferably, the pressure of the atomizing gas is 1.5-4.0 MPa. Higher pressure is beneficial for obtaining finer powder.

[0055] More preferably, the flow rate of the liquid is 10-25 kg / min, and the mass ratio of atomizing gas to molten liquid is 1.5-3:1.

[0056] More preferably, the Ni-Cr-B-Si alloy powder has a particle size of 45-150 μm and an oxygen content of less than 500 ppm. The powder has a good spherical shape and good flowability (flow rate measured by a Hall effect flowmeter ≤ 25 s / 50 g) to meet the stable production requirements of subsequent flux-cored welding wire.

[0057] In some embodiments, both the crack-inhibiting welding wire and the grain boundary repair welding wire are Ni-20Cr alloy strips wrapped with core powder, and the mass percentage of the core powder is 25-30%.

[0058] In some embodiments, when the crack-inhibiting welding wire is the positive electrode and the grain boundary repair welding wire is the negative electrode, the welding current is 200-220A to ensure the full melting and reaction of the high-melting-point functional phase (such as TiB2).

[0059] When the crack-inhibiting welding wire is used as the negative electrode and the grain boundary repair welding wire is used as the positive electrode, the welding current is 150-180A, which is used to maintain arc stability and the fluidity of the low-melting-point repair phase (Ni-Cr-B-Si).

[0060] In some embodiments, electromagnets are symmetrically arranged on both sides of the welding torch to generate a transverse alternating electromagnetic field perpendicular to the plane where the two welding wires are located, with a magnetic induction intensity of 0.1-0.3T.

[0061] The alternating frequency of the transverse alternating electromagnetic field is the same as the switching frequency of the welding current, which exerts a force on the generated charged droplets in the direction of the molten pool.

[0062] When the molten droplet detaches from the welding wire, it is not yet fully neutralized. The two welding wires carry net positive or net negative charges respectively, and their current directions are consistent. By allowing the direction of the electromagnetic field to switch synchronously with the direction of the welding current, according to the Lorentz force law (F = qv × B), the charged molten droplet experiences a force pointing towards the center of the molten pool in the transverse magnetic field. Its trajectory is forced to deflect inward, thereby achieving centripetal convergence and effectively suppressing outward scattering.

[0063] Preferably, a coaxial double-layer gas nozzle is provided on the outer periphery of the two welding wires, and a mixed gas of Ar and He is introduced into the outer gas nozzle. The mass percentage of He in the mixed gas is 3-7%, forming a straight laminar gas protective curtain at the end of the welding wire.

[0064] Ar gas is introduced into the inner gas nozzle, forming a rotating airflow at the end of the welding wire and creating a low-pressure zone in the center of the arc zone. The molten droplets move towards the center of the molten pool under the pressure gradient.

[0065] The outer linear laminar gas protective curtain can effectively isolate the surrounding air and prevent the molten pool from oxidizing; the addition of He can improve the arc energy and thermal conductivity.

[0066] The rotating airflow on the inner side creates a low-pressure zone at the center of the arc region, thereby generating a centripetal pressure gradient pointing towards the center. This pressure gradient exerts an aerodynamic drag on the flying molten droplets, pushing them towards the center of the molten pool. As a powerful supplement to electromagnetic control, it further reduces spatter and makes the cladding layer width more concentrated.

[0067] More preferably, the flow rate of the mixed gas introduced into the outer gas nozzle is 12-18 L / min; and the flow rate of Ar gas introduced into the inner gas nozzle is 6-10 L / min.

[0068] In some embodiments, the wire feed rate ratio of crack-inhibiting welding wire to grain boundary repair welding wire is 5-7:3-5.

[0069] In some embodiments, the arc voltage is 25-30V; the interlayer temperature is ≤150℃.

[0070] The present invention will be further described below with reference to the embodiments.

[0071] Example 1

[0072] IN738 alloy was repaired by welding using a dual-wire indirect arc welding method. The welding wires used were all flux-cored wires with a diameter of 1.6 mm. The core powder was composed of Ni-20Cr alloy strip (0.2 mm thick) coated with Ni-20Cr alloy strip. The weight ratio of the core powder in the welding wire was 25%.

[0073] 1. Welding wire formula:

[0074] Crack-inhibiting welding wire: The core powder composition is: IN738 powder 95%, TiB2 powder (particle size 5μm) 2.0%, CeO2 powder 1.0%, Hf powder 0.5%, CaF2 powder 1.5%, where % is by mass percentage;

[0075] Grain boundary repair welding wire: The core powder composition is: 10% Ni-14Cr-3.0B-3.5Si alloy powder, 85% IN738 powder, 2.0% Mn powder, 0.2% Mg powder, and 2.8% SiO2 powder, where % is by mass percentage;

[0076] Ni-14Cr-3.0B-3.5Si alloy powder refers to a powder with a Ni matrix containing 14% Cr, 3.0% B, and 3.5% Si, where % represents mass percentage.

[0077] The Ni-14Cr-3.0B-3.5Si alloy powder was prepared by high-purity inert gas atomization. The specific process steps are as follows:

[0078] (1) Ingredient preparation and pretreatment:

[0079] Based on the target composition (Ni-14Cr-3.0B-3.5Si), accurately weigh electrolytic nickel and metallic chromium with a purity higher than 99.8%, as well as industrially pure low-carbon ferrochrome, ferrosilicon, and ferroboron alloy raw materials. Dry all raw materials in an oven at 100°C for 3 hours to remove surface-adsorbed moisture.

[0080] (2) Vacuum induction melting:

[0081] The pretreated raw materials were placed in an alumina crucible and then placed in a vacuum induction melting furnace. The furnace chamber was evacuated to below 5 Pa, and then filled with 99.99% pure argon gas to a positive pressure of 20 kPa. Induction heating was started, and the furnace charge was heated to 1400℃, which is higher than the alloy liquidus temperature to ensure that all components are completely melted. This temperature was held for 30 minutes while electromagnetic stirring was performed to ensure that the alloy liquid composition was homogenized and fully degassed.

[0082] (3) Inert gas atomization:

[0083] The refined high-temperature alloy molten metal is passed through an intermediate ladle with a guide tube at the bottom to form a stable liquid flow. As the liquid flow falls, it is impacted and broken up by high-pressure inert gas (preferably argon) from an array of annular nozzles.

[0084] The key atomization parameter control ranges are as follows:

[0085] Atomizing gas pressure: 2.0 MPa. Higher pressure is beneficial for obtaining finer powder.

[0086] Flow rate of molten metal: The flow rate is controlled at 15 kg / min by controlling the orifice diameter of the tundish guide nozzle.

[0087] Gas / metal mass ratio (GMR): controlled between 1.5 and 3.0:1.

[0088] (4) Powder collection and processing:

[0089] The atomized metal droplets rapidly cool and solidify into spherical or near-spherical powder during their flight within an argon-filled atomization tower. The powder is collected at the bottom of the tower and in a cyclone separator. To obtain a particle size suitable for flux-cored wire filling, the collected powder needs to be sieved. A multi-stage vibrating screen is used to select powder with a particle size ranging from 45-150 μm (approximately corresponding to -100 mesh to +325 mesh) as the finished product.

[0090] (5) Quality Inspection:

[0091] The finished powder is inspected to ensure that its chemical composition is within the design range, the oxygen content is less than 500 ppm, the powder has a good spherical shape, and good flowability (the flow rate measured by the Hall flowmeter is ≤25s / 50g) to meet the stable production requirements of subsequent flux-cored welding wire.

[0092] 2. Welding process parameters:

[0093] like Figure 1 As shown, a high-frequency alternating polarity welding power source is used to periodically switch between the positive and negative poles of the crack suppression welding wire 1 and the grain boundary repair welding wire 2. The polarity switching frequency is 50Hz.

[0094] Welding current: When the crack-inhibiting welding wire is the positive electrode, the welding current is 200A; when the crack-inhibiting welding wire is the negative electrode, the welding current is 150A; a double-wire indirect arc is formed between the two welding wires 4, the molten droplets generated by the positive electrode are positive electrode molten droplets 5, and the molten droplets generated by the negative electrode are negative electrode molten droplets 6.

[0095] Wire feed speed ratio: The wire feed speed ratio of crack suppression type welding wire 1 to grain boundary repair type welding wire 2 is 7:5;

[0096] Arc voltage: 28V;

[0097] Electromagnets are symmetrically arranged on both sides of the welding torch to generate a transverse alternating electromagnetic field 3 with a direction perpendicular to the plane where the two welding wires are located. The transverse alternating magnetic field strength is 0.1T. The transverse alternating electromagnetic field 3 generates a Lorentz force 7 on the charged molten droplet pointing towards the center of the molten pool 8 of the workpiece 9, causing the molten droplet to move towards the molten pool 8.

[0098] Protective gas: A mixture of Ar and 3% He (3% by volume) is introduced through the outer gas inlet 10, with a flow rate of 12 L / min, and is ejected in a straight laminar flow to form a stable gas protective curtain 13, effectively isolating the surrounding air and preventing oxidation of the molten pool; pure Ar gas is introduced through the inner gas inlet 11, and flows out through a tangential outlet to form an inner swirling gas 12 with a flow rate of 6 L / min. Figure 2 As shown.

[0099] Interlayer temperature: 140℃.

[0100] After repair, non-destructive testing and metallographic analysis were performed on the weld layer. The results showed that the weld layer surface was smooth and free of visible cracks. No macroscopic cracks were found in the metallographic sections; only microcracks less than 2 μm wide were observed in a few areas, which were completely filled and healed by the low-melting-point phase. The heat-affected zone was small in width, with significant grain refinement; spatter was minimal, the welding efficiency was high, and the crack rate was 1.2%.

[0101] Example 2

[0102] IN738 alloy was repaired by welding using a dual-wire indirect arc welding method. The welding wires used were all flux-cored wires with a diameter of 1.6 mm. The core powder was composed of Ni-20Cr alloy strip (thickness 0.2 mm) coated with Ni-20Cr alloy strip. The weight ratio of the core powder in the welding wire was 30%.

[0103] 1. Welding wire formula:

[0104] Crack-inhibiting welding wire: The core powder composition is: IN738 powder 90%, TiB2 powder (particle size 10μm) 4.0%, CeO2 powder 2.0%, Hf powder 1.5%, CaF2 powder 2.5%, where % is by mass percentage;

[0105] Grain boundary repair welding wire: The core powder composition is: 20% Ni-16Cr-4.0B-4.5Si alloy powder, 75% IN738 powder, 3.0% Mn powder, 0.8% Mg powder, and 1.2% SiO2 powder. % is by mass percentage.

[0106] Ni-16Cr-4.0B-4.5Si alloy powder refers to a powder with a Ni matrix containing 16% Cr, 4.0% B, and 4.5% Si, where % represents mass percentage.

[0107] 2. Welding process parameters:

[0108] A high-frequency alternating polarity welding power source is used to periodically switch the two welding wires between the positive and negative poles. The polarity switching frequency is 100Hz.

[0109] Welding current: When the crack-inhibiting welding wire is used as the positive electrode, the welding current is 220A; when the crack-inhibiting welding wire is used as the negative electrode, the welding current is 180A.

[0110] Wire feed speed ratio: The mass ratio of crack suppression welding wire to grain boundary repair welding wire is 5:5;

[0111] Arc voltage: 30V;

[0112] Electromagnets are symmetrically arranged on both sides of the welding torch to generate a transverse alternating electromagnetic field with a direction perpendicular to the plane where the two welding wires are located. The transverse static magnetic field strength is 0.3T.

[0113] Protective gas: The outer layer is a mixture of Ar and 7% He, where 7% is the volume percentage. The flow rate of the mixed gas is 18 L / min, and it is sprayed out in a straight laminar flow to form a stable gas protective curtain, which effectively isolates the surrounding air and prevents the molten pool from oxidizing. The inner layer is a swirling pure Ar gas with a flow rate of 10 L / min.

[0114] Interlayer temperature: 120℃.

[0115] After repair, non-destructive testing and metallographic analysis were performed on the weld layer, such as... Figure 3As shown, the results indicate that the deposited layer is dense and free of cracks. In the metallographic structure, fine (Ti,Hf)B2 particles are dispersed between dendrites, and a thin layer of low-melting-point phase is visible at the grain boundaries, with no signs of microcracks. Due to the high current and wire feed speed, the deposition rate reached 4.5 kg / h. The arc was stable throughout the process, with almost no spatter. The crack rate was 0.5%.

[0116] Comparative Example 1

[0117] Using traditional solid wire MIG welding:

[0118] Repair was performed using 1.2mm diameter ERNiCrCoMo-1 solid welding wire (composition similar to IN738) and a standard MIG welding machine. The welding current was 200A, the arc voltage was 24V, and the shielding gas was pure Ar.

[0119] Results: Due to the huge heat input, numerous macroscopic cracks visible to the naked eye appeared in the repair layer and heat-affected zone, with a crack rate as high as 20%. The weld bead was severely deformed, and the repair failed.

[0120] Comparative Example 2

[0121] The difference from Example 1 is that the electromagnets on both sides of the welding torch are removed, while all other conditions are the same as in Example 1.

[0122] Results: During arc combustion, two distinct rows of molten droplets were observed repelling outwards, producing numerous spherical spatter particles that landed on the nozzle and workpiece. The weld bead surface was uneven, with jagged edges. Although cracking was effectively suppressed (crack rate approximately 2.5%), weld bead formation was poor, and material waste was significant. Figure 4 As shown.

[0123] Comparative Example 3

[0124] The difference from Example 1 is that a conventional DC power supply is used, the crack suppression welding wire is connected to the positive DC terminal, and the grain boundary repair welding wire is connected to the negative DC terminal, without switching the polarity. All other conditions are the same as in Example 1.

[0125] Results: The arc stability was poor, and the melting rates of the two welding wires were uneven. The droplets on the negative electrode side were large, with a low transition frequency; while the positive electrode side showed a fine, spray-like transition. Both droplets tended to diverge outwards. Although the magnetic field had some confinement effect, spatter was still quite severe. The final weld bead formation was inconsistent, and the quality was unstable.

[0126] Comparative Example 4

[0127] The difference from Example 1 is that a traditional single-layer gas nozzle is used to deliver Ar+5%He mixed gas at 20L / min (the total flow rate is similar to that of Example 1), which is a straight laminar flow; all other conditions are the same as those in Example 1.

[0128] Compared to Comparative Examples 2 and 3, the spattering effect was improved, but some small droplets still escaped the confinement range of the electromagnetic field, especially when the arc shape fluctuated slightly. The width of the cladding layer was about 30% wider than that of Invention Example 1, the center height was insufficient, and the concentration of the cladding metal was poor. This indicates that relying solely on the electromagnetic field, there is still room for improvement in the confinement effect.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A welding method for nickel-based superalloy twin-wire indirect arc additive repair, characterized in that: Includes the following steps: Nickel-based superalloys were repaired by twin-wire indirect arc welding. The welding wires used included crack-inhibiting welding wire and grain boundary repair welding wire, both of which were flux-cored welding wires. The flux core of the crack-inhibiting welding wire, by weight, includes the following components: 90-95 parts of IN738 master alloy powder, 2-4 parts of TiB2 powder, 1-2 parts of CeO2 powder, 0.5-1.5 parts of metallic hafnium powder, and 1-3 parts of calcium fluoride powder. The flux core of the grain boundary repair welding wire comprises, by weight, the following components: 10-20 parts Ni-Cr-B-Si alloy powder, 75-85 parts IN738 master alloy powder, 2-3 parts metallic manganese powder, 0.2-0.8 parts metallic magnesium powder, and 1-3 parts silicon dioxide powder; wherein the Ni-Cr-B-Si alloy powder has Ni as the matrix component and contains 5-20% Cr, 0.8-4% B, and 1.6-5% Si, where % is by weight. During welding repair, the switching frequency of the positive and negative poles of the welding power source between the two welding wires is 50-100Hz.

2. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 1, characterized in that: The Ni-Cr-B-Si alloy powder contains Ni as the matrix component and 14-16% Cr, 3.0-4.0% B and 3.5-4.5% Si, where % is by mass percentage.

3. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 2, characterized in that: The preparation method of the Ni-Cr-B-Si alloy powder is as follows: after drying nickel, chromium, low-carbon ferrochrome, ferrosilicon and ferroboron alloy, they are mixed according to the stoichiometric ratio and smelted under an inert atmosphere at a temperature of 1300-1450℃ for 20-40 minutes. After the molten liquid is formed into a liquid stream, it is pulverized by atomizing gas to obtain atomized metal droplets; The atomized molten metal droplets are cooled and solidified to obtain the product.

4. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 3, characterized in that: The pressure of the atomizing gas is 1.5-4.0 MPa; the flow rate of the liquid is 10-25 kg / min; and the mass ratio of the atomizing gas to the molten liquid is 1.5-3:

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5. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 1, characterized in that: Both crack-inhibiting and grain boundary repair welding wires are made of Ni-20Cr alloy strips with core powder encapsulated in 25-30% by mass.

6. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 1, characterized in that: When the crack-inhibiting welding wire is the positive electrode and the grain boundary repair welding wire is the negative electrode, the welding current is 200-220A; When the crack-inhibiting welding wire is the negative electrode and the grain boundary repair welding wire is the positive electrode, a constant DC current of 150-180A is used.

7. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 1, characterized in that: Electromagnets are symmetrically arranged on both sides of the welding torch to generate a transverse alternating electromagnetic field perpendicular to the plane where the two welding wires are located, with a magnetic induction intensity of 0.1-0.3T. The alternating frequency of the transverse alternating electromagnetic field is the same as the switching frequency of the welding current, which exerts a force on the generated charged droplets in the direction of the molten pool.

8. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 7, characterized in that: Coaxial double-layer gas nozzles are set around the outer periphery of the two welding wires. A mixture of Ar and He gas is introduced into the outer gas nozzle. The mass percentage of He in the mixture is 3-7%, forming a straight laminar gas protective curtain at the end of the welding wire. Ar gas is introduced into the inner gas nozzle, forming a rotating airflow at the end of the welding wire and creating a low-pressure zone in the center of the arc zone. The molten droplets move towards the center of the molten pool under the pressure gradient.

9. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 1, characterized in that: The flow rate of the mixed gas introduced into the outer gas nozzle is 12-18 L / min; the flow rate of Ar gas introduced into the inner gas nozzle is 6-10 L / min.

10. The welding method for nickel-based superalloy twin-wire indirect arc additive repair according to claim 1, characterized in that: The wire feed speed ratio of crack suppression welding wire to grain boundary repair welding wire is 5-7:3-5.

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