A laser welding method for niobium-tungsten alloy and nickel-based superalloy dissimilar joint

Abstract

The application provides a laser welding method for a Nb-W alloy and a nickel-based high-temperature alloy heterogeneous joint, and belongs to the technical field of laser welding of heterogeneous metals. The Nb-W alloy, a Cu intermediate layer and the nickel-based high-temperature alloy are sequentially butted and fixed, the upper end of the Cu intermediate layer is higher than the two side base metals, and the lower end of the Cu intermediate layer is lower than the two side base metals; the center of the Cu intermediate layer is taken as a 0mm position, a laser beam is offset by 0.2-0.3mm to the Nb-W alloy side for incidence, laser welding is carried out under the protection of inert gas, and the heat input of a laser heat source is controlled in the laser welding process so that the Cu intermediate layer is completely melted, and part of the two side base metal is melted. The laser welding method can not only solve the problem of cracking immediately after laser welding of the Nb-W alloy and the nickel-based high-temperature alloy heterogeneous joint, but also can obtain good joint tensile strength.

Description

Technical Field

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

[0002] Niobium-tungsten alloys possess good room-temperature plasticity, deep-machining properties, and weldability, as well as high high-temperature strength. The Nb521 niobium-tungsten alloy (Nb-5W-2Mo-1Zr) developed in my country is widely used in the manufacture of the thrust chamber body of dual-element liquid rocket engines. With the increasing demands of model development, the application of Nb521 niobium-tungsten alloy in my country's aerospace field is becoming more extensive, not only in dual-element liquid rocket engines but also in certain high-temperature components of other high-speed aircraft.

[0003] Nickel-based superalloys are currently widely used in the aerospace field. They are nickel-based alloys that are strengthened by solid solution of tungsten and molybdenum and reinforced by boron, cerium and zirconium at the grain boundaries. They have high plasticity, high creep strength, good oxidation resistance and stamping and welding properties, making them suitable for manufacturing combustion chamber flame tubes, afterburner shells, regulating vanes and other high-temperature components of aero engines that operate at 950°C for extended periods.

[0004] As the operating temperatures of high-temperature structural materials in aerospace increase, the use of niobium-tungsten alloys is also rising, leading to a growing demand for heterogeneous joining with other high-temperature metals. Joining tungsten-niobium alloys with nickel-based superalloys has significant practical implications; it can effectively reduce the cost and weight of parts, and also improve their operating temperature and service life.

[0005] Achieving high-performance heterojunctions between niobium-tungsten alloys and nickel-based superalloys can expand the design space for service structures. Laser welding, with its high energy density, low heat input, and lack of vacuum chamber requirement, is the preferred fusion welding method for heterojunctions. However, direct laser welding of niobium-tungsten / nickel-based superalloy joints can easily lead to the formation of brittle phases in the weld zone, resulting in immediate post-weld cracking.

[0006] Zhang et al. from Harbin Institute of Technology used electron beam welding of Nb-GH3128 and found that cracking was the main problem in Nb-GH3128 electron beam welded joints. A brittle reaction layer composed of Ni6Nb7 / LaCues phase near the fusion line on the Nb side was the key factor initiating cracking along the reaction layer. By using beam deflection to weld to the GH3128 side, a crack-free joint was obtained. The joint had a maximum room temperature tensile strength of about 163 MPa, which is about 65% of that of the Nb base material. The fracture surface was a clear brittle fracture (Zhang G, Chen G, Cao H, et al. Electron beam offset welding to ameliorate metallic compatibility and mechanical performance of refractory metal / Ni-base superalloy dissimilaralloys: Nb / GH3128[J]. Materials Science and Engineering: A, 2022, 840: 142966.). Although this welding method yields crack-free welded joints, the resulting joints have low tensile strength, only 163 MPa, which is insufficient to meet industrial requirements. Summary of the Invention

[0007] The purpose of this invention is to provide a laser welding method for dissimilar joints of niobium-tungsten alloy and nickel-based superalloy, which can not only solve the problem of immediate cracking after laser welding of dissimilar joints of niobium-tungsten alloy and nickel-based superalloy, but also obtain good tensile strength of the joint.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] This invention provides a laser welding method for a dissimilar joint between a niobium-tungsten alloy and a nickel-based superalloy, comprising the following steps:

[0010] The niobium-tungsten alloy, Cu intermediate layer and nickel-based high-temperature alloy are sequentially joined and fixed so that the upper end of the Cu intermediate layer is higher than the two base materials on both sides and the lower end is lower than the two base materials on both sides.

[0011] With the center of the Cu intermediate layer as the 0mm position, the laser beam is incident on the niobium-tungsten alloy side offset by 0.2-0.3mm, and laser welding is performed under inert gas protection; during the laser welding process, the heat input of the laser heat source is controlled so that the Cu intermediate layer is completely melted, and the base metal on both sides is partially melted.

[0012] Preferably, the upper end of the Cu intermediate layer is 0.5 to 0.75 mm higher than the upper surface of the two parent materials, and the lower end is 0.25 to 0.5 mm lower than the lower surface of the two parent materials.

[0013] Preferably, the thickness of the Cu intermediate layer is 0.5 mm.

[0014] Preferably, the defocusing amount of the laser welding is -2 to 0 mm.

[0015] Preferably, the power of the laser welding is 3500-4500W and the welding speed is 35-45mm / s.

[0016] Preferably, the niobium-tungsten alloy comprises Nb521 alloy.

[0017] Preferably, the nickel-based superalloy includes GH3128 alloy.

[0018] Preferably, an inert gas is continuously introduced to purge the air from the welding device before laser welding; and an inert gas is continued to be introduced after laser welding.

[0019] Preferably, the flow rate of the inert gas before, during, and after laser welding is 15–20 L / min.

[0020] Preferably, the inert gas includes argon.

[0021] This invention provides a laser welding method for a dissimilar joint of niobium-tungsten alloy and nickel-based superalloy, comprising the following steps: sequentially butt-jointing and fixing the niobium-tungsten alloy, a Cu intermediate layer, and the nickel-based superalloy, such that the upper end of the Cu intermediate layer is higher than the base materials on both sides and the lower end is lower than the base materials on both sides; with the center of the Cu intermediate layer as the 0mm position, the laser beam is incident on the niobium-tungsten alloy side offset by 0.2-0.3mm, and laser welding is performed under inert gas protection. During the laser welding process, the heat input of the laser heat source is controlled so that the Cu intermediate layer is completely melted, and the base metals on both sides are partially melted.

[0022] This invention utilizes a Cu interlayer between dissimilar base metals on both sides for laser welding. Since Cu and Nb, as well as Cu and Ni, are infinitely miscible, this interlayer dilutes the molten pool and prevents direct contact between Nb and Ni, thus avoiding the formation of intermetallic compounds. Furthermore, Cu has a higher density than the base metals on both sides, and during melting, it tends to flow downwards due to gravity, making it more prone to undercut. ，This invention controls the upper end of the Cu intermediate layer to be higher than the base materials on both sides, and the lower end to be lower than the base materials on both sides. This ensures that the molten base materials on both sides do not directly contact and react to form intermetallic compounds, and avoids undercut defects in the weld, thus forming a crack-free and well-formed weld. Furthermore, Cu is a highly reflective material, and niobium-tungsten alloy is a refractory metal with a melting point much higher than Cu and nickel-based superalloys. By controlling the laser beam to be offset towards the niobium-tungsten alloy side by 0.2-0.3 mm, this invention ensures that the entire Cu intermediate layer melts, the metal on both sides melts, and the molten base materials on both sides enter the Cu weld, playing a role in solid solution strengthening, thereby improving the joint strength.

[0023] The results of the embodiments show that the present invention achieves solid-state bonding of dissimilar joints between niobium-tungsten alloy and nickel-based superalloy, and can obtain welds with good appearance and consistency, eliminate welding cracks, and significantly improve mechanical properties. For welding of Nb521 alloy and GH3128 alloy, the tensile strength of the joint can reach 370-389 MPa. Attached Figure Description

[0024] Figure 1 This is a schematic diagram showing that the height of the Cu intermediate layer is 0.5 mm higher than the base materials on both sides after the butt joint in Example 1.

[0025] Figure 2 This is a macroscopic morphology diagram of the weld in Example 1;

[0026] Figure 3 This is a cross-sectional topography of the weld in Example 1;

[0027] Figure 4 The image shows the macroscopic morphology of Comparative Example 1, which cracked directly after welding without the addition of a Cu intermediate layer.

[0028] Figure 5 The curve showing the relationship between tensile strength and tensile displacement of the joint in Example 1 is shown.

[0029] Figure 6 This is a schematic diagram showing that the height of the Cu intermediate layer is flush with the parent materials on both sides after the butt joint in Comparative Example 2.

[0030] Figure 7 This is a macroscopic morphology diagram of the weld in Comparative Example 2. Detailed Implementation

[0031] This invention provides a laser welding method for a dissimilar joint between a niobium-tungsten alloy and a nickel-based superalloy, comprising the following steps:

[0032] The niobium-tungsten alloy, Cu intermediate layer and nickel-based high-temperature alloy are sequentially joined and fixed so that the upper end of the Cu intermediate layer is higher than the two base materials on both sides and the lower end is lower than the two base materials on both sides.

[0033] With the center of the Cu intermediate layer as the 0mm position, the laser beam is incident on the niobium-tungsten alloy side offset by 0.2-0.3mm, and laser welding is performed under inert gas protection; during the laser welding process, the heat input of the laser heat source is controlled so that the Cu intermediate layer is completely melted, and the base metal on both sides is partially melted.

[0034] In this invention, a niobium-tungsten alloy, a Cu intermediate layer, and a nickel-based high-temperature alloy are sequentially joined and fixed, such that the upper end of the Cu intermediate layer is higher than the two base materials on both sides, and the lower end is lower than the two base materials on both sides.

[0035] This invention does not have any special requirements on the type of niobium-tungsten alloy; any niobium-tungsten alloy well known in the art is acceptable, such as Nb521 alloy. This invention also does not have any special requirements on the type of nickel-based high-temperature alloy; any nickel-based high-temperature alloy well known in the art is acceptable, such as GH3128 alloy.

[0036] In this invention, the thickness of the Cu intermediate layer is preferably 0.5 mm. By controlling the thickness of the Cu intermediate layer to 0.5 mm, this invention facilitates achieving better laser welding results.

[0037] In this invention, since the Cu interlayer is very thin, in the form of a Cu foil, the dimensions of the Cu interlayer after joining are expressed as thickness × width × height, corresponding to the dimensions of the two base materials as length × width × thickness. Preferably, the width of the Cu interlayer is the same as the width of the two base materials, meaning the front and rear ends of the Cu interlayer are flush with the front and rear surfaces of the two base materials, respectively.

[0038] In this invention, the upper end of the Cu intermediate layer is preferably 0.5–0.75 mm higher than the upper surfaces of the two base materials, more preferably 0.6–0.7 mm; the lower end of the Cu intermediate layer is preferably 0.25–0.5 mm lower than the lower surfaces of the two base materials, more preferably 0.3–0.4 mm. Compared to the two base materials, Cu has a higher density and tends to flow downwards during melting due to gravity, easily causing undercut. This invention, by controlling the upper end of the Cu intermediate layer to be higher than the two base materials and the lower end to be lower than the two base materials, ensures that the molten base materials on both sides do not directly contact and react to form intermetallic compounds, and avoids undercut defects in the weld, thereby forming a crack-free, well-formed weld.

[0039] Before docking, the present invention preferably pre-treats the niobium-tungsten alloy, the Cu intermediate layer, and the nickel-based high-temperature alloy respectively. The pre-treatment preferably includes: sanding, alkaline washing, rinsing with distilled water, ultrasonic cleaning with acetone immersion, and drying. The present invention does not have special requirements for the conditions of each step of the pre-treatment; conditions well known in the art can be used.

[0040] After the docking is completed, the present invention fixes the two base materials and the Cu intermediate layer on the welding fixture to ensure that the two base materials and the intermediate layer are tightly bonded without gaps.

[0041] After being fixed, the present invention uses the center of the Cu intermediate layer as the 0mm position and deflects the laser beam 0.2-0.3mm toward the niobium-tungsten alloy side for laser welding under inert gas protection. During the laser welding process, the heat input of the laser heat source is controlled to melt the entire Cu intermediate layer and partially melt the base metal on both sides.

[0042] In this invention, the laser beam is preferably incident on the niobium-tungsten alloy side by a 0.25 mm offset. Cu is a highly reflective material, and niobium-tungsten alloy is a refractory metal with a melting point much higher than that of Cu and nickel-based superalloys. This invention, through laser beam offset and energy input control, ensures the laser beam strikes the interface between the Cu intermediate layer and the niobium-tungsten alloy. This causes the high-melting-point niobium-tungsten alloy base material to partially melt through the keyhole effect or thermal conduction, while the low-melting-point Ni base material partially melts through thermal conduction. The molten base material from both sides enters the Cu weld, providing solid solution strengthening and thus improving the joint strength.

[0043] The present invention does not impose a special limit on the heat input of the laser welding. It can be adjusted according to the actual situation to achieve complete melting of the Cu intermediate layer and partial melting of the base metal on both sides.

[0044] In this invention, the defocusing amount of the laser welding is preferably -2 to 0 mm, more preferably -1 to 0 mm; the power of the laser welding is preferably 3500 to 4500 W, more preferably 3700 to 4200 W; and the welding speed is preferably 35 to 45 mm / s, more preferably 38 to 42 mm / s.

[0045] In this invention, the laser welding is preferably performed in a semi-enclosed inert gas protection device.

[0046] Preferably, in this invention, an inert gas is continuously introduced to purge air from the welding apparatus before laser welding, with the introduction time preferably being 45–60 seconds; preferably, an inert gas is continued to be introduced after laser welding, with the introduction time preferably being 15–30 seconds. In this invention, the inert gas preferably includes argon, and the purity of the argon is preferably ≥99.999%.

[0047] In this invention, the flow rate of the inert gas before, during and after laser welding is preferably 15-20 L / min, more preferably 16-18 L / min.

[0048] This invention employs a semi-closed protective device with an inert gas protective atmosphere to prevent gas from entering the molten pool during welding, which could lead to oxidation of the molten pool metal and the formation of porosity defects.

[0049] In this invention, the aspect ratio of the weld formed by laser welding is not less than 3.

[0050] The following detailed description of the laser welding method for dissimilar joints of niobium-tungsten alloy and nickel-based superalloy provided by the present invention, with reference to the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1

[0052] Laser welding was performed on Nb521 and GH3128 alloys. The Nb521 alloy measures 40mm (length) × 30mm (width) × 3mm (thickness), and the GH3128 alloy also measures 40mm (length) × 30mm (width) × 3mm (thickness). The Nb521 alloy, Cu interlayer, and nickel-based superalloy were pretreated sequentially by sanding, alkaline washing, distilled water rinsing, acetone immersion, ultrasonic cleaning, and drying. Then, the Cu interlayer solder was placed between the Nb521 and GH3128 alloy test plates. Figure 1 As shown, the Cu interlayer is in direct contact with the GH3128 and Nb521 alloys, while ensuring no gaps between the GH3128 / Cu and Cu / Nb521 interfaces. The Cu interlayer thickness is 0.5 mm. The upper part of the Cu interlayer is 0.6 mm higher than the upper surface of the base materials on both sides, the lower part is 0.3 mm lower than the base materials on both sides, and the front and rear parts are flush with the base materials on both sides. During welding, the laser beam is offset by 0.25 mm from the Cu interlayer towards the Nb521 side. Laser welding parameters: 4000W, defocusing amount 0, welding speed 45 mm / s; argon shielding gas flow rate is 20 L / min, with gas supply times of 60 s before welding to purge air from the device, continuous gas supply during welding, and 30 s after welding followed by gas supply before shutting off the gas. The macroscopic morphology of the weld is shown in [reference needed]. Figure 2 Cross-sectional morphology is shown in Figure 3 ,Depend on Figure 2 and Figure 3 It can be seen that the weld is well formed and there are no cracks.

[0053] Comparative Example 1

[0054] No Cu intermediate layer was added; otherwise, it was the same as in Example 1. The macroscopic morphology of the weld is shown below. Figure 4 The results show that without the addition of a Cu intermediate layer, GH3128 cracked directly after being welded to Nb521.

[0055] Mechanical tensile tests were performed on the Nb521 / GH3128 heterojunctions obtained in Example 1 and Comparative Example 1, with the results of Example 1 as follows: Figure 5As shown, the tensile strength of the joint is 373 MPa, the tensile strength of the Nb521 base material is 480 MPa, and the tensile strength of the GH3128 base material is 852 MPa. The joint strength can reach 77.7% of the strength of the Nb521 base material. Compared with the welded joint without the addition of the Cu intermediate layer (direct cracking), the present invention significantly improves the mechanical properties of the Nb521 / GH3128 heterojunction joint.

[0056] Comparative Example 2

[0057] The only difference from Example 1 is that the Cu intermediate layer has the same height as the two base materials, see... Figure 6 The rest is the same as in Example 1. After welding, it was found that the weld cracked after adding a Cu interlayer of the same height as the base material, such as... Figure 7 As shown.

[0058] As can be seen from the above embodiments and comparative examples, the laser welding method provided by the present invention can not only solve the problem of immediate cracking after laser welding of dissimilar joints of niobium-tungsten alloy and nickel-based superalloy, but also obtain good tensile strength of the joint.

[0059] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of laser welding a niobium tungsten alloy to a nickel-based superalloy heterojunction, characterized by, Includes the following steps: The niobium-tungsten alloy, Cu intermediate layer and nickel-based high-temperature alloy are sequentially joined and fixed so that the upper end of the Cu intermediate layer is higher than the two base materials on both sides and the lower end is lower than the two base materials on both sides. With the center of the Cu intermediate layer as the 0mm position, the laser beam is incident on the niobium-tungsten alloy side offset by 0.2~0.3mm, and laser welding is performed under inert gas protection; during the laser welding process, the heat input of the laser heat source is controlled so that the Cu intermediate layer is completely melted, and the base metal on both sides is partially melted; The upper end of the Cu intermediate layer is 0.5~0.75mm higher than the upper surface of the two base materials, and the lower end is 0.25~0.5mm lower than the lower surface of the two base materials. The thickness of the Cu intermediate layer is 0.5 mm.

2. The laser welding method according to claim 1, characterized in that, The defocusing amount of the laser welding is -2 to 0 mm.

3. The laser welding method according to claim 1 or 2, characterized in that, The laser welding power is 3500~4500W, and the welding speed is 35~45mm / s.

4. The laser welding method according to claim 1, characterized by, The niobium-tungsten alloy includes Nb521 alloy.

5. The laser welding method according to claim 1 or 4, characterized in that, The nickel-based superalloy includes GH3128 alloy.

6. The laser welding method according to claim 1, characterized by, Before laser welding, inert gas is continuously introduced to purge the air from the welding device; after laser welding, inert gas is continuously introduced.

7. The laser welding method according to claim 6, characterized in that, The flow rate of the inert gas before, during, and after laser welding is 15-20 L / min.

8. The laser welding method according to any one of claims 1, 6, or 7, characterized in that, The inert gas includes argon.

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