A method for laser cladding Nb assisted brazing of zirconium alloys and high entropy alloys

Abstract

The present application relates to zirconium alloy and high-entropy alloy welding technical field, especially to a kind of method for laser cladding Nb assisted brazing high-entropy alloy and zirconium alloy, including by laser cladding Nb on high-entropy alloy surface by in-situ reaction preparation NbCoCrFeMnNi eutectic high-entropy alloy transition layer, the surface of cladding layer and zirconium alloy surface are polished and pretreated to obtain the welding base material, after the welding base material and Zr63.2Cu36.8(wt.%) brazing filler foil are cleaned, the brazing filler foil is placed between two welding base materials, forms the welding sample, the welding sample is placed in vacuum brazing furnace, heated to 1010 o The brazing temperature of C, after holding at brazing temperature for 10 min, it is reduced to room temperature, and the brazing joint is obtained, compared with the joint directly brazed by AgCu filler, the joint strength obtained by laser cladding Nb assisted brazing is increased by 382%, and the present application realizes high-quality connection of zirconium alloy and high-entropy alloy dissimilar materials.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of zirconium alloy and high-entropy alloy welding, in particular to a method for laser cladding Nb assisted brazing of high-entropy alloy and zirconium alloy. BACKGROUND

[0002] Zirconium alloy has moderate mechanical properties, small neutron absorption cross section, excellent processing ability, radiation resistance, corrosion resistance, and good compatibility with nuclear fuel, and is widely used as internal core component material of nuclear reactor, such as fuel cladding, spacer grid, etc.

[0003] High-entropy alloy (HEAs) is a chemical disorder solid solution alloy mixed by 5-13 elements, which has excellent mechanical properties at low and high temperatures, good wear resistance and corrosion resistance, making it one of the potential structural materials in aerospace and nuclear industry. In particular, compared with the commonly used end plug materials (stainless steel and nickel-based high-temperature alloy), CoCrFeMnNi HEA with face-centered cubic (FCC) structure has higher structural stability in He ion irradiation environment due to its low mobility and point defects of He atoms.

[0004] In nuclear reactors, end plugs are usually welded to the fuel cladding on both sides. If CoCrFeMnNi high-entropy alloy, which can be used as plug material, is welded to zirconium alloy fuel cladding, it is of great significance to promote the manufacturing and application of high-entropy alloy structural materials in the nuclear field and obtain long-life and high-reliability nuclear reactors. However, due to the five elements in CoCrFeMnNi high-entropy alloy, it is easy to react with active zirconium during welding, forming a large amount of brittle zirconium-based compounds, which affects the performance of the joint. In addition, there is a large difference in thermal expansion coefficient between zirconium alloy (5.3×10 -6 K -1 ) and CoCrFeMnNi high-entropy alloy (15×10 -6 K -1 ), which easily causes large thermal residual stress during cooling and deteriorates the joint performance. SUMMARY

[0005] Therefore, the present application provides a method for laser cladding Nb assisted brazing of high-entropy alloy and zirconium alloy to solve the technical problems of large residual stress and a large number of brittle and hardened compounds distributed in the welding seam in the traditional welding process.

[0006] A method for laser cladding Nb assisted brazing of high-entropy alloy and zirconium alloy, which adopts the following steps:

[0007] Step one, polishing the surface of the high-entropy alloy for pretreatment, and preparing a cladding layer on the surface of the high-entropy alloy by laser cladding Nb powder;

[0008] Step two, the zirconium alloy to be welded surface and high entropy alloy forming cladding layer to be welded surface polishing pretreatment, so as to obtain the welding base material, Zr63.2Cu36.8(wt.%) eutectic alloy foil as the solder;

[0009] Step three, the zirconium alloy, high entropy alloy and solder foil obtained in step three are cleaned with acetone and anhydrous ethanol;

[0010] Step four, the Zr63.2Cu36.8 solder foil is placed between the high entropy alloy and the zirconium alloy to be welded surface to form a welded sample, and the welded sample is placed in a vacuum brazing furnace and heated to a brazing temperature of 1010 DEG C under vacuum, and then cooled to room temperature after being kept at the brazing temperature for 10 min; the high entropy alloy is CoCrFeMnNi high entropy alloy.

[0011] In steps one and two of the application, the surfaces to be welded of the high entropy alloy (before and after cladding) and the zirconium alloy are polished with 180#, 400#, 800#, 1200#, 2000# and 3000# metallographic sandpaper in sequence.

[0012] In step one of the application, the thickness of the cladding layer formed by laser cladding Nb powder on the surface of the high entropy alloy is 150-420 μm.

[0013] In step one of the application, the particle size of the Nb powder is 45-105 μm, and the parameters of laser cladding are power 800-1000 W, scanning speed 1000 mm / min and powder feeding speed 0.2-0.35 r / min.

[0014] In step two of the application, the thickness of the Zr63.2Cu36.8 solder foil is 200 μm.

[0015] In step three of the application, the zirconium alloy, high entropy alloy and Zr63.2Cu36.8 solder foil are first cleaned with acetone for 30 min, and then cleaned with anhydrous ethanol for 15 min, and then blown dry.

[0016] In step four of the application, the vacuum heating includes heating under a vacuum condition of 5x10 -3 Pa or less, heating to the brazing temperature at a rate of 10 DEG C / min, cooling to 200 DEG C at a rate of 5 DEG C / min after the brazing is completed, and finally cooling to room temperature with the furnace.

[0017] Compared with the prior art, the application has the following advantages:

[0018] The present application realizes effective connection between zirconium alloy and CoCrFeMnNi high-entropy alloy with high strength, since CoCrFeNi can have eutectic reaction with Nb (CoCrFeNi+Nb→FCC+(Co,Ni)2Nb), the cladding layer is mainly composed of FCC matrix+(Co,Ni)2Nb Laves eutectic structure and Nb-based solid solution with good plasticity, the eutectic structure can have high strength and plasticity at the same time, the Nb-based solid solution has good plasticity, and can reduce and release the residual stress of the joint during brazing, thereby improving the strength of the joint, and the Zr-Cu filler melts to form a solid-liquid interface, Nb reacts with Cr, Mn and Zr at the interface of the cladding layer and the filler seam to form (Zr,Nb)(Cr,Mn)2, thereby further improving the plasticity of the joint, thereby improving the strength of the joint. Compared with the joint obtained by brazing zirconium alloy and CoCrFeMnNi high-entropy alloy with traditional AgCu filler, the Zr63.2Cu36.8 filler as the intermediate brazing layer can effectively realize the connection between the two, and the cladding layer as a transition layer during brazing can effectively relieve the residual stress of the joint and control the interface reaction, thereby improving the strength of the joint. The brittle compounds in the filler seam are significantly reduced, the interface reaction is effectively controlled, and the joint performance is improved. The present application can be widely applied to the brazing connection of CoCrFeNi-based high-entropy alloy (such as CoCrFeNiCu, CoCrFeNiSn, Al 0.3 CoCrFeNi, etc.) and zirconium alloy. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 Backscattered electron image of the cladding layer obtained in Example 1 of the present application;

[0020] Figure 2 Backscattered electron image and fracture path diagram of the brazed joint obtained in Example 1 of the present application;

[0021] Figure 3 Backscattered electron image and fracture path diagram of the brazed joint obtained in Example 5 of the present application;

[0022] Figure 4 Backscattered electron image and fracture path diagram of the brazed joint obtained in the comparative example of the present application. DETAILED DESCRIPTION

[0023] In order for those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application, and all other embodiments obtained by those skilled in the art without creative labor on the basis of the embodiments in the present application belong to the scope of protection of the present application.

[0024] A method for laser cladding Nb assisted brazing of high-entropy alloy and zirconium alloy, comprising the following steps:

[0025] Step one, the surface to be cladded of CoCrFeMnNi high-entropy alloy is polished with 180#, 400#, 800#, 1200#, 2000# and 3000# metallographic sandpaper in turn to obtain the base material to be cladded, and a cladding layer is prepared on the surface of the high-entropy alloy by laser cladding Nb powder with a particle size of 45-105 μm;

[0026] Step two, the cladding surface of the CoCrFeMnNi high-entropy alloy obtained in step one and the zirconium alloy are polished with 800#, 1200#, 2000# and 3000# metallographic sandpaper in turn to obtain a smooth and flat cladding layer and the zirconium alloy, and Zr63.2Cu36.8(wt.%) eutectic alloy foil is used as the brazing filler metal;

[0027] Step three, the base material to be welded and the brazing filler metal foil obtained in step two are immersed in an acetone solution for ultrasonic cleaning for 30 min and then blown dry, and then placed in an anhydrous ethanol solution for ultrasonic cleaning for 15 min and then blown dry;

[0028] Step four, the Zr63.2Cu36.8(wt.%) brazing filler metal foil is placed between the high-entropy alloy and the zirconium alloy to be welded to form a sample to be welded, and the sample to be welded is placed in a vacuum brazing furnace, and the pressure of the vacuum brazing furnace is reduced to 5x10 -3 Pa, the temperature is raised to 1010℃ at a rate of 10℃ / min, and the temperature is maintained for 10 min, the temperature is reduced to 200℃ at a rate of 5℃ / min, and finally the temperature is cooled to room temperature with the furnace.

[0029] Example 1:

[0030] Step one, the surface to be cladded of CoCrFeMnNi high-entropy alloy is polished with 180#, 400#, 800#, 1200#, 2000# and 3000# metallographic sandpaper in turn to obtain the base material to be cladded, and a cladding layer is prepared on the surface of the high-entropy alloy by laser cladding Nb powder with a particle size of 45-105 μm;

[0031] Step two, the cladding surface of the CoCrFeMnNi high-entropy alloy obtained in step one and the zirconium alloy are polished with 800#, 1200#, 2000# and 3000# metallographic sandpaper in turn to obtain a smooth and flat cladding layer and the zirconium alloy.

[0032] Step three, the base material to be welded and the brazing filler metal foil obtained in step two are immersed in an acetone solution for ultrasonic cleaning for 30 min and then blown dry, and then placed in an anhydrous ethanol solution for ultrasonic cleaning for 15 min and then blown dry.

[0033] Step four, Zr63.2Cu36.8(wt.%) filler metal foil is placed between the high-entropy alloy and the zirconium alloy to be welded, and the welded sample is placed in a vacuum brazing furnace, and the pressure of the vacuum brazing furnace is reduced to 5x10 -3 When the temperature is below 200℃, the temperature is raised to 1010℃ at a rate of 10℃ / min, and the temperature is kept for 10min, and the temperature is reduced to 200℃ at a rate of 5℃ / min, and finally the furnace is cooled to room temperature. At this time, the shear strength of the brazed joint obtained at this time reaches 242.8MPa.

[0034] Example 2:

[0035] The difference between this embodiment and example 1 is that the laser powder feeding speed in step one is 0.2 r / min. The other steps are the same as the specific embodiment. At this time, the thickness of the cladding layer is 150 μm, and the shear strength of the joint reaches 195.2 MPa.

[0036] Example 3:

[0037] The difference between this embodiment and example 1 is that the laser powder feeding speed in step one is 0.25 r / min. The other steps are the same as the specific embodiment. At this time, the thickness of the cladding layer is 280 μm, and the shear strength of the joint reaches 225.8 MPa.

[0038] Example 4:

[0039] The difference between this embodiment and example 1 is that the laser powder feeding speed in step one is 0.35 r / min. The other steps are the same as the specific embodiment. At this time, the thickness of the cladding layer is 410 μm, and the shear strength of the joint reaches 201.8 MPa.

[0040] Example 5:

[0041] The difference between this embodiment and example 1 is that step one does not use laser cladding, but uses Zr63.2Cu36.8(wt.%) filler metal to directly braze HEA and Zr-3 alloy. The other steps are the same as the specific embodiment. At this time, the shear strength of the joint reaches 172.1 MPa.

[0042] Example 6

[0043] The difference between this embodiment and example 1 is that the laser power in step one is 750W, and the other steps are the same as the specific embodiment, at this time the thickness of the cladding layer is 300 μm, and the shear strength of the joint reaches 221.3 MPa.

[0044] Example 7

[0045] The difference between this example and example 1 is that the laser power in step one is 900 W, and other steps are the same as the specific example, at this time the thickness of the cladding layer is 420 pm, and the shear strength of the joint reaches 193.4 MPa.

[0046] In other embodiments, when the laser power is low, such as 700 W, the cladding layer cannot be formed, and when the laser power is high, such as 1000 W, a good cladding layer cannot be formed, and the thickness of the cladding layer is considered to be 0 pm.

[0047] Comparative Example: The backscattered electron image and fracture path of the joint obtained by directly brazing zirconium alloy and CoCrFeMnNi high-entropy alloy with AgCu filler metal in the prior art (890 o C / 10 min), from Figure 4 It can be seen that the microstructure of the joint is mainly composed of brittle reaction layer Zr(Cr,Mn)2 adjacent to the HEA side, brittle Zr2(Co,Cu,Ni,Fe) in the center of the brazing seam, Zr(Ag,Cu) and blocky Zr(Cr,Mn)2, thereby resulting in a shear strength of the joint of only 50.2 MPa. The joint mainly fractures in the brittle Zr(Cr,Mn)2 reaction layer. It is worth noting that due to stress concentration, significant cracks can be observed in the brittle Zr2(Co,Cu,Ni,Fe) phase in the brazing seam, which will affect the strength of the joint.

[0048] Figure 3 The backscattered electron image and fracture path of the joint obtained by directly brazing zirconium alloy and CoCrFeMnNi high-entropy alloy with Zr63.2Cu36.8(wt.%) filler metal (1010 o C / 10 min), the microstructure of the joint is mainly composed of brittle Zr(Cr,Mn2) layer adjacent to the HEA side and blocky Zr(Cr,Mn)2, Zr2(Cu,Ni,Co,Fe) in the brazing seam, the fracture of the joint starts at the HEA / Zr(Cr,Mn2) layer interface, and the crack propagates along the brittle Zr2(Cu,Ni,Co,Fe) in the brazing seam; compared with the microstructure of the joint obtained by directly brazing with AgCu filler metal, due to the rich amount of Zr element in the filler metal, Zrss is precipitated from the Zr(Cr,Mn2) layer during cooling, thereby resulting in a large amount of Zrss distributed in the Zr(Cr,Mn2) layer formed on the HEA side, which can improve the plastic deformation ability of the brittle reaction layer, thereby improving the shear strength of the joint, but due to stress concentration, a large number of micro-cracks are distributed in the brazing seam, which will affect the strength of the joint.

[0049] From Figure 1It can be seen that when the laser power is 800W, the scanning rate is 1000mm / min, and the powder feeding rate is 0.3r / min, the thickness of the cladding layer is about 370μm, and the microstructure thereof mainly consists of FCC+(Co,Ni)2Nb eutectic structure and residual Nb.

[0050] It can be seen from Figure 2 During brazing, the molten Zr-Cu filler metal wets and dissolves the base material, a part of the cladding layer and the Zr-3 base material dissolves into the filler metal, the solid / liquid interface is formed, Zr in the filler metal diffuses to the cladding layer direction and reacts with Nb, Cr and Mn in the cladding layer to form layered (Zr,Nb)(Cr,Mn)2 on the side adjacent to the cladding layer; at the same time, Nb, Cr and Mn in the cladding layer dissolved into the filler metal react with Zr in the filler metal to form massive (Zr,Nb)(Cr,Mn)2 in the brazing seam, during the cooling process, the primary (Zr,Nb)2Cu phase is first precipitated from the liquid phase, and the residual liquid phase undergoes eutectic reaction to form Zrss+(Zr,Nb)2Cu eutectic structure. Compared with the brittle phases Zr2(Cu,Ni,Co,Fe) and Zr(Cr,Mn)2 in the brazing seam obtained by directly brazing with Zr-Cu filler metal, the plasticity of (Zr,Nb)2Cu and (Zr,Nb)(Cr,Mn)2 phases formed in the brazing seam is significantly improved, which leads to the disappearance of all micro-cracks in the brazing seam and a substantial increase in the shear strength of the joint, up to 242.8MPa.

[0051] The test results show that when laser cladding Nb is used to assist in brazing CoCrFeMnNi high-entropy alloy and zirconium alloy, the brittle compound layer on the HEA side is significantly reduced; the Nb distributed in the cladding layer has good plasticity and a smaller thermal expansion coefficient than the HEA, which can reduce and release the residual stress of the joint during brazing, which is conducive to improving the strength of the joint. In addition, Nb in the cladding layer can be infinitely miscible with Zr, which can play a role in regulating the interfacial reaction, which is also beneficial to improving the strength of the joint; in the FCC+(Co,Ni)2Nb eutectic structure of the cladding layer, FCC has good plasticity, and (Co,Ni)2Nb phase has good strength, so that the cladding layer has good plasticity and strength, which is also conducive to relieving the residual stress of the joint.

Claims

1. A method for laser cladding Nb-assisted brazing of high-entropy alloys and zirconium alloys, characterized in that, The method adopts the following steps: Step one, polishing the surface of high-entropy alloy for pretreatment, preparing cladding layer on the surface of high-entropy alloy by laser cladding Nb powder, wherein the thickness of the cladding layer is 150-420 μm, and the power of laser cladding is 750-900 W; Step two, polishing the surface of zirconium alloy and the surface of high-entropy alloy forming cladding layer for pretreatment, thereby obtaining the base material to be welded, and Zr63.2Cu36.8(wt.%) eutectic alloy foil as the filler metal; Step three, cleaning the zirconium alloy, high-entropy alloy and filler metal foil obtained in step three with acetone and anhydrous ethanol; Step four, placing the Zr63.2Cu36.8 filler metal foil between the surfaces of high-entropy alloy and zirconium alloy to be welded to form a sample to be welded, and placing it in a vacuum brazing furnace, heating to a brazing temperature of 1010℃ in a vacuum environment, and then cooling to room temperature after holding at the brazing temperature for 10 min; The high-entropy alloy is CoCrFeMnNi high-entropy alloy.

2. The method of laser cladding Nb assisted brazing high-entropy alloy and zirconium alloy according to claim 1, characterized in that: In step one and step two, the surfaces of high-entropy alloy and zirconium alloy to be welded are polished with 180#, 400#, 800#, 1200#, 2000# and 3000# metallographic sandpaper in sequence.

3. The method of claim 1, wherein the method further comprises: In step one, the particle size of Nb powder is 45-105 μm, and the parameters of laser cladding are scanning speed 1000 mm / min and powder feeding speed 0.2-0.35 r / min.

4. The method of claim 1, wherein the method further comprises: In step two, the thickness of Zr63.2Cu36.8 filler metal foil is 200 μm.

5. The method of claim 1, wherein the laser cladding Nb assisted brazing high entropy alloy and zirconium alloy is characterized by: In step three, the zirconium alloy, high-entropy alloy and Zr63.2Cu36.8 filler metal foil are first cleaned with acetone for 30 min, and then cleaned with anhydrous ethanol for 15 min, and then blown dry.

6. The method of claim 1, wherein the laser cladding Nb assisted brazing high entropy alloy and zirconium alloy is characterized by: The vacuum heating described in step four includes heating at 5x10 -3 The heating was performed under a vacuum condition of 10 Pa, the temperature was raised to the brazing temperature at a rate of 10 °C / min, and after the brazing was completed, the temperature was lowered to 200 °C at a rate of 5 °C / min, and finally, the furnace was cooled to room temperature.

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