A high-entropy alloy brazing filler metal for high-nitrogen steel and a preparation method and application thereof

Abstract

The application provides a high-entropy alloy filler for high-nitrogen steel brazing, a preparation method and application thereof, and relates to the technical field of brazing. Specifically, the high-entropy alloy filler comprises the following elements in percentage of atomic number: Co 18% to 32%, Fe 12% to 24%, V 12% to 24%, Cu 12% to 24% and Ni 18% to 26%. The application can effectively avoid technical defects such as nitrogen content loss, nitride or carbide precipitation and welding porosity of high-nitrogen steel, and can effectively reduce the generation of intermetallic compounds in the high-nitrogen steel brazing joint. In addition, the application can significantly improve the strength of the weld and the high-temperature performance of the joint. The preparation process is simple, does not contain noble metal raw materials, is low in cost and has a good application prospect.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a high-entropy alloy brazing filler metal for brazing high-nitrogen steel, its preparation method, and its application. Background Technology

[0002] High-nitrogen steel possesses excellent properties such as high strength, good toughness, good processability, and good corrosion resistance. By using nitrogen instead of nickel, this steel grade exhibits good economic efficiency and biocompatibility, and is currently widely used in power, shipbuilding, marine engineering, military equipment, and medical devices. However, due to its high nitrogen content (0.3%–0.5%), high-nitrogen steel often produces weld porosity during welding due to nitrogen precipitation from the base metal, or induces the appearance of other hard and brittle phases, thereby weakening the material properties and reducing the overall performance of the welded joint.

[0003] Currently, research on high-nitrogen steel welding technology mainly focuses on TIG welding, MIG welding, gas shielded welding, laser welding, and their hybrid welding methods. For example, patent CN201410092256.X discloses a welding method and apparatus for high-nitrogen austenitic stainless steel medium-thick plates, and patent CN201210385839.2 discloses a laser-MIG-arc hybrid welding method for high-nitrogen steel. However, defects such as nitrogen content loss, nitride or carbide precipitation, and weld porosity may still exist. If the high-nitrogen steel base material does not melt during the brazing process, nitrogen loss can be avoided, and it is more suitable for joining joints with complex shapes, overcoming the porosity disadvantage of traditional welding methods.

[0004] Existing technologies have revealed that high-entropy alloys, through the synergistic effect of high-entropy and retarded diffusion, possess significant potential as brazing filler metals. They can suppress the formation of brittle intermetallic compounds at the interface, thereby improving the quality of welded joints and providing new insights into brazing material design. However, most existing research on brazing high-nitrogen steel focuses on welding high-nitrogen steel using conventional filler metals, with few studies involving the brazing of high-entropy alloy filler metals onto high-nitrogen steel.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a high-entropy alloy brazing filler metal for brazing high-nitrogen steel, which can effectively avoid defects such as nitrogen content loss, nitride or carbide precipitation, and weld porosity that occur in current high-nitrogen steel welding processes, and can also effectively reduce the formation of intermetallic compounds in high-nitrogen steel brazed joints.

[0007] The second objective of this invention is to provide a method for preparing the high-entropy alloy brazing filler metal for high-nitrogen steel brazing, which ensures the quality of the alloy brazing filler metal product while having good production efficiency and enabling mass production.

[0008] The third objective of this invention is to provide a brazing method for high-nitrogen steel, wherein the brazing is performed using the aforementioned high-entropy alloy brazing filler metal for high-nitrogen steel.

[0009] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted:

[0010] A high-entropy alloy brazing filler metal for high-nitrogen steel brazing, comprising the following elemental composition by atomic percentage:

[0011] Co 18%–32%, Fe 12%–24%, V 12%–24%, Cu 12%–24%, and Ni 18%–26%.

[0012] The preparation method of the high-entropy alloy brazing filler metal for high-nitrogen steel brazing includes the following steps:

[0013] Step 1: Prepare the raw materials according to the percentage of each element;

[0014] Step 2: Mix the raw material components and melt them. Repeat the melting process 3 to 6 times to obtain an alloy ingot.

[0015] Step 3: After melting the alloy ingot, a high-entropy alloy brazing strip is obtained by using a single-roller spinning method with rapid quenching technology; or, the alloy ingot is cut and polished to obtain a high-entropy alloy sheet.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) The CoFeNiCuV high-entropy brazing filler metal of the present invention has a suitable melting temperature, good high-temperature performance, and uniform metallographic structure, which avoids defects such as nitrogen content loss of high nitrogen steel, precipitation of nitrides or carbides and welding porosity in traditional welding.

[0018] (2) The high-entropy alloy brazing filler metal of the present invention has a high-entropy effect and a delayed diffusion effect, which has a significant inhibitory effect on the interdiffusion between the high-nitrogen steel base material and the brazing filler metal during the brazing process, as well as the formation of brittle intermetallic compounds in the joint, and can significantly improve the strength of the weld and the high-temperature performance of the joint.

[0019] (3) The high-entropy alloy brazing filler metal of the present invention includes brazing filler metal foil or sheet, which has uniform composition and is easy to assemble. It can meet the brazing scenarios of various high-nitrogen steels and can better control the brazing gap width. It is an ideal brazing filler metal material and is suitable for mass production.

[0020] (4) The high-entropy alloy brazing filler metal provided by the present invention does not contain precious metals such as Au and Pd, and the preparation process is simple and the cost is low, which has good economic and practical value. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 The DSC curve of the high-entropy alloy solder of Embodiment 1 of the present invention is provided;

[0023] Figure 2 EDS surface scan images of the high-entropy alloy solder of Embodiment 1 of the present invention are provided;

[0024] Figure 3 Electron micrographs of the high-entropy alloy brazing filler metal and high-nitrogen steel weld seam in Example 1 of the experimental examples of this invention are provided. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] The first aspect of the present invention is to provide a high-entropy alloy brazing filler metal for brazing high-nitrogen steel.

[0027] The high-entropy alloy solder comprises the following elemental composition by atomic percentage: Co 18%–32%, Fe 12%–24%, V 12%–24%, Cu 12%–24%, and Ni 18%–26%.

[0028] First, the main constituent elements of the high-entropy alloy solder are selected. Then, based on the high-entropy alloy design theory, a multi-component high-entropy alloy solder with high-entropy characteristics is designed and prepared to ensure that the solder has a microstructure dominated by solid solution. As a preferred embodiment, the high-entropy alloy solder must meet the following performance characteristics:

[0029] (a) The enthalpy of mixing (ΔH) of the high-entropy alloy solder mixThe value ranges from -20 kJ / mol to 5 kJ / mol.

[0030] (b) The mixing entropy (ΔS) of the high-entropy alloy solder mix The value ranges from 11 J / (K*mol) to 19.5 J / (K*mol).

[0031] (c) The atomic size difference (δ) of the high-entropy alloy solder is ≤6.6%.

[0032] In a preferred embodiment, the high-entropy alloy solder comprises the following elemental composition by atomic percentage: Co 20%–30%, Fe 15%–20%, V 15%–20%, Cu 15%–20%, and Ni 15%–25%.

[0033] As an optional implementation, the atomic percentages of the elemental composition of the high-entropy alloy solder include, but are not limited to: Co 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%; Fe 15%, 16%, 17%, 18%, 19%, 20%; V 15%, 16%, 17%, 18%, 19%, 20%; Cu 15%, 16%, 17%, 18%, 19%, 20%; Ni 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%. Any one of the listed values, or any range of values ​​formed by two of them, can be used.

[0034] In a preferred embodiment, the melting point of the high-entropy alloy brazing filler metal is 1100℃~1130℃.

[0035] In this invention, Cu and Ni have similar atomic radii and a small absolute value of mixing enthalpy, which can reduce the melting temperature of the brazing filler metal and improve the strength, plasticity and corrosion resistance of the brazed joint; Fe element reduces the cost of the brazing filler metal and improves economic efficiency; and V forms a solid solution with Fe, which can avoid the formation of brittle intermetallic compounds.

[0036] A second aspect of the present invention is to provide a method for preparing the high-entropy alloy brazing filler metal for high-nitrogen steel brazing as described above.

[0037] The preparation method includes the following steps: Step 1, preparing raw materials with each element composition according to the atomic percentage; Step 2, mixing the raw material components and melting them, and repeatedly melting them 3 to 6 times to obtain an alloy ingot; Step 3, melting the alloy ingot and then using rapid quenching technology to obtain a high-entropy alloy brazing strip by single-roller spinning; or, cutting and polishing the alloy ingot to obtain a high-entropy alloy sheet.

[0038] In a preferred embodiment, in step one, the raw materials include pure cobalt, pure iron, pure vanadium, and a copper-nickel alloy. It should be noted that the copper-nickel alloy should be customized according to the atomic percentages of copper and nickel. For example, when the atomic percentages of copper and nickel are 16% and 20% respectively, then the atomic ratio in the copper-nickel alloy used should also remain consistent (4:5).

[0039] In a preferred embodiment, in step one, the purity of the raw materials is ≥99.9%.

[0040] In a preferred embodiment, in step two, the melting includes one of vacuum arc melting, arc melting under a protective atmosphere, vacuum induction melting, or electromagnetic levitation melting.

[0041] In a preferred embodiment, in step two, all metal raw materials should be completely melted at the melting temperature, and there should be no insoluble solid phase in the melt; specifically, the melting temperature is 1900℃~2100℃, and the melting time for each melting is 20min~30min.

[0042] As an optional implementation, the melting temperature includes, but is not limited to, 1900, 1950, 2000, 2050, and 2100 (°C), and the melting time for each melting session includes, but is not limited to, 20, 22, 24, 25, 26, 28, and 30 (min).

[0043] In a preferred embodiment, in step two, the alloy ingot is obtained by repeatedly melting 4 to 5 times.

[0044] In a preferred embodiment, in step three, the thickness of the high-entropy alloy solder strip is 100μm to 150μm, and the thickness of the high-entropy alloy sheet is 150μm to 300μm.

[0045] In a preferred embodiment, in step three, alloy brazing strip is obtained by rapid cooling of the melt on a single roller; the molten alloy is sprayed onto the surface of a high-speed rotating cooling roller, forming a dynamically balanced molten pool on the roller surface during spraying, and the molten alloy is rapidly solidified to form a continuous amorphous or microcrystalline strip; in a specific implementation, the following steps may be included: placing the alloy ingot in a quartz tube with a flattened bottom end, and then placing the quartz tube in a vacuum strip spinning machine; after the machine is running, the alloy ingot melts into a liquid alloy, and then sprays it onto a rotating copper roller, rapidly cooling it to obtain a high-entropy alloy brazing strip.

[0046] In a more preferred embodiment, the vacuum conditions of the vacuum belt spinning machine include: evacuating to 10... -3 Pa ~ 5 × 10 -3Pa, and then a protective gas of 0.03 MPa to 0.1 MPa is introduced; the protective gas includes, but is not limited to, helium, neon or argon.

[0047] In a more preferred embodiment, the rotational speed of the copper roller is 20 m / s to 35 m / s.

[0048] A third aspect of the present invention is to provide a brazing method for high-nitrogen steel.

[0049] The brazing filler metal used in the described brazing method is the high-entropy alloy filler metal for brazing high-nitrogen steel provided in the first aspect. Those skilled in the art can perform the brazing process of high-nitrogen steel using conventional brazing methods, and this invention does not impose any limitations on this.

[0050] Example 1

[0051] Step 1: Prepare a high-entropy alloy solder of CoFeNiCuV with equal atomic ratios; convert the atomic percentage to mass percentage, i.e., Co 20.47 Fe 19.39 Ni 20.38 Cu 22.07 V 17.69 Then, pure cobalt, pure iron, pure vanadium and Cu50Ni50 alloy were weighed according to mass percentage, and the purity of each raw material was ≥99.9%. The raw materials were placed in an ultrasonic cleaning device and cleaned with a solution of alcohol and acetone (volume ratio 3:1).

[0052] Step two: Place all the above raw materials into the crucible of the vacuum induction furnace, and evacuate the furnace to 10°C using a vacuum pump. -3 Below Pa, Ar protective gas is introduced to 20 MPa, and then the high-frequency induction device is started to begin melting. After the alloy ingot is completely melted, the alloy is kept in a molten state for 25 minutes to allow the alloying elements to diffuse evenly. Then the induction power is turned off, and the alloy melt is quickly poured into the mold to obtain an ingot. After a total of 5 melting cycles, a CoFeNiCuV high-entropy alloy brazing ingot is obtained.

[0053] Step 3: The high-entropy alloy ingot is cut into a 400μm thick brazing filler sheet using an electrical discharge wire cutter. Then, it is polished with SiC sandpaper to finally prepare a 250μm thick CoFeNiCuV high-entropy alloy brazing filler sheet.

[0054] The CoFeNiCuV high-entropy alloy solder prepared in this embodiment has a mixing enthalpy of -1.78 kJ / mol, a mixing entropy of 13.38 J / (K*mol), an atomic size difference of 2.63%, and a valence electron concentration of 8.6, which meets the design criteria for high-entropy alloys.

[0055] The solder sheet prepared in this embodiment was subjected to differential scanning calorimetry and energy dispersive spectroscopy (EDS) tests, and the test results are as follows: Figure 1 , Figure 2 As shown. (Through) Figure 1 According to the DSC test curve, the melting point of the CoFeNiCuV high-entropy alloy solder is approximately 1127.7℃. Figure 2 The distribution information of all elements within the region and the distribution information of each element within it are given respectively.

[0056] Example 2

[0057] Step 1: Calculate the atomic ratio of Co. 1.2 FeNiCu 0.8 The atomic percentage of V high-entropy alloy solder converted to mass percentage, i.e., Co 24.64 Fe 19.46 Ni 20.45 Cu 17.71 V 17.75 Then, pure cobalt, pure iron, pure vanadium and Cu40Ni50 alloy were weighed according to mass percentage, and the purity of each raw material was ≥99.9%. The raw materials were placed in an ultrasonic cleaning device and cleaned with a solution of alcohol and acetone (volume ratio 3:1). After mixing, the proportioned raw materials were obtained.

[0058] Step two: Place all the above raw materials into the crucible of the vacuum induction furnace, and evacuate the furnace to 10°C using a vacuum pump. -3 Below Pa, Ar protective gas is introduced to 20 MPa, and then the high-frequency induction device is started to begin melting. After the alloy ingot is completely melted, the alloy is kept in a molten state for 30 minutes to allow the alloy elements to diffuse evenly. Then the induction power is turned off, and the alloy melt is quickly poured into the mold to obtain the ingot. After a total of 5 repeated meltings, a Co1.2FeNiCu0.8V high-entropy alloy brazing ingot is obtained.

[0059] Step 3: After crushing the alloy ingot, place it into a quartz tube with a flattened bottom end. Then, place the quartz tube into a rapid solidification vacuum spinning machine and evacuate it to a vacuum level of 3×10⁻⁶. -3 After Pa, Ar protective gas of 0.05 MPa is introduced, and after induction melting, the melt is sprayed onto a copper wheel with a linear velocity of 25 m / s to prepare an amorphous foil strip with a thickness of 100 μm.

[0060] The CoFeNiCuV high-entropy alloy solder prepared in this embodiment has a mixing enthalpy of -6.92 kJ / mol, a mixing entropy of 13.32 J / (K*mol), an atomic size difference of 2.8%, and a valence electron concentration of 8.52, which meets the design criteria for high-entropy alloys.

[0061] Example 3

[0062] This is essentially the same as Example 1, except that the atomic ratio of the high-entropy alloy solder is CoFe. 0.75 Ni 1.25 Cu 1.25 V 0.75 .

[0063] Example 4

[0064] This is essentially the same as Example 1, except that the atomic ratio of the high-entropy alloy solder is CoFeNi. 1.2 CuV 0.8 .

[0065] Example 5

[0066] The process is basically the same as in Example 1, except that in step two, the alloy is repeatedly melted a total of 4 times and kept in a molten state for 30 minutes.

[0067] Comparative Example

[0068] Brazing filler metal (AgCuNi) for conventional high-nitrogen steel.

[0069] Test case

[0070] The assembled P580 high-nitrogen steel workpiece and the high-entropy brazing filler metal prepared in the above embodiments and comparative examples are placed in a vacuum brazing furnace. The furnace temperature is raised to 800°C at a rate of 10°C / min, then raised to 1170°C at a rate of 5°C / min and held at this temperature for 15 minutes. The furnace temperature is then lowered to 100°C at a rate of 10°C / min and then cooled to room temperature with the furnace, thus completing the high-nitrogen steel brazing.

[0071] The shear strength of the joints of high-nitrogen steel was tested, and the results are shown in Table 1.

[0072] Furthermore, scanning electron microscopy was performed on the high-nitrogen steel brazed joint obtained in Example 1, as shown in... Figure 3 As shown, the weld formation is good, with no obvious defects such as porosity or microcracks. Based on the differences in the interfacial microstructure, the weld is mainly composed of two characteristic regions: the brazing seam (region I) and the interfacial reaction layer (region II). Region I is mainly composed of Fe-Ni solid solution phase and a small amount of Cu-based solid solution phase, while region II is composed of Cu-based solid solution phase, Fe-Ni solid solution phase, and dispersed black VN. The main body of the weld is an FCC solid solution structure, which can improve the plasticity of the joint and play a role in relieving stress; the IMC intermetallic compound is dispersed in the joint, improving the interfacial bonding strength.

[0073] Table 1

[0074] Example 1 241.56 Example 2 221.21 Example 3 228.63 Example 4 235.74 Example 5 237.56 Comparative Example 198.20

[0075] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such substitutions and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A high-entropy alloy brazing filler metal for brazing high-nitrogen steel, characterized in that, The high-entropy alloy solder comprises the following elemental composition by atomic percentage: Co 18%~32%, Fe 12%~24%, V 12%~24%, Cu 12%~24% and Ni 18%~26%.

2. The high-entropy alloy brazing filler metal for high-nitrogen steel brazing according to claim 1, characterized in that, The high-entropy alloy solder comprises the following elemental composition by atomic percentage: Co 20%~30%, Fe 15%~20%, V 15%~20%, Cu 15%~20% and Ni 18%~25%.

3. The high-entropy alloy brazing filler metal for high-nitrogen steel brazing according to claim 1, characterized in that, The mixing enthalpy of the high-entropy alloy solder is -20kJ / mol to 5kJ / mol; The mixed entropy of the high-entropy alloy solder is 11 J / (K*mol) ~ 19.5 J / (K*mol); The atomic size difference of the high-entropy alloy brazing filler metal is ≤6.6%.

4. The method for preparing high-entropy alloy brazing filler metal for high-nitrogen steel brazing as described in any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: Step 1: Prepare the raw materials according to the percentage of each element; Step 2: Mix the raw material components and melt them. Repeat the melting process 3 to 6 times to obtain an alloy ingot. Step 3: After melting the alloy ingot, a high-entropy alloy brazing strip is obtained by using a single-roller spinning method with rapid quenching technology; or, the alloy ingot is cut and polished to obtain a high-entropy alloy sheet.

5. The method for preparing high-entropy alloy brazing filler metal for high-nitrogen steel brazing according to claim 4, characterized in that, In step one, the raw materials include pure cobalt, pure iron, pure vanadium, and copper-nickel alloy; The purity of all raw materials is ≥99.9%.

6. The method for preparing high-entropy alloy brazing filler metal for high-nitrogen steel brazing according to claim 4, characterized in that, In step two, the melting includes one of vacuum arc melting, arc melting under a protective atmosphere, vacuum induction melting, or electromagnetic levitation melting.

7. The method for preparing high-entropy alloy brazing filler metal for high-nitrogen steel brazing according to claim 4, characterized in that, In step two, the melting temperature is 1900℃~2100℃, and the melting time for each melting is 20min~30min.

8. The method for preparing high-entropy alloy brazing filler metal for high-nitrogen steel brazing according to claim 4, characterized in that, In step three, the thickness of the high-entropy alloy solder strip is 100μm~150μm, and the thickness of the high-entropy alloy sheet is 150μm~300μm.

9. The method for preparing high-entropy alloy brazing filler metal for high-nitrogen steel brazing according to claim 4, characterized in that, In step three, the alloy ingot is placed in a quartz tube with a flattened bottom end, and then the quartz tube is placed in a vacuum strip spinning machine. After the vacuum strip spinning machine is running, the alloy ingot melts into a liquid state and is then sprayed onto a rotating copper roller, where it is rapidly cooled and a high-entropy alloy brazing wire strip is obtained.

10. A brazing method for high-nitrogen steel, characterized in that, Brazing is performed using the high-entropy alloy brazing filler metal for high-nitrogen steel as described in any one of claims 1 to 3.

Images