TiVNbTaX (X= Ni, Co) refractory high-entropy alloy brazing filler metal and preparation method and brazing method thereof

Abstract

The invention discloses TiVNbTaX refractory high-entropy alloy brazing filler metal and a brazing method thereof, and the TiVNbTaX refractory high-entropy alloy brazing filler metal is characterized in that the brazing filler metal comprises the following elements in percentage by atom: 14.00 to 16.75 percent of Ti, 14.00 to 16.75 percent of V, 14.00 to 16.75 percent of Nb, 14.00 to 16.75 percent of Ta and 33.00 to 44.00 percent of X, and the X is Ni or / and Co element. The liquidus of the brazing filler metal is located between 1050 DEG C and 1250 DEG C, the brazing temperature is 30-50 DEG C higher than the liquidus, and the brazing time is 8-15 min; and then cooling to 800-900 DEG C, and keeping the temperature for 1-2 hours, so that the Ni and Co elements are fully diffused to the base metal on the two sides. According to the TiVNbTa refractory high-entropy alloy brazing method, TiVNbTa refractory high-entropy alloy brazing can be achieved, and high-entropy transformation of a brazing seam structure is achieved.

Description

Technical Field

[0001] The invention relates to a TiVNbTaX (X=Ni, Co) refractory high entropy alloy solder, a preparation method and a brazing method thereof, belonging to the technical field of welding, and mainly used for a refractory high entropy alloy composed of Ti, V, Nb and Ta elements or a refractory high entropy alloy with similar components. Background Art

[0002] Refractory high entropy alloys are multi-component alloys composed of high-melting-point refractory elements such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W according to the design concept of high entropy alloys. Sometimes non-refractory elements such as Al, Si, Co, and Ni are added to regulate the comprehensive properties of the alloy. The most common crystal structure of refractory high entropy alloys is the single-phase BCC structure. Because of its good strength in a large temperature range, it has become a high-temperature structural replacement material with broad prospects. However, most refractory high entropy alloys have poor room temperature plasticity. TiVNbTa and TiZrHfNbTa are typical representatives of the few refractory high entropy alloys that have both high strength and good plasticity.

[0003] The cast TiVNbTa refractory high entropy alloy has a tensile strength of 915MPa and an elongation of 8.56% at room temperature. It has significantly better corrosion resistance than stainless steel and nickel-based high-temperature alloys in high-temperature, high-pressure acidic environments, and has better corrosion resistance than TiZrHfNbTa in F-containing acidic environments, making it a replacement material for heat exchangers working in acidic environments. Compared with stainless steel and nickel-based high-temperature alloys, although TiVNbTa refractory high entropy alloys have a higher density and a higher price, when used as a coating material or composite plate, it will significantly increase the service life of heat exchangers in high-temperature, high-pressure acidic environments without much impact on weight and cost, thereby achieving significant economic benefits.

[0004] In the production process of heat exchangers, brazing is one of the most commonly used welding methods, but the performance of the brazed seam, especially the corrosion resistance, is often significantly lower than that of the parent material, becoming a weak area of ​​the entire component. When brazing with heterogeneous brazing materials such as Al-based, Ti-based, Ni-based, and Ag-based, the resulting joint is more likely to form a galvanic cell in a corrosive environment, significantly reducing the corrosion resistance of the joint and causing component failure. In order to overcome the problem that the corrosion resistance of the TiVNbTa refractory high entropy alloy brazed joint is significantly lower than that of the parent material, it is imperative to design the brazing material and explore its brazing process.

[0005] The brazing alloy disclosed in Chinese Patent No. 201310196017.4 contains 60-90% nickel, 1-10% boron, 1-10% boron and less than 10% active metal elements, wherein the active metal elements include titanium, zirconium, hafnium, vanadium and other elements. Titanium, zirconium, hafnium, vanadium and other elements are added as active metal elements in the brazing alloy, and the total content is low. If used for brazing TiVNbTa refractory high entropy alloys, the desired high entropy brazing seam cannot be formed to improve the joint performance. Similarly, the brazing alloy disclosed in Chinese Patent No. 201710202944.0 has nickel, cobalt and chromium as the main elements, germanium with a weight ratio of 10-18% and boron with a weight ratio of 1.5-3.5% as important additive elements, and at least one refractory element is selected from molybdenum, tungsten, tantalum and niobium as an additive element. The alloy contains few types and low contents of refractory elements. If it is used for brazing TiVNbTa refractory high entropy alloys, it cannot form the desired high entropy brazing seam to improve the joint performance. Summary of the invention

[0006] The purpose of the present invention is to develop a TiVNbTaX refractory high entropy alloy brazing filler metal with a liquidus line between 1050 and 1250°C, and to provide a preparation method and a brazing method thereof. The TiVNbTa refractory high entropy alloy is brazed by filling the brazing filler metal, and the alloy is kept warm during the subsequent cooling process to promote the diffusion of Ni and Co elements into the base material, thereby forming a high entropy joint and improving the mechanical properties and corrosion resistance of the welded joint.

[0007] The present invention is achieved in that:

[0008] The invention designs a TiVNbTaX refractory high entropy alloy solder. The atomic percentages of the elements in the solder are Ti: 14.00-16.75%, V: 14.00-16.75%, Nb: 14.00-16.75%, Ta: 14.00-16.75%, and X: 33.00-44.00%, wherein X is Ni or / and Co element.

[0009] Furthermore, the atomic percentage of each element in the solder is Ti: 14.50-16.25%, V: 14.50-16.25%, Nb: 14.50-16.25%, Ta: 14.50-16.25, X: 35.00-42.00%, X is Ni and / or Co element.

[0010] The melting point of the solder is between 1050 and 1250° C., and within the range of X: 33.00 to 44.00 atomic percent, the melting point of the solder decreases as the X content increases.

[0011] When X is a mixture of Ni and Co, the atomic percentage of the element with the smaller content among the two is not less than 10.00%, and the balance is the other element.

[0012] The present invention also provides a method for preparing a TiVNbTaX refractory high entropy alloy solder, wherein the TiVNbTaX alloy ingot is prepared by induction melting or arc melting under industrial pure argon protection conditions, then vacuum gas atomization or other crushing methods are used to prepare the powder, and finally the powder solder with a suitable particle size is obtained by powder screening.

[0013] The specific steps include:

[0014] S1. Use high-purity Ti, V, Nb, Ta, Ni and / or Co raw materials with a purity of not less than 99.0%, calculate the required weight of various pure metals according to the atomic percentage, and then weigh according to the calculated results;

[0015] S2. The above pure metal raw materials are melted into alloy ingots by arc melting or induction melting under industrial pure argon protection;

[0016] S3. Prepare powdered solder using vacuum gas atomization powder making equipment or crush and grind the alloy ingot into powder using a crusher or ball mill, and finally use a powder screening tool to screen out solder powder of the required particle size.

[0017] The brazing method of TiVNbTaX refractory high entropy alloy solder specifically comprises the following steps:

[0018] S1. Preparation before welding: Carry out surface treatment and assembly of the sample before welding according to the actual welding requirements, and pre-place the powder solder at the place to be connected;

[0019] S2. Brazing process: put the assembled sample together with the fixture into the vacuum brazing furnace, evacuate the vacuum, and then heat to 30-50℃ above the melting point of the brazing material, keep the temperature for 8-15min for brazing;

[0020] S3. Diffusion process: After cooling to 800-900°C, keep warm for 1-2 hours to promote the homogenization diffusion of the joint elements and obtain a high-entropy brazing joint with a single solid solution.

[0021] Beneficial effects:

[0022] The TiVNbTaX solder involved in the present invention has a certain correlation with the commonly used titanium-based solder, but the commonly used titanium-based solder generally uses Ni and Cu as elements to reduce the melting temperature, such as Ti-15Cu-25Ni. In addition, Zr and Ti are infinitely solid-soluble, and the addition of Zr can further reduce the melting point of the solder, so titanium-zirconium-based solder is also very common, such as Ti-37.5Zr-15Cu-10Ni. The basic idea of ​​reducing the melting point of these solders is mainly to utilize the low melting point eutectic between Ti, Zr and Ni and Cu. However, the addition of Cu is not conducive to improving the corrosion resistance of the brazing seam, which is inconsistent with the goal of improving the corrosion resistance of the TiVNbTa refractory high entropy alloy brazing seam of the present invention. In order to obtain a brazing seam with good corrosion resistance after welding, the TiVNbTaX solder involved in the present invention abandons the Cu element, adds the Ni element on the basis of the original elements of TiVNbTa, and utilizes the low melting point eutectic between Ni and Ti, V, Nb, and Ta to reduce the melting point of the solder. In order to further improve the melting reduction effect, the Co element, which can also produce a low melting point eutectic with Ti, V, Nb, and Ta, is added to the solder. At the same time, the addition of Co is cleverly used to increase the mixing entropy of the solder joint, making it easier for the solder joint structure to undergo a high entropy transformation during the homogenization diffusion process, thereby quickly forming a high entropy alloy solder joint. Compared with common solders, this solder abandons the Cu element and uses the Co element, which is beneficial to improving the corrosion resistance of the joint; the Ni-Co element is used to reduce the melting point of the solder and improve the melting reduction effect, thereby obtaining a solder melting point that can adapt to industrial production; the addition of the Co element is used to increase the mixing entropy of the solder joint, promote the high entropy transformation of the solder joint structure, and further improve the mechanical properties and corrosion resistance of the joint. The design concept of TiNiNbZr, TiNiNbZrHf, ZrTiNiNbHf and ZrTiNiNbHf solders disclosed in Chinese patents 201910401272.5, 202010391924.4, 202011555726.3 and 202011197088.2 is different from the design concept of the present invention to obtain a high entropy solder joint. The solders involved in the above four inventions all use Ti (201910401272.5), Zr (202011555726.3, 202011197088.2) or Ti and Zr (202010391924.4) as main elements, and the total content of the main elements is not less than 52%. Ni element is used as a eutectic melting element, and its addition amount does not exceed 21.5%. The final solder joint presents a eutectic structure morphology. The present invention is based on the design concept of obtaining a high entropy brazing seam presenting a single-phase solid solution structure. The refractory elements Ti, V, Nb, and Ta in the brazing material are in equal or nearly equal atomic ratios, and one or two of them are not used as the main elements. In order to fully reduce the melting point of the brazing material, the amount of Ni element added in the present invention is between 33.00 and 44.00% (atomic percentage). In addition, the present invention finally obtains a high entropy brazing seam presenting a single-phase solid solution structure through the combination of the brazing material composition and the brazing process to improve the joint performance.Compared with the prior art, the present invention has the following advantages:

[0023] 1. The present invention can provide solder for refractory high entropy alloys composed of Ti, V, Nb, and Ta elements or refractory high entropy alloys with similar compositions.

[0024] 2. The present invention can reduce the liquidus line of the solder to between 1050 and 1250° C. by adding Ni and Co elements, thereby facilitating the brazing connection of refractory high entropy alloys.

[0025] 3. The present invention adopts a brazing method combining brazing and diffusion, so that the Ni and Co elements in the joint can fully diffuse to the parent materials on both sides, thereby forming a high entropy alloy brazing seam and improving the mechanical properties and corrosion resistance of the joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is (TiVNbTa) 0.67 Ni 0.33 Macroscopic microstructure of refractory high entropy alloy solder before it is crushed into powder.

[0027] Figure 2 The present invention is (TiVNbTa) 0.67 Ni 0.33 High-magnification microstructure of refractory high-entropy alloy solder before it is crushed into powder.

[0028] Figure 3 The present invention (TiVNbTa) is used 0.67 Ni 0.33 The microstructure morphology of the joint obtained by keeping the refractory high entropy alloy solder powder at 1280℃ for 10min and then cooling to 850℃ and keeping it for 1h. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with embodiments:

[0030] A TiVNbTaX refractory high entropy alloy solder, wherein the atomic percentages of the elements in the solder are Ti: 14.00-16.75%, V: 14.00-16.75%, Nb: 14.00-16.75%, Ta: 14.00-16.75%, and X: 33.00-44.00%, wherein X is Ni or / and Co element.

[0031] Furthermore, the atomic percentage of each element in the solder is Ti: 14.50-16.25%, V: 14.50-16.25%, Nb: 14.50-16.25%, Ta: 14.50-16.25, X: 35.00-42.00%, X is Ni and / or Co element.

[0032] The melting point of the solder is between 1050 and 1250° C., and within the range of X: 33.00 to 44.00 atomic percent, the melting point of the solder decreases with the increase of the X content. The melting point of the solder can be adjusted by adjusting the X content.

[0033] When X is a mixture of Ni and Co, the atomic percentage of the element with less content in the two is not less than 10.00%, and the balance is the other element, which can increase the mixing entropy of the solder. The content of Ni and Co elements can also be adjusted arbitrarily according to needs.

[0034] The present invention also provides a method for preparing a TiVNbTaX refractory high entropy alloy solder, wherein the TiVNbTaX alloy ingot is prepared by induction melting or arc melting under industrial pure argon protection conditions, then vacuum gas atomization or other crushing methods are used to prepare the powder, and finally the powder solder with a suitable particle size is obtained by powder screening.

[0035] The specific steps include:

[0036] S1. Use high-purity Ti, V, Nb, Ta, Ni and / or Co raw materials with a purity of not less than 99.0%, calculate the required weight of various pure metals according to the atomic percentage, and then weigh according to the calculated results;

[0037] S2. The above pure metal raw materials are melted into alloy ingots by arc melting or induction melting under industrial pure argon protection;

[0038] S3. Prepare powdered solder using vacuum gas atomization powder making equipment or crush and grind the alloy ingot into powder using a crusher or ball mill, and finally use a powder screening tool to screen out solder powder of the required particle size.

[0039] The brazing method of TiVNbTaX refractory high entropy alloy solder specifically comprises the following steps:

[0040] S1. Preparation before welding: Carry out surface treatment and assembly of the sample before welding according to the actual welding requirements, and pre-place the powder solder at the place to be connected;

[0041] S2. Brazing process: put the assembled sample together with the fixture into the vacuum brazing furnace, evacuate the vacuum, and then heat to 30-50℃ above the melting point of the brazing material, keep the temperature for 8-15min for brazing;

[0042] S3. Diffusion process: After cooling to 800-900℃, keep warm for 1-2h to promote uniform diffusion of joint elements and obtain a joint with good metallurgical bonding.

[0043] Examples 1-6 respectively prepare solders according to the atomic percentage compositions of the elements in the following table:

[0044] Atomic percentage composition table of each element in Examples 1-6

[0045]

[0046] Figure 1 and 2 The structure of the as-cast solder corresponding to the composition ratio shown in Example 1, Figure 3 For filling (TiVNbTa) 0.67 Ni 0.33 The solder is a refractory high entropy material of TiVNbTa. The solder is kept at 1280℃ for 10 minutes, then cooled to 850℃ and kept for 1 hour to obtain the joint structure. Figure 1 and 2 The organizational morphology shown in the figure shows that before the solder is crushed into powder, it is mainly in lamellar structure, including gray phase 1, gray-white phase 2 and gray-black phase 3. Among them, the atomic percentages of Ti, V, Nb, Ta and Ni in gray phase 1 are 17.44%, 18.33%, 19.00%, 15.82% and 29.40%, respectively; the atomic percentages of Ti, V, Nb, Ta and Ni in gray-white phase 2 are 10.74%, 19.67%, 20.07%, 23.11% and 26.40%, respectively; the atomic percentages of Ti, V, Nb, Ta and Ni in gray-black phase 3 are 48.51%, 1.18%, 3.65%, 3.74% and 42.92%, respectively. Gray phase 1 and gray-white phase 2 are TiVNbTaNi solid solutions, and gray-black phase 3 is a TiNi intermetallic compound. According to Figure 3 The microstructure of the joint shown in the figure shows that the brazing seam is well bonded with the parent materials on both sides, and the Ni element in the brazing seam is fully diffused into the parent materials on both sides, forming a solid solution brazing seam microstructure and realizing the high entropy transformation of the brazing seam.

Claims

1. A TiVNbTaX refractory high entropy alloy solder, characterized in that: The atomic percentages of the elements in the solder are Ti: 14.00-16.75%, V: 14.00-16.75%, Nb: 14.00-16.75%, Ta: 14.00-16.75%, X: 33.00-44.00%, wherein X is Ni or / and Co element.

2. The TiVNbTaX refractory high entropy alloy solder according to claim 1, characterized in that: The atomic percentages of the elements in the solder are Ti: 14.50-16.25%, V: 14.50-16.25%, Nb: 14.50-16.25%, Ta: 14.50-16.25, X: 35.00-42.00%, where X is Ni or / and Co element.

3. The TiVNbTaX refractory high entropy alloy solder according to claim 1, characterized in that: The melting point of the solder is between 1050 and 1250° C., and within the range of X: 33.00 to 44.00 atomic percent, the melting point of the solder decreases as the X content increases.

4. The TiVNbTaX refractory high entropy alloy solder according to claim 1, characterized in that: When X is a mixture of Ni and Co, the atomic percentage of the element with the smaller content among the two is not less than 10.00%, and the balance is the other element.

5. The method for preparing the TiVNbTaX refractory high entropy alloy solder according to any one of claims 1 to 4, characterized in that: The TiVNbTaX alloy ingot is prepared by induction melting or arc melting under industrial pure argon protection, and then made into powder by vacuum gas atomization or other crushing methods, and finally the powder brazing material with suitable particle size is obtained by powder screening.

6. The preparation method according to claim 5, characterized in that: The specific steps include: S1. Use high-purity Ti, V, Nb, Ta, Ni and / or Co raw materials with a purity of not less than 99.0%, calculate the required weight of various pure metals according to the atomic percentage, and then weigh according to the calculated results; S2. The above pure metal raw materials are melted into alloy ingots by arc melting or induction melting under industrial pure argon protection; S3. Prepare powdered solder using vacuum gas atomization powder making equipment or crush and grind the alloy ingot into powder using a crusher or ball mill, and finally use a powder screening tool to screen out solder powder of the required particle size.

7. The brazing method of the TiVNbTaX refractory high entropy alloy brazing material according to any one of claims 1 to 4, characterized in that: The specific steps include: S1. Preparation before welding: Carry out surface treatment and assembly of the sample before welding according to the actual welding requirements, and pre-place the powder solder at the place to be connected; S2. Brazing process: put the assembled sample together with the fixture into the vacuum brazing furnace, evacuate the vacuum, and then heat to 30-50℃ above the melting point of the brazing material, keep the temperature for 8-15min for brazing; S3. Diffusion process: After cooling to 800-900°C, keep warm for 1-2 hours to promote the homogenization diffusion of the joint elements and obtain a high-entropy brazing joint with a single solid solution.

Images