CN107160059A - A kind of preparation of Ni base solders for soldering Nb Ti high temperature alloys and method for welding - Google Patents

Abstract

The invention discloses a preparation and brazing method of Ni-based brazing filler metal for brazing Nb-Ti superalloy, belonging to the field of welding materials. The composition and content of the brazing filler metal in the present invention are: Ni: 60-70%, Ti: 20-30%, Nb: 5-15%. Ni-Ti-Nb high-temperature solder was prepared by vacuum arc melting technology, and Nb-Ti high-temperature alloy was vacuum brazed with this solder. The shear strength can reach more than 550MPa. The brazing temperature of the Ni-Ti-Nb solder in the present invention is higher than that of traditional Ag-based, Al-based and Au-based solders, and can give full play to the high-temperature performance of the Nb-Ti alloy. The Nb-based superalloy is brazed with Ni-Ti-Nb solder, and its room temperature shear strength can reach more than 550MPa. The solder described in the present invention can also be used for brazing connections of other Ni-based, Ti-based and Nb-based superalloys.

Description

A kind of preparation and brazing method of Ni-based solder for brazing Nb-Ti superalloy

technical field

The invention relates to a brazing material preparation and a brazing method for brazing Nb-based superalloys, and belongs to the field of welding materials.

Background technique

Nb-Ti superalloy is a new type of (βTi, Nb) solid solution alloy with a body-centered cubic structure, which has a higher melting point than nickel-based alloys, good room temperature plasticity and medium temperature strength. Nb-Ti alloys not only have good mechanical properties, but adding a large amount of Ti to Nb can greatly improve the oxidation resistance of Nb alloys. Depending on the amount of Ti added, the density of these alloys is generally 6.2-6.9g/cm ³ , while the density of superalloys is generally 8.1-8.6g/cm ³ . Therefore, Nb-Ti superalloys can replace Ni and superalloys. Applied to the key components of the spacecraft. As a new type of high-temperature material, to realize the practical application of Nb-Ti superalloy, its material joining technology is very important. At present, there are mainly three common joining techniques for superalloys, namely fusion welding, diffusion welding and brazing. Among them, brazing has many advantages, such as relatively low brazing temperature, can connect structures with complex shapes, can realize high-precision connections, and can realize the connection of dissimilar materials, and the process is simple. Therefore, brazing technology has been widely used in the field of connection of high temperature materials.

At present, among the common commercial solders, the brazing temperature of Ag-based, Al-based and Au-based solders is relatively low, and the actual service temperature of brazed joints is generally lower than 500°C, which is not suitable for brazing of Nb-Ti superalloys. Welding (Materials Science and Engineering A, 2012, 551: 133-139). Among the high-temperature solders, Ni-based or Ti-based solders are mainly used. The brazing temperature of such solders is generally at 1000-1300 °C. Such as Ni-Cr, Ni-Cr-Si and Ni-Cr-B and other solders, Ti-based solders such as Ti-Ni, Ti-Zr-Cu-Ni-Co, Ti-Cu-Ni, Ti-Ni-V Brazing filler metals such as Ni-Ti-Nb are used for brazing filler metals Ti ₃ Al, TiNi, nickel-based superalloys and C _f /SiC composite materials, etc. (Journal of the European Ceramic Society 2003, 23:547-553, Science and Technology of Welding and Joining, 2011, 16(2): 193-198, Materials Science and Engineering: A, 2015, 636: 522-528). Brazing joints using the above-mentioned solders generally have high bonding strength and good oxidation resistance. At the same time, elements such as Ti, Cr, and Nb are active elements that can react with common ceramics at the interface to improve the shear of brazing joints. cutting strength.

For different matrix materials, the composition and content of solder should also be different, but there are few reports about the welding of Nb-based superalloys at present, and there are no suitable brazing materials and related processes to weld it. The present invention mainly solves the problem of Nb-based superalloys. -The problem of lack of brazing materials and brazing processes related to Ti superalloys.

In order to achieve a good connection to the Nb-Ti superalloy, the solder and the brazing joint should meet the following requirements: ① It is necessary to seek a solder with a melting point as high as possible, with good oxidation resistance, to meet its high-temperature use requirements; ②The solder and Nb-Ti alloy have good wettability; ③The internal stress of the brazed joint should be relatively low and have a sufficiently high strength.

Contents of the invention

The present invention mainly solves the problem of lack of brazing material and brazing process related to Nb-Ti superalloy, and provides a preparation method and brazing process of brazing material for vacuum brazing Nb-Ti superalloy. The brazing material and brazing process of the present invention The method can also be applied to other Ni-based, Ti-based and Nb-based superalloys.

The selection of suitable solder is very important to obtain high-performance joints to meet the service conditions of the base material. Factors such as the physical and chemical compatibility, wettability, and matching thermal expansion coefficient between the solder and the base material need to be considered comprehensively.

In order to enhance the wettability between the solder and the Nb-Ti matrix alloy, so that the brazed joint has higher strength and oxidation resistance, the present invention selects Ni-Ti-Nb alloy as the solder system. The solder system has the following advantages: ① Ti and Nb elements in the solder are the main elements of the matrix, which can ensure good wettability between the solder and the substrate; ② Ni elements in the solder have two First, it is used as a melting point adjusting element to adjust the melting point of the solder; secondly, the Ni element can react with both Ti and Nb in the matrix to form NiTi ₂ , NiTi, Ni ₃ Ti, Ni ₃ Nb and NiNb and other metals. ③ Ni-Ti-Nb solder has good plasticity, which is beneficial to the plastic deformation and stress release of brazed joints, and the alloy has excellent high temperature oxidation resistance.

A method for preparing Ni-based solder for brazing Nb-Ti superalloys, characterized in that the components and contents of the solder are: Ni: 60-70%, Ti: 20-30%, Nb : 5-15%. The preferred components of the above solder are: Ni: 63-67%, Ti: 20-25%, Nb: 8-12%.

Above-mentioned solder is prepared according to the following steps and process:

(1) Preparatory stage: choose electrolytic nickel (Ni), sponge titanium (Ti), niobium block (Nb) as raw material, the purity of Ni is more than 99.95%, and the purity of Ti and Nb reaches more than 99.9%; Raw material is acetone solution and The alcohol solution was ultrasonically cleaned for 10-15 minutes, and dried at room temperature;

(2) Smelting stage: Before smelting, use a mechanical pump to vacuum the furnace to 0.1 Pa and keep it for 2-4 minutes, then turn on the molecular pump to pump the furnace to a vacuum above 6×10 ^-2 Pa, and then fill it with high Pure argon; during smelting, in order to homogenize the alloy composition, the alloy is smelted at least 5 times under the action of electromagnetic stirring, and then vacuum cast; weighed after smelting, the weight loss of the sample is within 0.1%, and the actual composition of the alloy is considered to be basically the same as the nominal composition. unanimous.

The microstructure of the solder prepared by the above method is shown in Figure 1. It can be seen that the solder elements are evenly distributed, in which the white chrysanthemum shape is (βTi, Nb) continuous solid solution, and the gray and white lamellar shape is eutectic structure {(βTi ,Nb)+Ti ₂ Ni}, the gray phase is the Ti ₂ Ni phase, and the black phase is the rich-Ti phase. From the DSC curve of the solder alloy (Fig. 2), it can be seen that the melting point of the solder alloy is about 945.7°C. During the brazing process, the brazing temperature should be higher than the melting point of the solder, so the brazing temperature range is set at 1050-1200°C. Figure 3 is the wetting kinetic curve of Ni-Ti-Nb solder on the surface of Nb-Ti superalloy at 1150 °C. It can be seen that the solder and Nb-Ti superalloy have good wettability, and the wetting time is about The final wetting angle is about 3.8°.

The brazing process of the solder brazing Nb-Ti superalloy prepared by said method and process is as follows:

(1) Cut the solder into thin slices with the same shape as the substrate to be welded by the wire cutting method, and then grind it to a thickness of about 200 μm with No. 2000 sandpaper; at the same time, use No. 2000 sandpaper to polish the surface of the substrate to be welded to remove the surface of the substrate. Oxide layer, ultrasonically clean the solder and base material with alcohol and then blow dry.

(2) The solder is placed between the Nb-based superalloys and assembled into a structure of Nb-Ti/Ni-Ti-Nb/Nb-Ti alloy; the structure is put into a vacuum brazing furnace, and then vacuumed to The vacuum degree is above 3.0×10 ^-3 Pa, the temperature is raised to the brazing temperature of 1050-1200°C at a rate of 5°C/min, and the brazing connection is 5-20min; then the furnace is vacuum cooled to room temperature to complete the welding.

In the present invention, the key to ensuring the shear strength of the Nb-Ti/Ni-Ti-Nb brazing joint is to control the generation of brittle phases in the brazing joint. Fig. 4 is a photo of the microstructure of Nb-Ti/Ni-Ti-Nb brazed joints brazed at 1150°C for 15 minutes. It can be seen that there are four phases in the weld microstructure at the same time, which are bright gray (βTi , Nb) continuous solid solution, chrysanthemum-like (βTi, Nb) + TiNi eutectic structure, dark gray Ti ₂ Ni intermetallic compound, black Ti-rich phase. Among them, the first two phases are ductile phases, and the latter two phases are brittle phases. When the brazing time is short, the weld structure mainly consists of (βTi, Nb) continuous solid solution, (βTi, Nb) + TiNi eutectic structure, and some brittle Ti ₂ Ni intermetallic compounds. The continuous solid solution of (βTi, Nb) and the eutectic structure of (βTi, Nb) + TiNi in the weld structure all disappear, leaving only the brittle Ti ₂ Ni intermetallic compound and Ti-rich phase, so the brazing time is too long Long, will lead to a decrease in the shear strength of the brazed joint. However, when the brazing time is too short, although the solder and the substrate have good wettability, too short a time will lead to insufficient reaction and diffusion of the alloying elements in the solder and the substrate, resulting in low strength of the welded joint. Therefore, the preferred range of the above process conditions is: brazing temperature 1100-1150° C., brazing connection 10-15 minutes.

The beneficial effects of the invention are: the brazing temperature of the Ni-Ti-Nb solder in the invention is higher than that of traditional Ag-based, Al-based and Au-based solders, and the high-temperature performance of the Nb-Ti alloy can be fully utilized. Ni-Ti-Nb solder is used to braze Nb-based superalloys, and its room temperature shear strength can reach more than 550MPa. The solder described in the present invention can also be used for brazing connections of other Ni-based, Ti-based and Nb-based superalloys.

Description of drawings

Fig. 1 is the Ni-Ti-Nb brazing filler metal as-cast structure photo prepared by the present invention;

Fig. 2 is the DSC curve figure of the solder prepared by the present invention;

Fig. 3 is the wetting kinetics curve of solder prepared by the present invention on the surface of Nb-Ti superalloy at 1150°C;

Fig. 4 is the electron backscatter photo of the welded joint under the condition that the brazing temperature of Ni-Ti-Nb solder is 1150°C and the brazing connection time is 15 minutes;

detailed description

The solder for brazing the Nb-based superalloy is prepared, and the components and contents of the solder are as follows: Ni: 65%, Ti: 25%, and Nb: 10%.

The solder preparation process is as follows:

(1) Preparatory stage: choose electrolytic nickel (Ni), sponge titanium (Ti), niobium block (Nb) as raw material, the purity of Ni is more than 99.95%, and the purity of Ti and Nb reaches more than 99.9%; Raw material is acetone solution and Alcohol solution was ultrasonically cleaned for 10-15 minutes, and dried at room temperature;

(2) Smelting stage: Before smelting, use a mechanical pump to vacuum the furnace to 0.1 Pa and keep it for 3 minutes, then turn on the molecular pump to pump the furnace to a vacuum above 6×10 ^-2 Pa, and then fill it with high-purity argon During smelting, in order to homogenize the composition of the alloy, the alloy was repeatedly smelted at least 5 times under the action of electromagnetic stirring, and then vacuum cast; weighed after smelting, the weight loss of the sample was within 0.1%, and the actual composition of the alloy was considered to be basically the same as the nominal composition.

The brazing process steps are as follows:

(1) The solder is cut into 0.5mm thick thin slices by wire electric discharge cutting method, the shape is the same as the surface of the Nb-based superalloy to be welded, the solder and the substrate are polished with 2000 SiC sandpaper to remove the oxide layer, and then the solder and The substrate is ultrasonically cleaned in alcohol solution for 10-15 minutes, and dried at room temperature;

(2) Assembling the solder and the substrate into a structure of Nb-Ti/Ni-Ti-Nb/Nb-Ti, putting it into a vacuum brazing furnace, and then vacuuming to a vacuum degree of 3.0×10 ^-3 Pa or more, with Heat up at 5°C/min to a brazing temperature of 1050-1200°C, braze connection for 10-20 minutes; finally cool down to room temperature with the furnace vacuum to complete the welding.

Example:

The brazing temperature is selected as 1050°C, 1100°C, 1150°C and 1200°C respectively, and the brazing connection time is 10min, 15min and 20min. The following table lists the mechanical test results of the brazing temperature, brazing connection time and brazing joint of Ni-Ti-Nb solder welding Nb-based alloy in 12 groups of embodiments:

The above examples show that when the brazing temperature is 1100-1150° C. and the brazing time is 10-15 minutes, the shear strength of the brazed joint can reach more than 550 MPa, which can realize good welding of Nb-Ti superalloy.

Claims (4)

1. A preparation method for a Ni-base solder for brazing Nb-Ti superalloy, characterized in that the components and content of the solder are by atomic percentage: Ni: 60-70%, Ti: 20-30% , Nb: 5-15%; the specific preparation steps are: (1) Preparatory stage: choose electrolytic nickel (Ni), sponge titanium (Ti), niobium block (Nb) as raw material, the purity of Ni is more than 99.95%, and the purity of Ti and Nb reaches more than 99.9%; Raw material is acetone solution and The alcohol solution was ultrasonically cleaned for 10-15 minutes, and dried at room temperature; (2) Smelting stage: Before smelting, use a mechanical pump to vacuum the furnace to 0.1 Pa and keep it for 2-4 minutes, then turn on the molecular pump to pump the furnace to a vacuum above 6×10 ^-2 Pa, and then fill it with high Pure argon; during smelting, in order to homogenize the alloy composition, the alloy is smelted at least 5 times repeatedly under the action of electromagnetic stirring, and then vacuum cast. 2. the preparation method of the Ni-based solder for brazing Nb-Ti superalloy described in claim 1 is characterized in that the scope of Ni-based solder by atomic percentage is: Ni: 63～67%, Ti: 20-25%, Nb: 8-12%. 3. a method for adopting the Ni-base solder brazing Nb-Ti superalloy described in claim 1 or 2, is characterized in that brazing process is as follows: (1) Cut the solder into thin slices with the same shape as the substrate to be welded by the wire cutting method, and then grind it to a thickness of 200 μm with No. 2000 sandpaper; at the same time, use No. 2000 sandpaper to polish the surface of the substrate to be welded to remove oxidation on the surface of the substrate Layer, ultrasonically clean the solder and base material with alcohol and then blow dry; (2) The solder is placed between the Nb-based superalloys and assembled into a structure of Nb-Ti/Ni-Ti-Nb/Nb-Ti alloy; the structure is put into a vacuum brazing furnace, and then vacuumed to The vacuum degree is above 3.0×10 ^-3 Pa, the temperature is raised to the brazing temperature of 1050-1200°C at a rate of 5°C/min, and the brazing connection is 5-20min; then the furnace is vacuum cooled to room temperature to complete the welding. 4. The method for brazing Nb-Ti superalloys as claimed in claim 3, characterized in that the brazing conditions and processes are as follows: brazing temperature is 1100-1150° C., brazing time is 10-15 minutes, and finally vacuum-cooled with the furnace.