CN114799395B - Vacuum brazing method of dissimilar nickel-based superalloys to improve joint strength stability - Google Patents

Abstract

The invention discloses a vacuum brazing method for dissimilar nickel-based superalloys for improving the strength and stability of joints, and belongs to the technical field of superalloy welding. It includes the following steps: cleaning the surface of the alloy and cleaning the parts to be welded; assembling and positioning by energy storage welding; heating the components to be welded to 600-700°C and keeping it warm, then heating to 850-950°C and keeping it warm, and then heating to 1050-1070°C ℃ and keep warm for 10-15min for vacuum brazing; heat the welded components to 1010-1040℃, keep warm for 3-5h for homogenization, and then oil quench and cool to room temperature. The method of the invention eliminates the hard and brittle phase in the central region of the weld seam, a solid solution structure is completely formed inside the weld seam, and the uniformity of the microstructure is obviously improved. This process has unexpected effects in improving the uniformity and stability of the joint strength, and is especially suitable for brazed joints with a gap value of 60-150 μm, which is of great promotion value. The test results of multiple sets of mechanical properties show that the standard deviation of the shear strength and the tensile strength of the joint at 730° C. are reduced by more than 70% after being treated by the process of the present invention.

Description

Vacuum brazing method of dissimilar nickel-based superalloys to improve joint strength stability

technical field

The invention relates to a vacuum brazing method for dissimilar nickel-based superalloys that improves the strength and stability of joints, and belongs to the technical field of superalloy welding.

Background technique

Aeroengine is a very representative high-tech product. As the heart of the aircraft, it is the key to promoting the development and progress of the national aviation industry. The hot-end component is the core key component of an aero-engine. These components need to work stably for a long time under complex and harsh environments such as high temperature, corrosion, stress and vibration, and their performance directly determines the thrust-to-weight ratio and working efficiency of the engine. At present, the engine hot end parts are mainly made of superalloys, especially nickel-based superalloys.

There are many kinds of nickel-based superalloys, and different grades of alloys have different properties and characteristics. GH3536 alloy is a solid-solution strengthened nickel-based deformed superalloy with excellent cold and hot forming and welding properties, and has good oxidation resistance and mechanical properties below 900 °C. The GH4738 alloy belongs to the γ′ phase precipitation-strengthened nickel-based deformable superalloy. Its outstanding features are excellent strength-toughness matching and microstructure stability. It has high yield strength and fatigue crack growth resistance between 760-870 °C. With the continuous improvement of the performance of aero-engines, the requirements for the structural complexity and service performance of superalloy components have become more stringent. Reliable connections between different grades of nickel-based wrought superalloys can give full play to their respective advantages, which is of great practical significance for promoting the advancement of engine technology.

Welding technology can quickly realize the connection of two parts and is widely used in the field of superalloys. Laser welding, arc welding and other fusion welding processes can be carried out at room temperature or under special conditions. The welding equipment is simple, but the fusion welding needs to partially melt the base metal, the welding temperature is high, the thermal stress value after welding is large, and the microstructure of the base metal will be reduced. Uniformity. In contrast, the heating temperature of vacuum brazing is relatively low, there is no need to melt the base metal, and the surface of the joint is smooth and air-tight, and the same or different metals can be connected. In addition, since the welding is performed in a vacuum environment, the surface quality of the welded alloy is high. At present, vacuum brazing has become a key manufacturing process technology for superalloy components, and has broad application prospects in the future.

Considering the sample size and assembly accuracy in the vacuum brazing process, it is difficult and expensive to set the gap value in a small range. Taking the GH3536 and GH4738 alloy brazed components processed by the traditional vacuum brazing process as an example, when the joint gap value exceeds 60 μm, a large area of hard and brittle phases such as borides is easily formed at the center of the weld, which not only seriously reduces the Toughness, and the joint strength values are uneven and vary greatly. Therefore, it is necessary to develop a vacuum brazing method for dissimilar nickel-based superalloys that improves the strength and stability of joints, thereby improving the service stability and safety of brazed components.

Contents of the invention

In view of the deficiencies in the prior art, the purpose of the present invention is to provide a vacuum brazing method for dissimilar nickel-based superalloys that improves the strength and stability of the joints, so as to achieve a more stable connection between the alloys.

In order to achieve the above object, the present invention provides the following technical proposal: a vacuum brazing method for dissimilar nickel-based superalloys that improves the strength and stability of joints, comprising the following steps:

Step 1, preparation before welding: remove the oxide skin on the surface of the alloy by mechanical method until the metallic luster is exposed, then polish the surface with 1500# sandpaper, and clean the parts to be welded in sequence with acetone and alcohol;

Step 2, assembly and positioning: sandwich the intermediate layer alloy between the prepared alloys to be welded to form a "sandwich" brazing assembly, and then use energy storage electric welding to fix the alloy to be welded and press it tightly; the intermediate layer alloy is Foil-like amorphous nickel-based solder with a thickness of 60-150 μm;

Step 3, furnace brazing: Put the assembled components to be welded into a vacuum brazing furnace and evacuate to below 10 ^-3 Pa; heat up to 600-700°C at a rate of 5-15°C/min, and keep warm for 10 -20min; heat up to 850-950°C at a rate of 5-15°C/min, hold for 20-30min; heat up to 1050-1070°C at a rate of 5-10°C/min, hold for 10-15min for vacuum brazing; welding The final component is cooled in sections with the furnace at a rate of 4 °C/min to 900 °C, and then high-purity nitrogen is passed through the furnace to rapidly cool the component to room temperature before it is released from the furnace;

Step 4, homogenization treatment: place the welded assembly in a heating furnace, raise the temperature to 1010-1040°C at a rate of 15-30°C/min, keep it warm for 3-5h, and then cool it to room temperature by oil quenching.

Further, the dissimilar nickel-based superalloys are solid solution strengthened GH3536 alloy and γ′ phase precipitation strengthened GH4738 alloy respectively.

Further, the nickel-based solder described in step 2 is BNi-2 solder with a melting point of 980-1000°C, and its composition is: B: 2.75-3.5%, Si: 4-5%, Cr: 6-8%, Fe: 2.5-3.5%, Ni: balance.

Further, in step 3, before brazing, the temperature is raised in stages to make the brazing assembly more evenly heated.

Compared with prior art, the beneficial effect of the present invention is:

1) The present invention promotes the interdiffusion of elements between the brazing filler metal and the alloy base material by appropriately raising the brazing heat preservation temperature, prolonging the brazing heat preservation time, and matching the homogenization treatment after welding; disappeared, the solid solution structure was completely formed inside, and the uniformity of the microstructure was significantly improved. This process has an unexpected effect in improving the uniformity and stability of the joint strength, and lays the foundation for the long-term reliable and stable operation of vacuum brazing components. The standard deviations of shear strength and tensile strength of brazed joints after treatment under high temperature conditions are 8.0 and 7.5 MPa, which can be reduced by 72% and 78% respectively compared with those before process optimization.

2) The homogenization treatment temperature of the present invention is close to the complete remelting temperature of the γ′ phase in the GH4738 alloy, and the homogenization treatment is cooled by oil quenching. Therefore, this treatment not only homogenizes the internal structure of the weld, but also achieves the purpose of solution treatment of the GH4738 alloy, which lays a good foundation for the subsequent further aging treatment.

3) The process of the present invention is simple to operate, has low requirements on equipment, and has great application and promotion value, especially suitable for brazing connection processes with a joint gap value in the range of 60-150 μm; similar methods can be extended to other dissimilar nickel-based superalloy systems .

Description of drawings

Figure 1 is the microstructure of the joint area after the process described in Example 1.

Fig. 2 is the microstructure of the joint area after the process described in Comparative Example 1.

Detailed ways

Although the existing vacuum brazing method can realize the rapid connection of different grades of nickel-based superalloys, when the joint gap is slightly large, a large area of hard and brittle phases such as borides is easily formed in the center of the weld, resulting in large fluctuations in the joint strength value .

The present invention obtains a new vacuum brazing method for dissimilar nickel-based superalloys that improves the strength and stability of joints through a large number of tests and explorations. Among them, the dissimilar nickel-based superalloys for vacuum brazing are solid solution-strengthened GH3536 alloy and γ′ phase precipitation-strengthened GH4738 alloy; the solder used is BNi-2 nickel-based solder, which contains Cr, Fe, Si, B, etc. Alloying elements with a melting point of 980-1000°C; the size of the joint gap is 60-150 μm, and the specific gap value is controlled by the thickness of the foil-shaped amorphous nickel-based solder. The brazing method comprises the following steps:

Step 1: Use mechanical methods to remove the oxide skin on the surface of the alloy to be welded until the metallic luster is exposed, then polish the surface with 1500# sandpaper, and clean the parts to be welded with acetone and alcohol in sequence.

The purpose of this step is to ensure that the surface of the alloy before welding is smooth and free of scale, oil and other impurities.

Step 2: Put foil-shaped solder between the alloys to be welded to form a "sandwich" brazing assembly, and then use energy storage welding to fix the alloy and press it tightly.

The purpose of this step is to fix the alloy and prevent deviations in the size of the joint gap during welding.

Step 3: Put the assembled components to be welded into a vacuum brazing furnace and evacuate to below 10 ^-3 Pa; heat up to 600-700°C at a rate of 5-15°C/min, and keep warm for 10-20min; Heat up to 850-950°C at a rate of -15°C/min and hold for 20-30 minutes; heat up to 1050-1070°C at a rate of 5-10°C/min and hold for 10-15 minutes for vacuum brazing; the welded components are 4 The rate of °C/min is cooled to 900 °C with the furnace, and then high-purity nitrogen gas is passed through the furnace to rapidly cool the components to room temperature and then come out of the furnace.

The main purpose of this step is to increase the brazing temperature and time under the premise of ensuring that the base metal alloy is not significantly corroded, thereby increasing the content of solid solution in the weld and reducing the precipitation of brittle phases such as borides in the central area. In addition, the staged heating of this step allows for more uniform heating of the brazed components. In the cooling stage, the purpose of slow cooling with the furnace is to slow down the solidification rate, thereby reducing the welding thermal stress; the purpose of rapid cooling with nitrogen gas is to reduce the impact of high temperature and long-term exposure on the microstructure of the alloy, and at the same time improve production efficiency.

Step 4: Put the welded components in a heating furnace, raise the temperature to 1010-1040°C at a rate of 15-30°C/min, keep warm for 3-5h, and then cool to room temperature by oil quenching.

The purpose of this step is to promote the interdiffusion of elements between the base metal and the weld by keeping the heat for a long time under high temperature conditions, so that harmful phases such as borides in the central area of the weld can be fully decomposed and disappeared, and the uniformity of the weld structure can be improved. The homogenization treatment temperature is close to the complete remelting temperature of the γ′ phase in the GH4738 alloy, and the oil quenching after homogenization can achieve the purpose of solid solution treatment of the alloy base metal while homogenizing the microstructure inside the weld, and provide a solid solution for the subsequent aging process. Handling lays the groundwork.

的GH3536、GH4748合金样品为例进行介绍阐述，焊接面为圆形端面，所用钎料成分如下表1所示。The present invention is described in further detail below in conjunction with embodiment. In this embodiment, the size is

The GH3536 and GH4748 alloy samples of GH3536 and GH4748 are used as examples to introduce and explain. The welding surface is a circular end surface, and the components of the solder used are shown in Table 1 below.

BNi-2 nickel-based solder composition (wt.%) in the embodiment of table 1

Element Cr B Si Fe Ni content 6.9 3.1 4.5 3.1 margin

Example 1

Step 1: Remove the oxide skin on the alloy surface by mechanical method until the metallic luster is exposed, then polish the surface with 1500# sandpaper, and clean the parts to be welded with acetone and alcohol in sequence;

Step 2: Put a foil-shaped solder with a thickness of 100 μm between the prepared alloys to be welded to form a "sandwich" structure brazing assembly, and then use energy storage electric welding to fix the alloy to be welded and press it tightly;

Step 3: Put the assembled components to be welded into a vacuum brazing furnace and evacuate to below 10 ^-3 Pa; raise the temperature to 650°C at a rate of 15°C/min and keep it warm for 12 minutes; raise the temperature at a rate of 10°C/min to 870°C, hold for 20 minutes; heat up to 1050°C at a rate of 8°C/min, hold for 15 minutes for vacuum brazing; the welded components are cooled to 900°C with the furnace at a rate of 4°C/min, and then the furnace is passed through high-purity Nitrogen makes the components cool down to room temperature quickly and then out of the furnace;

Step 4: Place the welded assembly in a heating furnace, raise the temperature to 1020°C at a rate of 20°C/min, keep it warm for 4 hours, and then cool it to room temperature by oil quenching.

As shown in Figure 1, after this process, the internal structure of the weld is relatively uniform, and there is no obvious other precipitated phase in the central area.

Example 2

Step 1: Remove the oxide skin on the alloy surface by mechanical method until the metallic luster is exposed, then polish the surface with 1500# sandpaper, and clean the parts to be welded with acetone and alcohol in sequence;

Step 2: Put a foil-shaped solder with a thickness of 110 μm between the prepared alloys to be welded to form a "sandwich" structure brazing assembly, and then use energy storage electric welding to fix the alloy to be welded and press it tightly;

Step 3: Put the assembled components to be welded into a vacuum brazing furnace and evacuate to below 10 ^-3 Pa; raise the temperature to 700°C at a rate of 12°C/min and keep it warm for 15 minutes; raise the temperature at a rate of 15°C/min to 900°C, hold for 25 minutes; heat up to 1060°C at a rate of 5°C/min, hold for 12 minutes for vacuum brazing; the welded components are cooled to 900°C with the furnace at a rate of 4°C/min, and then the furnace is passed through high-purity Nitrogen makes the components cool down to room temperature quickly and then out of the furnace;

Step 4: Put the welded assembly in a heating furnace, raise the temperature to 1030°C at a rate of 15°C/min, keep it warm for 5 hours, and then cool it to room temperature by oil quenching.

Comparative example 1

Step 1: Remove the oxide skin on the alloy surface by mechanical method until the metallic luster is exposed, then polish the surface with 1500# sandpaper, and clean the parts to be welded with acetone and alcohol in sequence;

Step 2: Put a foil-shaped solder with a thickness of 100 μm between the prepared alloys to be welded to form a "sandwich" structure brazing assembly, and then use energy storage electric welding to fix the alloy to be welded and press it tightly;

Step 3: Put the assembled components to be welded into a vacuum brazing furnace and evacuate to below 10 ^-3 Pa; raise the temperature to 850°C at a rate of 15°C/min and keep it warm for 25min; raise the temperature at a rate of 8°C/min To 1030°C, hold for 8 minutes for vacuum brazing; the welded components are cooled to 900°C with the furnace at a rate of 4°C/min, and then high-purity nitrogen is passed through the furnace to rapidly cool the components to room temperature before being released from the furnace;

Compared with the microstructure of the joint area after the process described in Example 1, there is a large area of hard and brittle phases such as borides in the central area of the weld after this process (as shown in Figure 2).

performance testing

The samples processed by vacuum brazing in Example 1 and Comparative Example 1 were subjected to a shear strength test at 730° C., and the test results are shown in Table 2.

Table 2 Joint shear strength test results

sample Shear strength/MPa Standard deviation/MPa Example 1 225, 219, 208, 228, 206, 217, 226, 211 8.0 Comparative example 1 238, 168, 169, 182, 188, 217, 239, 233 28.8

The samples processed by vacuum brazing in Example 1 and Comparative Example 1 were tested for tensile strength at 730° C., and the test results are shown in Table 2.

Table 3 Joint tensile strength test results

sample Tensile strength/MPa Standard deviation/MPa Example 1 259, 271, 269, 281, 278, 283, 274, 266 7.5 Comparative example 1 280, 270, 265, 235, 265, 172, 223, 219 33.8

In Table 2 and Table 3, comparative example 1 is the joint strength of GH3536/GH4738 measured by traditional vacuum brazing process, while Example 1 is the joint strength of GH3536/GH4738 measured by the process of the present invention. It can be seen from the test results that after the process of the present invention is adopted, the joint strength stability is significantly improved, and the standard deviation of the joint strength is reduced by more than 70%, which solves the technical problem of poor joint strength stability in the actual production process.

In addition to the above implementations, the present invention may also have other implementations. All technical solutions in the form of equivalent replacement or equivalent transformation fall within the scope of protection required by the present invention.

Claims (2)

1. A dissimilar nickel-based superalloy vacuum brazing method improving joint strength stability, characterized in that it may further comprise the steps: Step 1, preparation before welding: remove the oxide skin on the surface of the alloy by mechanical method until the metallic luster is exposed, then polish the surface with 1500# sandpaper, and clean the parts to be welded in sequence with acetone and alcohol; Step 2, assembly and positioning: sandwich the intermediate layer alloy between the prepared alloys to be welded to form a "sandwich" brazing assembly, and then use energy storage electric welding to fix the alloy to be welded and press it tightly; the intermediate layer alloy is Foil-like amorphous nickel-based solder with a thickness of 60-150 μm; Step 3, furnace brazing: Put the assembled components to be welded into a vacuum brazing furnace and evacuate to below 10 ^-3 Pa; heat up to 600-700°C at a rate of 5-15°C/min, and keep warm for 10 -20min; heat up to 850-950°C at a rate of 5-15°C/min, hold for 20-30min; heat up to 1050-1070°C at a rate of 5-10°C/min, hold for 10-15min for vacuum brazing; welding The final component is cooled in sections with the furnace at a rate of 4 °C/min to 900 °C, and then high-purity nitrogen is passed through the furnace to rapidly cool the component to room temperature before it is released from the furnace; Step 4, homogenization treatment: place the welded components in a heating furnace, raise the temperature to 1010-1040°C at a rate of 15-30°C/min, keep warm for 3-5h, and then cool to room temperature by oil quenching; The dissimilar nickel-based superalloys are solid solution strengthened GH3536 alloy and γ′ phase precipitation strengthened GH4738 alloy; The nickel-based brazing filler metal described in step 2 is BNi-2 brazing filler metal, melting point is 980-1000 DEG C, in terms of mass percentage, its composition is: B: 2.75-3.5%, Si: 4-5%, Cr: 6 -8%, Fe: 2.5-3.5%, Ni: balance. 2. The method for vacuum brazing of dissimilar nickel-based superalloys according to claim 1, characterized in that step 3 raises the temperature in stages before brazing to make the brazing assembly more evenly heated.

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