CN116693314A - Low-stress high-temperature-resistant connection method for C/C composite material and high-temperature alloy - Google Patents

Abstract

The invention provides a low-stress and high-temperature-resistant connection method between a C/C composite material and a high-temperature alloy, comprising: using a mixed powder of Ni-Ti alloy powder and carbon-based powder as a connection material, and at a lower connection temperature, Ni-Ti The liquid formed by melting the alloy powder reacts in situ with the carbon-based powder in the gap between the C/C composite material and the superalloy to form a Ni-based solid solution-based composite connection layer strengthened by TiC particles, thereby realizing the C/C composite material and the superalloy. Low-stress, high-temperature resistant connections for superalloys. The connecting material of the invention is easy to prepare, low in cost, simple in process and strong in adaptability, and can realize connection of large gaps, unequal gaps and complex structures.

Description

A low-stress and high-temperature-resistant connection method for C/C composite materials and superalloys

technical field

The invention relates to the technical field of connecting composite materials and metals, in particular to a low-stress and high-temperature-resistant connection method for C/C composite materials and high-temperature alloys.

Background technique

Carbon fiber reinforced carbon-based composite materials (C/C composite materials) have excellent properties such as low density, high temperature resistance, thermal shock resistance, and high strength at high temperatures. They are ideal for manufacturing combustion chamber components, rocket nozzles, and thermal protection structures for hypersonic aircraft. It is an ideal material and has important application value in the new generation of strategic missiles and aerospace engines. However, the ductility and impact toughness of C/C composites are poor, and machining is difficult. In applications, they usually need to be connected with metals to form a composite structure. With the maturity of the C/C composite material preparation process and the improvement of its performance, its application in aerospace and advanced weapon systems is becoming more and more extensive. The research and development of reliable connection technology between C/C composite materials and metals, especially superalloys, has become an important issue. It is an important topic in the field of development of a new generation of high-performance engines in my country.

In recent years, there have been some research reports on the connection of C/C composite materials and metals at home and abroad. From the analysis of the material combination and application background of the connection, the main problems in the connection of C/C composite materials and metals for engines are as follows: 1 ) C/C composites are difficult to melt to form a liquid phase, and have extremely poor metallurgical compatibility with metals, so they cannot be directly melted and welded; 2) There is a large difference in thermal expansion coefficient between C/C composites and metals, and the connection is often It will form a large thermal stress, resulting in the reduction of joint strength or even direct cracking; 3) In the thrust chamber of the engine, the connection joints between C/C composite materials and metals usually serve in high temperature environments, and the temperature resistance requirements are high (often at 1200 ℃ above). At present, the methods that can realize the connection of C/C composite materials and metal mainly include diffusion welding and brazing. Although the diffusion welding method can realize the connection of C/C composite materials and metals, the thermal stress of the connection is large, and the performance of the joint is unstable; moreover, a large pressure needs to be applied during the connection process, and the structural adaptability is poor, so it is difficult to realize the actual large size or Connection of complex components. In contrast, the brazing method has a simple process, no pressure, and strong structural adaptability. It is the most appropriate method for connecting C/C composite materials and metals for engines. However, traditional brazing also has the problem of thermal stress in the connection, and the high temperature resistance of the joint is poor, which makes it difficult to meet the practical application requirements for the connection of C/C composite materials and metals. In order to alleviate the thermal stress of brazed joints and improve their high-temperature performance, composite brazing methods have been developed on the basis of traditional brazing at home and abroad.

Studies have shown that composite brazing adjusts the thermal expansion coefficient of the connection layer by adding a certain proportion of low thermal expansion coefficient enhancement phases to traditional solders (such as Ag-Cu-Ti, Ti-Zr-Cu-Ni, Ag-Ti, etc.), Such as SiC, etc., can effectively relieve the thermal stress of the connection and improve the strength of the joint; and adding a reinforcing phase can also improve the high-temperature strength of the joint to a certain extent. However, limited by the heat-resistant temperature (initial liquefaction temperature) of the low-melting metal solder matrix, although the existing composite brazing in the form of "directly adding reinforcement phase" can improve the high-temperature performance of the joint to a certain extent, it still cannot Fundamentally improve the heat-resistant temperature of the joint. Taking Ag-Cu-Ti as the matrix solder for composite brazing as an example, the maximum temperature resistance of the joint does not exceed 800 °C. Theoretically, the use of high-melting-point solder can improve the high-temperature performance and heat-resistant temperature of the joint, but high brazing temperature will greatly increase the thermal stress of the connection. connection is particularly disadvantageous. To sum up, how to solve the high temperature resistance problem of the joint compatiblely while reducing the thermal stress of the connection by composite brazing, and realize the "low stress/high temperature resistance" connection is the bottleneck problem that needs to be broken through in the connection of C/C composite materials and superalloys.

Contents of the invention

The purpose of the present invention is to solve the problems of "large connection thermal stress" and "poor joint high temperature resistance" existing in the connection of C/C composite materials (i.e. carbon fiber reinforced carbon matrix composite materials) and superalloys in a compatible manner, and provides a method based on ( Ni-Ti)+C→TiC+Ni reaction in-situ synthesis of TiC/Ni composite connection layer low stress high temperature resistant connection method.

A low-stress and high-temperature-resistant connection method for a C/C composite material and a superalloy, comprising:

The mixed powder of Ni-Ti alloy powder and carbon-based powder is used as the connection material. At a lower connection temperature, the liquid formed by melting the Ni-Ti alloy powder is in the weld gap between the C/C composite material and the superalloy and the carbon-based material. The powder reacts in situ to form a Ni-based solid solution-based composite connection layer reinforced by TiC particles.

By using the mixed powder of low-melting Ni-Ti alloy powder and carbon-based powder as the connecting material, at the connecting temperature, the low-melting Ni-Ti alloy powder will melt to form a liquid phase and wet the base metal to be welded (that is, C/C composite material and superalloy) and fill the weld gap; the carbon-based powder reacts with the demelting element Ti in the Ni-Ti liquid phase to synthesize TiC in situ at the connection temperature, so that the connection layer is isothermally solidified, and finally forms TiC particle-strengthened Ni Based solid solution-based composite connection layer, that is, TiC/Ni composite connection layer. The connection method can introduce the low thermal expansion TiC reinforcement phase into the connection layer through the (Ni-Ti)+C→TiC+Ni reaction to relieve the thermal stress of the connection, and quickly consume the demelting element Ti in the Ni-Ti alloy solder , forming a Ni-based solid solution matrix with a higher heat-resistant temperature, so it can realize the low-stress and high-temperature resistant connection of C/C composite materials and superalloys.

Optionally, the method includes:

Step S1, preparing the base metal to be welded: grinding the surface to be welded of the C/C composite material and the superalloy, removing surface impurities and oxide films, cleaning the C/C composite material and the superalloy, and drying them for later use;

Step S2, preparing the connecting material: weighing the Ni-Ti alloy powder and the carbon-based powder in proportion and mixing them uniformly to form a mixed powder, then adding an appropriate amount of organic solvent and stirring evenly to prepare a paste;

Step S3, preset connection material: evenly pre-set the prepared paste connection material between the C/C composite material and the high-temperature alloy surface to be welded, and press lightly to make the connection material and the two base materials to be welded (i.e. C /C composite material and superalloy) are fully contacted to form the part to be welded, and the connecting material is the preset layer;

Step S4, vacuum connection: put the parts to be welded into a vacuum brazing furnace and pump the furnace to a vacuum, then raise the temperature to the connection temperature, keep the temperature for a period of time, and slowly cool the furnace to room temperature.

Optionally, in step S1, use 240-600 mesh sandpaper to polish the surface to be welded; use alcohol and clean the C/C composite material and superalloy in an ultrasonic cleaner for 2-3 times; dry in a vacuum oven, The drying temperature is 40-60°C, and the drying time is 10-30 minutes.

Optionally, in step S2, the percentage of Ti atoms in the Ni-Ti alloy powder is 15-40%, and the particle size is 10-30 μm. Ni-Ti under this condition has a low melting point and can be formed at the joining temperature The liquid phase is beneficial to react with the carbon-based powder, and is conducive to the isothermal solidification of the connecting layer. The alloy powder is preferably Ni62Ti38.

Optionally, in step S2, the particle size of the carbon-based powder is 2-5 μm, and the carbon-based powder is at least one selected from diamond, graphite and carbon fiber; the mass fraction of the carbon-based powder in the mixed powder is 1%-6%.

Optionally, in step S2, the organic solvent is at least one selected from ethanol, α-terpineol, and gasoline-rubber, preferably α-terpineol.

Optionally, in step S3, the thickness of the preset layer is 0.4-0.7 mm.

Optionally, in step S4, the furnace is evacuated to a vacuum not higher than 5×10 ^-3 Pa.

Optionally, in step S4, the process of heating up to the connection temperature is: heating to 800-1000°C at a heating rate of 10-15°C/min; then heating to a connecting temperature of 1180-1300°C at a heating rate of 50°C/min. The purpose of slow temperature rise in the first stage is to enable the sample to be heated stably and evenly; the rapid temperature rise in the second stage is to make the sample to be welded reach the connection temperature as soon as possible, so as to reduce the gap between Ni-Ti alloy powder and C powder during the temperature rise stage. reaction between.

Optionally, in step S4, the heat preservation is 5-30 minutes; the furnace cooling rate is ≤5° C./min. This holding time is chosen because within this period of time, the connecting material can be fully melted to fill the weld gap, and excessive interfacial reaction between the connecting layer and the C/C composite can be avoided. The purpose of slow cooling is to minimize the residual thermal stress in the joint due to excessive cooling rate.

The beneficial effects brought by the technical solution provided by the present invention at least include:

(1) The connection method has the characteristics of "low temperature connection/high temperature service", and can realize low stress and high temperature resistant connection of C/C composite materials and high temperature alloys under low temperature and low pressure conditions.

(2) The connection method can quickly consume the low-melting Ni-Ti alloy solder while introducing a low thermal expansion TiC reinforcement phase into the connection layer to relieve the thermal stress of the connection through the (Ni-Ti)+C→TiC+Ni reaction The demelting element Ti forms a Ni-based solid solution-based connection layer with a higher heat-resistant temperature.

(3) The connection method adopts the mixed powder of low-melting Ni-Ti alloy powder plus C powder as the connection material, the connection material is easy to prepare, low in cost, simple in the process, and the powder state connection material has strong adaptability to the joint structure , can realize the connection of large gap, unequal gap and complex structure.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Figure 1 is a scanning electron microscope image of the connection joint between the C/C composite material and the GH3044 superalloy based on the in-situ synthesis of the TiC/Ni composite connection layer in Example 1 of the present invention;

2 is a scanning electron microscope image of the side interface structure of the C/C composite material based on the in-situ synthesis of the TiC/Ni composite connection layer and the GH3044 superalloy connection joint composite material in Example 1 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be described in detail below with reference to the drawings and specific embodiments.

Example 1

This embodiment is a low-stress and high-temperature-resistant connection method between a C/C composite material and a GH3044 superalloy based on in-situ synthesis of a TiC/Ni composite connection layer.

The C/C composite material involved is a two-dimensional wound and three-dimensional perforated structure with a density of 1.65-1.78g/cm ³ and cut into 5×5×5mm ³ cubes; the involved GH3044 superalloy is a solid solution strengthened Ni Base superalloy with a density of 8.89g/cm ³ , a melting temperature range of 1352-1375°C, and a thermal expansion coefficient of 16.28×10 ^-6 K ^-1 , cut into squares of 10×10×3mm ³ . The connection material involved is composed of Ni62Ti38 (atomic fraction) alloy powder and diamond powder, wherein the particle size of Ni-Ti alloy powder is 10-30 μm, the particle size of diamond powder is 2-5 μm, and the mass fraction of diamond powder in the mixed powder is 3 %.

The specific process of this embodiment includes the following steps:

Step 1, prepare the base metal to be welded. Grind the surface to be welded of the C/C composite material and GH3044 superalloy with 240-600 mesh sandpaper to remove surface debris and oxide film; put the polished composite material and superalloy into alcohol, and clean it repeatedly with an ultrasonic cleaner 3 times; after cleaning, put it into a vacuum drying oven to dry for later use, the drying temperature is 40°C, and the drying time is 10 minutes.

Step 2, prepare the connecting material. Weigh the Ni62Ti38 alloy powder and diamond powder in proportion, firstly mix the powder mechanically, then add an appropriate amount of α-terpineol and stir evenly to prepare a paste.

Step 3, preset connection materials. Preset the prepared paste connecting material evenly between the C/C composite material and the superalloy surface to be welded, and press lightly to make it fully contact with the two base materials; control the thickness of the preset layer to 0.5mm.

Step 4, vacuum connection. Put the parts to be welded with pre-set connection materials into a vacuum brazing furnace, close the furnace door tightly, and evacuate to 5×10 ^-3 Pa; then heat up to 1000°C at a heating rate of 15°C/min; /min heating rate to 1300°C connection temperature, keep warm for 25min and cool down in the furnace, cooling rate ≤5°C/min. Take out the connection sample when the temperature in the furnace drops to room temperature.

Step 5, joint tissue and performance testing. Cut the connecting joint along the cross-section by wire cutting method, use 150, 240, 400, 600, 800, 1000, 1200, 1500, 2000 mesh sandpaper to grind the cross-section of the joint step by step and then polish it to prepare metallographic samples. The microstructure of the joint was observed with an electron microscope, and the phase composition was identified by X-ray diffraction and energy spectrum analysis; the connection joint obtained in step 4 was put into a special fixture, and the room temperature and high temperature shear strength tests were carried out on an electronic universal testing machine. The loading rate was 0.5mm/min, record the maximum load output when the workpiece is sheared, convert the shear strength of the joint according to the maximum load, and take the average value of 5 samples as the final result. The shear strength of the obtained joint at room temperature is 32.1 MPa.

Example 2

This embodiment is a low-stress and high-temperature-resistant connection method between a C/C composite material and a GH4169 superalloy based on in-situ synthesis of a TiC/Ni composite connection layer.

The C/C composite material involved is a two-dimensional wound and three-dimensional perforated structure, with a density of 1.65-1.78g/cm ³ , cut into 5×5×5mm ³ cubes; the involved GH4169 superalloy is a precipitation-strengthened Ni-based High-temperature alloy with a density of 8.24g/cm ³ , a melting temperature range of 1260-1320°C, and a thermal expansion coefficient of 18.7×10 ^-6 K ^-1 , cut into squares of 10×10×3mm ³ . The connection material involved is composed of Ni62Ti38 (atomic fraction) alloy powder and graphite powder, wherein the particle size of Ni-Ti alloy powder is 10-30 μm, the particle size of graphite powder is 2 μm, and the mass fraction of diamond powder in the mixed powder is 2%.

The specific process of this embodiment includes the following steps:

Step 1, prepare the base metal to be welded. Grind the surface to be welded of the C/C composite material and GH4169 superalloy with 240-600 mesh sandpaper to remove surface debris and oxide film; put the polished composite material and superalloy into alcohol, and clean it repeatedly with an ultrasonic cleaner 3 times; after cleaning, put it into a vacuum drying oven to dry for later use, the drying temperature is 40°C, and the drying time is 10 minutes.

Step 2, prepare the connecting material. Weigh Ni62Ti38 alloy powder and graphite powder according to the proportion, firstly mix the powder mechanically, then add appropriate amount of α-terpineol and stir evenly to prepare a paste.

Step 3, preset connection materials. Preset the prepared paste connecting material evenly between the C/C composite material and the superalloy surface to be welded, and press lightly to make it fully contact with the two base materials; control the thickness of the preset layer to 0.5mm.

Step 4, vacuum connection. Put the parts to be welded with pre-set connection materials into a vacuum brazing furnace, close the furnace door tightly, and evacuate to 5×10 ^-3 Pa; then heat up to 1000°C at a heating rate of 15°C/min; /min heating rate to 1300°C connection temperature, keep warm for 25min and cool down in the furnace, cooling rate ≤5°C/min. Take out the connection sample when the temperature in the furnace drops to room temperature.

Step 5, joint tissue and performance testing. Cut the connecting joint along the cross-section by wire cutting method, use 150, 240, 400, 600, 800, 1000, 1200, 1500, 2000 mesh sandpaper to grind the cross-section of the joint step by step and then polish it to prepare metallographic samples. The microstructure of the joint was observed with an electron microscope, and the phase composition was identified by X-ray diffraction and energy spectrum analysis; the connection joint obtained in step 4 was put into a special fixture, and the room temperature and high temperature shear strength tests were carried out on an electronic universal testing machine. The loading rate was 0.5mm/min, record the maximum load output when the workpiece is sheared, convert the shear strength of the joint according to the maximum load, and take the average value of 5 samples as the final result. The shear strength of the obtained joint at room temperature is 28.0 MPa.

Example 3

This embodiment is a low-stress and high-temperature-resistant connection method between a C/C composite material and a GH4169 superalloy based on in-situ synthesis of a TiC/Ni composite connection layer.

The C/C composite material involved is a two-dimensional wound and three-dimensional perforated structure, with a density of 1.65-1.78g/cm ³ , cut into 5×5×5mm ³ cubes; the involved GH4169 superalloy is a precipitation-strengthened Ni-based High-temperature alloy with a density of 8.24g/cm ³ , a melting temperature range of 1260-1320°C, and a thermal expansion coefficient of 18.7×10 ^-6 K ^-1 , cut into squares of 10×10×3mm ³ . The connection material involved is composed of Ni62Ti38 (atomic fraction) alloy powder and chopped carbon fiber, wherein the particle size of Ni-Ti alloy powder is 10-30 μm, the length of carbon fiber is 0.3 mm, and the diameter of single filament is 6 μm. The mass of carbon fiber in the mixed powder The score is 3%.

The specific process of this embodiment includes the following steps:

Step 1, prepare the base metal to be welded. Grind the surface to be welded of the C/C composite material and GH4169 superalloy with 240-600 mesh sandpaper to remove surface debris and oxide film; put the polished composite material and superalloy into alcohol, and clean it repeatedly with an ultrasonic cleaner 3 times; after cleaning, put it into a vacuum drying oven to dry for later use, the drying temperature is 40°C, and the drying time is 10 minutes.

Step 2, prepare the connecting material. Weigh the Ni62Ti38 alloy powder and chopped carbon fiber powder in proportion, firstly mix the powder mechanically, then add an appropriate amount of α-terpineol and stir evenly to prepare a paste.

Step 3, preset connection materials. Preset the prepared paste-like connecting material evenly between the C/C composite material and the superalloy surface to be welded, and press lightly to make it fully contact with the two base materials; control the thickness of the preset layer to 0.7mm.

Step 4, vacuum connection. Put the parts to be welded with pre-set connection materials into a vacuum brazing furnace, close the furnace door tightly, and evacuate to 5×10 ^-3 Pa; then heat up to 1000°C at a heating rate of 15°C/min; /min heating rate to 1300°C connection temperature, keep warm for 25min and cool down in the furnace, cooling rate ≤5°C/min. Take out the connection sample when the temperature in the furnace drops to room temperature.

Step 5, joint tissue and performance testing. Cut the connecting joint along the cross-section by wire cutting method, use 150, 240, 400, 600, 800, 1000, 1200, 1500, 2000 mesh sandpaper to grind the cross-section of the joint step by step and then polish it to prepare metallographic samples. The microstructure of the joint was observed with an electron microscope, and the phase composition was identified by X-ray diffraction and energy spectrum analysis; the connection joint obtained in step 4 was put into a special fixture, and the room temperature and high temperature shear strength tests were carried out on an electronic universal testing machine. The loading rate was 0.5mm/min, record the maximum load output when the workpiece is sheared, convert the shear strength of the joint according to the maximum load, and take the average value of 5 samples as the final result. The shear strength of the obtained joint at room temperature is 34.3 MPa.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. Should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (10)

1. A low-stress and high-temperature-resistant connection method between a C/C composite material and a superalloy, characterized in that it comprises: The mixed powder of Ni-Ti alloy powder and carbon-based powder is used as the connection material. At a lower connection temperature, the liquid formed by melting the Ni-Ti alloy powder is in the weld gap between the C/C composite material and the superalloy and the carbon-based material. The powder reacts in situ to form a Ni-based solid solution-based composite connection layer reinforced by TiC particles. 2. The method according to claim 1, characterized in that the method comprises: Step S1, preparing the base material to be welded: grinding the surface to be welded of the C/C composite material and the superalloy, cleaning the C/C composite material and the superalloy, and drying them for later use; Step S2, preparing the connecting material: weighing the Ni-Ti alloy powder and the carbon-based powder in proportion and mixing them uniformly to form a mixed powder, then adding an appropriate amount of organic solvent and stirring evenly to prepare a paste; Step S3, preset connection material: evenly pre-set the prepared paste connection material between the C/C composite material and the superalloy surface to be welded, and lightly press the connection material to fully contact the two base materials to be welded to form The material to be welded is the preset layer; Step S4, vacuum connection: put the parts to be welded into a vacuum brazing furnace and pump the furnace to a vacuum, then raise the temperature to the connection temperature, keep the temperature for a period of time, and slowly cool the furnace to room temperature. 3. The method according to claim 1, characterized in that, in step S1, use 240-600 mesh sandpaper to polish the surface to be welded; use alcohol and clean the C/C composite material and superalloy 2-3 in an ultrasonic cleaning machine times; drying is carried out in a vacuum drying oven, the drying temperature is 40-60°C, and the drying time is 10-30min. 4. The method according to claim 1, characterized in that, in step S2, the percentage of Ti atoms in the Ni-Ti alloy powder is 15-40%, the particle size is 10-30 μm, and the alloy powder is preferably Ni62Ti38. 5. The method according to claim 1, characterized in that, in step S2, the particle size of the carbon-based powder is 2 to 5 μm, and the carbon-based powder is selected from at least one of diamond, graphite and carbon fiber; the carbon-based powder in the mixed powder The mass fraction of powder is 1%-6%. 6. The method according to claim 1, characterized in that, in step S2, the organic solvent is at least one selected from ethanol, α-terpineol, gasoline-rubber, preferably α-terpineol. 7. The method according to claim 1, characterized in that, in step S3, the thickness of the preset layer is 0.4-0.7 mm. 8. The method according to claim 1, characterized in that, in step S4, the furnace is evacuated to a vacuum not higher than 5×10 ^{−3 Pa} . 9. The method according to claim 1, characterized in that, in step S4, the process of raising the temperature to the connection temperature is: heating to 800-1000°C at a heating rate of 10-15°C/min; Heating rate Heating to 1180 ~ 1300 ℃ connection temperature. 10. The method according to claim 1, characterized in that, in step S4, the heat preservation is 5-30 minutes; the furnace cooling rate is ≤5°C/min.