A method for the production of a ceramic powder-metal diffusion couple without sintering

Abstract

This invention relates to the field of diffusion couple preparation, specifically a method for preparing ceramic powder-metal diffusion couples without sintering. The specific steps are as follows: A first portion of ceramic powder, a metal, and a second portion of ceramic powder are sequentially loaded into a mold from bottom to top, and a pressure of 20 MPa-50 MPa is applied. After holding the pressure, the mold is removed to obtain a pre-pressed diffusion couple blank. The blank is then placed in a container, evacuated until the absolute pressure inside the container is ≤50 Pa, and then sealed to obtain a sealed blank. The sealed blank is then subjected to cold isostatic pressing to obtain the ceramic powder-metal diffusion couple. This invention achieves densification and interfacial bonding between the ceramic powder and the metal at room temperature. This method completely avoids the high-temperature stage of traditional sintering processes, significantly reducing energy consumption and cost; it avoids problems caused by high temperatures such as metal oxidation, formation of brittle intermetallic compounds, grain growth, and ceramic phase transformation decomposition, and more realistically reflects the subsequent interdiffusion behavior.

Description

Technical Field

[0001] This invention relates to the field of diffusion couple preparation, specifically a method for preparing ceramic powder-metal diffusion couples without sintering. Background Technology

[0002] Diffusion couples are a key experimental method for studying interdiffusion behavior, phase equilibrium, and interfacial reactions between solid materials. Their core feature lies in bringing two different materials (or two different states of the same material) into close contact at a specific temperature and holding them at that temperature, promoting atomic diffusion across the interface to form a continuous compositional gradient and potential reaction layers. By analyzing the composition and microstructure of the diffusion region, key parameters such as interdiffusion coefficient, phase composition, reaction layer growth kinetics, and interfacial stability can be directly obtained. This experimental method plays a crucial role in the development of high-performance composite materials, electronic packaging, high-temperature structural components, and connection technologies.

[0003] Currently, the preparation of diffusion couples involving powders is highly dependent on high-temperature sintering or densification processes (e.g., CN101255060B, CN104190935B, CN105272333B, CN114964990B). The main methods include: (1) Bulk-to-bulk diffusion couple method: ceramic powder needs to be pre-formed and sintered at high temperature to prepare a dense ceramic block, and then precisely contacted with a metal block or metal foil before high-temperature annealing. Although this method has good interfacial contact, the pre-sintering process of the ceramic block is complicated and has poor applicability to ceramics that are difficult to sinter or prone to phase transformation at high temperatures. (2) Hot-press diffusion couple method: ceramic powder and metal sheet / powder are placed in a mold, and powder densification and interfacial diffusion are achieved simultaneously under high temperature and uniaxial pressure. This method eliminates the pre-sintering step, but the high-pressure environment may introduce additional stress, causing brittle ceramic particles to break and affecting diffusion behavior. (3) Spark plasma sintering (SPS) diffusion couple method: This method utilizes pulsed current to rapidly achieve powder densification and interfacial diffusion at relatively low temperatures and pressures. Although it is highly efficient, it still requires a high-temperature sintering process, the equipment is expensive, and the rapid heating and non-equilibrium process may interfere with the intrinsic diffusion behavior of the material.

[0004] The above methods cannot avoid the high-temperature sintering / densification steps, resulting in the following common problems in the preparation of diffusion couples: (1) high energy consumption and long cycle; (2) high temperature easily induces violent interfacial reactions, forming excessively thick reaction layers or brittle phases, interfering with or masking the true interdiffusion behavior (see Zhang M, Zhang J, Zhou R Y. Effect of Zr on the solid sintering process of SiBCN ceramics: Diffusion couple method experiment and DFT calculation[J]. Journal of the American Ceramic Society, 2024, 107(2):736-747); (3) difficult to apply to materials that are prone to volatility, decomposition, adverse phase transformation or abnormal grain growth at high temperatures. Therefore, it is urgent to develop a new method that can effectively prepare ceramic powder-metal diffusion couples with good interfacial contact and can truly reflect the interdiffusion behavior between materials, under the premise of completely avoiding the high-temperature sintering process. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing ceramic powder-metal diffusion couples without sintering, specifically including the following steps: (1) The first part of ceramic powder, metal and the second part of ceramic powder are loaded into the mold from bottom to top in sequence. A pressure of 20 MPa-50 MPa is applied to the upper surface of the second part of ceramic powder. After holding the pressure, the mold is demolded to obtain the pre-pressed diffusion bismuth preform. (2) The above-mentioned blank is placed into a container, and a vacuum is drawn until the absolute pressure inside the container is ≤50 Pa and then sealed to obtain a sealed blank; (3) The above-mentioned sealed blank is subjected to cold isostatic pressing treatment. After being taken out of the container, a ceramic powder-metal diffusion couple is obtained.

[0006] Further, in step (1), the particle size of the ceramic powder is 100 nm-99 μm, and the ceramic powder is one or more of alumina powder, magnesium oxide powder, aluminum nitride powder and boron nitride powder.

[0007] The metal is in the form of a block, sheet, or filament; the metal is a low-melting-point metal or a refractory metal, wherein the low-melting-point metal is one of copper, zinc, aluminum, and nickel, and the refractory metal is one of tantalum, tungsten, rhenium, and molybdenum, or an alloy of the above metals.

[0008] The ceramic powder needs to be pretreated by drying at 150-300℃ for 2-3 hours; the metal needs to be pretreated by ultrasonically cleaning with anhydrous ethanol and acetone for 10 minutes in sequence, and then blown dry.

[0009] The total amount of ceramic powder is the sum of the mass of the first part and the second part of ceramic powder. The proportion of the first part or the second part of ceramic powder is 30%-60% of the total amount of ceramic powder. The mass ratio of the metal to the ceramic powder is 1:500-1:2000. The height of the pre-pressed diffused bismuth preform is 10-20 mm.

[0010] The mold is a steel mold, and the pressure is applied by a jack, which can be a manual screw jack or a hydraulic jack. The pressure holding time is 20 s-60 s.

[0011] Furthermore, in step (2), the container is a rubber protective sleeve with a thickness of 0.1-0.3 mm, and the sealing is achieved by binding and tightening the container opening.

[0012] Furthermore, in step (3), the working medium for cold isostatic pressing is hydraulic oil, the pressure for cold isostatic pressing is 400-600 MPa, and the holding time is 1-30 min.

[0013] Advantages and beneficial effects of the present invention: This invention provides a method for preparing ceramic powder-metal diffusion couples without sintering. The core of this method lies in achieving densification and interfacial bonding between ceramic powder and metal at room temperature through a step-by-step physical pressing process of "pre-pressing, vacuum sealing, and cold isostatic pressing." This method completely avoids the high-temperature stage of traditional sintering processes, significantly reducing energy consumption and cost, and improving preparation efficiency. It avoids problems caused by high temperatures, such as metal oxidation, formation of brittle intermetallic compounds, grain growth, and ceramic phase transformation decomposition, ensuring a pure interface that more accurately reflects subsequent interdiffusion behavior. It overcomes the deficiency of insufficient interfacial bonding strength in traditional room-temperature powder compaction methods for preparing diffusion couples. The process is simple, safe, and widely applicable. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the ceramic powder-metal diffusion couple preparation process of the present invention; wherein, 1-ceramic powder, 2-metal, 3-jack, 4-rubber protective sleeve, 5-vacuum pump tube, 6-cold isostatic press, 7-L-HH hydraulic oil; Figure 2 The results show the characterization of the interface after diffusion experiments on the diffusion couple in Example 1; wherein, Figure 2 (a) is a scanning electron microscope image of the interface. Figure 2(b) shows the element line scan results at the corresponding interface position; Figure 3 The images shown are scanning electron microscope (SEM) images and elemental plane scans of the diffusion couple interface in Example 2. Figure 4 This is a scanning electron microscope image of the radial cross-section of the diffusion couple in Comparative Example 1. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the embodiments.

[0016] Example 1 Ceramic powder 1 is selected from alumina ceramic powder with a particle size of 0.8-1.2 μm, and 5 g is weighed for later use; metal 2 is selected from high-purity tantalum wire with a diameter of 100 μm (purity ≥99.95%), and three tantalum wires with a total mass of 0.005 g are cut for later use. First, the ceramic powder is placed in a vacuum oven for 2 h at a temperature of 200℃. The tantalum wire is ultrasonically cleaned with anhydrous ethanol and acetone for 10 min respectively, and then dried for later use. A cylindrical steel (alloy tool steel Cr12MoV) mold with an inner diameter of 20 mm, an outer diameter of 80 mm, and a height of 10 cm is selected and used in conjunction with a manual hydraulic jack 3. The overall preparation process of the diffusion couple is as follows. Figure 1 As shown, the specific steps are as follows: (1) First, place half of the alumina powder to be filled into a cylindrical mold. Use a flattening tool that matches the inner diameter of the mold to perform preliminary flattening of the powder to ensure that the powder surface is level and without protrusions or depressions. Place three pre-treated high-purity tantalum wires horizontally and without bending on the preliminary flattened powder surface. The axial direction of the tantalum wires is parallel to the radial direction of the mold. All tantalum wires are parallel to each other and in the same horizontal plane, and are parallel to the upper and lower end faces of the mold. The length of a single tantalum wire is 15 mm. One tantalum wire is placed in the center, and the other two tantalum wires are placed on both sides, with a distance of 5 mm between them and the middle tantalum wire. Then fill in the remaining half of the alumina powder. Use the flattening tool to press the surface lightly again to ensure flatness. Use a jack to apply a constant axial pressure of 30 MPa to the powder system in the mold. After holding the pressure for 30 seconds, demold to obtain a round pre-pressed blank with a diameter of 20 mm and a height of about 10 mm. (2) The blank obtained in step (1) is placed into the rubber protective sleeve 4 (Inco Medical, thickness is 0.1 mm). A small vacuum pump is used to evacuate the rubber protective sleeve through the vacuum pump tube 5. The vacuum is evacuated until the absolute pressure in the system is ≤50Pa and the evacuation time is ≥60 s. After confirming that there is no air leakage, the open end is immediately double-tied and sealed with nylon cable ties to ensure that there is no air backflow. (3) Place the sealed rubber protective sleeve into the L-HH hydraulic oil 7 of the cold isostatic press 6, press the sample with a constant isostatic pressure of 400 MPa, hold the pressure for 15 minutes, release the pressure and remove the rubber protective sleeve to complete the preparation of the insulating ceramic-metal diffusion couple (alumina-tantalum diffusion couple). The diameter and thickness of the diffusion couple obtained at this time are reduced by 1 mm and 0.5 mm respectively compared with those in step (1).

[0017] The prepared diffusion couple green blank was placed in a vacuum annealing furnace for annealing. The annealing process was as follows: under normal pressure of high-purity argon gas with a purity ≥99.999%, the temperature was raised to 1400℃ at a heating rate of 5℃ / min, held for 20 h, and then cooled to room temperature with the furnace to complete the diffusion experiment.

[0018] Result detection The samples after diffusion experiments were sealed with epoxy resin, then radially cut using diamond wire cutting. The cut samples were then sealed again with epoxy resin, followed by grinding and polishing before observation and characterization. The grinding and polishing process included: sequential grinding with 400-grit, 800-grit, 1200-grit, and 2000-grit sandpaper; followed by polishing with diamond polishing paste with a particle size of 1-5 μm. After ultrasonic cleaning and drying, the sample surface was sputter-coated with gold, and then the microstructure and elemental line scanning analysis were performed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

[0019] The characterization results of the alumina-tantalum diffusion couple prepared in Example 1 are as follows: Figure 2 As shown, the alumina-tantalum diffusion couple prepared in this embodiment exhibits good diffusion performance, specifically as follows: Firstly, Figure 2 (a) shows that the interface between alumina ceramic and pure tantalum wire is continuous and complete, without cracks, delamination, pores or interface debonding defects. Even though there is a difference in the coefficient of thermal expansion between the two materials, no interface failure caused by thermal mismatch occurred after high-temperature annealing at 1400℃, and the interface bonding force is excellent. Secondly, a continuous and uniformly thick diffusion transition layer is formed at the interface, without harmful diffusion defects such as concentrated precipitation of brittle reactive phases and Kirkendal pores, and the diffusion reaction is uniformly and stably distributed along the interface. Thirdly, the element line scan results corresponding to the interface positions are displayed as follows: Figure 2 (b) Tantalum underwent significant interdiffusion with aluminum and oxygen, forming a continuous elemental concentration gradient across the original interface. The effective diffusion layer thickness reached the micrometer level, confirming that the two formed a stable metallurgical bond, which meets the requirements for the preparation and research of diffusion couples.

[0020] Example 2 The raw materials used were magnesium oxide ceramic powder with a particle size of 0.8-1.2 μm and high-purity tungsten wire with a diameter of 100 μm (purity ≥99.95%). Other steps were the same as in Example 1, and the same diffusion experiment was performed.

[0021] The characterization results of the magnesium oxide-tungsten diffusion couple prepared in Example 2 are as follows: Figure 3 As shown, SEM morphology observation reveals that the interface between tungsten and magnesium oxide ceramics is continuous and intact, without cracks, delamination, debonding, or through-hole defects. Even with a significant difference in their thermal expansion coefficients, no interface failure due to thermal mismatch occurred after annealing at 1400℃ for 20 hours and furnace cooling. Furthermore, the magnesium oxide ceramics achieved good densification through the non-sintering cold isostatic pressing process of this invention, with only a few isolated closed pores, providing sufficient close contact conditions for interfacial atomic diffusion. EDS elemental distribution results for the corresponding interface region show significant interdiffusion between tungsten, magnesium, and oxygen, confirming the successful preparation of a magnesium oxide-tungsten diffusion couple with excellent interfacial bonding and significant elemental interdiffusion behavior using the method of this invention. A stable metallurgical bond is formed at the interface, fully meeting the research requirements for material interdiffusion behavior and interfacial reaction mechanisms. This also verifies the good universality of this method for different ceramic-metal systems.

[0022] Comparative Example 1 The comparative example uses the same raw materials as Example 2: magnesium oxide ceramic powder with a particle size of 0.8-1.2 μm and high-purity tungsten wire with a diameter of 100 μm (purity ≥99.95%). Except for omitting step (2) vacuum packaging and step (3) cold isostatic pressing in Example 2, the other steps in this comparative example are completely the same as in Example 2, and the same diffusion experiment was carried out.

[0023] The SEM morphology of the magnesium oxide-tungsten diffusion couple prepared in Comparative Example 1 is as follows: Figure 4 As shown, the interface between tungsten and magnesium oxide ceramic is completely debonded and separated, and the annular gap formed between them is filled with epoxy resin used for sample preparation, with no effective interfacial bonding; magnesium oxide ceramic has poor density and cannot form effective element interdiffusion and metallurgical bonding, which does not meet the research requirements of diffusion couple.

Claims

1. A method for preparing ceramic powder-metal diffusion couples without sintering, characterized in that, Includes the following steps: (1) The first part of ceramic powder, metal and the second part of ceramic powder are loaded into the mold from bottom to top in sequence. A pressure of 20 MPa-50 MPa is applied to the upper surface of the second part of ceramic powder. After holding the pressure, the mold is demolded to obtain the pre-pressed diffusion bismuth preform. (2) The above-mentioned blank is placed into a container, and a vacuum is drawn until the absolute pressure inside the container is ≤50 Pa and then sealed to obtain a sealed blank; (3) The above-mentioned sealed blank is subjected to cold isostatic pressing treatment. After being taken out of the container, a ceramic powder-metal diffusion couple is obtained.

2. The method for preparing a sinter-free ceramic powder-metal diffusion couple according to claim 1, characterized in that: In step (1), the particle size of the ceramic powder is 100 nm-99 μm, and the ceramic powder is one or more of alumina powder, magnesium oxide powder, aluminum nitride powder and boron nitride powder.

3. The method for preparing a sinter-free ceramic powder-metal diffusion couple according to claim 1, characterized in that: In step (1), the metal is in the form of a block, sheet or filament; the metal is a low melting point metal or a refractory metal, the low melting point metal is one of copper, zinc, aluminum and nickel, the refractory metal is one of tantalum, tungsten, rhenium and molybdenum, or an alloy of the above metals.

4. The method for preparing a sinter-free ceramic powder-metal diffusion couple according to claim 1, characterized in that: In step (1), the ceramic powder needs to be pretreated: dried at 150-300℃ for 2-3 hours; the metal needs to be pretreated: ultrasonically cleaned with anhydrous ethanol and acetone for 10 minutes in sequence, and then dried.

5. The method for preparing a sinter-free ceramic powder-metal diffusion couple according to claim 1, characterized in that: In step (1), the sum of the mass of the first part of ceramic powder and the second part of ceramic powder is the total amount of ceramic powder used, and the proportion of the first part of ceramic powder or the second part of ceramic powder is 30%-60% of the total amount of ceramic powder used; the mass ratio of the metal to the total amount of ceramic powder used is 1:500-1:2000; the height of the pre-pressed diffused bismuth blank is 10-20 mm.

6. The method for preparing a sinter-free ceramic powder-metal diffusion couple according to claim 1, characterized in that: In step (1), the mold is a steel mold, the pressure is applied by a jack, which is a manual screw jack or a hydraulic jack, and the pressure holding time is 20 s-60 s.

7. The method for preparing a sinter-free ceramic powder-metal diffusion couple according to claim 1, characterized in that: In step (2), the container is a rubber protective sleeve with a thickness of 0.1-0.3 mm, and the sealing is achieved by binding and tightening the container opening.

8. The method for preparing a sinter-free ceramic powder-metal diffusion couple according to claim 1, characterized in that: In step (3), the working medium for cold isostatic pressing is hydraulic oil, the pressure for cold isostatic pressing is 400-600 MPa, and the holding time is 1-30 min.

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