Co-sintering preparation method of multi-material product

Abstract

The invention discloses a co-sintering preparation method of a multi-material product, which comprises the following steps: respectively mixing N parts of alloy powder and M parts of other powder with a polymer binder to obtain (M + N) parts of materials, plastifying and molding the (M + N) parts of materials according to the structure of the multi-material product to obtain a multi-material green body, and sequentially degreasing and sintering the multi-material green body to obtain the multi-material product. And sintering at a solid-liquid coexistence state temperature to obtain a multi-material product. According to the invention, the polymer is used as a filler, the porosity difference during accumulation of different material powders is reduced, the sintering shrinkage of different materials is approximately consistent, and the alloy is in a solid-liquid phase coexistence state in the sintering process by using super-solid phase sintering of the alloy material, so that the original shape can be kept, the stress generated by sintering shrinkage can be relieved, and the service life of the alloy is prolonged. And defects are reduced, and multi-material co-sintering of the alloy material is achieved. The technology can be widely applied to production of multi-material mechanisms and functional parts in the fields of aerospace, automobile manufacturing, electronic devices and the like.

Description

Technical Field

[0001] The invention relates to a co-sintering preparation method for a multi-material product, belonging to the technical field of multi-material preparation and powder metallurgy engineering. Background Art

[0002] With the continuous development of modern manufacturing, especially in high-end industries such as aerospace, automobile manufacturing, and electronic devices, the complexity and diversity of product design are increasing. In many engineering applications, materials are required to have different properties and functions at the same time, such as high strength, high corrosion resistance, good conductivity, or excellent thermal stability. Traditional single materials cannot meet these multifunctional requirements, so multi-material systems came into being.

[0003] In the preparation process of powder metallurgy multi-material products, especially in the sintering process, due to the different melting points, thermal expansion coefficients and sintering shrinkage rates of different materials, cracks, warping or defects may appear in the final product. How to achieve efficient co-sintering and uniform bonding of different materials during the sintering process, and reduce the stress and defects caused by sintering shrinkage, is a key issue in the preparation of powder metallurgy multi-material products. Traditional multi-material co-sintering methods mostly rely on the selection of appropriate powders and the control of high-temperature sintering conditions, but these methods still have difficult-to-overcome problems such as melting point mismatch, shrinkage differences, and sintering defects. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a co-sintering preparation method for multi-material products. The preparation method of the present invention, by adopting polymer filling molding, using polymer to regulate shrinkage, and combining super solid phase sintering to slow down the stress and defects generated during shrinkage, effectively solves the shrinkage difference, stress concentration and defect problems in the sintering process of alloy materials and different materials, optimizes the shape retention and defect control during the sintering process, and provides a new solution for the high-quality manufacturing of multi-material products.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] The present invention provides a co-sintering preparation method for a multi-material product, wherein N parts of alloy powder and M parts of other powder are respectively mixed with a polymer binder to obtain (M+N) parts of material, and according to the structure of the multi-material product, the (M+N) parts are plasticized to obtain a multi-material green body, and the multi-material green body is sequentially degreased and sintered to obtain the multi-material product;

[0007] During the sintering, the sintering temperature is controlled to be the solid-liquid coexistence temperature of the alloy components in the multi-material green body, wherein the liquid phase volume fraction of the alloy components is 5-70%, preferably 20-40%.

[0008] The co-sintering preparation method of the present invention adopts polymer as filler, which reduces the difference in porosity when powders of different materials are piled up, makes the sintering shrinkage of different materials close to the same, and simultaneously utilizes the super solid phase sintering of alloy materials to make the alloy in a solid-liquid coexistence state during the sintering process, which can not only maintain the original shape but also relieve the stress caused by sintering shrinkage, reduce the generation of defects, and realize multi-material co-sintering of alloy materials.

[0009] In a preferred embodiment, N≥1, M≥1.

[0010] In a preferred embodiment, the alloy in the alloy powder is an alloy having a solid-liquid coexisting phase, and the alloy in the alloy powder is selected from one of stainless steel, titanium alloy, aluminum alloy, copper-based alloy, nickel-based alloy, cobalt-based alloy, and tungsten alloy powder.

[0011] In a preferred embodiment, the other powder is selected from at least one of ceramic powder and metal ceramic powder.

[0012] Among them, ceramic powders such as alumina, silicon carbide, etc., metal ceramic powders such as NiFe 2 O 4 Metal ceramic.

[0013] In a preferred embodiment, the mixing is carried out in a twin-rotor mixer, the mixing temperature is 5-30°C above the softening point of the polymer binder, the mixing time is 0.5-2h, and the rotor speed is 20-100rpm. After the mixing is completed, the mixture is cooled to obtain N portions of material.

[0014] In a preferred embodiment, the volume fraction of the raw material powder in the (M+N) parts of the material is 50-70%, preferably 52-64%, and more preferably 52-56%. In the present invention, by adding a larger component of polymer, the porosity of the raw material powder during stacking can be adjusted so that the porosity of different powders per unit volume is close to the same, thereby controlling the shrinkage of sintering.

[0015] Further preferably, among the (M+N) parts of materials, the difference in sintering yield of any part of the materials at the same temperature is ≤1.5%.

[0016] In the actual operation process, several small samples are used to test the sintering shrinkage rate of materials at different volume fractions. The shrinkage of each material is close by adjusting the powder volume fraction, and the specific volume fraction is determined. By controlling the volume fraction of the raw material powder, the difference in the sintering shrinkage rate of any material at the same temperature is ≤1.5%. The final defect degree is minimized and the material performance is better.

[0017] In a preferred embodiment, the polymer binder is selected from a wax-based binder, a water-based binder, and a plastic-based binder.

[0018] Further preferably, the wax-based binder is selected from at least one of paraffin wax, beeswax, microcrystalline wax, carnauba wax, and polyethylene wax binder.

[0019] Further preferably, the water-based binder is a polyethylene glycol binder.

[0020] Further preferably, the plastic-based binder is a polyoxymethylene binder.

[0021] Preferably, the forming method is selected from one of injection molding, extrusion 3D printing, and powder metallurgy rheological manufacturing.

[0022] Further preferably, the forming method is powder metallurgy rheological manufacturing. The process of powder metallurgy rheological manufacturing is as follows: (M + N) parts of materials are respectively crushed to obtain (M + N) parts of material particles. According to the structure of the multi-material component, the (M + N) parts of materials are sequentially laid in the mold, the mold is pre-pressed first, and then the mold is subjected to low-temperature hot pressing to form.

[0023] Even more preferably, the particle size of the (M + N) parts of material particles is 5 - 1000 μm, preferably 550 - 700 μm. The inventor found that there is an obvious relationship between the particle size of the material particles and the interface resolution. Only by controlling within the scope of the present invention can a multi-material product with uniform material distribution and clear interfaces between different materials be obtained.

[0024] In actual operation, a crusher is used for crushing, and then the particle material with a particle size within the above range is obtained through screening by a sieve.

[0025] Even more preferably, the pressure of the pre-pressing is 10 - 50 MPa.

[0026] In the present invention, a conventional hydraulic molding press is used. The particle materials of different materials are respectively laid at the corresponding positions in the mold according to the designed structure, and a pressure of 10 - 50 MPa is applied in advance to make the materials more compact and dense. If the pressure is too small, the green body is not firm, and the shape control of the final product is poor, and the product accuracy cannot be guaranteed. If the pressure is too large, the particles will be broken and the distribution will be uneven.

[0027] Even more preferably, the temperature of the low-temperature hot pressing is 5 - 30 °C above the softening point of the polymer binder, the pressure is 10 - 60 MPa, and the temperature is kept constant and the pressure is kept for 5 - 60 min. After pre-pressing, the mold is heated and pressurized to the above range, the temperature is kept constant and the pressure is kept, and a green body with clear interfaces and high density can be obtained. After debinding and sintering, a multi-material product with clear interfaces and high strength can be obtained.

[0028] In a preferred embodiment, the degreasing process first performs preliminary degreasing and then performs thermal degreasing, and the preliminary degreasing is selected from solvent degreasing or catalytic degreasing.

[0029] Further preferably, when the polymer binder is selected from a wax-based binder or a water-based binder, solvent degreasing is used.

[0030] Further preferably, when the polymer binder is selected from plastic-based binders, catalytic degreasing is used.

[0031] Different degreasing methods are adopted according to the selected adhesive systems, and the degreasing effect is better. Wax-based and water-based adhesive systems can be removed by solvent degreasing, and the degreasing of samples with a thickness of less than 15mm can be achieved. It is further preferred to use plastic-based adhesives and remove them by catalytic degreasing, which can achieve the degreasing of samples with a thickness of more than 30mm.

[0032] Further preferably, the temperature of the thermal debinding is 200-600° C. The sample after preliminary debinding is placed in a sintering furnace for thermal debinding to further remove residual binder at a temperature of 200-600° C. In the actual operation process, the debinding temperature can be improved according to the thermal decomposition behavior of the material, and a temperature step can be set in the area of ​​intense decomposition.

[0033] In a preferred embodiment, the sintering time is 30-200 min. In the present invention, the sintering temperature is within the super solid phase sintering temperature range of the alloy material, that is, within the solid-liquid coexistence temperature range. The liquid phase volume of the alloy material at different solid-liquid coexistence temperatures is obtained by testing, and the temperature range with a liquid phase volume fraction of 5-70% is selected for sintering. Further preferably, a temperature range with a liquid phase volume fraction of 20-40% is selected for sintering. The inventors have found that through super solid phase sintering, since part of the material becomes liquid during sintering, the stiffness of the material can be reduced, so that when it is subjected to stress caused by the contraction of another material, the interaction is reduced, and the generation of defects is reduced.

[0034] Principles and advantages

[0035] The present invention is the first to propose a co-sintering preparation method for multi-material products. The strategies of polymer filling and super solid phase sintering are adopted: 1. The polymer binder is blended with the powder material to realize the plasticization molding of the powder, and the sintering shrinkage behavior of the powder can be regulated at the same time; by adopting a specific polymer binder incorporation ratio, different materials can achieve consistent sintering shrinkage when the sintering density is close to the same. 2. Super solid phase sintering is adopted during sintering, and the alloy material is in a solid-liquid coexistence state. The grains and powder boundaries of the alloy form a liquid phase, which greatly reduces the stiffness of the system, can slow down the stress caused by the shrinkage of other components of the multi-material, and reduce the risk of defects; at the same time, the existence of the solid phase ensures that the original shape of the alloy is maintained. The combination of the two strategies can realize the co-firing of multi-material alloy materials.

[0036] The advantages of the present invention are as follows: (1) The material has a wide range of applicability and can be applied to various materials with solid-liquid coexistence states, and can be used for multi-material composites with all other powder metallurgy materials that can be sintered and densified. (2) By mixing with polymers, the powder has processing capabilities similar to polymers, and complex multi-material structure green bodies can be prepared by existing plasticizing molding methods such as injection molding, extrusion 3D printing, powder metallurgy rheological manufacturing, etc. (3) The incorporation of polymers makes the sintering shrinkage of powder materials controllable, and the sintering shrinkage of different materials can be matched by adjusting the incorporation volume of the polymer. (4) The co-sintering method based on super solid phase sintering can greatly reduce the generation of defects while maintaining the sintered shape, thereby achieving stable multi-material co-sintering of alloy materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 :Principle of co-sintering method for multi-material products.

[0038] Figure 2 : Cu-20Ni alloy and NiFe sintered in Example 1 and Comparative Example 1 2 O 4 Metal-ceramic multi-material component, the left is Example 1, and the right is Comparative Example 2.

[0039] Figure 3 : Microstructure and element distribution of the interface between the two materials of Example 1.

[0040] Figure 4 : Cu-20Ni alloy and NiFe sintered in Comparative Example 2 2 O 4 Metal-ceramic multi-material components. DETAILED DESCRIPTION

[0041] Example 1

[0042] In this embodiment, Cu-20Ni alloy and NiFe2 O 4 Metal ceramics. The specific steps are as follows:

[0043] Step S1, Cu-20Ni alloy powder and NiFe 2 O 4 The metal ceramic powder is mixed with a polyoxymethylene-based binder to obtain the material. The Cu-20Ni alloy powder and the NiFe 2 O 4 The volume fraction of the metal ceramic powder is set to 52%, the volume fraction of the polyoxymethylene-based binder system is 48%, and the mass fraction of the binder components is: polyoxymethylene: polypropylene: stearic acid = 90%: 7.5%: 2.5%; the mixing temperature is 180 °C, the mixing speed is 35 rpm, and the mixing time is 30 min;

[0044] Step S2, granulating the alloy and metal ceramic materials obtained in S1 in a screw extruder respectively to obtain cylindrical particles with a diameter of 2-3 mm and a height of 3-5 mm, with a processing temperature of 180° C. and a screw speed of 500 r / min.

[0045] Step S3, crushing the alloy and metal ceramic materials obtained in S2 with a crusher and sieving to obtain a granular material with an average particle size of 600 μm;

[0046] Step S4, laying the alloy particle material obtained in S3 in the mold in the shape of a five-pointed star, laying the metal ceramic particle material around it, applying a pressure of 10 MPa to compact it, then raising the temperature to 180°C, applying a pressure of 20 MPa and maintaining it for 5 minutes, and then cooling to obtain a multi-material structure green body.

[0047] Step S5, placing the multi-material structure green body obtained in S4 in a catalytic degreasing furnace for degreasing, the degreasing temperature is 120° C., oxalic acid and nitrogen gas are introduced, and the degreasing time is 30 hours.

[0048] Step S6, placing the sample after catalytic debinding in a sintering furnace for further thermal debinding and sintering, the thermal debinding temperature is in the range of 300-500°C, the time is 6h, the sintering temperature is 1170°C, and it is maintained for 90min. At this time, the Cu-20Ni alloy is in a super solid phase sintering state, the liquid phase volume is 35%, and the NiFe 2 O 4 The metal ceramic is in a solid phase sintering state.

[0049] Finally, we get Figure 2 The samples shown have high density, reaching more than 95%, completely retaining the morphology of the green body without any defects. The microstructure after sintering is evenly distributed, the interface between the two phases is clear, and the interface shear strength is 60MPa.

[0050] Example 2

[0051] The material system is the same as that of Example 1, except that the volume fraction of the powder in Cu-20Ni is increased to 56%, and the green body is formed by a rheological manufacturing method, and the specific steps are as follows:

[0052] Step S1, Cu-20Ni alloy and NiFe 2 O 4 The metal ceramics were mixed with polyoxymethylene-based binders to obtain materials. The volume fraction of the powder in the Cu-20Ni alloy material was 56%, and the volume fraction of the NiFe 2 O 4 The volume fraction of the powder in the metal ceramic material is 52%. After using the above different volume fractions, the Cu-20Ni alloy and NiFe 2 O 4 The difference in shrinkage rate of the metal ceramic after sintering is ≤1.5%, and the mass fraction of the binder components is: polyoxymethylene: polypropylene: stearic acid = 90%: 7.5%: 2.5%; the mixing temperature is 180°C, the mixing speed is 35rpm, and the mixing time is 30min;

[0053] Step S2, granulating the alloy and metal ceramic materials obtained in S1 in a screw extruder respectively to obtain cylindrical particles with a diameter of 2-3 mm and a height of 3-5 mm, with a processing temperature of 180° C. and a screw speed of 500 r / min.

[0054] Step S3, printing the alloy and metal ceramic materials obtained in S2 by using a dual-nozzle extrusion 3D printer to obtain a multi-material structure green body.

[0055] Step S4, placing the multi-material structure green body obtained in S3 in a catalytic degreasing furnace for degreasing, the degreasing temperature is 120° C., oxalic acid and nitrogen gas are introduced, and the degreasing time is 30 hours.

[0056] Step S5, placing the sample after catalytic debinding in a sintering furnace for further thermal debinding and sintering, the thermal debinding temperature is in the range of 300-500°C, the time is 6h; the sintering temperature is 1170°C, maintained for 90min, at which time the Cu-20Ni alloy is in a super solid phase sintering state, the liquid phase volume is 35%, and the NiFe 2 O 4 The metal ceramic is in a solid phase sintering state.

[0057] The final product has a higher density, NiFe 2 O 4 The density of the metal ceramic is 96%, the density of the Cu-20Ni alloy is 98%, the two-phase structure is evenly distributed and the interface is clear, and the interface shear strength is 65MPa.

[0058] Example 3

[0059] Adopt W-30Cu alloy system and Al 2 O 3 The ceramic system prepares multi-material structures. The specific steps are as follows:

[0060] Step S1, W-30Cu alloy powder and Al 2 O 3 The ceramic powders were mixed with water-based binders to obtain the materials. The loading amount of both powders was set to 54%, and the mass fraction of the binder components was: polyethylene glycol: low-density polyethylene: stearic acid = 80%: 15%: 5%; the mixing temperature was 150 °C, the mixing speed was 35 rpm, and the mixing time was 30 min;

[0061] Step S2, granulating the alloy and ceramic materials obtained in S1 in a screw extruder respectively to obtain cylindrical particles with a diameter of 2-3 mm and a height of 3-5 mm, with a processing temperature of 150° C. and a screw speed of 500 r / min.

[0062] Step S3, printing the alloy and ceramic materials obtained in S2 by using a dual-nozzle extrusion 3D printer to obtain a multi-material structure green body.

[0063] Step S4, placing the multi-material structure green body obtained in S3 in water for solvent degreasing, with the temperature set to 60° C. and the time being 24 hours.

[0064] Step S5, placing the degreased sample obtained in S4 in a sintering furnace for thermal degreasing and sintering, wherein the thermal degreasing temperature is 300-400°C, and the degreasing time is 6 hours; the sintering temperature is 1550°C, and the sintering time is 60 minutes. At this time, the W-30Cu alloy is in a solid-liquid coexistence sintering state, and Al 2 O 3 In solid phase sintering state.

[0065] In the final product, W-30Cu alloy phase and Al 2 O 3 The density of the ceramic phase is 98%, the two-phase microstructure is evenly distributed, the interface is clear, and the interface shear strength is 60MPa.

[0066] Comparative Example 1

[0067] The other conditions are the same as those in Example 1, except that the sintering temperature is 1190°C, at which time the liquid phase volume in the Cu-20Ni alloy accounts for more than 70%. The sintered product is as follows Figure 2As shown on the right, the product has not deformed and the preset two-phase shapes are maintained, but there are obvious and large holes on the surface of the alloy phase. The density of the metal ceramic phase reaches more than 95%, and the density of the alloy phase is less than 80%.

[0068] Comparative Example 2

[0069] The other conditions are the same as those in Example 1, except that the sintering temperature is 1140°C, at which time the Cu-20Ni alloy is in a solid phase sintering state. The sintered product is as follows Figure 4 As shown, the shapes of the alloy phase and the metal-ceramic phase are retained, but the shrinkage is uneven and there are obvious cracks on the surface of the product.

Claims

1. A co-sintering preparation method for a multi-material product, characterized in that: N parts of alloy powder and M parts of other powders are mixed with a polymer binder to obtain (M+N) parts of materials, and according to the structure of the multi-material product, the (M+N) parts of materials are plasticized to obtain a multi-material green body, and the multi-material green body is degreased and sintered in sequence to obtain the multi-material product; During the sintering, the sintering temperature is controlled to be the solid-liquid coexistence temperature of the alloy components in the multi-material green body, wherein the liquid phase volume fraction of the alloy components is 5-70%.

2. The co-sintering preparation method of a multi-material product according to claim 1, characterized in that: Said N≥1, M≥1; The alloy in the alloy powder is an alloy having a solid-liquid coexisting phase, and the alloy in the alloy powder is selected from one of stainless steel, titanium alloy, aluminum alloy, copper-based alloy, nickel-based alloy, cobalt-based alloy, and tungsten alloy powder; The other powder is selected from at least one of ceramic powder and metal ceramic powder.

3. A co-sintering preparation method for a multi-material product according to any one of claims 1-2, characterized in that: The mixing is carried out in a twin-rotor mixer, the mixing temperature is 5-30° C. above the softening point of the polymer binder, the mixing time is 0.5-2 hours, and the rotor speed is 20-100 rpm.

4. A co-sintering preparation method for a multi-material product according to any one of claims 1-2, characterized in that: The polymer binder is selected from one of a wax-based binder, a water-based binder, and a plastic-based binder; The wax-based binder is selected from at least one of paraffin wax, beeswax, microcrystalline wax, carnauba wax, and polyethylene wax binder; The water-based adhesive is a polyethylene glycol adhesive; The plastic-based adhesive is a polyoxymethylene adhesive.

5. A co-sintering preparation method for a multi-material product according to any one of claims 1-2, characterized in that: In the (M+N) parts of material, the volume fraction of raw material powder is 50-70%; Among the (M+N) parts of materials, the difference in sintering shrinkage rate of any part of the materials at the same temperature is ≤1.5%.

6. A co-sintering preparation method for a multi-material product according to any one of claims 1-2, characterized in that: The molding method is selected from injection molding, extrusion 3D printing, and powder metallurgy rheological manufacturing.

7. The co-sintering preparation method of a multi-material product according to any one of claim 6, characterized in that: The molding method is powder metallurgy rheological manufacturing molding, and the powder metallurgy rheological manufacturing molding process is: (M+N) parts of materials are crushed separately to obtain (M+N) parts of material particles, and (M+N) parts of materials are laid in the mold in sequence according to the structure of the multi-material product, and the mold is first pre-pressed, and then the mold is subjected to low-temperature hot pressing molding; The particle size of the (M+N) parts of material particles is 5-1000 μm. The pre-pressing pressure is 10-50 MPa; The temperature of the low-temperature hot pressing molding is 5-30° C. above the softening point of the polymer binder, the pressure is 10-60 MPa, and the temperature and pressure are maintained for 5-60 minutes.

8. A co-sintering preparation method for a multi-material product according to any one of claims 1-2, characterized in that: The degreasing process is to first perform preliminary degreasing and then perform thermal degreasing, and the preliminary degreasing is selected from solvent degreasing or catalytic degreasing.

9. A co-sintering preparation method for a multi-material product according to any one of claims 1-2, characterized in that: When the polymer binder is selected from a wax-based binder or a water-based binder, solvent degreasing is used; When the polymer binder is selected from plastic-based binders, catalytic degreasing is used; The temperature of the thermal degreasing is 200-600°C.

10. A co-sintering preparation method for a multi-material product according to any one of claims 1-2, characterized in that: The sintering time is 30-200 min.

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