A method of co-sintering a multi-material article

Abstract

The application discloses a co-sintering preparation method of a multi-material product, wherein N portions of alloy powder and M portions of other powder are respectively mixed with a polymer binder to obtain (M+N) portions of material, the (M+N) portions of material are plasticized to obtain a multi-material green body according to the structure of the multi-material product, and the multi-material green body is sequentially subjected to debinding and sintering at a solid-liquid coexistence temperature to obtain the multi-material product. The application uses a polymer as filling, reduces the difference in porosity when different material powders are stacked, makes the sintering shrinkage of different materials close to each other, simultaneously uses super-solid-phase sintering of an alloy material, makes the alloy in a solid-liquid phase coexistence state in the sintering process, can maintain the original shape, can relieve the stress generated by sintering shrinkage, reduces the generation of defects, and realizes the multi-material co-sintering of the alloy material. The technology can be widely applied to the production of multi-material mechanisms and functional components in the fields of aerospace, automobile manufacturing and electronic devices.

Description

TECHNICAL FIELD

[0001] The present application relates to a co-sintering preparation method of a multi-material product, and belongs to the technical field of multi-material preparation and powder metallurgy engineering. BACKGROUND

[0002] With the continuous development of modern manufacturing industry, especially in high-end industries such as aerospace, automobile manufacturing, 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 electrical conductivity or excellent thermal stability. Traditional single materials cannot meet these multi-functional requirements, so multi-material systems have emerged.

[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 occur in the final product. How to realize efficient co-sintering and uniform bonding of different materials in the sintering process, and reduce the stress and defects caused by sintering shrinkage, is the key problem to realize the preparation of powder metallurgy multi-material products. Traditional multi-material co-sintering methods mostly rely on suitable powder selection and control of high-temperature sintering conditions, but these methods still have problems such as mismatched melting points, shrinkage differences, and sintering defects that are difficult to overcome. SUMMARY

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

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0006] The present application provides a co-sintering preparation method of a multi-material product, which comprises the following steps: mixing N parts of alloy powder and M parts of other powder with a polymer binder to obtain (M+N) parts of material; according to the structure of the multi-material product, (M+N) parts of plastic forming are obtained to obtain a multi-material green body; and the multi-material green body is sequentially subjected to debinding and sintering to obtain a multi-material product.

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

[0008] The co-sintering preparation method of the present application uses polymer as filler, reduces the difference in porosity when different material powders are stacked, makes the sintering shrinkage of different materials close to each other, and uses super-solid-phase sintering of alloy materials to make the alloy in a solid-liquid coexistence state during sintering, so that the original shape can be maintained and the stress caused by sintering shrinkage can be relieved, thereby reducing the generation of defects and realizing multi-material co-sintering of alloy materials.

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

[0010] In a preferred embodiment, the alloy in the alloy powder is a solid-liquid coexistence phase alloy, 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 at least one of ceramic powder and cermet powder.

[0012] The ceramic powder is, for example, alumina or silicon carbide, and the cermet powder is, for example, NiFe2O4 cermet.

[0013] In a preferred embodiment, the mixing is performed in a double 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 mixing is completed, the N portions of material are cooled to obtain the N portions of material.

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

[0015] In a further preferred embodiment, in the (M+N) portions of material, the difference in sintering yield of any one portion of material at the same temperature is ≤1.5%.

[0016] In actual operation, the sintering shrinkage of the material at different volume fractions is tested by using several small samples, the volume fraction of the powder is adjusted to make the shrinkage of each material close to each other, the specific volume fraction is determined, and the volume fraction of the raw material powder is controlled to make the difference in sintering shrinkage of any one portion of material at the same temperature ≤1.5%, so that the final defect degree is the lowest and the material performance is the best.

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

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

[0022] Further preferably, the forming method is powder metallurgy rheological forming, and the powder metallurgy rheological forming process comprises: crushing (M+N) portions of material to obtain (M+N) portions of material particles, laying the (M+N) portions of material in the mold according to the structure of the multi-material component, pre-pressing the mold, and then low-temperature hot-pressing the mold.

[0023] Further preferably, the particle size of the (M+N) portions of material particles is 5-1000 μm, and preferably 550-700 μm. The inventors have found that the particle size of the material particles has a significant relationship with the interface resolution, and only when the particle size is controlled within the range of the present application, can a multi-material product with uniform material distribution and clear material interface be obtained.

[0024] In actual operation, a crusher is used for crushing, and then a screen is used for screening to obtain the particle material with the particle size within the above range.

[0025] Further preferably, the pre-pressing pressure is 10-50 MPa.

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

[0027] Further preferably, the low-temperature hot-pressing temperature is 5-30 ℃ above the softening point of the polymer binder, the pressure is 10-60 MPa, and the temperature and pressure are maintained for 5-60 min. After pre-pressing, the mold is heated and pressed to the above range, and then the temperature and pressure are maintained, so that a green body with a clear interface and high density can be obtained, and then the green body is defatted and sintered to obtain a multi-material product with a clear interface and high strength.

[0028] Preferably, the debinding process is first carried out by a preliminary debinding, and then by a thermal debinding, the preliminary debinding being selected from solvent debinding or catalytic debinding.

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

[0030] Further preferably, when the polymeric binder is selected from a plastic-based binder, catalytic debinding is used.

[0031] Different debinding methods are used according to the different binder systems selected, and the debinding effect is better, wherein the binder systems of wax-based and water-based can be removed by solvent debinding, and the debinding of samples with a thickness of less than 15 mm can be achieved; further preferably, a plastic-based binder is used, and the debinding of samples with a thickness of greater than 30 mm can be achieved by catalytic debinding.

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

[0033] Preferably, the sintering time is 30-200 min. In the present application, the sintering temperature is in the range of the super-solid-phase sintering temperature of the alloy material, i.e. in the range of the solid-liquid coexistence temperature, and the liquid phase volume of the alloy material at different solid-liquid coexistence temperatures is obtained by testing, and the temperature interval with a liquid phase volume fraction of 5-70% is selected for sintering. Further preferably, the temperature interval with a liquid phase volume fraction of 20-40% is selected for sintering, and the inventors have found that, by super-solid-phase sintering, a part of the material becomes liquid when sintering, which can reduce the rigidity of the material, reduce the interaction when the material is subjected to stress caused by the shrinkage of another material, and reduce the generation of defects.

[0034] Principle and advantage

[0035] The application initiatively proposes a co-sintering preparation method of multi-material products. The strategy of polymer filling and super-solid phase sintering is adopted: 1. The polymer binder is blended with the powder material, the plastic forming of the powder can be realized, and the sintering shrinkage behavior of the powder can be controlled; 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. The super-solid phase sintering is adopted during sintering, the alloy material is in a solid-liquid coexistence state, the liquid phase is formed at the grain boundary of the alloy, 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 reduces 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 multi-material co-sintering of the alloy material.

[0036] The advantages of the application are as follows: (1) The material has wide applicability, which can be applied to various materials with solid-liquid coexistence state, and can be multi-materially combined with all sintering densification powder metallurgy materials. (2) By mixing with the polymer, the powder has the processing ability similar to the polymer, and the complex multi-material structure green body can be prepared by the existing plastic forming method such as injection molding, extrusion type 3D printing, powder metallurgy rheological manufacturing and the like. (3) The incorporation of the polymer makes the sintering shrinkage of the powder material controllable, and the sintering shrinkage of different materials is matched by adjusting the incorporation volume of the polymer. (4) The co-sintering method based on the super-solid phase sintering can greatly reduce the generation of defects while maintaining the sintering shape, and realize the stable multi-material co-sintering of the alloy material. BRIEF DESCRIPTION OF DRAWINGS

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

[0038] Figure 2 : Cu-20Ni alloy and NiFe2O4 cermet multi-material components after sintering in example 1 and comparative example 1, left is example 1, right is comparative example 2.

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

[0040] Figure 4 : Cu-20Ni alloy and NiFe2O4 cermet multi-material components after sintering in comparative example 2. DETAILED DESCRIPTION

[0041] Example 1

[0042] In this embodiment, Cu-20Ni alloy and NiFe2O4 cermet are used. The specific steps are as follows:

[0043] Step S1, Cu-20Ni alloy powder and NiFe2O4 cermet powder are mixed with polyformaldehyde-based binder respectively to obtain material. The volume fraction of Cu-20Ni alloy powder and NiFe2O4 cermet powder is set to 52%, and the volume fraction of polyformaldehyde-based binder system is 48%. The mass fraction of the binder components is: polyformaldehyde: polypropylene: stearic acid = 90%: 7.5%: 2.5%. The mixing temperature is 180 ℃, the mixing speed is 35 rpm, and the mixing time is 30 min.

[0044] Step S2, the alloy and cermet material obtained in S1 are granulated in a screw extruder respectively to obtain cylindrical particles with a diameter of 2-3 mm and a height of 3-5 mm. The processing temperature is 180 ℃, and the screw speed is 500 r / min.

[0045] Step S3, the alloy and cermet material obtained in S2 is crushed by a crusher and sieved to obtain a particle material with an average particle size of 600 μm.

[0046] Step S4, the alloy particle material obtained in S3 is laid in the mold in the shape of a five-pointed star, and the cermet particle material is laid around it. A pressure of 10 MPa is applied to compact it, and then the temperature is raised to 180 ℃, a pressure of 20 MPa is applied and maintained for 5 min, and then cooled to obtain a green body of a multi-material structure.

[0047] Step S5, the green body of the multi-material structure obtained in S4 is placed in a catalytic debinding furnace for debinding. The debinding temperature is 120 ℃, oxalic acid and nitrogen gas are introduced, and the debinding time is 30 h.

[0048] Step S6, the sample after catalytic debinding is placed in a sintering furnace for further thermal debinding and sintering. The thermal debinding temperature is in the range of 300-500 ℃, the time is 6 h, the sintering temperature is 1170 ℃, and the holding time is 90 min. At this time, the Cu-20Ni alloy is in a super-solid phase sintering state, and the liquid phase volume is 35%. The NiFe2O4 cermet is in a solid phase sintering state.

[0049] The final sample is shown in Figure 2 The product has high density, all reaching more than 95%, completely retaining the morphology of the green body and without defects. The sintered structure is uniformly distributed, the two-phase interface is clear, and the interface shear strength is 60 MPa.

[0050] Example 2

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

[0052] Step S1, Cu-20Ni alloy and NiFe2O4 cermet were mixed with polyformaldehyde-based binder respectively to obtain the material. The volume fraction of the powder in the Cu-20Ni alloy material was 56%, and the volume fraction of the powder in the NiFe2O4 cermet material was 52%. After using the above different volume fractions, the shrinkage difference of Cu-20Ni alloy and NiFe2O4 cermet after sintering was ≤1.5%. The mass fraction of the binder components was polyformaldehyde: polypropylene: stearic acid = 90%:7.5%:2.5%. The mixing temperature was 180℃, the mixing speed was 35rpm, and the mixing time was 30min.

[0053] Step S2, the alloy and cermet materials obtained in S1 were granulated in a screw extruder to obtain cylindrical particles with a diameter of 2-3mm and a height of 3-5mm. The processing temperature was 180℃, and the screw speed was 500r / min.

[0054] Step S3, the alloy and cermet materials obtained in S2 were printed using a double-nozzle extrusion 3D printer to obtain a multi-material structure green body.

[0055] Step S4, the multi-material structure green body obtained in S3 was placed in a catalytic debinding furnace for debinding. The debinding temperature was 120℃, oxalic acid and nitrogen gas were introduced, and the debinding time was 30h.

[0056] Step S5, the sample after catalytic debinding was placed in a sintering furnace for further thermal debinding and sintering. The thermal debinding temperature was in the range of 300-500℃, and the time was 6h. The sintering temperature was 1170℃, and the holding time was 90min. At this time, the Cu-20Ni alloy was in a super-solid phase sintering state, and the liquid phase volume was 35%. The NiFe2O4 cermet was in a solid phase sintering state.

[0057] The final product has higher density. The density of NiFe2O4 cermet is 96%, and the density of Cu-20Ni alloy is 98%. The two-phase structure is uniformly distributed and the interface is clear. The interface shear strength is 65MPa.

[0058] Example 3

[0059] A multi-material structure was prepared using a W-30Cu alloy system and an Al2O3 ceramic system. The specific steps are as follows:

[0060] Step S1, W-30Cu alloy powder and Al2O3 ceramic powder were mixed with water-based binder respectively to obtain the material. The loading amount of the two powders was set to 54%. The mass fraction of the binder components was polyethylene glycol: low-density polyethylene: stearic acid = 80%:15%:5%. The mixing temperature was 150℃, the mixing speed was 35rpm, and the mixing time was 30min.

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

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

[0063] Step S4, the multi-material structure green body obtained in S3 was placed in water for solvent debinding, the temperature was set to 60°C, and the time was 24 h.

[0064] Step S5, the debinding sample obtained in S4 was placed in a sintering furnace for thermal debinding and sintering, the thermal debinding temperature was 300-400°C, the debinding time was 6 h; the sintering temperature was 1550°C, and the sintering time was 60 min, at this time the W-30Cu alloy was in a solid-liquid coexisting sintering state, and the Al2O3 was in a solid phase sintering state.

[0065] In the final product, the densities of the W-30Cu alloy phase and the Al2O3 ceramic phase were both 98%, the two-phase structure was uniformly distributed, the interface was clear, and the interface shear strength was 60 MPa.

[0066] Comparative Example 1

[0067] The other conditions were the same as in Example 1, except that the sintering temperature was selected to be 1190°C, at this time the liquid phase volume in the Cu-20Ni alloy was more than 70%, and the product after sintering was as shown in Figure 2 , the product did not deform, the pre-set two-phase shape was maintained, but there were large and obvious holes on the surface of the alloy phase, the metal ceramic phase density was more than 95%, and the alloy phase density was less than 80%.

[0068] Comparative Example 2

[0069] The other conditions were the same as in Example 1, except that the sintering temperature was selected to be 1140°C, at this time the Cu-20Ni alloy was in a solid phase sintering state, and the product after sintering was as shown in Figure 4 , the shapes of the alloy phase and the metal ceramic phase were maintained, but the shrinkage was uneven, and there were obvious cracks on the surface of the product.

Claims

1. A method of co-sintering fabrication of a multi-material article, characterized by: Mixing N parts of alloy powder and M parts of other powder respectively with polymer binder to obtain (M+N) parts of material, according to the structure of the multi-material product, shaping (M+N) parts of material to obtain a multi-material green body, and then sequentially performing debinding and sintering to obtain the multi-material product; N≥1 and M≥1; The alloy in the alloy powder is a solid-liquid coexisting phase alloy, 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 at least one selected from ceramic powder and cermet powder; In the (M+N) parts of material, the volume fraction of the raw material powder is 50-70 %; In the (M+N) parts of material, the difference between the sintering shrinkage rates of any two parts of material at the same temperature is ≤1.5 %; The shaping mode is powder metallurgy rheological forming, and the process of the powder metallurgy rheological forming is: crushing (M+N) parts of material to obtain (M+N) parts of material particles, laying (M+N) parts of material particles in a mold according to the structure of the multi-material product, pre-pressing the mold, and then low-temperature hot pressing the mold to form the multi-material green body; The particle size of the (M+N) parts of material particles is 5-1000 μm, The temperature of the low-temperature hot pressing is 5-30 ℃ higher than the softening point of the polymer binder, the pressure is 10-60 MPa, and the holding and pressure maintaining time is 5-60 min; During the sintering, the sintering temperature is controlled to be the solid-liquid coexisting state temperature of the alloy components in the multi-material green body, and the liquid phase volume fraction of the alloy components is 5-70 %.

2. A method of co-sintering a multi-material article according to claim 1, wherein: The mixing is performed in a double rotor mixer, the mixing temperature is 5-30 ℃ higher than the softening point of the polymer binder, the mixing time is 0.5-2 h, and the rotor speed is 20-100 rpm.

3. The method according to claim 1, wherein 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 at least one selected from paraffin wax, beeswax, microcrystalline wax, carnauba wax, and polyethylene wax binder. The water-based binder is a polyethylene glycol binder. The plastic-based binder is a polyformaldehyde binder. The pre-pressing pressure is 10-50 MPa.

4. A method of co-sintering of a multi-material article according to any one of claims 1, wherein: The debinding process includes preliminary debinding and thermal debinding, and the preliminary debinding is selected from solvent debinding or catalytic debinding.

5. The method of claim 3, wherein:

6. The method according to claim 5, wherein when the polymer binder is selected from a wax-based binder or a water-based binder, solvent debinding is adopted; when the polymer binder is selected from a plastic-based binder, catalytic debinding is adopted; The thermal debinding temperature is 200-600 ℃. The sintering time is 30-200 min. ​ 7. The method of claim 1, wherein: ​

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