A near-spherical metal-ceramic composite powder for rheological forming and its preparation method

Abstract

This invention discloses a near-spherical metal-ceramic powder for rheological forming and its preparation method. The method involves mixing fine ceramic phase powder, fine metal phase powder, and an organic binder to obtain a mixed powder. This mixed powder is then pressed into blocks, sieved, and granulated to obtain composite particle powder. The composite particle powder is then self-milled with fine metal binder phase powder to obtain a core-shell structured porous spherical composite powder. Finally, the porous spherical composite powder is pre-sintered to obtain spherical metal-ceramic composite powder. The method for preparing near-spherical metal-ceramic composite powder for rheological forming provided by this invention results in powder materials with good flowability, filling properties, and sufficient strength. The near-spherical particle shape imparts high filling density to the rheological forming feedstock and green body.

Description

Technical Field

[0001] This invention relates to the fields of powder metallurgy and powder engineering technology, specifically to a near-spherical metal ceramic powder for rheological forming and its preparation method. Background Technology

[0002] Cermets are an important class of composite materials prepared by powder metallurgy, mainly composed of a ceramic phase and a metal binder. Cermets with spinel oxide as the ceramic phase possess both corrosion resistance and good electrical conductivity. They are used in various fields such as metallurgy, aerospace, and energy. The traditional powder metallurgy process for preparing cermets includes mixing metal / ceramic phase particles, pressing, and sintering. When the ceramic phase is the main structure, traditional processes can only produce discontinuous island-like structures of the metal phase, limiting electrical conductivity. Furthermore, traditional forming methods are limited by molds and powder properties, making it difficult to form complex shapes and large-sized workpieces, thus restricting the application of cermet materials.

[0003] Rheological forming, as an emerging forming technology, combines the process characteristics of injection molding and gel extrusion. It is a forming technology that mixes powder with a high-temperature plasticizer to obtain a solid feedstock, and then fills the semi-solid feedstock into a mold through casting or extrusion above the softening temperature of the plasticizer. After cooling and solidification, a high-strength, high-density preform is formed. This technology features fast forming process, low feedstock viscosity, large preform volume, high strength, and high density. It can obtain powder metallurgy preforms that are larger in size, more complex in structure, and have higher strength than traditional processes such as injection molding. Powder pretreatment is a crucial step in rheoforming, including the following key points: First, better powder flowability facilitates feed flow and mold filling. Therefore, spheroidization of the particles is necessary. Patent CN115351290A discloses a method for obtaining spherical cermet powder through mixing and suspension shaping. Second, the powder particles need to possess a certain crushing strength to ensure stable particle flow under the pressure of compressed water. Patent CN114713827A provides a method for preparing spherical cermet powder for 3D printing using plasma spheroidization technology, resulting in high-density particles with high strength. Finally, using metal-coated ceramic particles can effectively improve the electrical conductivity of cermets. Patent CN115283670A discloses a method for chemically coating Mo-Fe alloy onto the surface of Ti(C,N) particles. However, existing methods only address one of the problems of powder flowability, strength, and coating structure. Rheological forming technology has extremely high requirements for the structure, flowability, and particle strength of metal-ceramic composite ceramics. Spherical composite powders produced by traditional methods cannot meet the above requirements at the same time. Therefore, it is of great significance to obtain a metal-ceramic composite powder that meets the requirements of rheological forming. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the first objective of this invention is to provide a method for preparing near-spherical metal-ceramic composite powders for rheoforming. The prepared spherical powders have the characteristics of core-shell structure, high density, uniform particle size, good flowability, and easy sintering. Furthermore, the preparation method provided by this invention is simple and low in cost.

[0005] A second objective of this invention is to provide a near-spherical metal-ceramic composite powder for forming prepared by the above-described preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing metal-ceramic composite powder for rheological forming. The method involves mixing a core raw material fine powder and an organic binder to obtain a mixed powder, pressing the mixed powder into blocks, sieving and granulating it to obtain composite particle powder, and then self-grinding and spheroidizing the composite particle powder with a metal binder phase fine powder to obtain a porous spherical composite powder with a core-shell structure. Finally, the porous spherical composite powder is pre-sintered to obtain spherical metal-ceramic composite powder. The core raw material fine powder is selected from ceramic phase fine powder and / or metal phase fine powder.

[0008] The preferred method involves first preparing ceramic phase powder, metallic phase powder, and metallic binder phase powder, and then crushing and classifying them respectively to obtain fine ceramic phase powder, fine metallic phase powder, and fine metallic binder phase powder.

[0009] Through crushing and grading, raw material powder with uniform particle size and narrow particle size distribution is obtained.

[0010] In a further preferred embodiment, the crushing method is to use a turbine nano-grinding mill for nano-grinding, and the operating parameters during nano-grinding are: rotation speed of 580-1500 rpm, flow rate of 50-500 L / H, and zirconium bead filling ratio of 60-70%.

[0011] In a further preferred embodiment, the grading method is to use a jet-type air classifier for grading, and the working parameters during grading are: feed rate 50-100 kg / h, working pressure 1.5-20 MPa, and cyclone collector air pressure 1.5-20 kPa.

[0012] In a preferred embodiment, the average particle size of both the ceramic phase fine powder and the metallic phase fine powder is 0.05–1 μm. The inventors have discovered that controlling the average particle size of the ceramic phase fine powder and the metallic phase fine powder within this range ensures the smooth progress of the spheroidization process and avoids slow spheroidization, low spheroidized particle strength, and low sintering activity caused by excessively low surface energy.

[0013] In a preferred embodiment, the particle size of the metal binder phase fine powder is 0.1–45 μm. Controlling the particle size of the metal binder phase fine powder within the above range ensures that it ultimately forms a uniformly dispersed coating layer.

[0014] In a preferred embodiment, the ceramic phase powder is selected from at least one of nickel ferrite, manganese ferrite, cobalt ferrite, zinc ferrite, copper ferrite, chromium ferrite, and iron ferrite (Fe3O4).

[0015] In a preferred embodiment, the metal in the fine metal phase powder is selected from at least one of W, Mo, Zr, Ti, Co, Ni, and Fe.

[0016] In a preferred embodiment, the metal in the metal binder phase fine powder is selected from at least one of Cu, Al, Zn, Sn, Ag, Au, and Pb.

[0017] In a preferred embodiment, when the core raw material powder is selected from ceramic phase fine powder and metal phase fine powder, the mass ratio of ceramic phase fine powder to metal phase fine powder is 8-12:1-4, more preferably 12:1-4. Controlling the mass ratio of ceramic phase fine powder to metal phase fine powder within the above range allows for uniform dispersion of ceramic phase and metal phase powders with significant density differences.

[0018] In a preferred embodiment, the organic binder is selected from at least one of paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, polyethylene glycol, polyvinyl alcohol, methylcellulose, and rubber. Adding a small amount of organic binder to the mixed powder can ensure particle bonding strength while increasing surface viscosity, thereby promoting the coating of the metal binder phase during self-grinding.

[0019] In a preferred embodiment, the mass fraction of the organic binder in the mixed powder is 1-8%, preferably 5-8%.

[0020] In a preferred embodiment, the mixed powder contains fine ceramic sintering aid powder, the particle size of which is 0.05–1 μm, and the mass fraction of the fine ceramic sintering aid powder in the mixed powder is 2–11%.

[0021] Adding fine ceramic sintering aid powder can further enhance the sintering activity of the powder.

[0022] In actual operation, ceramic sintering aid fine powder is also obtained by crushing and classifying the purchased ceramic sintering aid raw material powder.

[0023] In a preferred embodiment, the ceramic in the ceramic sintering aid powder is selected from one or more of chromium oxide, manganese oxide, cobalt oxide, nickel oxide, copper oxide, zinc oxide, yttrium oxide, zirconium oxide, and titanium oxide.

[0024] In a preferred embodiment, the ceramic phase fine powder, the metal phase fine powder, and the organic binder are mixed and then dried to obtain a mixed powder. The drying temperature is 100-120°C.

[0025] In a preferred embodiment, the mixing method is wet ball milling, the medium for wet ball milling is deionized water, the rotation speed of the wet ball milling is 60–200 rpm, and the wet ball milling time is 15–60 min. Wet ball milling ensures that the mixed powder is fully and uniformly dispersed.

[0026] In actual operation, wet ball milling can be carried out in a drum ball mill, and drying can be carried out in a blower drying oven.

[0027] In a preferred embodiment, the pressure for pressing into blocks is 30–50 MPa. By controlling the pressing pressure within this range, it is possible to press into briquettes while also effectively crushing them to obtain composite granular powder through sieving.

[0028] In a preferred embodiment, the granules obtained by sieving from -40 mesh to +100 mesh are the composite particle powder. The inventors have discovered that the composite particle powder with the above particle size has optimal flowability, which is beneficial for ensuring the smooth progress of self-grinding and balling.

[0029] In a preferred embodiment, the mass ratio of the composite particle powder to the fine metal binder phase powder is 5–10:1–1.5. Controlling the mass ratio of the composite particle powder to the fine metal binder phase powder within this range ensures that the fine metal binder phase powder coats the composite particles without agglomerating itself.

[0030] In a preferred embodiment, the self-grinding spheroidization is carried out in a drum ball mill, the rotational speed of the self-grinding spheroidization is 100-400 r / min, preferably 150-250 r / min, and the self-grinding spheroidization time is 10-40 h, preferably 20-30 h.

[0031] The self-grinding spheroidization process in this invention involves filling a drum-type ball mill with composite particle powder and fine metal binder powder. Under conditions of no grinding balls and no media, the particles are self-grinding for an extended period. During the high-speed rotation of the drum, the surface tension and inter-particle attraction of the powder particles cause them to spontaneously aggregate into near-spherical shapes. In this process, due to the high surface viscosity of the large-diameter composite particles containing the organic binder, a layer of fine metal binder powder initially adheres to them, forming an initial coating structure. Further rotation causes the surface tension between the fine powder particles to continuously thicken the coating layer. Simultaneously, collisions between the particles prevent the fine powder from agglomerating and gradually increase the sphericity of the coated particles, ultimately forming near-spherical particles with a certain regular shape.

[0032] The inventors discovered that using a drum ball mill can achieve simple, efficient, and uniform mixing, and has strong applicability and process controllability. By adjusting and controlling the drum speed and time parameters, the particle size and sphericity of the final powder can be effectively guaranteed.

[0033] In a preferred embodiment, the pre-sintering is carried out in a protective atmosphere, the pre-sintering temperature is 600-1000℃, and the holding time is 30-180min.

[0034] Pre-firing further densifies the spherical powder, eliminating internal defects, and also improves the strength of the composite powder.

[0035] In a further preferred embodiment, the protective atmosphere is selected from at least one of nitrogen, argon, helium, and carbon monoxide.

[0036] The present invention also provides a near-spherical metal-ceramic composite powder for rheological forming prepared by the above preparation method.

[0037] In a preferred embodiment, the average particle size of the spherical metal-ceramic composite powder used for rheological forming is 150–350 μm. Controlling the spherical metal-ceramic composite powder within this range through process parameters makes it suitable for use as a feedstock in rheological forming.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] (1) The method for preparing near-spherical metal-ceramic composite powder for rheological forming provided by the present invention utilizes self-grinding spheroidization technology to obtain metal-ceramic composite particles with a certain degree of sphericity and flowability. The powder is subjected to granulation, self-grinding and pre-sintering treatment, and has a controllable particle size range, thus solving the problem of feeding and filling performance during rheological forming.

[0040] (2) The method for preparing near-spherical metal-ceramic composite powder for rheological forming provided by the present invention improves the strength of the composite powder by pre-sintering, thereby solving the problem that particles may collapse under stress during the rheological forming process.

[0041] (3) The method for preparing near-spherical metal-ceramic composite powder for rheological forming provided by the present invention applies granulation and self-grinding spheroidization processes to prepare metal-ceramic composite powder with a core-shell structure, solving the problem that the metal phase of metal-ceramic cannot form an interconnected network, thus affecting conductivity. The powder material prepared by the method of the present invention has good flowability, filling properties and sufficient strength, and the near-spherical particle shape endows the rheological forming feedstock and green body with high filling density. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 A schematic diagram comparing the structures of metal-ceramic powders prepared by conventional methods and the metal-ceramic composite powders prepared by this invention.

[0044] Figure 2 This is a SEM image of the Cu-coated Ni / NiO / NiFe2O4 powder particles obtained in Example 1. Detailed Implementation

[0045] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention. The embodiments of the present invention include:

[0046] Example 1

[0047] A method for preparing Cu-coated Ni / NiO / NiFe2O4 cermet composite powder for rheological forming includes the following steps:

[0048] Step S1: Using nano-grinding and air classifying technology, each of the 100kg samples of NiO, NiFe2O4, Cu, and Ni with an average particle size of 5μm is crushed and classified to obtain ultrafine raw material powder with an average particle size of 0.4μm. The operating parameters of the nano-grinding mill are: rotation speed 600rpm, flow rate 50L / H, zirconium bead loading ratio 70%; the operating parameters of the spray air classifier are: feed rate 50kg / h, working pressure 15MPa, and cyclone collector air pressure 10KPa.

[0049] Step S2: Add 60 kg of ultrafine NiFe2O4 ceramic phase powder, 10 kg of ultrafine NiO powder, 20 kg of ultrafine Ni powder and 5 kg of PVA to 150 L of water, mix thoroughly by roller ball milling at 100 rpm, and then dry the moisture at 120 °C to obtain mixed powder.

[0050] Step S3: The mixed powder is pressed into blocks at 30MPa and then granulated by sieving to obtain composite granular powder of -40 mesh and +100 mesh.

[0051] Step S4: Using a drum ball mill, the composite particle powder is mixed with 10 kg of ultrafine Cu powder and milled for 10 hours at a milling speed of 200 r / min to obtain a porous spherical composite powder with a core-shell structure; the structure of the composite powder is shown below. Figure 1 ;

[0052] Step S5: Under a protective atmosphere, the porous spherical powder is pre-sintered to remove the organic binder. Specific parameters are: sintering temperature 900℃, sintering time 45 min, to obtain a preliminary dense spherical metal-ceramic composite powder. SEM images of the preliminary dense spherical powder are shown below. Figure 2 The main properties of the obtained powder are shown in Table 1.

[0053] Example 2

[0054] A method for preparing Cu-encapsulated Cu2O / NiFe2O4 cermet composite powder for rheological forming includes the following steps:

[0055] Step S1: Using nano-grinding and air classifying technology, each 100kg of Cu2O, NiFe2O4, and Cu with an average particle size of 5μm is crushed and classified to obtain ultrafine raw material powder with an average particle size of 0.4μm. The operating parameters of the nano-grinding mill are: rotation speed 600rpm, flow rate 50L / H, zirconium bead loading ratio 70%; the operating parameters of the spray air classifier are: feed rate 50kg / h, working pressure 15MPa, and cyclone collector air pressure 10KPa.

[0056] Step S2: Add 60 kg of ultrafine NiFe2O4 ceramic phase powder, 2 kg of ultrafine Cu2O powder and 5 kg of PVA to 150 L of water, stir thoroughly by roller ball milling at 100 rpm, and then dry the water at 120 °C to obtain mixed powder.

[0057] Step S3: The mixed powder is pressed into blocks at 30MPa and then granulated by sieving to obtain composite granular powder of -40 mesh and +100 mesh.

[0058] Step S4: Using a drum ball mill, the composite particle powder is mixed with 10 kg of ultrafine Cu powder and self-milled for 10 h at a self-milling speed of 200 r / min to obtain a porous spherical composite powder with a core-shell structure.

[0059] Step S5: Under a protective atmosphere, the porous spherical powder is subjected to pre-sintering treatment to remove the organic binder. The specific parameters are sintering temperature of 800℃ and sintering time of 60min, to obtain a preliminary dense spherical metal-ceramic composite powder. The main properties of the obtained powder are shown in Table 1.

[0060] Example 3

[0061] A method for preparing Ni-coated Ti / Fe3O4 cermet composite powder for rheological forming includes the following steps:

[0062] Step S1: Using nano-grinding and air classifying technology, each 100kg of Fe3O4, Ti, and Ni with an average particle size of 5μm is crushed and classified to obtain ultrafine raw material powder with an average particle size of 0.4μm. The operating parameters of the nano-grinding mill are: rotation speed 600rpm, flow rate 50L / H, zirconium bead loading ratio 70%; the operating parameters of the spray air classifier are: feed rate 50kg / h, working pressure 15MPa, and cyclone collector air pressure 10KPa.

[0063] Step S2: Add 60 kg of ultrafine Fe3O4 ceramic phase powder, 5 kg of ultrafine Ti powder and 5 kg of PVA to 150 L of water, mix thoroughly by roller ball milling at 100 rpm, and then dry the water at 120 °C to obtain mixed powder.

[0064] Step S3: The mixed powder is pressed into blocks at 30MPa and then granulated by sieving to obtain composite granular powder of -40 mesh and +100 mesh.

[0065] Step S4: Using a drum ball mill, the composite particle powder is mixed with 15 kg of ultrafine Ni powder and self-milled for 20 h at a self-milling speed of 200 r / min to obtain a porous spherical composite powder with a core-shell structure.

[0066] Step S5: Under a protective atmosphere, the porous spherical powder is subjected to pre-sintering treatment to remove the organic binder. The specific parameters are sintering temperature of 900℃ and sintering time of 30min, to obtain a preliminary dense spherical metal-ceramic composite powder. The main properties of the obtained powder are shown in Table 1.

[0067] Comparative Example 1,

[0068] Other conditions were the same as in Example 1, except that in step 2, the amount of organic binder added was 0. Due to the strength and surface viscosity of the granulated particles, the fine alloy phase powder failed to adhere during the self-grinding process, and a large number of particles broke. As shown in Appendix Table 1, compared with other examples, the powder in the comparative example failed to form a spherical core-shell structure, and the flowability of the powder particle size decreased significantly.

[0069] Table 1

[0070] Porosity (%) D50(μm) D90(μm) Flowability (s / 50g) Example 1 19.8 245 335 39 Example 2 17.5 246 343 47 Example 3 16.5 255 355 45 Comparative Example 1 — 48 104 72

[0071] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a metal-ceramic composite powder for rheological forming, characterized in that: The core raw material fine powder and organic binder are mixed to obtain a mixed powder. The mixed powder is pressed into blocks, sieved and granulated to obtain composite particle powder. The composite particle powder is self-ground and spheroidized with metal binder phase fine powder to obtain a core-shell structure porous spherical composite powder. The porous spherical composite powder is then pre-sintered to obtain spherical metal-ceramic composite powder. The core raw material fine powder is selected from ceramic phase fine powder and metal phase fine powder. The ceramic phase powder is selected from at least one of nickel ferrite, manganese ferrite, cobalt ferrite, zinc ferrite, copper ferrite, and chromium ferrite. The mixed powder also contains fine ceramic sintering aid powder, the particle size of which is 0.05~1μm, and the mass fraction of the fine ceramic sintering aid powder in the mixed powder is 2~11%. The pressure for pressing the blocks is 30~50MPa; The granules obtained by sieving and screening from -40 mesh to +100 mesh are the composite granular powder; The mass ratio of the composite particle powder to the fine powder of the metal binder phase is 5~10:1~1.5; The self-grinding spheroidization is carried out in a drum ball mill, with a rotation speed of 100~400 r / min and a spheroidization time of 10~40 h.

2. The method for preparing a metal-ceramic composite powder for rheological forming according to claim 1, characterized in that: First, ceramic phase powder, metallic phase powder, and metallic binder phase powder are prepared and crushed and classified to obtain fine ceramic phase powder, fine metallic phase powder, and fine metallic binder phase powder, respectively. The crushing method is to use a turbine-type nano-grinding mill for nano-grinding. The operating parameters for nano-grinding are: rotation speed of 580~1500rpm, flow rate of 50~500L / H, and zirconium bead filling ratio of 60~70%. The grading method is to use a jet-type air classifier for grading. The working parameters during grading are: feed speed 50~100kg / h, working pressure 1.5~20MPa, and cyclone collector air pressure 1.5~20KPa.

3. A method for preparing a rheoforming metal-ceramic composite powder according to claim 1 or 2, characterized in that: The average particle size of both the ceramic phase fine powder and the metallic phase fine powder is 0.05~1μm; The particle size of the fine powder of the metal binder phase is 0.1~45μm; The metal in the fine metallic powder is selected from at least one of W, Mo, Zr, Ti, Co, Ni, and Fe; The metal in the fine powder of the metal binder phase is selected from at least one of Cu, Al, Zn, Sn, Ag, Au, and Pb; When the core raw material fine powder is selected from ceramic phase fine powder and metal phase fine powder, the mass ratio of ceramic phase fine powder to metal phase fine powder is 8~12:1~4.

4. A method for preparing a rheoforming metal-ceramic composite powder according to claim 1 or 2, characterized in that: The organic adhesive is at least one of paraffin wax, carnauba wax, microcrystalline wax, polyethylene wax, polyethylene glycol, polyvinyl alcohol, methylcellulose, and rubber. In the mixed powder, the mass fraction of organic binder is 1-8%.

5. A method for preparing a rheoforming metal-ceramic composite powder according to claim 1 or 2, characterized in that: The ceramics in the fine powder of the ceramic sintering aid are selected from one or more of chromium oxide, manganese oxide, cobalt oxide, nickel oxide, copper oxide, zinc oxide, yttrium oxide, zirconium oxide, and titanium oxide.

6. A method for preparing a rheoforming metal-ceramic composite powder according to claim 1 or 2, characterized in that: The core raw material fine powder and organic binder are mixed by wet ball milling. The medium for wet ball milling is deionized water, the rotation speed of wet ball milling is 60~200 rpm, and the wet ball milling time is 15~60 min.

7. A method for preparing a rheoforming metal-ceramic composite powder according to claim 1 or 2, characterized in that: The pre-sintering is carried out in a protective atmosphere at a temperature of 600-1000℃ and a holding time of 30-180 minutes.

8. A near-spherical metal-ceramic composite powder for rheological forming prepared by the preparation method according to any one of claims 1-7, characterized in that: The average particle size of the spherical metal-ceramic composite powder used for rheological forming is 150~350μm.

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