WO2015161732A1

WO2015161732A1 - Method for preparing cobalt-coated nanometer wc crystal composite powder and ultra-fine grain cemented carbide

Info

Publication number: WO2015161732A1
Application number: PCT/CN2015/075305
Authority: WO
Inventors: 谭兴龙; 邓军旺; 王艳艳; 李礼
Original assignee: 湖南顶立科技有限公司
Priority date: 2014-04-25
Filing date: 2015-03-27
Publication date: 2015-10-29
Also published as: CN103909274A; CN103909274B

Abstract

A method for preparing cobalt-coated nanometer WC crystal composite powder comprises the following steps: (1) mixing raw materials with water to obtain a tungsten-cobalt composite saline solution, wherein the raw materials comprise the following components (by weight percentage), 40%-60% of violet tungsten oxide, 30%-52% of water-soluble cobalt salt, 4%-10% of carbon source, 1%-4% of PEG and 0.05%-3% of dispersant agent; (2) drying the tungsten-cobalt composite saline solution obtained in the step (1) to obtain cobalt-coated precursor powder; (3) reducing and carbonizing the cobalt-coated precursor powder obtained in the step (2) in reducing atmosphere to obtain the cobalt-coated nanometer WC crystal composite powder. The cobalt-coated nanometer WC crystal composite powder prepared by the method has stable performance, homogeneous component and fine WC grain size, and the components of the powder can be easily controlled.

Description

Method for preparing cobalt coated nano WC crystal composite powder and ultrafine crystal hard alloy

Technical field

The invention relates to a cemented carbide preparation technology, in particular to a method for preparing a cobalt coated nano WC crystal composite powder and an ultrafine grain WC-Co cemented carbide.

Background technique

Conventionally, alloys with WC grains of about 0.5 μm are called fine-grained hard alloys, and alloys with WC grains of between 0.2 μm and 0.5 μm are called ultrafine-grained hard alloys, and 0.2 μm or less is used. The alloy is called nanocrystalline cemented carbide. Ultra-fine cemented carbide is a high-hardness and high-quality ceramic material that has been found to have high hardness and high fracture toughness and ductility after using nano-sized WC/Co powder as raw material. Hard alloy material with wear resistance and high toughness. Ultrafine grained carbide is widely used in various fields of modern technology due to its special wear resistance, high hardness, and excellent fracture toughness and compressive strength. It has been used as a micro drill bit and lattice for processing integrated circuit boards. Printer printing needles, integral hole machining tools, woodworking tools, precision molds, dental drills, difficult-to-machine materials, etc. The key to preparing ultrafine grained cemented carbide is to prepare cobalt coated nano WC crystal composite powder. At present, the methods for preparing cobalt coated nano WC crystal composite powder are (1) fixed bed reaction method and (2) in situ carburization reduction method. (3) chemical precipitation method, (4) plasma method, (5) high energy ball milling method, (6) spray heat conversion method, (7) spray pyrolysis-fluidization continuous reduction carbonization preparation technology, (8) direct Reduction carbonization technology, (9) oxidation-reduction method, and (10) sol-gel method. However, there are problems in the above methods: (1) In the fixed bed method, the utilization rate of the reduced carbonized gas is not high, the particle size of the WC-Co powder is not uniform, and the performance fluctuates greatly; (2) the in-situ carburizing reduction method, There are a small amount of undecomposed polymer and free carbon in the preparation of WC-Co powder. The composition of the composite powder is related to the process parameters such as carbonization temperature, reaction time and atmosphere ratio, and the carbon content is difficult to control. (3) Chemical precipitation method, during preparation Easy to introduce impurities, the resulting precipitate is in colloidal state, filtration and washing, high cost, etc.; (4) Plasma method, the operation and production speed are fast, the obtained powder particles are uniform, but the cost is high, and the temperature is high Electrode is easy to melt Or evaporation, easy to contaminate the product; (5) high-energy ball milling method, this kind of technology is simple, WC crystal has a lot of defects, but the output is small, the abrasion is large, the product is easy to be contaminated, the powder is easy to agglomerate; (6) spray heat conversion method Rutgers University and Nanodyne in the United States jointly developed the use of water-soluble precursors to synthesize nano-WC-Co nano-WC-Co particles up to 20nm ~ 40nm. The biggest problem of this technology is high cost, complex process control, and difficult to achieve industrialization; (7) spray heat Solution-fluidization continuous reduction carbonization preparation technology can produce carbon-free phase (η phase) nano-WC-Co composite powder, which has high cost and complicated process control; (8) direct reduction carbonization technology, carbon content is difficult to control, Moreover, the free carbon content in the product is difficult to control; (9) the oxidation-reduction method, the prepared ultrafine tungsten carbide cobalt composite powder has a grain size of ≤0.5 μm, and the particle size is uniformly distributed, and the method is suitable for the recovery and reuse of the cemented carbide. (10) The sol-gel method, the drying of the precursor powder is carried out by a conventional drying method, and industrial production cannot be achieved.

In the prior art, the promising process is a cobalt-coated nano-WC crystal composite powder prepared by a spray conversion-reduction carbonization method, and the following two methods are mainly used: (1) the tungsten salt and the cobalt salt composite solution are spray-dried and then calcined, and then Adding a carbon source or introducing a carbon-containing atmosphere for reduction carbonization; (2) preparing a composite solution prepared from a tungsten salt, a cobalt salt, and a carbon source by spray drying, calcining, and then reducing carbonization, and the powder is converted into amorphous after calcination by the two methods. The structure of the structure, the reduction carbonization reaction is complicated, and the quality of the composite powder is difficult to control.

Summary of the invention

The object of the present invention is to provide a method for preparing WC-Co nanocrystals and ultrafine grained WC-Co cemented carbides. The WC-Co nanocrystals prepared by the method provided by the invention have stable properties, uniform composition and fine WC grains. The powder composition is easy to control.

The invention provides a preparation method of a cobalt-coated nano WC crystal composite powder, comprising the following steps:

1) mixing the raw material and water to obtain a tungsten-cobalt composite salt solution, the raw material comprising the following components: 40 wt% to 60 wt% of purple tungsten, 30 wt% to 52 wt% of water-soluble cobalt salt, and 4 wt% to 10 wt% of charcoal. Source, 1 wt% to 4 wt% PEG, and 0.05 wt% to 3% wt% dispersant;

2) drying the tungsten-cobalt composite salt solution obtained in the step 1) to obtain a cobalt coating Precursor powder;

3) The cobalt-coated precursor powder obtained in the step 2) is subjected to reduction carbonization treatment under a reducing atmosphere to obtain a cobalt-coated nano WC crystal composite powder.

Preferably, the water-soluble cobalt salt comprises one or more of cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt chloride and cobalt carbonate.

Preferably, the carbon source comprises one or more of carbon black, lamp black, ethylenediamine, fiber, pulp, acetylene black, carbon nanotubes, glucose, polypropylene, syrup and sucrose.

Preferably, the mass ratio of the raw material to the water is 1: (0.5 to 3.0).

Preferably, the temperature of the reduction carbonization treatment is 850 ° C ~ 1250 ° C;

The reduction carbonization treatment time is 30 min to 3 h.

Preferably, the reducing atmosphere is provided by a reducing gas comprising hydrogen;

The reducing gas including hydrogen further includes one or more of CH ₄ , C ₃ H ₈ , CO, and CO ₂ ;

The volume ratio of one or more of CH ₄ , C ₃ H ₈ , CO and CO ₂ to hydrogen is (90 to 99): (1 to 10).

Preferably, the tungsten-cobalt composite salt solution has a pH of 1 to 5.

The invention provides an ultrafine grain WC-Co cemented carbide prepared by the cobalt coated nano WC crystal composite powder obtained by the preparation method described in the above technical solution.

Preferably, the method for preparing a cemented carbide of ultrafine grained WC-Co comprises the following steps:

Dissolving the cobalt-coated nano-WC crystal composite powder obtained by the preparation method described in the above technical solution with water, and grinding to obtain a first mixture;

Drying the first mixture and mixing with a molding agent to obtain a second mixture;

Pressing the second mixture into a compact to obtain a compact;

The compact was sintered to obtain an ultrafine grained WC-Co cemented carbide.

Preferably, the mass ratio of the cobalt-coated nano-WC crystal composite powder to the dispersant is 100: (1.0 to 4.0);

The mass ratio of the total mass of the cobalt-coated nano WC crystal composite powder and the dispersant to the water is 100: (30 to 100).

The invention provides a preparation method of a cobalt-coated nano-WC crystal composite powder, comprising the following steps: 1) mixing a raw material and water to obtain a tungsten-cobalt composite salt solution, the raw material comprising the following components: 40 wt% to 60 wt% Purple tungsten, 30 wt% to 52 wt% water-soluble cobalt salt, 4 wt% to 10 wt% carbon source, 1 wt% to 4 wt% PEG, and 0.05 wt% to 3% wt% dispersant; 2) the step 1) The obtained tungsten-cobalt composite salt solution is dried to obtain a cobalt-coated precursor powder; 3) the cobalt-coated precursor powder obtained in the step 2) is subjected to reduction carbonization treatment under a reducing atmosphere to obtain a cobalt-coated nano-WC crystal. Composite powder. The preparation method provided by the invention adopts purple tungsten as a raw material, and the structure of the purple tungsten is favorable for the infiltration of reducing gas and carbon and the overflow of water vapor during the reduction carbonization process, so that the reduction carbonization reaction can be simultaneously performed on the surface and the interior of the purple tungsten, thereby Reducing carbonization to form more crystal nucleus of tungsten powder, the reaction speed is fast, and it is easier to prepare nano-carbide cobalt composite powder; and compared with the prior art, the method provided by the invention avoids the carbon source during the reduction carbonization process. Or the carbon-containing atmosphere on the turbidity of the nano-tungsten carbide-cobalt composite powder and the segregation of the carbon component in the composite powder are favorable for controlling the carbon content in the cobalt-coated nano-WC crystal composite powder. Therefore, the cobalt-coated nano-WC crystal composite powder prepared by the invention has stable performance, uniform composition, fine WC grains and easy control of powder composition.

In addition, compared with the prior art disclosed direct reduction carbonization spray-dried tungsten salt-carbon source-cobalt salt precursor composite powder, the method provided by the invention has short preparation process, simple process, less process and more favorable. Quality control of nano tungsten carbide cobalt composite powder.

DRAWINGS

1 is a schematic flow chart of preparing an ultrafine grained WC-Co cemented carbide according to an embodiment of the present invention;

2 is a TEM top view of a cobalt-coated precursor powder obtained in Example 1 of the present invention;

3 is a SEM top view of a cobalt-coated nano WC crystal composite powder obtained in Example 1 of the present invention;

4 is an XRD pattern of a cobalt-coated nano WC crystal composite powder obtained in Example 1 of the present invention;

Figure 5 is a metallographic view of a cemented carbide prepared in Example 9 of the present invention.

detailed description

2) drying the tungsten-cobalt composite salt solution obtained in the step 1) to obtain a cobalt-coated precursor powder;

The method provided by the invention uses purple tungsten as a raw material, and the interior of the purple tungsten has abundant cracks and voids, which is favorable for the infiltration of reducing gas and carbon and the overflow of water vapor during the reduction carbonization process, so that the reduction carbonization reaction is on the surface of the purple tungsten agglomerate and the purple The interior of the tungsten is simultaneously performed, so that the crystal nucleus of the tungsten powder is formed during the reduction carbonization, and the reaction speed is fast; and the method provided by the invention uniformly coats the cobalt salt on the surface of the purple tungsten and the carbon source by a water-soluble method, and adds the carbon source to Increasing the specific surface area of the powder, adding pure water to achieve uniform mixing at the molecular level, reducing the temperature of subsequent reduction carbonization. The method provided by the present invention avoids a carbon source or a carbon-containing atmosphere against nano-tungsten carbide compared to the prior art disclosed solution for reducing carbonized spray-dried tungsten salt-cobalt salt precursor powder using a carbon source or a carbon-containing atmosphere. The turbidity of the cobalt composite powder and the segregation of the carbon component in the composite powder reduce the control of the amount of carbon in the reduction carbonization process, so that the cobalt-coated nano-WC crystal composite powder prepared by the invention has stable properties, uniform composition and fine WC grains. The powder composition is easy to control.

In addition, compared with the prior art disclosed direct reduction carbonization spray-dried tungsten salt-carbon source-cobalt salt precursor composite powder, the method provided by the invention has a short process and a process Simple, less process, more conducive to the quality control of nano-tungsten carbide cobalt composite powder.

The invention mixes the raw material and water to obtain a tungsten-cobalt composite salt solution, and the raw material comprises the following components:

40 wt% to 60 wt% of purple tungsten, 30 wt% to 52 wt% of a water-soluble cobalt salt, 4 wt% to 10 wt% of a carbon source, 1 wt% to 4 wt% of PEG, and 0.05 wt% to 3 wt% of a dispersant.

The invention uses a purple tungsten, a water-soluble cobalt salt, a carbon source, a PEG and a dispersing agent as raw materials, and mixes the raw materials with water to obtain a tungsten-cobalt composite salt solution. In the present invention, the raw material comprises 40% by weight to 60% by weight of purple tungsten, preferably 40% by weight to 55% by weight, more preferably 45% by weight to 52% by weight, most preferably 46% by weight to 50% by weight. In the present invention, the purple tungsten is a loose particle group composed of needle-like or rod-like crystal grains, and the formed purple tungsten agglomerate has abundant cracks and voids therein, which is favorable for infiltration and reduction of reducing gas and carbon during reduction carbonization. The overflowing allows the reduction carbonization reaction to proceed simultaneously on the surface and inside of the purple tungsten agglomerate, so that the reduction carbonization produces more tungsten powder nuclei, and the produced crystal nuclei have a uniform particle size, so that the finally obtained cobalt coated nano WC The crystalline composite powder has a relatively uniform and small particle size. The source of the purple tungsten is not particularly limited in the present invention, and a purple tungsten which is well known to those skilled in the art may be used, such as a commercially available product of purple tungsten;

In the present invention, the raw material comprises 30% by weight to 52% by weight of a water-soluble cobalt salt, preferably 40% by weight to 52% by weight, more preferably 45% by weight to 50% by weight. In the present invention, the water-soluble cobalt salt preferably includes one or more of cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt chloride, and cobalt carbonate, and more preferably Co(NO ₃ ) ₂ ·6H ₂ O, One or more of cobalt acetate, cobalt oxalate, CoCl ₂ ·6H ₂ O, and cobalt carbonate. The invention adopts the water-soluble cobalt salt as a raw material, so that the cobalt salt can be uniformly coated on the surface of the purple tungsten and the carbon by the water-dissolving method, so that the uniform mixing at the molecular level is achieved, the temperature of the subsequent reduction carbonization is lowered, and the preparation of the nanometer is facilitated. Grade composite powder;

In the present invention, the raw material comprises 4% by weight to 10% by weight of a carbon source, preferably 5% by weight to 8% by weight, more preferably 5.5% by weight to 7.5% by weight. In the present invention, the carbon source preferably comprises one or more of carbon black, lamp black, ethylenediamine, fiber, pulp, acetylene black, carbon nanotubes, glucose, polypropylene, syrup and sucrose, Preference is given to carbon black and/or lamp black. Excellent Optionally, the invention uses carbon black and/or lamp black as a carbon source, which increases the specific surface area of the powder, facilitates contact between the cobalt salt and the purple tungsten and the carbon source, thereby achieving molecular level mixing and reducing subsequent reduction carbonization. The temperature is more favorable for preparing the nano-scale composite powder;

In the present invention, the raw material comprises 1% by weight to 4% by weight of polyethylene glycol (PEG), preferably 2% by weight to 3% by weight. The source of the polyethylene glycol is not particularly limited in the present invention, and polyethylene glycol which is well known to those skilled in the art, such as a commercially available product of polyethylene glycol, may be used. In the present invention, the polyethylene glycol preferably has an average molecular weight of 4,000.

In the present invention, the raw material comprises 0.05% by weight to 3% by weight of a dispersing agent, preferably 0.1% by weight to 3% by weight, more preferably 1% by weight to 2.8% by weight, most preferably 2% by weight to 2.5% by weight.

In the present invention, the dispersing agent is preferably one or more of polyvinyl butyral, ammonium citrate, potassium tripolyphosphate, polyvinyl alcohol, and polyethyl acrylate.

In the present invention, the raw materials described in the above technical solution are preferably added to water and stirred uniformly to obtain a tungsten-cobalt composite salt solution. The water is not particularly limited in the present invention, and water is well known to those skilled in the art. In the present invention, the water is preferably pure water; the mass ratio of the water to the raw material is preferably ( 0.5 to 3):1, more preferably (1.5 to 2.8):1, most preferably (1.5 to 2.5):1. In the present invention, the pH of the tungsten-cobalt composite salt solution is controlled by controlling the amount of water to be added. In the present invention, the pH of the tungsten-cobalt composite salt solution is preferably from 1 to 5, more preferably from 2 to 4.

After obtaining the tungsten-cobalt composite salt solution, the tungsten-cobalt composite salt solution of the present invention is dried to obtain a cobalt-coated precursor powder. The method of the present invention is not particularly limited, and a dry technical solution well known to those skilled in the art may be employed. In the present invention, the drying is preferably spray drying, and the inlet temperature of the spray drying is preferably from 180 ° C to 260 ° C, more preferably from 190 ° C to 250 ° C, most preferably from 200 ° C to 240 ° C; The drying gas outlet temperature is preferably from 80 ° C to 150 ° C, more preferably from 90 ° C to 140 ° C, and most preferably from 100 ° C to 130 ° C.

Preferably, in the drying process, an inhibitor is added to the tungsten-cobalt composite salt solution; in the present invention, the inhibitor is preferably Cr ₂ C ₃ and VC; the present invention is directed to the Cr ₂ C ₃ and The source of the VC is not particularly limited, and may be Cr ₂ C ₃ and VC well known to those skilled in the art, and may be a single Cr ₂ C ₃ and VC, or a solid solution of Cr ₂ C ₃ and VC. In this technical solution, a raw material for preparing a cobalt-coated nano WC crystal composite powder includes a purple tungsten, a water-soluble cobalt salt, a carbon source, a PEG, a dispersant, and an inhibitor; wherein the inhibitor contains Cr ₂ C _{3 in} the raw material. The mass fraction is preferably from 0.1% to 1.0%, more preferably from 0.3% to 0.8%, most preferably from 0.4% to 0.6%; the VC is preferably from 0.1% to 1.0% by mass of the raw material, more preferably It is 0.3% to 0.8%, and most preferably 0.4% to 0.6%.

After the cobalt-coated precursor powder is obtained, the cobalt-coated precursor powder is subjected to reduction carbonization treatment in a reducing atmosphere to obtain a cobalt-coated nano-WC crystal composite powder. In the present invention, it is preferred that a reducing gas is introduced into the cobalt-coated precursor composite powder to carry out a reduction carbonization treatment. In the present invention, the reducing gas preferably includes hydrogen, more preferably further includes one or more of CH ₄ , C ₃ H ₈ , CO and CO ₂ ; in an embodiment of the invention, the reducing gas may Specifically, it is a mixture of H ₂ and natural gas, and may also be a mixture of H ₂ and C ₃ H ₈ , or a mixture of H ₂ and CO _{2 , or} a mixture of H ₂ and CO; in the present invention The volume ratio of one or more of CH ₄ , C ₃ H ₈ , CO and CO ₂ to hydrogen is preferably (90 to 99): (1 to 10), more preferably (95 to 99): (1 to 5), most preferably (98 to 99): (1 to 2). In the present invention, the temperature of the reduction carbonization treatment is 850 ° C to 1250 ° C, more preferably 900 ° C to 1200 ° C, most preferably 950 ° C to 1150 ° C; the time of the reduction carbonization treatment is preferably 30 min to 3 h, It is more preferably 1 h to 2.5 h, and most preferably 1.5 h to 2.0 h.

The cobalt-coated nano-WC crystal composite powder prepared by the method provided by the invention has a small particle size and uniform distribution; the composition is uniform and the performance is stable.

The invention also provides an ultrafine grained WC-Co cemented carbide prepared by the cobalt-coated nano WC crystal composite powder obtained by the preparation method described in the above technical solution.

In the present invention, the method of preparing an ultrafine grained WC-Co cemented carbide preferably includes the following steps:

Cobalt-coated nano-WC crystal obtained by the dispersing agent and the preparation method described in the above technical solution The bulk composite powder is mixed with water and ground to obtain a first mixture;

Pressing the second mixture into a compact to obtain a compact;

The compact was sintered to obtain an ultrafine grained WC-Co cemented carbide.

In the present invention, the cobalt-coated nano WC crystal composite powder prepared by the above technical solution is mixed with a dispersing agent and water, and ground to obtain a first mixture. In the present invention, the dispersing agent is preferably one or more of ethyl cellulose, imported METAMAXB-29, and sodium aluminate. The present invention is not particularly limited in the kind of the water, and water which is well known to those skilled in the art may be used. In the present invention, the water is preferably pure water.

In the present invention, the mass ratio of the cobalt-coated nano-WC crystal composite powder to the dispersant is 100: (1.0 to 4.0), more preferably 100: (2.0 to 3.0); the cobalt-coated nano-WC crystal composite The mass ratio of the total mass of the powder and the dispersant to the water is preferably 100: (30 to 100), more preferably 100: (40 to 90), and most preferably 100: (50 to 80).

In the present invention, the cobalt-coated nano WC crystal composite powder, the dispersant and water are preferably ground and mixed in a planetary ball mill to obtain a first mixture having a uniform composition. In the present invention, the ratio of the milled pellets is preferably (4 to 15):1, more preferably (6 to 13):1, more preferably (8 to 12):1; It is 400 r/min; the polishing time is preferably from 12 h to 48 h, more preferably from 15 h to 45 h, and most preferably from 18 h to 42 h.

After obtaining the first mixture, the first mixture is dried by the present invention and mixed with a molding agent to obtain a second mixture. In the present invention, a molding agent may be added to the first mixture during the drying process, or the first mixture may be mixed with the molding agent, and the obtained mixture may be dried to obtain a second mixture. . In the present invention, the mass ratio of the molding agent to the first mixture is preferably 100: (4 to 15), more preferably 100: (6 to 13), and most preferably 100: (8 to 12). . The type of the molding agent is not particularly limited in the present invention, and a molding agent well known to those skilled in the art may be used, and a paraffin rubber molding agent may be used.

The method of the invention is not particularly limited, and the person skilled in the art is employed. A well-known dry technical solution may be used, such as any of vacuum drying, infrared drying, ultrasonic drying or vibration drying. In the present invention, the drying temperature is preferably from 80 ° C to 100 ° C, more preferably from 85 ° C to 95 ° C; and the drying time is preferably 2.5 h.

After obtaining the second mixture, the present invention press-molds the second mixture to obtain a compact. The method and apparatus for press forming of the present invention are not particularly limited, and the press forming method and equipment used in the preparation of the cemented carbide known to those skilled in the art may be used, for example, a hydraulic machine of 20 tons may be used. The two mixtures were pressed to obtain strips having a size of 26 mm x 8.4 mm x 5.76 mm. For the size and shape of the compact, those skilled in the art can press the molded body of different shapes and sizes according to actual needs, and the present invention has no particular limitation.

After obtaining the compact, the present invention sinters the molded body to obtain an ultrafine grained WC-Co cemented carbide. In the present invention, the molded body is preferably subjected to low pressure sintering in a vacuum or a protective atmosphere to obtain an ultrafine grained WC-Co cemented carbide. In the present invention, the protective atmosphere may be nitrogen or an inert gas, and the present invention is not particularly limited; the degree of vacuum of the vacuum is preferably <100 pa. In the present invention, the sintering temperature is preferably from 1380 ° C to 1420 ° C, more preferably from 1390 ° C to 1410 ° C; the sintering time is preferably from 0.5 h to 1.5 h, more preferably from 0.75 h to 1.25 h; The pressure for sintering is preferably 15 kN to 25 kN, and more preferably 18 kN to 22 kN.

The cobalt-coated nano-WC crystal composite powder prepared by the preparation method of the above technical solution is used as a raw material, and the cobalt-coated nano-WC crystal composite powder obtained by the invention has uniform composition, fine and uniform WC crystal grains, and stable performance, thereby The preparation of the ultrafine grained WC-Co cemented carbide has high performance.

Referring to FIG. 1 , FIG. 1 is a schematic flow chart of preparing an ultrafine grained WC-Co cemented carbide according to an embodiment of the present invention, and the specific process is as follows:

Mixing purple tungsten, cobalt salt, carbon source, PEG, dispersant and pure water to obtain a tungsten-cobalt composite salt solution; spray-drying the tungsten-cobalt composite salt solution to obtain a cobalt-coated precursor powder; Precursor powder is subjected to reduction carbonization to obtain cobalt-coated nano WC crystal a granular composite powder; the cobalt-coated nano-WC crystal composite powder is ball-milled, and a molding agent is added, and the obtained mixture material is compression-molded to obtain a compact; the compact is subjected to pressure sintering to obtain an ultrafine crystal WC. -Co cemented carbide.

In order to further illustrate the present invention, the method for preparing a cobalt-coated nano-WC crystal composite powder and the ultra-fine-grained WC-Co cemented carbide provided by the present invention are described in detail below with reference to the examples, but they are not to be construed as limiting the scope of the present invention. Limited.

Example 1

1) Add 50kg of purple tungsten, 47.5kg of water-soluble cobalt acetate, 6.5kg of carbon black, 2kg of PEG, 0.4kg of Cr ₂ C ₃ , 0.5kg of VC and 2kg of polyvinyl alcohol dispersant to 350kg of pure water and stir evenly to adjust the pH value of the solution = 5, obtaining a tungsten-cobalt composite salt solution;

2) The tungsten-cobalt composite salt solution obtained in the step 1) is spray-dried, and the intake air temperature is 260 ° C, the outlet temperature is 120 ° C, to obtain a cobalt coated precursor powder;

The obtained precursor powder is subjected to scanning electron microscope (SEM) scanning analysis, and the result is shown in FIG. 2. FIG. 2 is a SEM topographical view of the cobalt-coated precursor powder obtained in Example 1 of the present invention, which can be viewed from FIG. It can be seen that the cobalt coated precursor powder obtained by the method provided by the invention has uniform particle size, uniform dispersion and small particle size.

3) The precursor powder obtained in the step 2) was subjected to reduction carbonization treatment at a temperature of 1100 ° C under a condition of H ₂ :CH ₄ (volume ratio) = 8:2 to obtain a cobalt-coated nano WC crystal grain composite powder.

The SiC scan analysis of the obtained cobalt-coated nano-WC crystal grain composite powder is carried out according to the present invention. The results are shown in FIG. 3 , and FIG. 3 is a SEM topographical view of the cobalt-coated nano WC crystal powder obtained in Example 1 of the present invention. It can be seen from FIG. 3 that the cobalt-coated nano-WC crystal composite powder prepared by the method provided by the invention has uniform particle size and fine WC crystal grains.

The obtained cobalt-coated nano-WC crystal grain composite powder is subjected to X-ray diffraction analysis, and the results are shown in FIG. 4. FIG. 4 is an XRD pattern of the cobalt-coated nano-WC crystal grain composite powder obtained in Example 1 of the present invention. It can be seen from FIG. 4 that the cobalt-coated nano-WC crystal composite powder obtained by the method provided by the invention has a single phase and uniform composition.

Example 2

The cobalt-coated nano WC crystal composite powder was prepared by the technical solution of Example 1, except that 1.0 kg of VC-Cr ₂ C ₃ solid solution was used in place of Cr ₂ C ₃ and VC in Example 1.

Example 3

1) Add 50kg of purple tungsten, 47.5kg of water-soluble cobalt acetate, 7.0kg of lamp black, 2kg of PEG, 0.4kg of Cr ₂ C ₃ , 0.5kg of VC and 2kg of polyvinyl alcohol dispersant to 360kg of pure water and stir evenly to adjust the pH of the solution. Value = 5, obtaining a tungsten-cobalt composite salt solution;

2) The tungsten-cobalt composite salt solution obtained in the step 1) is spray-dried, the inlet temperature is 260 ° C, and the outlet temperature is 120 ° C to obtain a cobalt-coated precursor powder;

The invention obtains the precursor powder by scanning electron microscopy (SEM) scanning analysis, and the knot The results show that the cobalt coated precursor powder obtained by the method provided by the invention has uniform particle size and small particle size;

3) The precursor powder obtained in the step 2) is subjected to reduction carbonization treatment at a temperature of 1100 ° C under H ₂ : C ₃ H ₈ (volume ratio) = 98.5: 1.5 for 40 min to obtain a cobalt-coated nano WC crystal composite. powder.

The SiC scan analysis of the cobalt-coated nano-WC crystal composite powder obtained by the invention shows that the cobalt-coated nano-WC crystal composite powder prepared by the method provided by the invention has smaller particle size and uniform uniform particle size;

The XRD analysis of the obtained cobalt-coated nano-WC crystal composite powder by the present invention shows that the cobalt-coated nano-WC crystal composite powder obtained by the invention has a single phase and uniform composition.

Example 4

The cobalt-coated nano WC crystal grain composite powder was prepared by the technical scheme of Example 3, except that this embodiment used 1.0 kg of VC-Cr ₂ C ₃ solid solution instead of Cr ₂ C ₃ and VC of Example 3.

Example 5

1) Add 50 kg of purple tungsten, 42.25 kg of cobalt carbonate, 6.3 kg of carbon black, ₂ kg of PEG, 0.4 kg of Cr ₂ C ₃ , 0.5 kg of VC and 2 kg of polyvinyl alcohol dispersant to 300 kg of pure water and stir evenly to adjust the pH of the solution. =5, obtaining a tungsten-cobalt composite salt solution;

2) The tungsten-cobalt composite salt solution obtained in the step 1) is spray-dried, the inlet temperature is 260 ° C, and the outlet temperature is 125 ° C to obtain a cobalt-coated precursor powder;

The obtained precursor powder is subjected to scanning electron microscopy (SEM) scanning analysis, and the results show that the cobalt-coated precursor powder obtained by the method provided by the invention has uniform particle size and small particle size;

3) The precursor powder obtained in the step 2) was subjected to reduction carbonization treatment at a temperature of 1100 ° C under a condition of H ₂ :CH ₄ (volume ratio) = 98.5:1.5 to obtain a cobalt-coated nano WC crystal grain composite powder.

The SiC scanning analysis of the obtained cobalt-coated nano-WC crystal composite powder shows that the cobalt-coated nano-WC crystal composite powder prepared by the method provided by the invention has small particle size, uniform dispersion and uniform particle size;

Example 6

The cobalt-coated nano WC crystal grain composite powder was prepared by the technical scheme of Example 5, except that 0.9 kg VC-Cr ₂ C ₃ solid solution was used in this example to replace Cr ₂ C ₃ and VC in Example 5.

Example 7

1) Add 50 kg of purple tungsten, 22.25 kg of cobalt carbonate, 20 kg of cobalt acetate, 6.0 kg of carbon black, 2.5 kg of PEG, 0.4 kg of Cr ₂ C ₃ , 0.5 kg of VC and 2 kg of polyvinyl alcohol dispersant to 300 kg of pure water and stir evenly. Adjusting the pH of the solution to 5 to obtain a tungsten-cobalt composite salt solution;

3) The precursor powder obtained in the step 2) was subjected to reduction carbonization treatment at a temperature of 1100 ° C under a condition of H ₂ :CH ₄ (volume ratio) = 98:2 to obtain a cobalt-coated nano WC crystal grain composite powder.

The SiC scan analysis of the cobalt-coated nano-WC crystal composite powder obtained by the invention shows that the cobalt-coated nano-WC crystal composite powder prepared by the method provided by the invention has small particle size, uniform dispersion and uniform particle size;

The XRD analysis of the cobalt-coated nano-WC crystal composite powder obtained by the invention shows that the cobalt-coated nano-WC composite powder obtained by the invention has a single phase and a composition. Evenly.

Example 8

The cobalt-coated nano WC crystal grain composite powder was prepared by the technical scheme of Example 5, except that 0.9 kg VC-Cr ₂ C ₃ solid solution was used in this example to replace Cr ₂ C ₃ and VC in Example 7.

Example 9

1) 500 g of the cobalt-coated nano WC crystal composite powder prepared in Example 1, 10 g of the imported B-29 dispersant and 40% pure water were ground and mixed in a planetary ball mill at a high speed for 24 hours, and the ratio of the ball to the concrete was 15: 1, to obtain a uniform composition of the mixture;

2) The mixture obtained in the step 1) is placed in a dry box, dried at 80 ° C, and then 10% of the paraffin rubber molding agent is uniformly mixed therein;

3) The material obtained in step 2) is pressed into a strip of 26 mm × 4.5 mm × 6.82 mm on a 20-ton hydraulic press;

4) The strip obtained in step 3) is pressure sintered in a 6 MPa low-pressure furnace. The sintering parameters are: vacuum degree <20 pa, temperature 1410 ° C, pressure 20 kN, pressure sintering and holding pressure for 1 hour, filling with high pressure argon gas, An ultrafine grained WC-Co cemented carbide article was obtained.

According to the present invention, the obtained ultrafine grain WC-Co cemented carbide product is subjected to metallographic analysis, and the results are shown in FIG. 5. FIG. 5 is a metallographic phase of the ultrafine grained WC-Co cemented carbide prepared in Example 9 of the present invention. As can be seen from Fig. 5, the ultrafine grained WC-Co cemented carbide obtained by the method of the present invention has fine and uniform crystal grains.

The hardness of the cemented carbide article prepared in the present example was 92.5 HRA, the grain size was 400 nm, and the density was 14.86 g/cm ³ .

Example 10

1) 500 g of Example 3 was prepared to prepare a cobalt-coated nano WC crystal composite powder, 10 g of an imported B-29 dispersant, and 40% pure water was ground and mixed in a planetary ball mill at a high speed for 30 hours, and the ratio of the ball to the material was 15: 1, to obtain a uniform composition of the mixture;

2) The mixture obtained in step 1) is placed in a dry box and dried at 100 ° C. The paraffin rubber molding agent with a weight of 10% added is uniformly mixed;

3) The material obtained in step 2) is pressed into a strip of 26 mm × 8.45 mm × 6.82 mm on a 20-ton hydraulic press;

4) The strip obtained in step 3) is pressure sintered in a 6MPa low-pressure furnace. The sintering parameters are: vacuum degree <100pa, temperature=1400°C, pressure=20kN, pressure sintering and holding pressure for 1 hour, filling with high pressure argon gas, An ultrafine grained WC-Co cemented carbide article was obtained.

The invention obtains the metallographic analysis of the obtained ultrafine grained WC-Co cemented carbide product, and the results show that the ultrafine grained WC-Co cemented carbide obtained by the method provided by the invention has fine and uniform crystal grains;

The ultrafine grained WC-Co cemented carbide article obtained in the present example was found to have a hardness of 91.8 HRA, a grain size of 450 nm and a density of 14.82 g/cm ³ .

Example 11

1) 500 g of Example 5 prepared cobalt coated nano WC crystal composite powder, 10 g of imported B-29 dispersant and pure water having a weight of 40% were ground and mixed in a planetary ball mill at a rate of 400 r/min for 36 hours. Ball to material ratio = 15:1, to obtain a uniform composition;

2) The mixture obtained in the step 1) is placed in a dry box, dried at 90 ° C, and then 10% of the paraffin rubber molding agent is added thereto to be uniformly mixed;

4) The strip obtained in step 3) is pressure sintered in a 6 MPa low-pressure furnace. The sintering parameters are: vacuum degree <100pa, temperature=1420°C, pressure=20kN, pressure sintering and holding pressure for 1 hour, filling with high pressure argon gas, An ultrafine grained WC-Co cemented carbide article was obtained.

The ultrafine grained WC-Co cemented carbide article prepared in the present example has a hardness of 93.2 HRA, a grain size of 400 nm and a density of 14.08 g/cm ³ .

Example 12

1) 500 g of Example 7 prepared cobalt coated nano WC grain composite powder, 10 g of imported B-29 dispersant and pure water having a weight of 40% were ground and mixed in a planetary ball mill at a rate of 400 r/min for 34 hours. Ball to material ratio = 15:1, to obtain a uniform composition;

2) The mixture obtained in the step 1) is placed in a dry box, dried at 85 ° C, and a paraffin rubber molding agent having a weight of 10% is added thereto and uniformly mixed;

4) The strip obtained in step 3) is pressure sintered in a 6MPa low-pressure furnace. The sintering parameters are: vacuum degree <100pa, temperature=1410°C, pressure=20kN, pressure sintering and holding pressure for 1 hour, filling with high pressure argon gas, An ultrafine grained WC-Co cemented carbide article was obtained.

The ultrafine grained WC-Co cemented carbide product prepared in the present example has a hardness of 92.2 HRA, a grain size of 420 nm and a density of 14.8 g/cm ³ .

It can be seen from the above examples that the present invention provides a method for preparing a cobalt-coated nano-WC crystal composite powder, comprising the following steps: 1) mixing a raw material and water to obtain a tungsten-cobalt composite salt solution, the raw material comprising the following components; 40% by weight to 60% by weight of purple tungsten, 30% by weight to 52% by weight of water-soluble cobalt salt, 4% by weight to 10% by weight of carbon source, 1% by weight to 4% by weight of PEG and 0.05% by weight to 3% by weight of dispersing agent; 2) The tungsten-cobalt composite salt solution obtained in the step 1) is dried to obtain a cobalt-coated precursor powder; 3) the cobalt-coated precursor powder obtained in the step 2) is subjected to reduction carbonization treatment under a reducing atmosphere to obtain Cobalt coated nano WC crystal composite powder. The preparation method provided by the invention adopts purple tungsten as a raw material, and the structure of the purple tungsten is favorable for the infiltration of reducing gas and carbon and the overflow of water vapor during the reduction carbonization process, so that the reduction carbonization reaction can be simultaneously performed on the surface and the interior of the purple tungsten, thereby Reducing carbonization to form more crystal nucleus of tungsten powder, the reaction speed is fast, and it is easier to prepare nano-carbide cobalt composite powder; Compared with the prior art, the method provided by the invention avoids the clogging of the nano tungsten carbide-cobalt composite powder and the segregation of carbon components in the composite powder in the carbonization process or the carbon-containing atmosphere during the reduction carbonization treatment, and is favorable for controlling the cobalt coating. Carbon content in the nano-WC crystal composite powder. Therefore, the cobalt-coated nano-WC crystal composite powder prepared by the invention has stable performance, uniform composition, fine WC grains and easy control of powder composition.

The above description is only a preferred embodiment of the present invention, and it should be noted that those skilled in the art can also make several improvements and retouchings without departing from the principles of the present invention. It should be considered as the scope of protection of the present invention.

Industrial applicability

The invention provides a method for preparing WC-Co nanocrystalline and ultrafine crystalline WC-Co cemented carbide. The method avoids the clogging of the nano tungsten carbide-cobalt composite powder and the segregation of carbon components in the composite powder during the carbonization treatment, and the carbon in the cobalt-coated nano-WC crystal composite powder is controlled. content. The obtained WC-Co nanocrystals have stable properties, uniform composition, fine WC crystal grains, and easy control of powder composition. In addition, the method provided by the invention has short preparation process, simple process and few processes, and is more favorable for quality control of the nano tungsten carbide cobalt composite powder.

Claims

A preparation method of cobalt coated nano WC crystal composite powder, comprising the following steps:

1) mixing the raw material and water to obtain a tungsten-cobalt composite salt solution, the raw material comprising the following components: 40 wt% to 60 wt% of purple tungsten, 30 wt% to 52 wt% of water-soluble cobalt salt, and 4 wt% to 10 wt% of charcoal. Source, 1 wt% to 4 wt% PEG, and 0.05 wt% to 3% wt% dispersant;

2) drying the tungsten-cobalt composite salt solution obtained in the step 1) to obtain a cobalt-coated precursor powder;

3) The cobalt-coated precursor powder obtained in the step 2) is subjected to reduction carbonization treatment under a reducing atmosphere to obtain a cobalt-coated nano WC crystal composite powder.
The production method according to claim 1, wherein the water-soluble cobalt salt comprises one or more of cobalt nitrate, cobalt acetate, cobalt oxalate, cobalt chloride, and cobalt carbonate.
The preparation method according to claim 1, wherein the carbon source comprises carbon black, lamp black, ethylenediamine, fiber, pulp, acetylene black, carbon nanotubes, glucose, polypropylene, syrup, and sucrose. One or several.
The production method according to claim 1, wherein the mass ratio of the raw material to the water is 1: (0.5 to 3.0).
The preparation method according to claim 1, wherein the temperature of the reduction carbonization treatment is 850 ° C to 1250 ° C; and the time of the reduction carbonization treatment is 30 min to 3 h.
The preparation method according to claim 1, wherein the reducing atmosphere is composed of a reducing gas including hydrogen; and the reducing gas including hydrogen further comprises one of CH 4 , C 3 H 8 , CO and CO 2 One or more; the volume ratio of one or more of CH 4 , C 3 H 8 , CO and CO 2 to hydrogen is (90 to 99): (1 to 10).
The preparation method according to claim 1, wherein the tungsten-cobalt composite salt solution has a pH of from 1 to 5.
The ultrafine grained WC-Co cemented carbide prepared by the cobalt-coated nano WC crystal composite powder obtained by the preparation method according to any one of claims 1 to 7.
The ultrafine grained WC-Co cemented carbide according to claim 8, wherein the method for producing an ultrafine grained WC-Co cemented carbide comprises the steps of: dispersing the agent and any one of claims 1 to 7. The cobalt-coated nano-WC crystal composite powder obtained by the preparation method is mixed with water and ground to obtain a first mixture; the first mixture is dried and mixed with a molding agent to obtain a second mixture; The second mixture is compression molded to obtain a compact; the compact is sintered to obtain an ultrafine grain WC-Co cemented carbide.
The ultrafine grained WC-Co cemented carbide according to claim 9, wherein the mass ratio of the cobalt-coated nano-WC crystal composite powder to the dispersant is 100: (1.0 to 4.0); The mass ratio of the total mass of the nano-WC crystal composite powder and the dispersant to the water is 100: (30 to 100).