WO2015169132A1

WO2015169132A1 - Method for preparing wc-co powder used for thermal spraying

Info

Publication number: WO2015169132A1
Application number: PCT/CN2015/075274
Authority: WO
Inventors: 戴煜; 谭兴龙; 邓军旺; 王艳艳
Original assignee: 湖南顶立科技有限公司
Priority date: 2014-05-09
Filing date: 2015-03-27
Publication date: 2015-11-12
Also published as: CN103920887A; CN103920887B

Abstract

A method for preparing WC-Co powder comprises the following steps: mixing tungsten carbide, water soluble cobalt salt, a carbon source and water to obtain mixed slurry; after ball-milling and even-blending are conducted on the mixed slurry, conducting spray granulation to obtain WC precursor powder coated by the cobalt salt; and conducting reduction and carbonization on the WC precursor powder coated by the cobalt salt, to obtain WC-Co powder. In the method, the water soluble cobalt salt serves as a cobalt source, and the WC precursor powder coated by the cobalt salt is prepared by using a liquid phase method, so that the cobalt is evenly coated on the surface of the WC in a solution molecular form, and reduction and carbonization are conducted on the WC precursor powder coated by the cobalt salt to obtain the WC-Co powder. The WC-Co powder is even in granularity, controllable in ingredients, even in powder ingredients, and free of W₂C, η-Co₃W₃C, η-Co₆W₆C, metal tungsten and the like in the ingredients; has high degree of sphericity and good mobility; and does not cause the decarburization phase and phase decomposition on the surface of a spraying substrate.

Description

Method for preparing WC-Co powder for thermal spraying

Technical field

The invention relates to the technical field of thermal spraying materials, in particular to a method for preparing WC-Co powder for thermal spraying.

Background technique

WC-Co-based cermet is the most studied and widely used cermet in carbide-based cermet. The thermal spray coating of WC-Co cermet is widely used in aerospace, due to its good hardness and toughness. Automotive, metallurgy, machinery and other fields. The preparation of WC-Co powder coating by supersonic flame spraying (HVOF) technology is a research hotspot, which can replace the hard chrome technology with high energy consumption and serious pollution to solve the wear resistance of spacecraft and repair worn parts.

In the prior art, the preparation method of WC-Co powder for metal thermal spraying WC-Co powder includes melting method, sintering-crushing method, plasma spheroidizing method and agglomeration sintering (spray granulation)-crushing method, etc., but melting The spray powder produced by the method and the sintering crushing method has irregular morphology, poor sphericity, poor flowability, low powder deposition rate, poor bonding strength between the coating and the substrate, and cracks and even peeling of the coating during use. And the failure, while the production process brings dust and noise pollution to the surrounding environment. For the plasma spheroidization method, since the entire spheroidization process is carried out in a high temperature and protective atmosphere environment, the equipment is required to be high and the production cost is high. For the traditional agglomeration sintering-crushing method, although the thermal spraying powder with excellent performance can be obtained, the powder has a long holding time in the high-temperature sintering process, consumes a large amount of energy, and the powder after sintering is bonded in a block shape, and needs to be crushed. Grading, prolonging the production cycle, increases production costs.

At present, a spray granulation method has been developed, which is one of the current industrial production methods of WC-Co powder metal thermal spraying. For example, the application numbers are CN201110336004.3, CN201210061980.7, CN201110321680.3 and CN201210370225.7. The preparation of WC-Co thermal spray powder by spray granulation method is basically the same. A thermally sprayed tungsten carbide-cobalt composite powder with excellent properties was prepared. However, these methods have the problems of adding a molding agent during the preparation process, increasing the subsequent dewaxing process, crushing and sieving, and causing pollution to the environment during the dewaxing process.

Summary of the invention

It is an object of the present invention to provide a method for preparing WC-Co powder for thermal spraying for thermal spraying. The method provided by the present invention avoids dewaxing, crushing and sieving, shortens the process flow, and uniformly coats the WC grains in the Co phase.

The present invention provides a method of preparing a WC-Co powder for thermal spraying, comprising the steps of:

Mixing tungsten carbide, water-soluble cobalt salt, carbon source and water to obtain a mixed slurry;

The mixed slurry is ball milled and then spray granulated to obtain a cobalt salt coated WC precursor powder;

The cobalt salt is coated with a WC precursor powder to carry out reduction carbonization to obtain a WC-Co powder.

Preferably, the water-soluble cobalt salt is one or more of cobalt nitrate, cobalt acetate, cobalt chloride and cobalt sulfate.

Preferably, the mass ratio of the tungsten carbide, the water-soluble cobalt salt and the carbon source is a:b:c, 50≤a≤70, 28≤b≤49, 0<c≤2.

Preferably, the tungsten carbide has a particle size of 0.1 μm to 8.0 μm.

Preferably, the carbon source comprises one or more of carbon black, lamp black, carbon nanotubes and organic carbon.

Preferably, the mixed slurry has a mass content of cobalt of from 3 wt% to 20 wt%.

Preferably, the reduction carbonization is carried out in an atmosphere of a reducing gas;

The reducing gas includes hydrogen and methane.

Preferably, the volume ratio of the hydrogen gas to the methane is (90 to 99): (1 to 10).

Preferably, the temperature of the reduction carbonization is 950 ° C to 1350 ° C.

Preferably, the reduction carbonization time is from 5 min to 60 min.

The present invention provides a method for preparing a WC-Co powder for thermal spraying, comprising the steps of: mixing tungsten carbide, a water-soluble cobalt salt, a carbon source and water to obtain a mixed slurry; and grinding and mixing the mixed slurry. Thereafter, spray granulation is carried out to obtain a cobalt salt-coated WC precursor powder; the cobalt salt is coated with the WC precursor powder to carry out reduction carbonization to obtain a WC-Co powder. The method provided by the invention uses a water-soluble cobalt salt as a cobalt source, and prepares a cobalt salt-coated WC precursor powder by a liquid phase method, so that cobalt is coated on the surface of the WC as a solution ion, and the cobalt salt is coated. The WC precursor powder is reduced in carbonization to obtain a WC-Co powder. The invention adopts water-soluble cobalt salt and organic carbon instead of forming agent to avoid dewaxing, and does not need to crush and sieve the obtained product, thereby shortening the process flow.

Moreover, the method provided by the present invention avoids the direct addition of cobalt metal to segregate the components caused by the uneven mixing. At the same time, the WC-Co powder prepared by the invention has high free carbon content, so that no decarburization phase is generated at high temperature during thermal spraying on the surface of the base material; and the invention can be reduced to carbonized into spherical WC at low temperature. Co powder, can be used as thermal spray powder, uniform particle size; low energy consumption, low equipment investment; controllable composition, uniform powder composition, no W ₂ C, η-Co ₃ W ₃ C, η-Co ₆ W in the composition ₆ C, metal tungsten, etc.; high sphericity and good fluidity, no decarburization phase and phase decomposition of the sprayed substrate surface.

DRAWINGS

1 is a schematic flow chart of preparing a WC-Co powder according to an embodiment of the present invention;

2 is a SEM photograph of a precursor powder obtained in Example 2 of the present invention at 2000 magnifications;

3 is a SEM photograph of 2000 times magnification of WC-Co powder obtained in Example 2 of the present invention;

4 is an XRD photograph of a cobalt-coated nano WC obtained in Example 2 of the present invention;

5 is a SEM photograph and a surface distribution of W and Co elements of the WC-Co powder obtained in the second embodiment of the present invention at a magnification of 5000 times;

Fig. 6 is a photograph showing a metallographic photograph of a WC-Co powder obtained in the second embodiment of the present invention at a magnification of 1000 and 1500 times.

detailed description

The invention adopts water-soluble cobalt salt and organic carbon instead of forming agent to avoid dewaxing, and does not need to crush and sieve the obtained product, thereby shortening the process flow. In the invention, the water-soluble cobalt salt is used as the cobalt source, and when the cobalt salt-coated WC precursor powder is prepared by the liquid phase method, the cobalt is uniformly mixed in a molecular form without causing segregation of components. The WC-Co powder prepared by the invention has uniform particle size, high sphericity, good fluidity, and uniform and controllable composition, and does not decompose the decarburized camera phase on the surface of the sprayed substrate when used for thermal spraying.

The present invention mixes tungsten carbide, a water-soluble cobalt salt, a carbon source and water to obtain a mixed slurry. In the present invention, tungsten carbide, a water-soluble cobalt salt and a carbon source are preferably added to water and mixed to obtain a mixed slurry. In the present invention, the water-soluble cobalt salt is preferably one or more of cobalt nitrate, cobalt acetate, cobalt chloride and cobalt sulfate, more preferably cobalt acetate; the carbon source preferably comprises carbon black, lamp black One or more of carbon nanotubes and organic carbon, more preferably carbon black, lamp black, ethylene diamine, fiber, pulp, acetylene black, carbon nanotubes, glucose, polyacrylonitrile, syrup and sucrose One or several; in an embodiment of the invention, the water may be pure water. In the present invention, the grain size of the tungsten carbide is preferably from 0.1 μm to 8.0 μm, more preferably from 0.2 μm to 1.0 μm; in the embodiment of the present invention, the tungsten carbide may have a particle size of from 0.5 μm to 0.6 μm.

The present invention has no particular limitation on the source of the tungsten carbide, the water-soluble cobalt salt, the carbon source and the water, and the tungsten carbide, the water-soluble cobalt salt, the carbon source and the water which are well known to those skilled in the art can be used, for example, the city can be used. Selling goods. Specifically, in the embodiment of the present invention, a commercially available tungsten carbide having a grade of GWC002 may be used.

In the present invention, the mass ratio of the tungsten carbide, the water-soluble cobalt salt and the carbon source is preferably a:b:c, 50≤a≤70, 28≤b≤49, 0<c≤2, more preferably 55 ≤ a ≤ 65, 30 ≤ b ≤ 45, 0.5 ≤ c ≤ 1.5; the mass ratio of the total mass of the tungsten carbide, the water-soluble cobalt salt and the carbon source to water is preferably 1: (0.5 to 3), more preferably 1: (1 to 2.5), most preferably 1: (1.5 to 2.0); the mass content of cobalt in the mixed slurry is preferably from 3% by weight to 20% by weight, more preferably from 5% by weight to 18% by weight, most preferably 6% by weight. % ~ 17wt%.

After the mixed slurry is obtained, in the present invention, the mixed slurry is ball milled and then spray granulated to obtain a cobalt salt coated WC precursor powder. The method for ball milling and mixing in the present invention is not particularly limited, and a technical solution of ball milling and mixing well known to those skilled in the art may be employed, such as rolling ball milling. In the present invention, the time for the ball mill to mix is preferably from 3 h to 12 h, more preferably from 4 h to 12 h, and most preferably from 6 h to 10 h.

In the present invention, the inlet blasting temperature of the spray granulation is preferably from 180 ° C to 300 ° C, more preferably from 200 ° C to 280 ° C, most preferably from 220 ° C to 260 ° C; and the outlet blasting temperature of the spray granulation is preferably It is 80 ° C to 180 ° C, more preferably 100 ° C to 170 ° C, most preferably 120 ° C to 160 ° C; the centrifugal atomization rotational speed of the spray granulation is preferably from 6000 r / min to 15000 r / min, more preferably 8000 r / From min to 13500 r/min, most preferably from 10,000 r/min to 12000 r/min.

After obtaining a cobalt salt-coated WC precursor powder, the present invention reduces carbonization of the cobalt salt-coated precursor to obtain a WC-Co powder. The present invention preferably reductively carbonizes the cobalt salt precursor in a reducing gas atmosphere, preferably including hydrogen and methane. In the present invention, the volume ratio of the hydrogen gas to the methane is preferably (90 to 99): (1 to 10), more preferably (95 to 99): (1 to 5), and most preferably (98 to 99). : (1 to 2). In the present invention, the temperature of the reduction carbonization is preferably 950 ° C to 1350 ° C, more preferably 1100 to 1300 ° C, most preferably 1150 ° C to 1250 ° C; the reduction carbonization time is preferably 5 min to 60 min, more preferably It is 10 min to 40 min, and most preferably 20 min to 30 min.

Referring to FIG. 1 , FIG. 1 is a schematic flow chart of preparing a WC-Co powder according to an embodiment of the present invention. First, a tungsten carbide, a cobalt acetate, and an organic carbon are formulated into a mixed slurry; and the mixed slurry is subjected to ball milling and then spray granulated. Obtaining a cobalt salt coated WC precursor powder; and then the cobalt salt The coated WC precursor powder is reduced in carbonization to obtain a WC-Co powder.

The present invention performs scanning electron microscopy scanning analysis on the obtained cobalt salt-coated WC precursor powder and WC-Co powder, and as a result, it can be seen that the cobalt salt-coated WC precursor powder and WC-Co powder obtained by the method provided by the present invention are obtained. Uniform particle size, high sphericity, and thus higher fluidity;

The WC-Co powder obtained by the invention is subjected to X-ray diffraction analysis, and the results show that the cobalt-coated nano WC-Co component obtained by the method provided by the invention is uniform, and no W ₂ C, η-Co ₃ W ₃ C, η-Co ₆ W ₆ C, metal tungsten, etc.; the content of free carbon is high, so that it does not generate a decarburization phase at a high temperature on the surface of the base material when used for thermal spraying.

The present invention provides a method for preparing a WC-Co powder for thermal spraying, comprising the steps of: mixing tungsten carbide, a water-soluble cobalt salt, a carbon source and water to obtain a mixed slurry; and grinding and mixing the mixed slurry Thereafter, spray granulation is carried out to obtain a cobalt salt-coated WC precursor powder; the cobalt salt is coated with the WC precursor powder to carry out reduction carbonization to obtain a WC-Co powder. The method provided by the invention uses a water-soluble cobalt salt as a cobalt source, and prepares a cobalt salt-coated WC precursor powder by a liquid phase method, so that cobalt is uniformly coated on the surface of the WC in a molecular form, and then the cobalt salt is coated. The WC precursor powder is reduced in carbonization to obtain a WC-Co powder. The invention adopts water-soluble cobalt salt and organic carbon instead of forming agent to avoid dewaxing, and does not need to crush and sieve the obtained product, thereby shortening the process flow.

In order to further illustrate the present invention, the method for preparing the cobalt-coated nano WC powder provided by the present invention will be described in detail below with reference to the examples, but they cannot be understood as The scope of the invention is limited.

Example 1

1) 50Kg tungsten carbide powder having a particle size of 0.5 μm to 0.6 μm, 21 Kg of cobalt acetate and 560 g of carbon nanotubes are dissolved in pure water having a mass of 1.5 times the total mass of the solid, and formulated into a mixed slurry having a cobalt content of 10% by weight;

2) After the ball slurry obtained in the step 1) is ball milled for 6 hours, spray granulation is carried out. During the spray granulation process, the inlet air temperature is 260 ° C, the outlet air temperature is 160 ° C, and the centrifugal atomization speed is 12000 r/min. , obtaining a cobalt salt coated WC precursor powder;

3) The precursor powder obtained in the step 2) was subjected to reduction carbonization in an atmosphere of H ₂ :CH ₄ (volume ratio) = 98.5:1.5 at 1150 ° C for 60 minutes to obtain a WC-Co powder.

The physical properties and chemical compositions of the obtained WC-Co powders were examined. The results are shown in Table 1. Table 1 shows the physical properties and chemical compositions of the WC-Co powders obtained in the examples of the present invention.

Example 2

1) 50Kg tungsten carbide powder having a particle size of 0.5μm to 0.6μm, 29Kg of cobalt acetate, and 600g of carbon black are dissolved in pure water having a mass of 1.8 times the total mass of the solid to prepare a mixed slurry having a cobalt content of 12% by weight;

2) After the ball slurry obtained in the step 1) is ball milled for 8 hours, spray granulation is carried out. During the spray granulation process, the inlet air temperature is 260 ° C, the outlet air temperature is 140 ° C, and the centrifugal atomization rotation speed is 10000 r / min. , obtaining a cobalt salt coated WC precursor powder;

The obtained precursor powder is subjected to scanning electron microscope scanning analysis, and the result is shown in FIG. 2. FIG. 2 is a SEM photograph of the precursor powder obtained in Example 2 of the present invention at 2000 times magnification. As can be seen from FIG. 2, the present invention The obtained precursor powder has a uniform particle size and a spherical shape;

3) The precursor powder obtained in the step 2) was subjected to reduction carbonization in an atmosphere of H ₂ : CH ₄ (volume ratio) = 98.65: 1.35 at 1250 ° C for 40 min to obtain a WC-Co powder.

The invention performs scanning electron microscopy scanning analysis on the obtained WC-Co powder, and the result is shown in FIG. 3 is a SEM photograph of 2000 times magnification of the WC-Co powder obtained in Example 2 of the present invention. As can be seen from FIG. 3, the WC-Co powder prepared by the present invention has uniform particle size and high sphericity.

The WC-Co powder obtained by the present invention is subjected to X-ray diffraction analysis, and the results are shown in FIG. 4. FIG. 4 is an XRD photograph of the cobalt-coated nano WC obtained in Example 2 of the present invention, as can be seen from FIG. The WC-Co powder component prepared by the invention is uniformly mixed; W2C, η (Co ₃ W ₃ C, Co ₆ W ₆ C), metal tungsten or the like does not appear in the WC-Co powder.

The WC-Co powder obtained by the invention is subjected to field emission scanning electron microscopy to enlarge the element surface distribution photograph at 5000 times, and the result is shown in FIG. 5. FIG. 5 is a magnified 5000 of cobalt-coated nano WC-Co powder obtained in Example 2 of the present invention. The SEM photograph and the surface distribution of the W and Co elements are doubled, wherein (a) is a SEM photograph of the cobalt-coated nano-WC-Co powder obtained in Example 2 of the present invention at a magnification of 5000 times, and (b) is Example 2 of the present invention. The obtained cobalt-coated nano-WC-Co powder is magnified 5000 times under the W element surface distribution photograph, (c) is a cobalt-coated nano-WC-Co powder obtained in Example 2 of the present invention, magnified 5000 times under the Co element surface distribution photo, It can be seen from Fig. 5 that the WC-Co powder prepared by the invention has a uniform distribution of W and Co phases, and the Co phase uniformly coats the WC grains.

The obtained WC-Co powder is subjected to cross-section metallographic analysis photograph, and the result is shown in FIG. 6. FIG. 6 is a metallographic profile of the cobalt-coated nano-WC-Co powder obtained in Example 2 of the present invention at 1000 and 1500 times magnification. Photograph (a) is a photograph of a metallographic cross-section of a cobalt-coated nano-WC-Co powder obtained in Example 2 of the present invention at a magnification of 1000 times, and (b) a magnified cobalt-coated nano-WC-Co obtained in Example 2 of the present invention. The 1500 times lower metallographic cross-section photograph, as can be seen from FIG. 6, the WC-Co powder, WC, and Co phase prepared by the present invention are uniformly distributed.

Example 3

1) 50Kg tungsten carbide powder with a particle size of 0.5μm to 0.6μm, 43.5Kg cobalt acetate, 1.4Kg The sucrose is dissolved in pure water having a mass of 3.0 times the total mass of the solid, and is formulated into a mixed slurry having a cobalt content of 17% by weight;

2) After the mixture slurry obtained in the step 1) is ball-milled for 8 hours, spray granulation is carried out. In the spray granulation, the inlet air temperature is 260 ° C, the outlet air temperature is 160 ° C, and the centrifugal atomization rotation speed is 10000 r / min. , obtaining a cobalt salt coated WC precursor powder;

3) The precursor powder obtained in the step 2) was subjected to reduction carbonization in an atmosphere of H ₂ : CH ₄ (volume ratio) = 98.5 : 1.5 at 1250 ° C for 30 min to obtain a cobalt-coated nano WC-Co powder.

Table 1 Physical properties and chemical composition of WC-Co powder obtained by the examples of the present invention

It can be seen from Table 1 that the WC-Co powder prepared by the invention has uniform particle size, uniform and controllable composition, and does not cause component segregation; and the WC-Co powder prepared by the invention has high free carbon content, so that the body is made. During the thermal spraying process, the sprayed powder does not produce a decarburized phase at high temperatures.

It is apparent from the above examples that the present invention provides a method for preparing a WC-Co powder for thermal spraying, comprising the steps of: mixing tungsten carbide, a water-soluble cobalt salt, a carbon source and water to obtain a mixed slurry; The mixed slurry is ball milled and mixed, and then spray granulated to obtain a cobalt salt coated WC precursor powder; the cobalt salt is coated with the WC precursor powder for reduction carbonization to obtain a WC-Co powder. The method provided by the invention uses a water-soluble cobalt salt as a cobalt source, and prepares a cobalt salt-coated WC precursor powder by a liquid phase method, so that the cobalt is coated in a solution ion form. On the surface of the WC, the cobalt salt-coated WC precursor powder is reduced and carbonized to obtain a WC-Co powder. The invention adopts water-soluble cobalt salt and organic carbon instead of forming agent to avoid dewaxing, and does not need to crush and sieve the obtained product, thereby shortening the process flow.

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 method for preparing WC-Co powder provided by the invention uses a water-soluble cobalt salt as a cobalt source, and prepares a cobalt salt-coated WC precursor powder by a liquid phase method, so that cobalt is uniformly coated on the surface of the WC in a solution molecular level form. Then, the cobalt salt coated WC precursor powder is reduced and carbonized to obtain a WC-Co powder. The WC-Co powder obtained by the invention has uniform particle size, controllable composition, uniform powder composition, no W ₂ C, η-Co ₃ W ₃ C, η-Co ₆ W ₆ C, metal tungsten, etc. in the composition; high sphericity And the fluidity is good, the decarburization phase and the decomposition of the phase do not occur on the surface of the sprayed substrate.

Claims

A method for preparing a WC-Co powder for thermal spraying, comprising the steps of: mixing tungsten carbide, a water-soluble cobalt salt, a carbon source and water to obtain a mixed slurry; and grinding the mixed slurry to perform spray granulation, A cobalt salt coated WC precursor powder is obtained; the cobalt salt is coated with a WC precursor powder for reduction carbonization to obtain a WC-Co powder.
The method according to claim 1, wherein said water-soluble cobalt salt is one or more of cobalt nitrate, cobalt acetate, cobalt chloride and cobalt sulfate.
The method according to claim 1, wherein the mass ratio of said tungsten carbide, water-soluble cobalt salt and carbon source is a:b:c, 50 ≤ a ≤ 70, 28 ≤ b ≤ 49, 0 < c ≤ 2.
The method according to claim 1, wherein the tungsten carbide has a particle size of from 0.1 μm to 8.0 μm.
The method of claim 1 wherein the carbon source comprises one or more of carbon black, lamp black, carbon nanotubes, and organic carbon.
The method according to claim 1, wherein the mixed slurry has a mass content of cobalt of from 3 wt% to 20 wt%.
The method according to claim 1, wherein said reducing carbonization is carried out in an atmosphere of a reducing gas; said reducing gas comprises hydrogen and methane.
The method according to claim 7, wherein the volume ratio of hydrogen to methane is (90 to 99): (1 to 10).
The method of claim 1 wherein said reducing carbonization temperature is from 950 ° C to 1350 ° C.
The method according to claim 1, wherein the reduction carbonization time is from 5 min to 60 min.