KR100601096B1 - METHOD FOR MANUFACTURING NANO-STRUCTURED WC-Co POWDERS FOR THERMAL SPRAY COATING - Google Patents

Abstract

The present invention relates to a nanostructured tungsten carbide-cobalt-based powder for thermal spray coating, a method for preparing the same, and a nanostructured thermal spray coating using the same. To this end, the method for preparing a nanostructured tungsten carbide-cobalt-based powder for thermal spray coating according to the present invention comprises preparing a mixture of a tungsten carbide-cobalt mixture, a dispersant and a solvent, and adding a binder and a plasticizer to the mixture to partially aggregate the powder. Preparing the prepared slurry, spray drying the partially aggregated slurry to prepare spherical granules, and heat treating the spherical granules to remove organic matter contained in the spherical granules. Through this invention it is possible to greatly improve the wear resistance of the thermal spray coating.

Thermal spray coating, tungsten carbide, cobalt, slurry, partial coagulation

Description

Method for producing nanostructured tungsten carbide-cobalt powder for thermal spray coating {METHOD FOR MANUFACTURING NANO-STRUCTURED WC-Co POWDERS FOR THERMAL SPRAY COATING}

1 is a conceptual diagram of a nanostructured WC-Co powder according to an embodiment of the present invention.

Figure 2 is a graph showing the particle size distribution of the WC-Co powder in the partially agglomerated slurry during the production of the nanostructured WC-Co powder according to an embodiment of the present invention.

3 (A) is a scanning electron micrograph showing the shape of the WC-Co powder granules prepared according to Experimental Example 1 of the present invention, Figure 3 (B) is a scanning electron showing the cross-sectional microstructure of the same powder granules A scanning electron microscope (SEM) photograph.

4 is a scanning electron micrograph of the WC-Co granules prepared according to Experimental Example 3 of the present invention.

5 is a scanning electron micrograph showing the distribution of Co in the WC-Co powder prepared according to Experimental Example 3 of the present invention.

Figure 6 is a scanning electron micrograph of the WC-Co granules prepared according to Experimental Example 1 of the present invention and the thermal spray coating prepared using the same.

Figure 7 is a scanning electron micrograph of the WC-Co granules prepared according to Comparative Example 1 of the prior art and the spray coating cross section prepared using the same.

Figure 8 is a scanning electron micrograph of the WC-Co granules prepared according to Comparative Example 2 of the prior art and the spray coating cross section prepared using the same.

9 is a conceptual diagram of a micro-based WC-Co powder according to the prior art.

10A is a conceptual diagram of a nanostructured WC-Co powder according to the prior art, and FIG. 10B is a scanning electron micrograph.

The present invention relates to a nanostructured tungsten carbide-cobalt-based powder for thermal spray coating, a method of manufacturing the same, and a thermal spray coating using the same, and more particularly, to a thermally coated nanostructured tungsten carbide-cobalt-based powder prepared using a partially aggregated slurry. The present invention relates to a powder, a preparation method thereof, and a thermal spray coating using the same.

The thermal spray coating refers to a technique of forming a coating in which a powder or a linear material is formed into a molten droplet by using a high temperature heat source while rapidly colliding with a base material to form a coating laminated by quench solidification. In this case, since the coating is formed on the surface of the base material by using materials having different properties, the defects can be compensated for while maintaining the properties of the base material, and the function of the material can be varied, but there is an advantage in that it can be upgraded. In addition, since a thick film can be formed at a high speed, and materials such as metal, ceramic, glass, and plastic can also be used, there is an advantage in that a coating can not be obtained by other methods.

Representative examples of the thermal spray coating material include WC (tungsten carbide) -Co (cobalt). The WC-Co thermal spray coating material is a material in which the hard metal phase WC particles and the binder Co metal are mixed, and have a constant hardness and impact resistance. Therefore, it is not only widely used in various industrial parts for the purpose of improving wear resistance, but also made of bulk material through sintering and used in cutting tools.

For the production of such WC-Co thermal spray coating, WC particles having a diameter of several micrometers (µm) are generally used. 9 is a conceptual diagram of such a micrometer-based WC-Co powder according to the prior art, when spray-drying the mixture slurry containing the WC particles shown on the left easily obtains spherical powder suitable for the spray coating process as shown on the right Can be. However, in the case of using such a micrometer-based WC-Co powder, research on the development of nanostructured WC-Co powder has been actively conducted in order to further improve the properties of the spray coating to some extent.

Korean Patent Registration No. 213683 relates to a method for preparing fine WC-Co composite powder by mechanical chemistry method, and fine particle WC comprising a composite process of spray drying method, ball milling method and carburization reaction method using carbon black. The manufacturing method of -Co composite powder is disclosed. Here, the present invention discloses a fine WC-Co composite powder having nanoparticles having a WC particle size of about 0.1 μm for determining the mechanical properties of cemented carbide and having a uniform distribution of Co, which is excellent in hardness and compressive strength.

In addition, U. S. Patent No. 5,352, 269 discloses a method of preparing nanostructured ultrafine WC powder by spray-drying an aqueous solution containing a water-soluble W salt and a Co salt, followed by gas reaction.

However, such nanostructured WC-Co powder is a technique for producing a powder mainly used as a sintered material, and has many problems when used in a spray coating process. For example, when the nanostructured WC-Co powder is manufactured by a spray conversion method, the pore inside the powder has a lot of donuts as well as the hollow shape.

FIG. 10A is a conceptual view of a nanostructured WC-Co powder according to the prior art. In the case of preparing a powder having a general size of nanometer (nm) dispersed on the left side by a spray conversion method, The shape of the nanostructured WC-Co powder is modified. Figure 10 (B) is a scanning electron micrograph of the nanostructured WC-Co powder according to the prior art, showing the shape of the nanostructured WC-Co powder in the form of a donut when prepared by the method described above.

As shown in FIG. 10B, since the WC-Co powder is hollow and has defects formed therein, serious problems occur during the spray coating process. In other words, since the WC-Co powder is nanometer in size, the ratio of the surface area to the powder volume is large, causing severe decarburization and phase decomposition upon heat source exposure in the thermal spray coating. In particular, localized particle heating in the thermal spray coating accelerates decarburization and phase decomposition of the coating. In addition, the hollow or recessed powder shape defects generated by uneven drying of the liquid phase during spray drying during the powder manufacturing process continuously remain in the coating after the thermal spraying coating to increase the porosity of the coating and reduce the bonding strength of the coating. And ultimately adversely affect the final properties, such as the wear resistance of the sprayed coating.

The present invention is to solve the above-described problems, it is possible to control the defects of the coating layer caused by the manufacturing defects of the feedstock as well as the defects due to its own physicochemical properties when using nanostructured raw materials. To provide a nanostructured WC-Co powder for thermal spray coating.

In addition, the present invention is to provide a method for producing a nano-structured WC-Co powder for thermal spray coating most suitable for thermal spray coating.

And the present invention is to provide a nano-structured thermal spray coating having the optimum properties by using the above-described spray coating nanostructured WC-Co powder.

In order to achieve the above object, a method of preparing nano-based tungsten carbide (WC) -cobalt (Co) powder for thermal spray coating may include preparing a mixture of a tungsten carbide-cobalt mixture, a dispersant, and a solvent. Adding a binder and a plasticizer to the mixture to prepare a partially aggregated slurry, spray drying the partially aggregated slurry to produce spherical granules, and heat treating the spherical granules to obtain organic matter contained in the spherical granules. Removing the step.

In preparing the partially aggregated slurry, a surfactant may be added and stirred.

In the step of preparing the partially agglomerated slurry, the tungsten carbide-cobalt mixture is preferably contained in the partially agglomerated slurry from 40.0 wt% to 80.0 wt%.

And in the step of preparing the mixture, the tungsten carbide-cobalt mixture may comprise 7.0 to 20.0 wt% of cobalt, with the remainder being tungsten carbide and other impurities.

It is preferable that the particle size of tungsten carbide is 1 micrometer or less.

In the step of mixing the mixture, the corrosion resistant element can be further mixed with the tungsten carbide-cobalt mixture.

Here, the corrosion resistant element is preferably at least one of nickel (Ni) and chromium (Cr).

In preparing the partially agglomerated slurry, the dispersant added to the slurry is preferably 0.01 wt% to 1.0 wt%.

Further, the dispersant added to the slurry is more preferably 0.1wt% to 1.0wt%.

In preparing the mixture, the solvent is preferably an aqueous solvent.

The dispersant may be any one or more selected from the group consisting of ammonium polymethacrylate, polyethylene amine, and lignosulfate.

In preparing the mixture, the solvent may be an organic solvent.

In the preparing of the mixture, the dispersant may be at least one selected from the group consisting of polyvinyl pyrollidone having a molecular weight of 10,000 to 100,000, and a copolymer dispersant having a carboxyl group and a saturated hydrocarbon group.

In the step of preparing the mixture, the organic solvent is ethyl alcohol, isopropyl alcohol, toluene and a mixture of ethyl alcohol, acetone and a mixture of ethyl alcohol, and isopropyl alcohol and It is preferably at least one selected from the group consisting of a mixture of acetone.

The organic solvent is a mixture of toluene and ethyl alcohol, and the ratio of toluene to ethyl alcohol is preferably 60 wt% / 40 wt% to 85 wt% / 15 wt%.

The organic solvent is a mixture of acetone and ethyl alcohol, and the ratio of acetone to ethyl alcohol is preferably 30 wt% / 70 wt% to 70 wt% / 30 wt%.

The organic solvent is a mixture of isopropyl alcohol and acetone, and the ratio of isopropyl alcohol to acetone is preferably 30 wt% / 70 wt% to 70 wt% / 30 wt%.

In the step of preparing the partially aggregated slurry, the surfactant is preferably 0.01 wt% to 5.00 wt% of polyoxyethylene tert-octylphenyl ether.

Nanostructured tungsten carbide-cobalt-based powder according to the present invention can be prepared by the above-described method.

Nanostructured spray coating according to the present invention may be made of nanostructured tungsten carbide-cobalt-based powder.

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 and 2. These embodiments of the present invention are merely for illustrating the present invention, the present invention is not limited thereto.

1 is a conceptual diagram of a nanostructured WC-Co powder according to an embodiment of the present invention, which shows a state of manufacturing a spherical nanostructured WC-Co powder by spray drying a partially aggregated slurry.

As shown in FIG. 1, after preparing the partially aggregated slurry shown on the left side, the resultant is spray-dried to prepare a nanostructured WC-Co powder for thermal spray coating of the spherical granules shown on the right side. Hereinafter, a method of manufacturing the spray-coated nanostructured WC-Co powder will be described in detail.

First, a partially aggregated slurry is prepared by the following method.

A mixture of a WC-Co mixture, a dispersant, and a solvent is prepared, and then a binder and a plasticizer are added thereto to prepare a slurry, and then a surfactant is added and stirred to prepare a partially aggregated slurry. Wherein the WC-Co mixture comprises 7.0 wt% to 20.0 wt% Co, with the remainder being WC and other impurities. If Co is less than 7.0wt%, there is a problem in that the function as a binder cannot be properly performed, and if Co is more than 20.0wt%, an excessive amount of metal material is present, which adversely affects wear resistance.

It is preferable that the particle size of WC before use as a nano powder is 1 micrometer or less, and improves the characteristics of a spray coating, such as abrasion resistance. Preferably, the partially aggregated slurry contains 40.0 wt% to 80.0 wt% of the WC-Co mixture. If the amount of the WC-Co mixture contained in the partially agglomerated slurry is less than 40.0 wt%, it takes a long time to produce a certain amount of granules, which is uneconomical, and the amount of the WC-Co mixture contained in the partially agglomerated slurry is 80.0 If the wt% is exceeded, the slurry may not be smoothly supplied during spray drying due to the excessive powder content, and the nozzle may be clogged to stop working. Therefore, by containing 40.0 wt% to 80.0 wt% of the WC-Co mixture in the partially aggregated slurry, the manufacturing process can be simplified and the working time can be reduced.

As such, in the step of mixing the tungsten carbide-cobalt mixture, the corrosion resistant elements may be further mixed. As the corrosion resistant element, Ni, Cr or a mixture thereof can be used. Corrosion resistance can be improved by adding a corrosion resistant element to the tungsten carbide-cobalt mixture to produce a thermal spray coating. In this case, Ni may be added about 10 wt%, and Cr may be added about 4 wt%. Ni or Cr is added in an appropriate amount so that the thermal spray coating requires corrosion resistance, but the amount is limited to a certain range in order to prevent deterioration of properties of the tungsten carbide, that is, hardness and wear resistance.

The slurry is selected from the group consisting of water as a solvent or a mixture of ethyl alcohol, isopropyl alcohol, toluene and ethyl alcohol as a solvent, a mixture of acetone and ethyl alcohol, or a mixture of isopropyl alcohol and acetone. One or more organic solvents can be used.

Dissolution is determined in a solvent according to its own characteristics, such as a binder and a plasticizer incorporated into the slurry. Due to these property differences, the solvent should be selected according to the properties of the material to be dissolved. For example, a solvent may be selected depending on whether the substance is polar or nonpolar. In the case of a polar substance, a polar solvent and an alcohol are mixed, and in the case of a nonpolar substance, a nonpolar solvent and toluene are mixed and used. When one type of solvent is used, defects are caused in subsequent manufacturing processes depending on the difference in characteristics such as the drying rate and viscosity of the solvent, and therefore, usually two or more solvents are mixed and used. In the embodiment of the present invention, since a nonpolar material is used as the binder, it is preferable to use a nonpolar solvent.

When toluene and ethyl alcohol mixed liquid are used as the organic solvent, the ratio of toluene to ethyl alcohol is preferably 60wt% / 40wt% to 85wt% / 15wt%. If the ratio of toluene to ethyl alcohol is less than 60/40 wt%, ethyl alcohol is volatilized during the manufacturing process to reduce the amount of ethyl alcohol in the final solution than the initial input. In addition, when the ratio of toluene to ethyl alcohol exceeds 85wt% / 15wt%, the toluene is excessively contained in the solution, and the drying rate is remarkably decreased, making granule formation itself difficult. Therefore, by adjusting the ratio of toluene to ethyl alcohol to 60wt% / 40wt% to 85wt% / 15wt%, it is possible to obtain a drying rate suitable for dissolving the polymer material and forming granules.

Alternatively, when using acetone and ethyl alcohol mixed solution as the organic solvent, the ratio of acetone to ethyl alcohol is preferably 30wt% / 70wt% to 70wt% / 30wt%. If the ratio of acetone to ethyl alcohol is less than 30 wt% / 70 wt%, ethyl alcohol is volatilized during the manufacturing process to reduce the amount of ethyl alcohol in the final solution. And when the ratio of acetone to ethyl alcohol exceeds 70 / 30wt%, it is difficult to form granules itself due to the excessive content of acetone in the solution. Therefore, by adjusting the ratio of acetone to ethyl alcohol to 30wt% / 70wt% to 70wt% / 30wt%, it is possible to obtain the drying rate required for dissolving the polymer material and forming granules.

Alternatively, in the case where a mixed solution of isopropyl alcohol and acetone is used as the organic solvent, the ratio of isopropyl alcohol to acetone is preferably 30 wt% / 70 wt% to 70 wt% / 30 wt%. If the ratio of isopropyl alcohol to acetone is less than 30 wt% / 70 wt%, acetone is volatilized during the manufacturing process to reduce the amount of acetone in the final solution. In addition, when the ratio of isopropyl alcohol to acetone exceeds 70/30 wt%, the granulation itself becomes difficult due to the excessive content of isopropyl alcohol in the solution. Therefore, by adjusting the ratio of isopropyl alcohol to acetone to 30wt% / 70wt% to 70wt% / 30wt%, it is possible to obtain the drying rate required for dissolving the polymer material and forming granules.

The mixture of the WC-Co mixture, the dispersant and the solvent is milled and mixed uniformly. Next, the binder and the plasticizer are added to further mill for a predetermined time to prepare a slurry. The above-described milling method is merely for illustrating the present invention, and the present invention is not limited thereto. The mixture can thus also be mixed in other ways. In addition, the dispersing agent and the binder may be used separately for water-based and non-aqueous, depending on whether the solvent is water or an organic solvent.

As described above, when water is used as the solvent, any one or more dispersants selected from the group consisting of ammonium polymethacryl, polyetherene amine, and ligno sulfate may be used as the dispersant.

In contrast, when an organic solvent is used, the dispersant may be a polyvinyl pyrollidone having a molecular weight of 10,000 to 100,000 and a copolymer dispersant having a carboxyl group and a saturated hydrocarbon group (KD1, KD2, KD3) (Hypermer KD-series polymeric one or more dispersants selected from the group consisting of dispersants for electronic and advanced ceramics.

In the slurry, 0.01 wt% to 1.0 wt% of a dispersant may be added, and preferably 0.1 wt% to 1.0 wt% of a dispersant may be added. When the amount of the dispersant to be added is less than 0.01 wt%, aggregation by hardening between the polymer materials is unlikely to occur, so that the slurry does not partially aggregate. In particular, when the amount of the dispersant to be added is 0.1 wt% or more, partial aggregation of the slurry occurs well. On the other hand, when the amount of the dispersant to be added exceeds 1.0wt%, there is a problem that the dispersion state of the powder in the solution is maintained as it is by the repulsion between the polymer material while the surface of the powder is all coated with a polymer material.

Meanwhile, as the plasticizer, phthalate-based materials are used in the range of 0.05 wt% to 2.00 wt% of the total weight of the slurry. The binder may use a material that can be easily understood by those skilled in the art.

0.01 wt% to 0.20 wt% of surfactant is added to the slurry thus prepared and stirred to keep the slurry in a stable state. In order to increase the drying rate by lowering the surface tension of the solution by adding a surfactant to increase the drying rate, a surfactant as described above is added to increase the yield. The surfactant lowers the interfacial energy between the solvent and the WC-Co powder during spray drying to promote granule formation, which is 0.01 wt% to 5.00 wt% Trioton X manufactured by Union Carbide, USA. -100 (polyoxyethylene tert-octylphenyl ether, polyoxyethyl tertiary-octylphenyl ether) can be used. If the amount of Trioton X-100 used as the surfactant is less than 0.01wt%, there is no addition effect. If the amount of Trioton X-100 is more than 5.00wt%, the workability decreases due to the foaming caused by excessive addition and the prepared spray A decrease in the density of the granules is shown. As a result, the properties of the granules are changed and the physical properties of the final thermal spray coating layer are lowered.

Figure 2 is a graph showing the particle size distribution of the WC-Co powder in the partially agglomerated slurry during the preparation of the nanostructured WC-Co powder according to an embodiment of the present invention, the case where the partially agglomerated slurry is aqueous (●) and non-aqueous It is a graph which shows particle size distribution of WC-Co powder in the case of (■).

As shown in FIG. 2, the partially aggregated WC-Co powder aggregates have a size of about 1 μm to 10 μm. In particular, when non-aqueous slurries, such as an organic solvent, are used, it turns out that the magnitude | size of the partially aggregated WC-Co powder aggregate is larger than when using aqueous slurries, such as water. The formation principle of such a WC-Co powder aggregate is as follows.

When preparing a mixture of the WC-Co mixture, the dispersant and the solvent, the dispersant is partially adsorbed onto the surface of the WC-Co powder having a particle size of several tens of nm. Accordingly, bridging flocculation occurs between the particles to partially aggregate the WC-Co powder to form a WC-Co powder aggregate. This aggregate has a great strength and does not redistribute even when a strong external force is applied. The size of the crosslinked agglomerated aggregate may vary depending on the molecular weight of the polymer forming the crosslink, the surface adsorber, and the shear stress applied during the mixing.

The partially aggregated slurry is spray dried with a spray dryer to prepare granules. Granules are prepared while controlling the slurry feed amount during spray drying in the range of 20 ml / min to 100 ml / min. Depending on the type of spray dryer to adjust the rotational speed or spray pressure of the nozzle, the nozzle is rotated to 3000rpm to 9000rpm and spray dried at a spray pressure of 0.2kg / cm ² to 0.4kg / cm ² . Here, when the nozzle rotation speed is less than 3000rpm, there is a problem that the granule yield is reduced, and when the nozzle rotation speed exceeds 9000rpm, there is a problem that the size of the granules is reduced. In addition, when the spray pressure is less than 0.2kg / cm ² , the granule size is increased but the granule yield is reduced, when the spray pressure exceeds 0.4kg / cm ² there is a problem that the granule yield is increased but the granule size is reduced. Therefore, by adjusting the nozzle rotation speed and spray pressure as described above, it is possible to constantly adjust the size of the granules and to maintain the granule yield properly.

On the other hand, by adjusting the solid phase content of the slurry used during spray drying can be uniformly controlled pore distribution in the granules and porosity can be adjusted. By controlling the porosity and the pore distribution form inside each granule, it is possible to dissolve the granules uniformly and uniformly in the spraying flame during spray coating. Therefore, it is possible to minimize the decarburization of nano-sized WC particles as well as to produce a spray coating having a significantly low porosity. Ultimately, the thermal spray coating powder having the optimum porosity and powder strength suitable for the thermal spray coating can be produced, and the wear resistance and hardness of the thermal spray coating are remarkably improved.

When preparing the granules by spray drying the partially agglomerated slurry, the liquid slurry may be uniformly dried as a whole to form spherical granules. By heat-treating these spherical granules, the organic substance contained in a granule is removed. Since the heat treatment temperature for removing the organic matter in the granules is about 400 ° C., and complete decomposition is possible at 600 ° C., the spray-dried granules are subjected to a degreasing heat treatment in a temperature range of 400 ° C. to 600 ° C. under an inert gas atmosphere or a vacuum atmosphere.

In the case of the WC-Co granules prepared from the aqueous slurry, a reduction reaction is required to remove the oxides formed on the surface of the powder, so that the WC-Co granules are heat treated at a temperature ranging from 400 ° C to 900 ° C under a hydrogen gas atmosphere. After the degreasing is completed, the granules are heat-treated in a temperature range of 1000 ° C. to 1300 ° C. under a vacuum atmosphere to impart proper strength during thermal spray coating. In order to sufficiently remove the adsorbed water, the granules should be heated to about 800 ° C. to 900 ° C., and the granule heat treatment in vacuum is heat treated at a temperature of less than 1300 ° C. to prevent excessive grain growth due to melting of the Co.

The WC-Co powder thus prepared is preferably formed by spray coating using a super velocity oxy-fuel spraying method (HVOF method). Supersonic flame spraying generates flame by injecting high pressure oxygen gas and fuel. Thus, since the feedstock powder is heated and accelerated by using the generated flame as a heat source, the temperature of the heat source is relatively low, thereby preventing decarburization and phase decomposition of the thermal spray coating. In addition, since the particle acceleration rate is very high, such as 800 m / s, it is possible to obtain a spray coating structure of dense tissue.

This supersonic flame spraying method first improves the surface roughness by blasting and washing the surface of the base material in order to improve the adhesion with the thermal spray coating, and then feeds the WC-Co powder as a feed material into the flame of the supersonic flame spraying device through the powder supply device. Inject Accordingly, the thermal spray coating is formed by heating and accelerating the WC-Co powder to be laminated on the base material surface. The main process parameters of the supersonic flame spraying method include spraying distance, fuel amount, and oxygen amount, and by adjusting these key process variables, the characteristics of the spray coating can be optimized.

Hereinafter, the present invention will be described in more detail with reference to experimental examples of the present invention. These experimental examples are only for illustrating the present invention, and the present invention is not limited thereto.

Experimental Example

A partially aggregated slurry was prepared using a WC-Co mixture made of nanostructured WC-Co powders consisting of 12.0 wt% Co and the remainder WC and other impurities.

First, a mixture of various weighted WC-Co mixtures, dispersants in cationic electrolytes, and aqueous or non-aqueous solvents was prepared. This mixture was mixed by ball milling for 4-20 hours to prepare a uniform slurry. Next, benzylbutyl phthalate was added as a plasticizer, polyvinyl butyl was added as a binder, and ball milling was further performed for 4 to 8 hours to prepare a spray drying slurry.

The slurry was spray dried using a pneumatic spray dryer while maintaining a slurry feed amount of 20.0 ml / min to prepare granules. The granules thus prepared were degreased at a temperature of 300 ° C. to 600 ° C. Next, the granules were heat-treated in a vacuum at a temperature ranging from 1000 ° C. to 1300 ° C. to prepare a spray coating WC-Co powder.

The present invention was tested several times as follows by varying its composition in the above-described manner.

Experimental Example 1

A slurry was prepared using 67.98 wt% WC-Co powder, 31.85 wt% isopropyl alcohol as solvent, 0.07 wt% cationic electrolyte as dispersant, 0.030 wt% polyvinylbutyl as binder, 0.030 wt% benzylbutyl phthalate as plasticizer, And spray drying it to prepare a spray coating WC-Co powder.

Experimental Example 2

53.20 wt% of WC-Co powder, 45.77 wt% of a mixture of acetone and ethyl alcohol as a solvent, 0.93 wt% of a cationic electrolyte as a dispersant, 0.050 wt% of polyvinylbutyl as a binder, 0.030 wt% of benzylbutyl phthalate as a plasticizer, as a surfactant A slurry was prepared using Triton-X 100 0.030 wt%, and spray dried to prepare a WC-Co powder for spray coating.

Experimental Example 3

50.00 wt% WC-Co powder, 49.39 wt% water as solvent, 0.01 wt% cationic electrolyte as dispersant, 0.050 wt% polyvinylbutyl as binder, 0.030 wt% as benzylbutyl phthalate as plasticizer, Triton-X 100 0.500 as surfactant Slurry was prepared using wt%, and spray dried to prepare WC-Co powder for spray coating.

Experimental Example 4

WC-Co powder 74.70wt%, water 24.59wt% as solvent, cationic electrolyte 0.37wt% as dispersant, polyvinylbutyl 0.050wt% as binder, benzylbutyl phthalate 0.030wt% as plasticizer, Triton-X 100 0.500 as surfactant Slurry was prepared using wt%, and spray dried to prepare WC-Co powder for spray coating.

Experimental Example 5

A slurry was prepared using 61.30 wt% of WC-Co powder, 38.48 wt% of solvent as a solvent, 0.12 wt% of cationic electrolyte as a dispersant, 0.060 wt% of polyvinylbutyl as a binder, and 0.030 wt% of benzylbutyl phthalate as a plasticizer. Spray drying to prepare a spray coating WC-Co powder.

Comparative Example 1

A commercially produced and commercially available product of Nanodyne was tested using a nano-sprayed powder having a nanostructure of Nanocarb P powder WC-10Co. Here, the WC-Co powder contained 10% Co.

Comparative Example 2

Experiments were carried out using the WC-12Co test powder, currently a commercially available and commercially available product of NanoTech. Here, the WC-Co powder contained 12% Co.

Hereinafter, the WC-Co granules prepared according to Experimental Example 1 and Example 3 of the present invention will be described based on scanning electron micrographs of the WC-Co granules prepared according to Experimental Example 1 and Experimental Example 3 described above.

3 (A) is a scanning electron micrograph showing the shape of the WC-Co powder granules prepared according to Experimental Example 1 of the present invention, Figure 3 (B) is a scanning electron showing the cross-sectional microstructure of the same powder granules Photomicrograph.

As shown in (A) of FIG. 3, the WC-Co powder granules prepared according to Experimental Example 1 of the present invention have a spherical shape, and the WC-Co powder granules of FIG. It can be observed that the cross-sectional microstructure also maintains a spherical shape. As described above, since the WC-Co powder granules have a spherical shape, defects do not exist in the inside thereof, thereby forming a spray coating having an optimal structure.

Figure 4 is a scanning electron micrograph of the WC-Co granules prepared according to Experimental Example 3 of the present invention, an enlarged view of the WC-Co granules prepared by spray drying the aqueous slurry.

As shown in FIG. 4, it can be observed that the WC-Co granules have a more perfect spherical shape, especially when using an aqueous slurry. As such, since the WC-Co granules have a spherical shape, the thermal spray coating may not only be optimally formed but also may be nano-sized, thereby improving characteristics such as wear resistance.

5 is a scanning electron micrograph showing the distribution of Co in the WC-Co powder prepared according to Experimental Example 3 of the present invention, which shows an enlarged Co distribution in the WC-Co powder prepared by spray drying the aqueous slurry after heat treatment.

It can be seen that Co represented by the white point in FIG. 5 is evenly distributed in the matrix form WC-Co powder shown in black. This is due to the phenomenon that the slurry is dried uniformly throughout during spray drying using partially aggregated slurry. Thus, since Co is evenly distributed in the WC-Co powder, it is possible to obtain a thermal spray coating having excellent properties when applied to the thermal spray coating.

As described above, in the case of the WC-Co powder prepared according to Experimental Examples 1 to 5 of the present invention, since the spherical form is excellent, the spray coating is excellent. The amount of dispersant added to the slurry here is all included in the range of 0.01wt% to 1.0wt%. Referring to the superiority of the thermal spray coating through the thermal spray coating cross section of Experimental Example 1.

Figure 6 is a scanning electron micrograph of the WC-Co granules prepared according to Experimental Example 1 of the present invention and the spray coating cross-section prepared using the same, the same WC-Co granules in three different magnification (described below) The scanning electron microscope photograph taken by the above is shown on the left side, and the scanning electron microscope picture of the thermal spray coating cross section manufactured using this is shown on the right side.

As shown in Figure 6, in the case of the WC-Co granules prepared according to Experimental Example 1 of the present invention because it is a spherical shape, there are no internal defects, the spray coating cross section can be observed to have a dense structure without pores therein have. Thus, when forming the thermal spray coating according to Experimental Example 1 of the present invention, it can be seen that the characteristics are excellent.

In contrast, when the WC-Co granules of Comparative Example 1 and Comparative Example 2 of the prior art and the thermal spray coating prepared using the same were observed, it was found that many defects exist.

7 is a scanning electron micrograph of the WC-Co granules of Comparative Example 1 of the prior art and the spray-coated cross section prepared using the same, in which the same WC-Co granules were photographed at two different magnifications. The scanning electron micrograph of the thermal spray coating cross section manufactured using this is shown on the right side.

As shown in FIG. 7, the WC-Co granules prepared in the same manner as the comparative example 1 of the prior art are not spherical but irregularly dispersed, and thus, many defects are present therein. Therefore, when forming the thermal spray coating with such WC-Co granules, as can be seen from the results of the carbon content in the coating in Table 1 and the ratio of WRD / WC peak ratio of XRD, decarburization and phase decomposition of the WC particles during the thermal spraying process It occurs badly and the wear resistance of a coating material falls as can be seen from the wear amount of Table 1.

8 is a scanning electron micrograph of the WC-Co granules prepared according to Comparative Example 2 of the prior art and the spray-coated cross section prepared using the same, wherein the same WC-Co granules were shot at two different magnifications. The electron micrograph is shown on the left side, and the scanning electron micrograph of the thermal spray coating cross section manufactured using this is shown on the right side.

As shown in Figure 8, the conventional WC-Co granules of Comparative Example 2 is considered to be spherical when looking at the scanning electron microscope picture of the upper left, but when viewed from the scanning electron microscope picture of the left bottom magnified 10 times, It can be seen that a defect exists. As described above, defects such as pores present in the thermal sprayed powder remain in the coating prepared using the thermal sprayed powder, and as shown in the right scanning electron micrograph of FIG. 8, there are many defects such that the porosity inside the thermal sprayed coating reaches 2.35%. Due to such defects, the wear resistance is reduced as shown in the wear amount of Table 1 below.

The characteristic values of the WC-Co powder and the thermal spray coating according to the above Experimental Examples 1 to 5 and Comparative Examples 1 and 2 are shown in Table 1 below. All WC-Co powders were coated under the same thermal spraying process using supersonic flame spraying. At this time, the spraying distance was 330mm, the fuel amount was 6.0gph and the oxygen amount was 2000scfh. These process conditions were based on the WC-Co based on the evaluation results of the characteristics measured after manufacturing the coating material with various changes. Optimized conditions for powder. The abrasion resistance test was carried out using a sand wear test (ASTM standard G65) at a rotational speed of 200 rpm for 10 minutes. In the wear resistance test, the weight loss of the thermal spray coating due to abrasion is measured and this is used as a criterion for evaluation of wear resistance.

In Table 1, the specific WC / WC peak ratio of XRD was evaluated by comparing the degree of phase decomposition of WC with high temperature exposure during the thermal spraying process through X-ray diffraction analysis of the sprayed coating surface. A high value means that the WC particles of the thermal spray coating are decomposed, which causes deterioration of properties such as wear resistance of the thermal spray coating. In addition, in Table 1, the granule porosity is a value measured by image analysis when the cross section of the granule is observed by a scanning electron microscope.

As shown in Table 1, it can be seen that the thermal spray coating according to Experimental Example 1 of the present invention is superior to the thermal spray coating according to Comparative Example 1 and Comparative Example 2 of the prior art in hardness and wear resistance. These results show that the porosity of the WC-Co powder exhibits the best mechanical properties under optimum conditions. This is because the WC-Co powder proceeds into the flame during the thermal spray coating, and because of the porosity, the WC-Co powder is properly melted to prevent decarburization. This is because the thermal spray coating tissue according to Experimental Example 1 of the present invention is more dense than the thermal spray coating tissue according to Comparative Examples 1 and 2 and no decarburization occurs. In addition, since the thermal spray coating according to Experimental Example 1 of the present invention has a high strength, the binding strength of the intragranular aggregates is high, and as a result, the WC-Co powder has the property of not being broken when the powder is supplied or when the flame passes.

As described above, the method for producing nanostructured WC-Co powder according to the present invention is prepared from a partially aggregated slurry by mixing a dispersant, so that a WC-Co powder without spherical internal defects can be produced, and thus There is an advantage that the characteristics are improved.

In addition, it is possible to produce a WC-Co powder having a high strength and an appropriate porosity through the method as described above, so that the WC-Co powder is not broken during the spray coating, it is appropriately melted when passing through the flame, high hardness and high It can provide the property of wear resistance.

Although the present invention has been described above, it will be readily understood by those skilled in the art that various modifications and variations are possible without departing from the spirit and scope of the claims set out below.

Claims (20)

As a method of manufacturing nano-based tungsten carbide (WC) -cobalt (Co) powder for thermal spray coating, Preparing a mixture of a tungsten carbide-cobalt mixture, a dispersant and a solvent, Adding a binder and a plasticizer to the mixture to produce a partially aggregated slurry, Spray drying the partially aggregated slurry to produce spherical granules, and Heat-treating the spherical granules to remove organic substances contained in the spherical granules Method of producing a nanostructured tungsten carbide-cobalt-based powder comprising a. In claim 1, In the step of preparing the partially aggregated slurry, a method for producing a nanostructured tungsten carbide-cobalt-based powder by adding a surfactant and stirring. In claim 1, In the step of preparing the partially aggregated slurry, The method for producing a nanostructured tungsten carbide-cobalt-based powder in which the tungsten carbide-cobalt mixture is contained 40.0wt% to 80.0wt% in the partially aggregated slurry. In claim 1, In the step of preparing the mixture, The tungsten carbide-cobalt mixture comprises 7.0 to 25.0 wt% of cobalt, the remainder being tungsten carbide and other impurities. In claim 4, A method for producing a nanostructured tungsten carbide-cobalt based powder having a particle diameter of the tungsten carbide is 1 μm or less. In claim 4, Method of producing a nanostructured tungsten carbide-cobalt-based powder by further mixing the corrosion-resistant element in the tungsten carbide-cobalt mixture. In claim 6, The corrosion-resistant element is at least one of nickel (Ni) and chromium (Cr) at least one method of producing a nanostructured tungsten carbide-cobalt-based powder. In claim 1, In the step of preparing the partially aggregated slurry, Dispersant added to the slurry is 0.01wt% to 1.0wt% of the nanostructured tungsten carbide-cobalt-based powder manufacturing method. In claim 8, Dispersant added to the slurry is 0.1wt% to 1.0wt% of the nanostructured tungsten carbide-cobalt-based powder manufacturing method. In claim 1, In the step of preparing the mixture, The solvent is a method of producing a nanostructured tungsten carbide-cobalt-based powder is an aqueous solvent. In claim 10, The dispersing agent is a method for producing a nanostructured tungsten carbide-cobalt-based powder of any one or more selected from the group consisting of ammonium polymethacrylate, polyethylene amine and lignosulfate. In claim 1, In the step of preparing the mixture, The solvent is a method for producing a nanostructured tungsten carbide-cobalt-based powder is an organic solvent. In claim 12, In the step of preparing the mixture, The dispersing agent is a polyvinyl pyrollidone having a molecular weight of 10,000 to 100,000 (polyvinyl pyrollidone) and a copolymer structure dispersing agent having a carboxyl group and a saturated hydrocarbon group at least one selected from the group consisting of nanostructured tungsten carbide-cobalt-based powder. In claim 12, In the step of preparing the mixture, The organic solvent is a group consisting of a mixture of ethyl alcohol, isopropyl alcohol, isopropyl (toluene) and ethyl alcohol, a mixture of acetone and ethyl alcohol, and a mixture of isopropyl alcohol and acetone Method for producing a nanostructured tungsten carbide-cobalt-based powder of any one or more selected from. The method of claim 14, The organic solvent is a mixture of toluene and ethyl alcohol, the ratio of toluene to ethyl alcohol is 60wt% / 40wt% to 85wt% / 15wt% method for producing a nanostructured tungsten carbide-cobalt-based powder. The method of claim 14, The organic solvent is a mixture of acetone and ethyl alcohol, the ratio of acetone to ethyl alcohol is 30wt% / 70wt% to 70wt% / 30wt% method for producing nanostructured tungsten carbide-cobalt-based powder. The method of claim 14, The organic solvent is a mixture of isopropyl alcohol and acetone, the ratio of isopropyl alcohol to acetone is 30wt% / 70wt% to 70wt% / 30wt% method for producing nanostructured tungsten carbide-cobalt-based powder. In claim 2, The surfactant is a method of producing a nanostructured tungsten carbide-cobalt-based powder of 0.01wt% to 5.00wt% polyoxyethylene tert-octylphenyl ether. delete delete

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