KR20080065480A - Method for coating with copper-tungsten composite material by using cold spraying process - Google Patents

Abstract

A method of coating copper-tungsten composite material is provided to form a coating layer by a simple process, and to coat a uniform composite material layer of high density without pollution caused by impurities. A method of coating copper-tungsten composite material comprises the steps of: preparing coating particles by mixing tungsten particles with copper particles, and coating the tungsten particles and copper particles on an object by spraying the particles in high speed through a cold spraying process. An average grain size of the tungsten particles is 40 to 60% of an average grain size of the copper particles. The average grain size of the copper particles is 5 to 40um.

Description

Coating method of tungsten / copper composite material using low temperature spraying process {METHOD FOR COATING WITH COPPER-TUNGSTEN COMPOSITE MATERIAL BY USING COLD SPRAYING PROCESS}

1 is a layout view showing the configuration of a low-temperature injection device used in the present invention,

2 is a schematic diagram schematically illustrating a phenomenon in which powder is coated by low temperature spraying;

3 is a photograph of an aluminum substrate coated with a tungsten / copper composite material according to an embodiment of the present invention with a scanning electron microscope, and

Figure 4 is a graph comparing the results of the phase analysis by the X-ray diffractometer of the tungsten / copper composite coating layer coated with an embodiment of the present invention with the results of the phase analysis of the tungsten, copper particles before coating.

The present invention relates to a coating method of a tungsten / copper composite material using a low temperature spraying process, and more particularly, to obtain a composite layer having a simpler and more uniform operation than a conventional method used for coating a tungsten / copper composite material. The present invention relates to a new composite coating method.

Tungsten / copper composites are coated on the surface of parts as ultra high voltage battery contact materials requiring high arc resistance and good wear resistance, heat dissipating materials for high-power integrated circuits, and shape charge liner materials for thermal warheads. The thermal expansion coefficient and heat transfer coefficient can be easily controlled according to the microstructure, composition, and purity of the material, and thus, it is also used as a coating layer of heat dissipating material such as a heat sink for electronic package material.

As a method for coating the tungsten / copper composite material as described above, various methods have been conventionally used, for example, liquid sintering, impregnation, mechanical alloying and thermal spraying.

Liquid phase sintering is a method of mixing and molding tungsten powder and copper powder and sintering at a temperature above the melting point of copper. In order to increase the sintered density during the sintering, the powder is treated in various ways, and a typical one is mechanical alloying. The mechanical alloying method is a method for producing a tungsten / copper composite material from an oxide powder.

In the case of using the liquid phase sintering method, even if the copper is melted to achieve uniform mixing between the copper and tungsten, there is a problem in that the solubility between the copper and tungsten is low and the specific gravity difference is large so that they are not uniformly mixed. In addition, in order to solve this problem and to increase the density of the sintered body, an active sintering method of adding a sintering active agent such as cobalt (Co) or nickel (Ni) has emerged. In addition, the thermal / electrical properties of the copper present in the matrix in the composite material are not only lowered, but also a problem occurs that grain growth occurs and the structure is coarse, and thus the active sintering method has not been a suitable alternative. In addition, a method of forming the sintered body more uniformly by the mechanical alloying method has also been proposed. However, even by the mechanical alloying method, the sintered body is contaminated by the ball introduced to apply the shear force, which is not preferable.

As a method different from the above methods, an impregnation method can be mentioned. The impregnation method can obtain a high density W / Cu alloy, but is not suitable for use in a wide range of applications because of limitations on alloy composition, shape and structure.

Therefore, the method of coating the composite material using the same powder has not only various problems as described above but also a complicated manufacturing process such as molding and sintering, and thus has a disadvantage in that the manufacturing cost is increased and productivity is lowered.

As another method of manufacturing a composite material without using a powder material as described above, a thermal spray coating method may be used. This method uses a high temperature plasma heat source to melt tungsten / copper and then melts these melts on the substrate surface. It refers to a method of spraying and depositing on. When coated by this method, the coating property is good, but there is a possibility that pores are formed due to solidification shrinkage inside the microstructure, and since the melting point of tungsten and copper is greatly different, the flame up to the melting point of tungsten may cause evaporation of copper. In addition, copper oxide is formed by the time taken from the nozzle inlet to the substrate, and as a result, the characteristics of the composite material are deteriorated.

The present invention is to solve the above-mentioned problems of the prior art, and to form a coating layer by a simple process, as well as a method of coating a uniform and dense composite layer without causing problems of contamination by impurities. It aims to provide.

Coating method of the tungsten / copper composite material of the present invention for achieving the above object comprises the steps of preparing a coating particle mixed with tungsten particles and copper particles; And spraying the tungsten particles and the copper particles at a high speed onto the subject by using a low temperature spraying method.

At this time, the average particle size of the tungsten particles is preferably 40 to 60% of the average particle size of the copper particles.

And it is effective that the average particle size of the said copper particle is 5-40 micrometers.

In particular, it is more preferable that the average particle size of the said copper particle is 10-20 micrometers.

In addition, the volume fraction of the copper particles in the coated particles is 10 to 40%, the volume fraction of the tungsten particles is preferably 90 to 60%.

The carrier gas is preferably heated to a temperature of 300 to 500 ° C during low temperature spraying.

In addition, the carrier gas used at low temperature injection is preferably helium, nitrogen or a mixed gas thereof.

At this time, the pressure immediately before the nozzle of the carrier gas is 20 to 25 bar (bar) when the carrier gas is helium, 20 ~ 29 bar when the nitrogen, 20 ~ (25 when the mixed gas of nitrogen and helium It is preferable that it is + nitrogen flow fraction / 4) bar.

In addition, the coating particles may be coated by preheating at a temperature of 500 ~ 600 ℃ before spraying.

In addition, the injection flow rate of the coating particles is preferably 10 ~ 30g / min.

In addition, the distance between the jet nozzle and the subject of the low temperature jetting device is preferably 20 to 50 mm.

Hereinafter, the present invention will be described in detail.

The inventors of the present invention have studied in order to solve the above-mentioned problems of the prior art and achieve the object of the present invention, and when a tungsten and copper are coated on a desired subject by a low temperature spraying method, a good tungsten / copper composite coating layer can be obtained. It has been found that the invention can be reached.

That is, the present invention is characterized in that tungsten and copper are simultaneously coated on a subject by a cold spray method.

Low-temperature spraying, unlike thermal spraying, accelerates coated particles at high speeds above the critical speed at which the coated particles can be coated on the substrate by using high-pressure gases such as nitrogen, helium, and air. When the coating material is plastically deformed by the kinetic energy of the coating particles, it refers to a technology that is combined with the base material to be coated. 1 shows a schematic form of a low temperature spray coating apparatus which is generally used to explain the low temperature spray coating method in more detail.

As can be seen in Figure 1, the cold spray coating machine is a gas supply device (1), control panel (2), gas heating device (3), powder supply device (4) and de Laval nozzle (5) It includes. Gas supplied from the gas supply device 1 is controlled by the gas amount control panel 2 is divided into a gas heating device 3 and the powder supply device (4) is supplied. The gas heating device 3 heats the gas to a high temperature to induce a speed increase due to the expansion of the gas, and the powder feeding device 4 supplies the powder to the gas supplied from the control panel 2 by the gas. It serves to enable the powder to be fed to the de Laval nozzle (5). Immediately after the powder feeding device 4, a powder heating device 9 capable of heating the powder may be provided. The powder heating device (9) is a device for heating the powder by mounting a heating element on the outside of the tube through which the powder passes, and increases the temperature of the powder to increase the deformation and toughness of the powder when the powder collides with the subject. do. Immediately before the de Laval nozzle 5, the mixture of powder and gas supplied from the powder feeder 4 and the heated high speed gas supplied from the gas heater 3 meet to form a high speed gas / powder mixture. The deLaval nozzle 5 is injected into a high velocity gas / powder jet stream. DeLaval nozzle is a nozzle that is used to increase the speed of the gas to the supersonic speed above the speed of sound as it has a form that the inner diameter of the nozzle is reduced (converge) and then diverged again in the nozzle length direction. The powder transported by the gas injected at supersonic speed through the de Laval nozzle collides with the subject at a high speed close to the speed of the gas as shown in FIG. 2, and the kinetic energy of the powder is separated between the subject / powder. It is converted into the energy required for bonding, thus obtaining a powder-coated subject.

However, the tungsten and the copper is different in density and coating property, so that when the coating is performed by a general low temperature spraying method, it is difficult to stack them in a desired ratio and it is difficult to ensure uniformity of the material. In other words, it is difficult to maintain the kinetic energy of the powder to a similar degree even when sprayed by the same carrier gas because the density of tungsten and copper are different, and the ratio of tungsten and copper is kept uniform because the strain and the toughness of the powder itself are different. It is difficult to form a coating layer in the state.

According to the inventors of the present invention, in order to solve such a problem, it is necessary to limit the particle sizes of tungsten and copper used at low temperature injection differently. In other words, if the average particle size (diameter per sphere) of tungsten is 40 to 60% of the copper particle size, it is possible to simultaneously secure a speed above the critical speed at which tungsten and copper can adhere to the object. Can be mixed to form a uniform and strong coating layer.

If the average particle size of the tungsten is less than 40% of the copper particle size, the tungsten energy of the tungsten is too low compared to the kinetic energy of the copper particles, and thus the tungsten lamination rate is low. If exceeded, the high density of tungsten increases the mass of the particles themselves, thereby reducing the tungsten particle acceleration effect by the carrier gas, thereby lowering the tungsten deposition rate. Therefore, the average particle size of the tungsten is preferably in the range of 40 to 60% of the average particle size of the copper particles.

Moreover, it is preferable that the average particle size of the copper particle used is 5-40 micrometers. If the average particle size of the copper particles is less than 5 μm, the mass of the copper particles decreases, so that the kinetic energy decreases, and as a result, the average particle size of the copper particles is 40 μm. When exceeded, the mass of the particles is excessively large, thereby reducing the copper particle acceleration effect by the carrier gas. Therefore, it is preferable that it is 5-40 micrometers, and, as for the average particle size of copper particle, it is more preferable that it is 10-20 micrometers.

When the tungsten particles and the copper particles are maintained in the above-described range, a coating layer in which tungsten particles and copper particles are uniformly laminated at a high lamination rate may be obtained. At this time, the ratio of the tungsten particles and copper particles may vary depending on the characteristics of the coating layer to be formed, but considering the tungsten / copper ratio used in the commonly used tungsten / copper composite coating layer, the copper particles are deposited rate of tungsten Considering that it is improved, it is preferable that the copper particles are contained in the volume fraction 10 to 40% in the particles sprayed at low temperature. In addition, tungsten is preferably contained 90 to 60%.

However, it should be noted that the volume ratio means the volume ratio of copper particles and tungsten particles in the powder to be sprayed, and does not mean the ratio of these particles in the coating layer coated on the subject. Typically, the ratio of copper particles in the coating layer coated on the surface of the defense article such as ballistics is about 20 to 30% based on the volume fraction, and the ratio used in heat sinks is about 10 to 20%, depending on various other uses. The ratio may vary. In a typical case, since tungsten is poorer in coating than copper, the tungsten lamination efficiency is lowered. Therefore, the tungsten ratio in the coating layer is often lower than that of the tungsten when sprayed.

Under these conditions, the tungsten particles and the copper particles are prepared for cold spray coating, followed by the cold spraying of the tungsten particles and the copper particles.

It is preferable that the temperature of the gas heated by the gas heating apparatus at the said low temperature spraying is 300-500 degreeC. When the gas is injected from the DeLaval nozzle (5) is adiabatic expansion due to the shape of the portion (diverge portion) in which the nozzle diameter increases to change into a gas jet having a high velocity, the temperature of the gas is secured to a certain level or more In order to ensure sufficient gas velocity by adiabatic expansion. In order to ensure a sufficient gas velocity, the higher the temperature of the gas is, the better, and therefore, there is no need to specifically set the upper temperature limit of the gas in this respect. However, when the temperature of the gas is high, the load on the device is high, so it is preferable to set the temperature as the upper limit to about 500 ° C in the device currently used.

At this time, the gas used is not particularly limited, but helium, nitrogen or a mixed gas thereof is more preferably used.

The gas pressure just before the nozzle at the time of injection is slightly different depending on the type of gas, but 20 to 29 bar (nitrogen) for the nitrogen, 20 to 25 bar for the helium is preferred. In the case of a mixed gas of nitrogen and helium, the lower limit may be set equal to 20 bars, and the upper limit is between 25 and 29 bar in proportion to the flow rate ratio of nitrogen and helium (that is, 25+ nitrogen flow rate / 4). You just need to decide on When the pressure of the gas is low, the coating particles have a sufficient speed, so that the coating layer is hardly formed on the object. The higher the gas pressure, the higher the particle velocity, but there is a limit there, and if the pressure is increased further, the device may be loaded, so the upper limit of the gas pressure is set in the above range.

The mass flow rate of the coated particles is preferably in the range of 10 to 30 g / min based on the mass flow rate of the entire tungsten / copper particles. If the mass flow rate of the coated particles is less than 10 g / min, it is difficult to control the flow rate of the coated particles during powder feeding. On the contrary, if the coated particle flow rate exceeds 30 g / min, the flow rate of the coated particles increases excessively compared to the gas. Is reduced and is not appropriate because the device is overloaded to match the particle velocity.

In addition, when the powder is coated without special preheating, the deformation and toughness of the powder particles may not be good, which may cause problems such as cracking of the particles during coating. This phenomenon is more severe in the case of tungsten with poor toughness. In order to improve the toughness and deformability of the coated particles, it is necessary to preheat the powder to a predetermined temperature range or more. In the case of forming a composite material layer by simultaneously coating tungsten / copper particles as in the present invention, the preheating device for the particles The internal temperature (hereinafter, simply preheated temperature) is preferably maintained at 500 ° C or higher. However, if the temperature is too high, problems such as melting of the powder may occur as well as the device load may increase, so the upper limit of the preheating temperature is set to 600 ° C. Therefore, it is preferable that the preheating temperature which preheats a powder is 500-600 degreeC.

When the tungsten / copper particles are spray coated at low temperature, the distance between the nozzle and the subject is a major factor to smoothly coat the particles. In the simultaneous coating of the tungsten / copper particles, the gap between the nozzle tip and the subject is used. It is preferable to make it into 20-50 mm. When the distance exceeds 50 mm, the distance from the nozzle to the object reaching the object is too far, resulting in a noticeable decrease in the rate of coating particles, resulting in a failure to reach the subject at a sufficient speed, resulting in a reduction in the lamination rate. . On the contrary, when less than 20 mm, nozzle clogging may occur due to the backflow of gas.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, it is necessary to note that the following examples are not intended to limit the scope of the present invention, but are merely illustrative of the present invention described in order to help the understanding of the present invention. This is because the scope of the present invention is determined by the matters described in the claims and the matters reasonably inferred therefrom.

(Example)

The tungsten / copper mixed particles were coated on an aluminum substrate (subject) under the conditions described in Table 1.

Item Condition Type of gas used helium Gas temperature 500 ℃ Gas pressure 25 bar Tungsten: Copper Ratio 7: 3 Copper particle size 20㎛ average Tungsten particle size Average 10㎛ Coating Particle Mass Flow Rate 20 g / min Coating particle preheating temperature 500 ℃ Distance between nozzle and substrate 30 mm

The photograph of the surface of an aluminum substrate coated with a tungsten / copper composite material under the above-described conditions is shown in FIG. 3 using a scanning electron microscope (SEM). As shown in FIG. 3, it was confirmed that a coating layer in which tungsten and copper particles were uniformly distributed on the surface was formed.

Another data observing the properties of the tungsten / copper composite coating layer is shown in FIG. Figure 4 is a result of phase analysis of the tungsten / copper composite coating layer coated under the conditions of the present embodiment using an X-ray diffractometer (XRD), as shown in the figure other than the tungsten and copper phase included in the initial powder It can be seen that no other phase of is detected. Therefore, when the tungsten / copper composite material is coated by the low temperature spraying method proposed in the present invention, oxides are formed by material oxidation, chemical bonding between two components, or other impurities are not added. I could confirm it.

As mentioned above. According to the W / Cu composite material manufacturing method of the present invention, since it does not go through the molding and sintering process of the conventional powder metallurgy, it is easy to automate, and has a productivity improvement and a manufacturing cost reduction by simplifying the manufacturing process. In addition, since it can be produced at a lower process temperature than the high temperature plasma spray, it is possible to prevent the formation of oxides and secondary phases in the material, it can have excellent physical properties. In addition, the desired physical properties can be designed according to the mixing ratio of the powder, porosity is easy to control.

Claims (11)

Preparing coated particles in which tungsten particles and copper particles are mixed; And Coating the tungsten particles and the copper particles at a high speed onto a subject by using a low temperature spraying method; Coating method of the tungsten / copper composite material comprising a. The method of claim 1, wherein the average particle size of the tungsten particles is 40 to 60% of the average particle size of the copper particles. The method for coating a tungsten / copper composite material according to claim 1 or 2, wherein the copper particles have an average particle size of 5 to 40 µm. The method of claim 3, wherein the average particle size of the copper particles is 10 ~ 20㎛. The method for coating a tungsten / copper composite according to claim 1 or 2, wherein the volume fraction of the copper particles in the coated particles is 10-40%, and the volume fraction of the tungsten particles is 90-60%. The method for coating a tungsten / copper composite material according to claim 1 or 2, wherein the carrier gas is heated to a temperature of 300 to 500 DEG C during low temperature spraying. The method for coating a tungsten / copper composite material according to claim 1 or 2, wherein the carrier gas used for low temperature spraying is helium, nitrogen, or a mixed gas thereof. 8. The method of claim 7, wherein the pressure immediately before the nozzle of the carrier gas is 20 to 25 bar when the carrier gas is helium, 20 to 29 bar when nitrogen, and a mixed gas of nitrogen and helium. A tungsten / copper composite coating method, characterized in that it is 20 ~ (25+ nitrogen content fraction / 4) bar. The method of claim 1 or 2, wherein the coating particles are preheated and coated at a temperature of 500 ~ 600 ℃ before spraying. The method of claim 1 or 2, wherein the spray flow rate of the coating particles is 10 ~ 30g / min, the coating method of the tungsten / copper composite material. The method of coating a tungsten / copper composite material according to claim 1 or 2, wherein the distance between the spray nozzle and the subject of the low temperature spraying device is 20 to 50 mm.

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