KR101789300B1 - Method for preparing silver-diamond composites using spark plasma sintering process and silver-diamond composites prepared thereby - Google Patents

Abstract

The present invention relates to (a) a step of ball milling powder and diamond powder to prepare a composite powder; (b) preparing a silver-diamond composite material by spark plasma sintering (SPS) the composite powder prepared in the step (a).
According to the method for producing a silver-diamond composite material according to the present invention, silver powder and diamond powder are ball-milled to produce a composite powder having a uniform degree of dispersion, and the resulting composite powder is subjected to spark plasma sintering (SPS ) Process, it is possible to easily manufacture high density homogeneous silver-diamond composites and to control the conductivity of the composite material according to the necessity by controlling the content of silver powder, so that it can be utilized in various fields Possible materials can be manufactured.
In addition, the silver-diamond composite material produced by the above method exhibits excellent mechanical properties (density, Vickers hardness, etc.) and can be applied to manufacturing parts in various fields such as automobiles, trains, ships, and aerospace, And can be effectively used for manufacturing bushings requiring high strength and abrasion resistance.

Description

[0001] The present invention relates to a method of manufacturing a silver-diamond composite material using a discharge plasma sintering process, and a silver-diamond composite material produced thereby,

The present invention relates to a method of manufacturing a silver-diamond composite material by using a discharge plasma sintering process and a silver-diamond composite material produced thereby.

The silver-diamond composite is excellent in conductivity, but has a high strength and a high density of silver (Ag). It has excellent abrasion resistance and hardness, but it is about 3.5 times lighter than silver (Ag) It is a composite material reinforced by combining the mechanical properties of diamond with the excellent electrical properties of silver. The above-described silver-diamond composite material not only has excellent thermal stability but also exhibits a relatively low coefficient of thermal expansion as compared with semiconductors and ceramics. Thus, the silver-diamond composite material can be heat-treated in heat control devices, microelectronic devices, photoelectrons, It shows characteristics suitable for control device.

Conventionally, in order to manufacture the silver-diamond composite material as described above, a method of coating a silver nitrate on the surface of diamond particles or coating diamond particles on porous silver particles to form a silver- However, the above-mentioned methods are not only complicated in the production process due to the necessity of heating the silver nitrate to the melting temperature or making the silver particles of the porous structure, and the diamond is weak in bonding force with other materials, It is difficult to fabricate a composite material exhibiting one characteristic. Therefore, it is necessary to study a method that can overcome this problem.

Korean Patent Laid-Open No. 10-2009-0017020 (Publication Date: Feb. 18, 2009) Korean Patent No. 10-0894122 (published on Apr. 20, 2009) Korea Patent No. 10-1201259 (published on November 14, 2012)

The present invention has been devised to solve the problems of the prior art as described above, and it is an object of the present invention to provide a manufacturing method of a silver-diamond composite material capable of easily combining silver and diamond to various products requiring high strength and abrasion resistance .

According to an aspect of the present invention, there is provided a method for manufacturing a composite powder, comprising the steps of: (a) ball milling powder and diamond powder to produce a composite powder; And (b) spar plasma sintering (SPS) the composite powder prepared in step (a) to produce a silver-diamond composite material.

Also, the composite powder includes 40 to 90% by volume of silver powder and 10 to 60% by volume of diamond powder.

Also, the silver powder has a particle size (D50) of 1 to 5 mu m.

The diamond powder has a particle size (D90) of 0.1 to 10 mu m.

In the step (a), a planetary ball milling process is performed by setting the weight ratio of the silver powder and the diamond powder to the balls to 10: 1 to 1:10. do.

The planetary ball milling process is performed at 100 to 500 rpm for 1 to 20 hours.

The step (c) is characterized in that discharge plasma sintering is performed at a pressure of 30 to 100 MPa.

The step (c) is characterized in that discharge plasma sintering is performed at a temperature of 700 to 900 ° C.

The step (c) is characterized in that discharge plasma sintering is performed for 3 to 20 minutes.

The present invention also provides a silver-diamond composite material produced by the above-described method.

Further, the silver-diamond composite material includes 70 vol% silver and 30 vol% diamond, and has a Vickers hardness of 140 HV.

According to the method for producing a silver-diamond composite material according to the present invention, silver powder and diamond powder are ball-milled to produce a composite powder having a uniform degree of dispersion, and the resulting composite powder is subjected to spark plasma sintering (SPS ) Process, it is possible to easily manufacture high density homogeneous silver-diamond composites and to control the conductivity of the composite material according to the necessity by controlling the content of silver powder, so that it can be utilized in various fields Possible materials can be manufactured.

In addition, the silver-diamond composite material produced by the above-described method exhibits excellent mechanical properties and can be applied to manufacturing parts in various fields such as automobiles, trains, ships, and aerospace. Particularly, And can be effectively used for manufacturing bushings and the like.

1 is a process diagram showing a method for producing a silver-diamond composite material according to the present invention.
FIG. 2 is an electron microscope image of a composite powder prepared by performing a planetary ball milling process at 250 rpm for 10 hours according to Example 1. FIG.
Fig. 3 is an electron microscope image of the composite powder prepared by the method according to (a) Example 2-1, (b) Example 2-2, and (c) Example 2-3.
FIG. 4 is a graph showing the relationship between the composite powder (Ag-30vol% + D powder), the silver-diamond composite sintered body (Ag-30vol% + D composite) and pure silver powder Ray diffraction pattern (XRD diffraction pattern).
FIG. 5 is an electron microscope image of a composite powder prepared by the method according to Example 1. FIG.
6 is an electron microscope image of a composite powder prepared by the method according to Example 2-3.
FIG. 7 is an electron microscope image of a composite powder prepared by the method according to Example 3. FIG.
8 is an actual image of a silver-diamond composite sintered body produced by the method according to (a) Example 1, (b) Example 2-3, and (c) Example 3.
9 is a photograph of a sintered silver-diamond composite material produced by the method according to (a) Example 2-3, (b) Example 4, and (c) Example 5.

Hereinafter, the present invention will be described in detail.

The present invention relates to (a) a step of ball milling powder and diamond powder to prepare a composite powder; And (b) spar plasma sintering (SPS) the composite powder prepared in the step (a) to produce a silver-diamond composite material. 1).

The step (a) is a step of ball milling silver powder and diamond powder to produce a composite powder. In this step, the two kinds of powders are ball-milled to have a uniform degree of dispersion A composite powder can be produced.

The silver powder may have a particle size (D50) of 1 to 5 占 퐉, and the diamond powder may have a particle size (D90) of 0.1 to 10 占 퐉 and may be subjected to a discharge plasma sintering process So that a composite material excellent in physical properties can be produced.

For reference, the particle size (D50) of the silver powder means a 50% volume cumulative particle size measured by a laser diffraction scattering particle size distribution measurement method, and the particle size (D90) of the diamond powder is determined by a laser diffraction scattering formula Means the 90% volume cumulative particle size measured by the particle size distribution measurement method.

Particularly, the particle size of the diamond powder may affect the density, mechanical characteristics, etc. of the composite material to be produced in a step to be described later, and it is preferable to select the particle size of the diamond powder in consideration thereof. In this step, (D90) of 0.1 to 10 [mu] m so as to be able to produce a composite material by discharge plasma sintering.

When the average particle diameter of the diamond powder is less than 0.1 mu m, the diamond powder is hardly uniformly dispersed and aggregated together with silver during the sintering process. When the average particle diameter of the diamond powder exceeds 10 mu m, It is preferable to use a diamond powder having an average particle size within the above range because the creep characteristics are deteriorated and a composite material having a nonuniform structure can be formed. Thus, a silver-diamond composite material excellent in mechanical strength can be produced . More preferably, the diamond has a particle size (D90) of 0.1 to 2 占 퐉.

The silver-diamond composite material can be affected by the volume fraction of diamond by mechanical properties, so that the composite powder contains 40 to 90% by volume of silver powder and 10 to 60% by volume of diamond powder If the volume fraction of the diamond powder is less than 10% by volume, the mechanical properties are poor. When the volume fraction of diamond powder is more than 60% by volume, it is difficult to reduce the electrical characteristics and to form composite particles having a uniform size. Preferably, the composite powder contains diamond in a volume fraction of 30% by volume to produce a composite material having excellent mechanical properties and electrical characteristics. Furthermore, the conductivity of the composite material can be controlled by adjusting the volume fraction of silver.

In this step, the silver powder and the diamond powder may be mixed through various ball milling processes such as electric ball milling, stirring ball milling, and planetary ball milling to produce a homogeneous composite powder.

Preferably, in this step, a composite powder can be produced by performing a planatary ball milling process, and the weight ratio (BPR) of the silver powder to the diamond powder to the ball is adjusted to 10: 1 to 1: 1: 10 to perform the planetary ball milling process. Preferably, the planar ball milling process is performed by setting the BPR to 6: 1. Thus, a homogeneous composite powder can be produced.

Also, the planetary ball milling process may be performed at 100 to 500 rpm for 1 to 20 hours. When the time for performing the planetary ball milling process is less than 1 hour, the silver powder and the diamond powder form coarse particles There may be a problem that the physical properties of the composite material are deteriorated when the composite material is produced through the discharge plasma sintering in a step to be described later. More preferably, the planetary ball milling process is performed at 250 rpm for 5 to 10 hours to prepare a homogeneous composite powder.

Further, in this step, in order to ball mill the silver powder and the diamond powder, a release agent is additionally supplied to the mixed powder of the silver powder and the diamond powder to prevent the sticking phenomenon which may occur during the ball milling process And stearic acid is a typical example of the release agent. At this time, the releasing agent may be added to the mixed powder of the silver powder and the diamond powder in such a range as not to impair the physical properties.

Further, in this step, the composite powder prepared as described above may be further prepared to prepare a molded body, and the composite body may be manufactured by the discharge plasma sintering of the molded body as described above. The molded body can be used without limitation as long as it is a conventional method of forming a molded body using powder, and a typical example of a method of manufacturing a pre-molded body by supplying a composite powder to a mold is described.

For example, the composite powder may be filled in a mold provided in a chamber of a spark plasma sintering apparatus to prepare a preform. The mold may be provided in various shapes such as a bar shape or a plate shape, and a mold made of a material stable at high temperatures may be used so that it can not act as an impurity in a discharge plasma sintering process to be described later.

The step (b) is a step of spark plasma sintering (SPS) of the composite powder to produce a silver-diamond composite material.

In the discharge plasma sintering, a spark discharge phenomenon occurs due to a pulsed direct current flowing between the particles of the composite powder by applying a direct current to the composite powder under a pressure applied condition, thereby generating a high energy of a discharge plasma momentarily generated The composite powder can be sintered by the heat diffusion due to the electric field diffusion and the electric resistance of the mold, the applied pressure and the electric energy, and the complex powder can be densified in a short time to form the composite material. It is possible to achieve effective control of crystal grain growth of the composite material and to produce a composite material having a uniform microstructure.

In the present invention, for the discharge plasma sintering process, for example, a chamber having an upper electrode and a lower electrode to form a space for accommodating a mold capable of generating a discharge plasma by sintering the composite powder by supplying a current, A temperature sensing unit capable of detecting a temperature in the chamber, and a controller for controlling the temperature of the chamber to discharge the inside of the chamber to the outside And a control unit for controlling the temperature of the discharge plasma sintering process according to a temperature sensed by the temperature sensing unit and an operating unit capable of controlling the control unit, A discharge plasma sintering process can be performed.

In this step, in order to sinter discharge plasma of the composite powder, impurities are removed from the gas phase existing in the chamber by evacuating the inside of the chamber until the inside of the chamber is evacuated by using a pump provided in the discharge plasma apparatus , And the discharge plasma sintering process can be performed by preventing oxidation.

Further, the composite powder may be heated to a sintering temperature at a heating rate of 100 ° C / min to heat the composite powder, and then the discharge plasma sintering may be performed. The composite powder is heat- A uniformly structured silver-diamond composite material can be formed by supplying a uniform temperature to the inside and the outside of the composite powder through the plasma sintering process.

Also, in the discharge plasma sintering process, the growth rate of the silver-diamond composite particles can be controlled by controlling the rate of temperature rise, and thus the size of the silver-diamond composite material to be manufactured can be controlled.

The discharge plasma sintering process is preferably performed at a temperature of 700 to 900 DEG C for 3 to 20 minutes to produce a silver-diamond composite material. If the sintering temperature of the discharge plasma is less than 700 캜, a sintered body having a low density is produced. If the sintering temperature of the discharge plasma exceeds 900 캜, the grain size of the diamond composite material may rapidly increase and mechanical properties may be deteriorated. Further, when the discharge plasma sintering process is performed for less than 3 minutes, it is difficult to expect a sufficient sintering effect due to incomplete sintering, and when the sintering time exceeds 20 minutes, energy consumption is increased, It is difficult to expect the densification effect by the above.

In addition, the discharge plasma sintering process may be performed under a pressure of 30 to 100 MPa to pressurize the composite powder to produce a silver-diamond composite material. When the pressure is less than 30 MPa, the density of the silver- If the pressure exceeds 100 MPa, cracks may occur in the silver-diamond composite material due to the high pressure, so that the discharge plasma sintering process can be performed under the above conditions. More preferably, the discharge plasma sintering process is performed for 5 minutes at a temperature of 850 ° C and a pressure of 50 MPa to produce a silver-diamond composite material having excellent mechanical properties. The silver- - The diamond composite material is excellent in mechanical properties of the composite material by forming a composite material containing pure silver and diamond only, without generating a secondary phase or an oxide formed by the combination of silver and diamond .

Further, in this step, the silver-diamond composite material may further be cooled after sintering the silver-diamond composite material as described above, thereby obtaining a silver-diamond composite material having excellent mechanical properties .

In this step, the silver-diamond composite material may be cooled to maintain a pressure of 10 to 100 MPa to suppress formation of voids and the like formed on the surface and inside of the silver-diamond composite material.

According to the method for producing a silver-diamond composite material according to the present invention, the silver powder and the diamond powder are ball-milled to produce a composite powder having a uniform dispersion degree, and the composite powder is spark- plasma sintering (SPS) process, it is possible to easily fabricate a high density homogeneous silver - diamond composite material and to control the conductivity of the composite material according to need by controlling the content of silver powder It is possible to manufacture materials usable in various fields.

The present invention also provides a silver-diamond composite material produced by the above-described method.

In particular, the silver-diamond composite material may include 70% by volume of silver and 30% by volume of diamond, and the silver-diamond composite material containing silver and diamond in the volume fraction has a lower density than pure silver, Vickers hardness of 140 HV shows excellent mechanical properties.

Therefore, the above-described silver-diamond composite material exhibits excellent mechanical properties (density, Vickers hardness, etc.) and can be applied to manufacturing parts in various fields such as automobiles, trains, ships, and aerospace. Especially, And can be effectively used for the production of bushings and the like.

Hereinafter, the present invention will be described in more detail with reference to examples.

The embodiments presented are only a concrete example of the present invention and are not intended to limit the scope of the present invention.

≪ Example 1 >

(D50 = 2 占 퐉) having a particle size (D50) of 2 占 퐉 occupying 50% of the entire particle size distribution and a particle size (D90) occupying 90% nm diameter single crystal nano diamond powder (D90 = 125 nm) was supplied to a planetary ball milling apparatus, and 1 g of strearic acid was added thereto. The balls were set at a weight ratio of the ball and the composite powder set at 6: 1, and a planetary ball milling process was performed at 250 rpm for 10 hours to prepare a composite powder (FIG. 2) , And an interval of 10 minutes: 10 minutes in an atmospheric environment.

The composite powder thus prepared was charged into a mold (graphite material), and the mold was mounted in a chamber of a discharge plasma sintering apparatus. The chamber was adjusted to a vacuum state and a discharge plasma sintering process was performed for 5 minutes under the conditions of a temperature of 850 DEG C and a pressure of 50 MPa by applying an electric current to the upper electrode and the lower electrode, A silver-nano diamond composite sintered body (Ag-10vol% + 125nm D composite) was prepared.

≪ Example 2-1 >

Except that 30 volume% of the nano diamond powder was supplied and a planetary ball milling process was performed for 1 hour to prepare a composite powder (5h ball milled Ag-30vol% 125nm D powder). To prepare a silver-nano diamond composite sintered body (1 h ball milled, Ag-30 vol% 125 nm D composite).

≪ Example 2-2 >

Except that 30 volume% of the nano diamond powder was supplied and the planetary ball milling process was performed for 5 hours to prepare a composite powder (5h ball milled Ag-30vol% 125nm D powder). To prepare a silver-nano diamond composite sintered body (5h ball milled, Ag-30vol% 125nm D composite).

≪ Example 2-3 >

Except that 30 volume% of nano diamond powder was supplied and a planetary ball milling process was performed for 10 hours to prepare a composite powder (10h ball milled Ag-30vol% 125nm D powder). A silver-nano diamond composite sintered body (Ag-30vol% 125nm D composite) as shown in Figs. 8 (b) and 9 (a) was prepared.

≪ Example 3 >

8 (c), except that the composite powder (Ag-60 vol%, 125 nm D powder) was prepared by supplying 60 vol% of the nano diamond powder, Nano diamond composite sintered body (Ag-60vol% 125nm D composite) was prepared.

<Example 4>

9 (b), using the same method as in Example 2-3 except that a nano diamond powder (D90 = 250 nm) having a particle size D90 of 250 nm was used, - Nanodiamond composite sintered body (Ag-30vol% 250nm D composite) was prepared.

&Lt; Example 5 >

9 (c), except that a diamond powder (D90 = 2 占 퐉) having a grain size (D90) of 2 占 퐉 was used, Diamond composite sintered body (Ag-30vol% 2 탆 D composite) was prepared.

<Comparative Example>

Except that only silver powder (D50 = 2 占 퐉) was used. The pure Ag bulk was prepared by performing the planetary ball milling process and the spark discharge plasma process.

&Lt; Experimental Example 1 > Effect of execution time of ball milling process

In order to analyze the influence of the execution time of the ball milling process on the physical properties of the composite material in the production of the composite material sintered body, the composite powder prepared by the method according to Examples 2-1 to 2-3 using a scanning electron microscope The surface was photographed using an electron microscope, and the results are shown in FIG.

As shown in Fig. 3, the composite powder of Example 2-1 (Fig. 3 (a)) prepared by performing the ball milling process for 1 hour was prepared by inducing cold welding of particles, agglomeration was performed to form a coarse particle and a composite powder having uneven particles was formed. On the other hand, the composite powder of Example 2-2 (Fig. 3 (b)) prepared by performing the ball milling process for 5 hours and the composite powder of Example 2-3 3 (c)) shows that the coarse particles are destroyed and the particles of the composite powder are refined and saturated with the purified particles. Accordingly, it is preferable to perform the ball milling process for 5 hours or more to produce a composite powder. Since the particles are uniformly dispersed in the composite powder by performing the ball milling process for 5 hours or more, It was confirmed that homogeneous composite materials can be produced by spark plasma discharge sintering process.

<Experimental Example 2> Phase change analysis of the silver-diamond composite sintered body manufactured

The composite powder (Ag-30vol% D powder) of Example 2-3 and the silver-nano diamond composite of Example 2-3 were used to analyze the phase change of the silver- An XRD diffraction pattern of the material sintered body (Ag-30vol% D composite) and pure silver powder (Ag powder) was performed. The results are shown in FIG.

As shown in FIG. 4, the silver-nano diamond composite sintered body of Example 2-3 was found to have the same XRD pattern as that of pure silver powder, so that no phase change was caused by the spark plasma discharge sintering process , And it was confirmed that no change of the component according to the process occurred.

&Lt; Experimental Example 3 >

In order to analyze the influence of the content of diamond on the silver-diamond composite material, a scanning electron microscope was used to compare the results of Example 1 (Fig. 5), Example 2-3 (Fig. 6) and Example 3 The morphological characteristics of the composite powders were analyzed.

As shown in FIG. 5 and FIG. 7, the composite powder of Example 3 including the composite powder of Example 1 and the 60 volume% of the nano diamond powder including 10 volume% of the nano diamond powder had an uneven particle size As shown in FIG. 6, it can be seen that the composite powder of Example 2-3 containing 30% by volume of the nano diamond powder has particles having a uniform size, The volume fraction of the sintered powder affects the homogenization of the sintered powder.

The density (g / cm) and the Vickers hardness of the silver-diamond composite sintered body produced by the methods according to Examples 1 to 3 and Comparative Examples were analyzed in order to analyze the influence of the content of diamond on the composite material (hardness, HV) were measured. The results are shown in Table 1 below.

sample Density (g / cm) Hardness (HV) Comparative Example 10.49 (100%) 25 HV Example 1 9.79 (93%) 96 HV Example 2-3 8.39 (87%) 140 HV Example 3 6.29 (83%) 104 HV

As shown in Table 1, the silver-nano diamond composite sintered bodies of Examples 1, 2-3, and 3 all had a lower density than the pure silver bulk of the comparative example, And the density tends to decrease as the volume fraction of the diamond increases. Thus, it can be seen that the volume fraction of the diamond affects the characteristics of the composite material there was.

Particularly, in the case of Example 2-3 in which the volume fraction of diamonds was 30% by volume, it was confirmed that the hardness was the most excellent. The Vickers hardness increased with the volume fraction of diamonds up to 30% by volume, It was confirmed that the silver-nano diamond composite sintered body of Example 2-3 had the most excellent mechanical strength, so that the optimum volume fraction of diamond could be determined.

<Experimental Example 4> Analysis of influence of particle size of diamond powder

In order to analyze the influence of the particle size of the diamond powder on the silver-diamond composite material, the silver-nano diamond composite material prepared by the method according to Example 2-3, Example 4, - Density of diamond composite sintered body and Vickers hardness were measured, and the results are shown in Table 2 below.

sample Density (g / cm) Hardness( HV ) Comparative Example 10.49 (100%) 25 HV Example 2-3 8.39 (87%) 140 HV Example 4 8.39 (91%) 124 HV Example 5 8.39 (91%) 111 HV

As shown in Table 2, the diameter of the diamond powder did not affect the density of the composite material, but it was confirmed that the smaller the particle size of the diamond powder, the more excellent the hardness of the composite material. - The Vickers hardness of the sintered body of the nano diamond composite material is higher than that of the comparative example by about 6 times, even though the density is lower than that of the silver piece of the comparative example. Thus, the silver- It is possible to apply the present invention to the manufacture of parts in various fields such as ships, aerospace, and the like, and particularly, it can be effectively used for manufacturing bushings requiring high strength and abrasion resistance.

Claims (11)

(a) comprises: ball milling a diamond powder having a powder and particle size (D90) of 0.1 to 0.125 占 퐉 to prepare a composite powder comprising 70 vol% silver powder and 30 vol% diamond powder; And
(b) spar plasma sintering (SPS) of the composite powder prepared in step (a) at a pressure of 50 to 100 MPa and a temperature of 850 to 900 ° C to produce a silver-diamond composite material / RTI &gt; A method for manufacturing a silver-diamond composite material. delete The method according to claim 1,
Wherein the silver powder has a particle size (D50) of 1 to 5 占 퐉. delete The method according to claim 1,
Wherein the step (a) comprises the step of performing a planetary ball milling process by setting the weight ratio of the silver powder and the diamond powder to the ball to 10: 1 to 1:10. Method of manufacturing a diamond composite. 6. The method of claim 5,
Wherein the planetary ball milling step is performed at 100 to 500 rpm for 1 to 20 hours. delete delete The method according to claim 1,
Wherein the step (b) is performed for 3 to 20 minutes by discharge plasma sintering. A silver-diamond composite material produced by the method of any one of claims 1, 3, 5, 6, and 9. 11. The method of claim 10,
70 volume% silver and 30 volume% diamond, and the Vickers hardness is 140 HV.

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