Cubic boron nitride-magnesium composite and preparation method therefor

Abstract

The present invention provides a cubic boron nitride-magnesium composite comprising, at a high volume ratio, a cubic boron nitride powder having excellent mechanical properties and high thermal conductivity. Provided, according to one aspect of the present invention, is a composite comprising: a magnesium matrix; and a cubic boron nitride powder distributed in the magnesium matrix. According to one embodiment of the present invention, the volume ratio of the cubic boron nitride powder in the composite may have a range of 40 vol% to 90 vol%.

Description

Cubic boron nitride-magnesium composite and method for manufacturing the same

[0001] The present invention relates to a cubic boron nitride-magnesium composite, and more specifically, to a solid-moment cubic boron nitride-magnesium composite having high thermal conductivity and a method for manufacturing the same.

[0002] The present invention relates to a project (Project No.: 2710003345, Project No.: 00281508) and a project (Project No.: 2710017825, Project No.: 00444649) carried out with funding from the Ministry of Science and ICT.

[0003] With the advancement of high-performance semiconductor technologies such as AI, electric vehicles, and 6G communication, the performance of semiconductor devices is increasing rapidly. As this increase in performance inevitably entails heat generation, the importance of thermal dissipation materials is growing. In particular, power semiconductors have enabled high-power applications as their control output per unit volume has increased approximately 1,000-fold over the past 50 years. Consequently, they have become capable of playing a key role in next-generation growth industries such as electric vehicles, unmanned aerial vehicles, and eco-friendly power generation, leading to an expected explosive increase in demand for thermal dissipation materials for cooling power semiconductors.

[0004] In particular, in order to lower the coefficient of thermal expansion of heat dissipation materials, aluminum composites are being manufactured by mixing low thermal expansion metals (Mo, W) or ceramics (SiC) with aluminum. However, in order to lower the coefficient of thermal expansion of such composites to 8 ppm / K or less, thermal conductivity must be significantly sacrificed, so there is a problem that the thermal conductivity cannot exceed 200 W / m·K.

[0005] The technical problem that the technical concept of the present invention aims to solve is to provide a cubic boron nitride-magnesium composite containing cubic boron nitride (cBN) having excellent mechanical properties and high thermal conductivity in a high volume ratio. However, this problem is exemplary, and the technical concept of the present invention is not limited thereto.

[0006] According to one aspect of the present invention, a composite material comprising a magnesium matrix; and cubic boron nitride powder distributed in the magnesium matrix is ​​provided.

[0007] According to one embodiment of the present invention, the volume percentage of the cubic boron nitride powder in the composite material may range from 40 volume% to 90 volume%.

[0008] According to one embodiment of the present invention, the magnesium may have a purity of 99.9 weight% or more.

[0009] According to one embodiment of the present invention, the cubic boron nitride powder may have an average particle size of 15 μm to 300 μm.

[0010] According to one embodiment of the present invention, the cubic boron nitride powder may have a volume ratio of a first powder having an average particle size in the range of 35 μm to 45 μm and a second powder having an average particle size in the range of 3 μm to 7 μm in the range of 6:4 to 8:2.

[0011] According to one embodiment of the present invention, the cubic boron nitride-magnesium composite material may have a thermal conductivity of 200 W / mK to 600 W / mK.

[0012] According to one embodiment of the present invention, 4 ppmK -1 To 12 ppmK -1 It can have a coefficient of thermal expansion.

[0013] According to another aspect of the present invention, a method for manufacturing a cubic boron nitride-magnesium composite is provided.

[0014] According to one embodiment of the present invention, the manufacturing method may include the steps of: placing cubic boron nitride powder inside a mold; placing solid magnesium on the cubic boron nitride powder; sealing the mold and removing fluid inside the mold to create a vacuum atmosphere inside the sealed space; heating and melting the solid magnesium; pressurizing the molten magnesium to impregnate the molten magnesium into the cubic boron nitride powder; and cooling the molten magnesium impregnated into the cubic boron nitride powder to solidify it into a solid state to manufacture a composite material.

[0015] According to one embodiment of the present invention, the step of heating and melting the solid magnesium can be performed at a temperature in the range of 600°C to 700°C in the vacuum atmosphere.

[0016] According to the technical concept of the present invention, by including cubic boron nitride powder in a high volume ratio, a cubic boron nitride-magnesium composite material having excellent thermal conductivity and a reduced coefficient of thermal expansion can be provided. The effects of the present invention described above are illustrative and the scope of the present invention is not limited by these effects.

[0017] FIG. 1 is a flowchart illustrating a method for manufacturing a cubic boron nitride-magnesium composite according to one embodiment of the present invention.

[0018] Figure 2 shows a liquid-phase pressurizing device used in the method for manufacturing the cubic boron nitride-magnesium composite material shown in Figure 1.

[0019] Figure 3 shows the results of observing the microstructure of cubic boron nitride-magnesium composites using an electron microscope.

[0020] Figure 4 is the result of performing a component analysis of a cubic boron nitride-magnesium composite according to one embodiment of the present invention using EDS (energy dispersive spectroscopy).

[0021] Figure 5 is a graph showing the thermal conductivity and flexural stress of cubic boron nitride-magnesium composites according to one embodiment of the present invention.

[0022] Figures 6 and 7 are the results of observing the microstructure of cubic boron nitride-magnesium composites according to one embodiment of the present invention using an electron microscope.

[0023] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The embodiments of the present invention are provided to more completely explain the technical concept of the present invention to those skilled in the art, and the following embodiments may be modified in various different forms, and the scope of the technical concept of the present invention is not limited to the following embodiments. Rather, these embodiments are provided to make the present disclosure more faithful and complete and to fully convey the technical concept of the present invention to those skilled in the art. In this specification, the same reference numerals denote the same elements throughout. Furthermore, various elements and areas in the drawings are depicted schematically. Accordingly, the technical concept of the present invention is not limited by the relative sizes or spacing depicted in the attached drawings.

[0024] The technical concept of the present invention is to provide a cubic boron nitride-magnesium composite material and a method for manufacturing the same, which includes a high volume percentage of cubic boron nitride powder having an average particle size within a predetermined range, thereby enabling excellent thermal conductivity and a reduced coefficient of thermal expansion. The cubic boron nitride has the advantage of possessing not only low thermal expansion but also high thermal conductivity.

[0025] A cubic boron nitride-magnesium composite according to one embodiment of the present invention comprises a magnesium matrix and cubic boron nitride powder distributed in the magnesium matrix. Hereinafter, the cubic boron nitride-magnesium composite may be referred to as a composite for convenience. The magnesium matrix can be understood as a configuration in which the cubic boron nitride powder is filled between the cubic boron nitride powders to bond the cubic boron nitride powders together and enable the composite to maintain a certain shape.

[0026] The above magnesium (Mg) is pure magnesium with a purity of 99.9 weight% or higher. This means that the content of pure magnesium is 99.9 weight% or higher, and the impurities inevitably mixed in during the manufacturing process of magnesium are 0.1 weight% or lower.

[0027] A cubic boron nitride-magnesium composite according to one embodiment of the present invention may have high thermal conductivity compared to a composite in which a magnesium alloy is used instead of pure magnesium, by including pure magnesium with a purity of 99.9 weight% or higher. In addition, as a related physical property, the cubic boron nitride-magnesium composite according to one embodiment of the present invention may have a thermal conductivity of 200 W / mK to 600 W / mK.

[0028] The volume percentage of cubic boron nitride powder in the above cubic boron nitride-magnesium composite is in the range of 40 volume% to 90 volume%.

[0029] The cubic boron nitride powder may have a mean particle size in the range of 15 μm to 300 μm. Depending on the mean particle size of the cubic boron nitride powder, the bending strength and thermal conductivity exhibited by the cubic boron nitride-magnesium composite have contrasting characteristics. As the mean particle size of the cubic boron nitride powder decreases, the thermal conductivity of the composite decreases but the bending strength increases. This is attributed to the fact that the thermal conductivity decreases due to the increase in inter-particle interfacial resistance caused by the fine powder, and the bending strength increases as the high-hardness cubic boron nitride powder is finely dispersed.

[0030] If the average particle size of the boron nitride powder is less than 15 μm, a problem may arise in which the thermal conductivity decreases as the interface between the small cubic boron nitride powder and the magnesium matrix increases due to increased interfacial thermal resistance. If the average particle size of the cubic boron nitride powder exceeds 300 μm, a problem may arise in which the bending strength decreases as the number of high-hardness cubic boron nitride powders decreases and the mechanical bonding at the interface between the cubic boron nitride powder and the magnesium matrix weakens.

[0031] The cubic boron nitride powder constituting the cubic boron nitride-magnesium composite according to one embodiment of the present invention is provided with an average particle size in the range of 15 μm to 300 μm, thereby allowing it to be provided in the composite at a higher volume fraction, for example, 40 volume% to 90 volume%. That is, the cubic boron nitride powder is provided to have a solid mass and be uniformly dispersed within the composite, thereby providing a cubic boron nitride-magnesium composite that has excellent thermal conductivity and a reduced coefficient of thermal expansion.

[0032] The cubic boron nitride powder constituting the cubic boron nitride-magnesium composite according to one embodiment of the present invention may be a mixture of cubic boron nitride powders having different average particle sizes in a predetermined ratio. For example, the cubic boron nitride powder may be a mixture of a first powder having an average particle size in the range of 35 μm to 45 μm and a second powder having an average particle size in the range of 3 μm to 7 μm, with a volume ratio in the range of 6:4 to 8:2 (i.e., volume of the first powder:volume of the second powder = 6:4 to 8:2). This means that the volume ratio of the first powder within the total mixed powder in which the first powder and the second powder are mixed has a range of 60% to 80%. If the volume ratio of the first powder is less than 60%, the dispersibility of the first powder is reduced and there may be a problem with the second powders aggregating together, and conversely, if the volume ratio of the first powder exceeds 80%, there may be a problem with the second powder not adequately filling the empty space of the first powder.

[0033] In the case of a composite material mixed with cubic boron nitride powders having different average particle sizes, compared to a composite material composed solely of cubic boron nitride powder having a single average particle size, the cubic boron nitride powder is included in the composite material at a higher volume fraction, thereby allowing for a lower coefficient of thermal expansion.

[0034] FIG. 1 is a flowchart illustrating a method for manufacturing a cubic boron nitride-magnesium composite according to an embodiment of the present invention, and FIG. 2 shows a liquid-phase pressurizing device used in the method for manufacturing a cubic boron nitride-magnesium composite illustrated in FIG. 1. In the following description, cubic boron nitride powder and magnesium will not be described if they overlap with the content already described above.

[0035] Referring to FIGS. 1 and 2, a method (S100) for manufacturing a cubic boron nitride-magnesium composite according to one embodiment of the present invention first performs the step (S110) of placing cubic boron nitride powder inside a lower mold (100).

[0036] Next, a step (S120) of placing solid magnesium on the cubic boron nitride powder is performed. To do this, solid magnesium is also loaded into the lower mold (100).

[0037] Next, the upper part of the lower mold (100) is closed with the upper mold (140) and sealed, and then the fluid inside the lower mold (100) is sucked out using an ejector (130) to create a vacuum atmosphere inside the sealed space (S130). By precisely controlling the above process in a vacuum atmosphere, a method for manufacturing a cubic boron nitride-magnesium composite material can be provided that improves the mechanical strength, thermal conductivity, and durability of the composite material.

[0038] Next, solid magnesium can be heated and melted to form liquid magnesium (120) (S140). At this time, heating and melting can be performed at a temperature in the range of 600°C to 700°C in the vacuum atmosphere.

[0039] Next, the liquid magnesium (120) is pressed with an upper mold (140) so that the molten liquid magnesium (120) is impregnated into the cubic boron nitride powder (110) (S150).

[0040] Next, the cubic boron nitride powder (110) impregnated with liquid magnesium (120) can be cooled to solidify the liquid magnesium (120) and finally form a cubic boron nitride-magnesium composite (S160). The cooling step can be performed by forming a cooling fluid channel (141) within the upper mold (140), then flowing a cooling fluid through the cooling fluid channel (140), and allowing the cooling fluid to absorb heat. However, this is not limited to this, and various cooling methods can be used, such as cooling the mold with air or water while it is closed.

[0041] After cooling is complete, the mold is opened to obtain the manufactured cubic boron nitride-magnesium composite.

[0042] A method for manufacturing a cubic boron nitride-magnesium composite according to one embodiment of the present invention forms the cubic boron nitride-magnesium composite using a liquid-phase pressurization process performed under a vacuum atmosphere. Molten liquid magnesium is pressurized to impregnate the cubic boron nitride powder. Accordingly, in the cubic boron nitride-magnesium composite, the cubic boron nitride powder, which functions as a reinforcing agent to improve mechanical properties and as a thermal conductor, can be uniformly dispersed within the magnesium metal matrix.

[0043] Experimental example

[0044] Preferred experimental examples are presented below to aid in understanding the present invention. However, the following experimental examples are intended only to aid in understanding the present invention and do not limit the present invention. Details not described herein can be sufficiently technically inferred by those skilled in the art, so their description is omitted.

[0045] Table 1 shows the thermal conductivity properties of the embodiments of the present invention and comparative examples.

[0046] Classification Composite Thermal Conductivity (W / mK) Example 1 15 μm cBN / Mg 244.486 Example 2 40 μm cBN / Mg 252.29 Example 3 100 μm cBN / Mg 364.34 Example 4 300 μm cBN / Mg 409.91 Comparative Example 1 AZ3 193.410 Comparative Example 2 40 μm cBN / AZ3 1165.666 Comparative Example 35 μm cBN / Mg 173.99

[0047]

[0048] Examples 1 to 4 are cubic boron nitride-magnesium composites, which are composites manufactured using a liquid-phase pressurization process in a vacuum atmosphere as described above, using cubic boron nitride powder (cBN) with average particle sizes of 15, 40, 100, and 300 μm, respectively, and pure magnesium (Mg) with a purity of 99.9% as raw materials.

[0049] Comparative Example 1 is an AZ1 alloy, which is one of the magnesium alloys (in “AZ31,” “A” represents aluminum, “Z” represents zinc, and “31” represents the aluminum content of the alloy (about 3 wt%)), and Comparative Example 2 is a composite material prepared using cubic boron nitride powder with an average particle size of 40 μm and the AZ1 alloy as raw materials. Both Comparative Example 1 and Comparative Example 2 were prepared using a liquid-phase pressurization process in a vacuum atmosphere, in the same way as the Examples.

[0050] Referring to Table 1, all of the embodiments satisfy the thermal conductivity range of the present invention, which is 200 W / mK to 600 W / mK, whereas Comparative Example 1 and Comparative Example 2 both fall below the thermal conductivity range of the present invention.

[0051] In Comparative Examples 1 and 2, the low thermal conductivity is attributed to the alloy elements changing the crystal structure, increasing interfacial resistance, and lowering thermal conductivity due to non-uniform distribution.

[0052] Comparative Example 3 is a composite material manufactured using the liquid-phase pressurization process in a vacuum atmosphere described above, using cubic boron nitride powder (cBN) with an average particle size of 5 μm and pure magnesium (Mg) with a purity of 99.9% as raw materials. In the case of Comparative Example 3, the thermal conductivity showed a low value of less than 200 W / mK. This is interpreted as being due to the decrease in thermal conductivity caused by an increase in interfacial thermal resistance as the interface between the small-sized cubic boron nitride powder and the magnesium matrix increases.

[0053] Figure 3 shows the results of observing the microstructures of Comparative Example 3, Examples 1, 3, and 4 using an electron microscope. The photographs placed at the top left (5 μm cBN), top right (15 μm cBN), bottom left (100 μm cBN), and bottom right (300 μm cBN) of Figure 3 are the results of observing the microstructures of Comparative Example 3, Examples 1, 3, and 4, respectively.

[0054] Referring to Fig. 3, it can be seen that cubic boron nitride powder (black portion) is uniformly distributed on a magnesium matrix (white portion). The volume percentages of Examples 1, 3, and 4 are 68.3%, 63.8%, and 66.3%, respectively, and the volume percentage of the uniformly dispersed cubic boron nitride powder in the examples all exceeded 60%, indicating a high volume percentage.

[0055] Figure 4 shows the results of performing a component analysis of Example 3 using EDS (energy dispersive spectroscopy). Referring to Figure 4, it can be seen that a magnesium matrix is ​​filled between the cubic boron nitride powders.

[0056] Figure 5 is a graph showing the thermal conductivity and flexural stress of Examples 1, 3, and 4. Referring to Figure 5, it can be seen that as the average particle size of the cubic boron nitride powder decreases, the flexural stress increases, but the thermal conductivity of the composite decreases.

[0057] Table 2 shows the density, elastic modulus, thermal conductivity, and coefficient of thermal expansion of embodiments of the present invention.

[0058] Classification Composite Density (g / cm²) 3 Elastic modulus (GPa) Thermal conductivity (W / mK) Coefficient of thermal expansion (CTE, ppmK) -1 Example 240 µm cBN / Mg2.762169.62337.27 Example 55+40 µm cBN / Mg2.9641922335.2

[0059] Example 5 was prepared in the same manner as Example 2, except that the cubic boron nitride powder used in the manufacture of the composite material was a mixture of powders with an average particle size of 40 μm and 5 μm in a volume ratio of 7:3.

[0060] Referring to Table 2, both composites of Example 2 and Example 5 have a thermal expansion coefficient of 4 ppmK, which is within the range of the present invention. -1 To 12 ppmK -1 It satisfies the condition. However, in the case of Example 5, a composite material mixed with cubic boron nitride powder having average particle sizes of 40 μm and 5 μm, it can be confirmed that it has a lower coefficient of thermal expansion compared to Example 2, a composite material composed only of cubic boron nitride powder having a single average particle size of 40 μm.

[0061] This is attributed to the fact that in the case of Example 5, in which 40 μm and 5 μm particles are mixed, the volume ratio of cubic boron nitride in the composite increases, which not only increases the proportion of cubic boron nitride powder, a material with a low coefficient of thermal expansion, but also the uniform distribution of small particles promotes stress dispersion and thermal expansion inhibition effects, thereby playing a role in reducing the coefficient of thermal expansion of the composite.

[0062] In the case of Example 5, the high cBN content resulted in high values ​​for density and elastic modulus, as well as a low value for the coefficient of thermal expansion. Although the thermal conductivity of the composite material may increase as the volume fraction increases, the addition of 5 μm cBN increased the interfacial area between the reinforcing material and the matrix, thereby increasing the interfacial thermal resistance. Consequently, the increase in thermal conductivity due to the increase in volume fraction and the decrease in thermal conductivity due to the addition of small particles occurred simultaneously, resulting in a thermal conductivity similar to that of Example 2.

[0063] Figure 6 shows the result of observing the microstructure of Example 2 with an electron microscope, and Figure 7 shows the result of observing the microstructure of Example 5 with an electron microscope.

[0064] Referring to Figure 6, it indicates that the cubic boron nitride powder having an average particle size of 40 μm can be included in the composite material at a volume percentage of about 60 volume% (64.2 volume%).

[0065] Referring to FIG. 7, it indicates that the cubic boron nitride powder can be included in the composite material at a volume percentage of approximately 75 volume% (75.1 volume%) by mixing boron nitride powders having average particle sizes of 40 μm and 5 μm in a volume ratio of 7:3. In the case of a composite material mixed with cubic boron nitride powders having average particle sizes of 40 μm and 5 μm, the boron nitride powder is included in the composite material at a higher volume fraction compared to a composite material composed solely of cubic boron nitride powder having a single average particle size, thereby having a lower coefficient of thermal expansion.

[0066] It will be obvious to those skilled in the art that the technical concept of the present invention described above is not limited to the aforementioned embodiments and attached drawings, and that various substitutions, modifications, and changes are possible within the scope of the technical concept of the present invention.

Claims

1. Magnesium base; and A composite material comprising cubic boron nitride powder distributed in the magnesium matrix above, In the above composite material, the volume percentage of the cubic boron nitride powder ranges from 40 volume% to 90 volume%, The above magnesium has a purity of 99.9 weight% or higher, Cubic boron nitride-magnesium composite.

2. In Paragraph 1, The above cubic boron nitride powder has an average particle size of 15 μm to 300 μm, Cubic boron nitride-magnesium composite.

3. In Paragraph 1, The above cubic boron nitride powder is, A first powder having an average particle size in the range of 35 μm to 45 μm and a second powder having an average particle size in the range of 3 μm to 7 μm, wherein the volume ratio of the first powder having an average particle size in the range of 3 μm to 7 μm is in the range of 6:4 to 8:2, Cubic boron nitride-magnesium composite.

4. In Paragraph 1, Having a thermal conductivity of 200 W / mK to 600 W / mK, Cubic boron nitride-magnesium composite.

5. In Paragraph 1, 4 ppmK -1 To 12 ppmK -1 having a coefficient of thermal expansion, Cubic boron nitride-magnesium composite.

6. Step of placing cubic boron nitride powder inside the mold; A step of placing solid magnesium on the above cubic boron nitride powder; A step of sealing the mold and removing the fluid inside the mold to create a vacuum atmosphere inside the sealed space; A step of heating and melting the above-mentioned solid magnesium; A step of pressurizing molten magnesium to impregnate the molten magnesium into the cubic boron nitride powder; and The method includes the step of manufacturing a composite material by cooling molten magnesium impregnated into the above-mentioned cubic boron nitride powder to solidify it into a solid state; The volume percentage of the cubic boron nitride powder in the above composite material has a range of 40 volume% to 90 volume%, Method for manufacturing cubic boron nitride-magnesium composite.

7. In Paragraph 6, The above cubic boron nitride powder has an average particle size of 15 μm to 300 μm, Method for manufacturing cubic boron nitride-magnesium composite.

8. In Paragraph 6, The above cubic boron nitride powder is, A first powder having an average particle size in the range of 35 μm to 45 μm and a second powder having an average particle size in the range of 3 μm to 7 μm, wherein the volume ratio of the first powder having an average particle size in the range of 3 μm to 7 μm is in the range of 6:4 to 8:2, Method for manufacturing cubic boron nitride-magnesium composite.

9. In Paragraph 6, The step of heating and melting the above-mentioned solid magnesium is, Performed at a temperature in the range of 600°C to 700°C in the above vacuum atmosphere, Method for manufacturing cubic boron nitride-magnesium composite.

10. In Paragraph 6, The above magnesium has a purity of 99.9 weight% or higher, Method for manufacturing cubic boron nitride-magnesium composite.

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