A method for preparing liquid metal heat-conducting sheet by using spark plasma sintering process

Abstract

The application discloses a method for preparing a liquid metal heat-conducting sheet by adopting a spark plasma sintering process. The preparation method adopts bismuth-based, indium-based, tin-based and other low-melting-point metal and alloy powder as raw materials, and can also add other metal or non-metal reinforcing phases. The liquid metal powder and the reinforcing phases are combined by adopting a spark plasma sintering mode to obtain a liquid metal composite material with good comprehensive performance. Then, the sintered liquid metal blank is machined according to the required size, and a high-heat-conducting liquid metal heat-conducting sheet meeting the size precision requirement is obtained. Compared with the prior art, the application has the advantages of simple process, easy control, low cost, high heat conductivity, good universality, and is suitable for large-scale production and has a good development prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heat dissipation material preparation, and particularly relates to a method for preparing a liquid metal heat conduction sheet by using a spark plasma sintering process. BACKGROUND

[0002] Spark plasma sintering (SPS) is a rapid sintering technology. The technology controls a direct current pulse voltage to act on powder, and realizes densification of materials under the action of an external pressure by using discharge impact pressure, Joule heat, spark discharge phenomena and high-temperature plasma generated by pulse discharge between the powder. Compared with conventional sintering methods, the SPS technology has the advantages of fast heating speed, short sintering time, energy saving and environmental protection. The materials prepared by using the SPS technology have the characteristics of fine particles, high density and excellent performance, and can be used for preparing metals, ceramics, composite materials and functional materials, and show great potential in the preparation of advanced materials such as composite materials and nanomaterials.

[0003] With the development of industry, high-thermal-conductivity materials are paid more and more attention. For example, in the field of aviation, with the increasing complexity of spacecraft functions, the integration degree and power of electronic devices are gradually improved, and the heat dissipation problem of high-power-density electronic chips needs to be solved urgently. The liquid metal sheet belongs to an interfacial material and is widely used, especially in the field of interfacial materials, and therefore is widely concerned. However, the existing process for preparing the liquid metal-based heat conduction sheet (such as the process of mechanical stirring smelting, pouring forming, drying cooling, calendering sheeting and die cutting) sometimes has the problems of uneven organization composition and low density, especially after adding reinforcing particles. It is difficult to form a solid solution with the liquid metal for the difficult-to-dissolve reinforcing particles in the above existing technology, and the composition of the heat conduction sheet is more uneven. Therefore, a new preparation process needs to be developed to solve the problems of uneven organization composition and low density. SUMMARY

[0004] The present application mainly solves the technical problem of providing a method for preparing a liquid metal heat conduction sheet by using a spark plasma sintering process. The SPS technology is used to prepare a liquid metal heat conduction sheet with fine particles and high density, and other reinforcing phase materials can also be added. The base powder (herein referred to as liquid metal powder) is mechanically alloyed with the reinforcing material, and then sintered to form an alloy, so as to improve the performance of the existing liquid metal heat conduction sheet, meet various functional requirements, and broaden the application range and application space of the liquid metal.

[0005] To solve the above technical problems, one technical solution adopted by the present application is that the present application provides a method for preparing a liquid metal heat conduction sheet by using a spark plasma sintering process, comprising the following steps:

[0006] S1: Weigh the powder according to the composition of the heat-conducting sheet;

[0007] S2: After mixing the above powders, use a high-energy ball mill to mechanically alloy the mixed powders;

[0008] S3: Sieve the ball-milled powder and select powder with a particle size ≤74μm to ensure good compactness of the powder during sintering, and dry the powder at 40-80℃ for 1-2 hours;

[0009] S4: The dried mixed powder is sintered by spark plasma to obtain a dense liquid metal billet;

[0010] S5: The sintered liquid metal blank is machined to the required dimensions to obtain a liquid metal heat-conducting sheet that meets the dimensional accuracy requirements.

[0011] Furthermore, the powder composition of the heat-conducting sheet in step S1 includes liquid metal powder;

[0012] The liquid metal powder is an alloy prepared from any one or at least two of gallium, indium, tin, zinc, lead, and bismuth.

[0013] Furthermore, the powder composition of the heat-conducting sheet also includes reinforcing phase powder, which may be copper powder, silicon carbide powder, diamond powder, graphene powder, thermally conductive ceramic powder, etc.

[0014] The reinforcing phase powder accounts for 1-10 wt% of the total powder weight. If the proportion of the reinforcing phase powder is too small, the reinforcing effect will not be achieved, while if the proportion is too large, the reinforcing phase will easily agglomerate during sintering, resulting in uneven composition of the sintered product.

[0015] Furthermore, the reinforcing phase powder is at least one of copper powder, silicon carbide powder, diamond powder, and graphene powder, but is not limited thereto.

[0016] Furthermore, in step S2, the balls in the high-energy ball mill are hard alloy balls, the ball-to-material ratio is 12:1 to 8:1, the rotation speed is ≤3000 rpm / min, the ball milling time is greater than or equal to 6 hours, and the ball milling jar is filled with argon gas for protection.

[0017] To elaborate further, the discharge plasma sintering process in step S4 is as follows: the sintering temperature is 200-800℃, the sintering mold is a graphite mold, the sintering pressure is 30-50MPa, and the holding time is 5-20 minutes.

[0018] Furthermore, in step S4, the powder is coated with a layer of graphite film, and then the coated powder is placed in the sintering mold to prevent liquid metal leakage; or multiple layers of graphite pads are placed in the sintering mold, and the size of the graphite pads matches the inner cylindrical surface of the sintering mold.

[0019] The sintering mold is a cylindrical mold. The graphite pad is placed at both ends of the powder and mates with the inner cylindrical surface of the sintering mold.

[0020] In step S5, the machining process involves grinding the surface to the required dimensions using a grinding machine, and then slicing it to the required thickness using an internal cylindrical cutter.

[0021] Alternatively, machining can be performed by rolling the sintered billet to the required thickness using a rolling mill, followed by slicing with a slicing machine. However, this is not the only option; other thin-sheet processing methods can also be used.

[0022] In step S5, after machining, the liquid metal heat-conducting sheet is ground and polished to obtain a liquid metal heat-conducting sheet that meets the dimensional accuracy requirements.

[0023] The beneficial effects of this invention are:

[0024] In the preparation method proposed in this invention, liquid metal powder or metal powder with added reinforcing particles is sintered by spark plasma to form a dense alloy. That is, a strong pulsed current is continuously applied to the powder to achieve rapid densification. At the same time, the dual action of pressure and high temperature calcination can further densify the heat-conducting sheet. Therefore, the heat-conducting sheet produced in this way has a more uniform composition and a denser structure compared with heat-conducting sheets prepared by other processes.

[0025] Even better, modified particles can be added simultaneously. SPS technology can effectively disperse particles into liquid metal or alloys, improving various properties of the heat-conducting sheet and making the liquid metal heat-conducting sheet multifunctional, such as higher thermal conductivity, good magnetic permeability, and good electrical conductivity. This results in the preparation of high-performance novel liquid metal sheets that can meet multiple functional requirements, broadening the application range and scope of liquid metals.

[0026] The specific parameters selected in the sintering process of this invention are designed to optimize the performance of the sintered product. The sintering parameters of this invention are reasonably set. For example, the sintering time should not be too long, otherwise it will lead to "over-firing," causing the material to soften during annealing and resulting in a decrease in the material's compressibility. If the time is too short, it will lead to "under-firing," resulting in insufficient interfacial bonding, low density, and a small effective area to withstand compression, leading to low compressive strength. Furthermore, since the matrix material is liquid metal powder, it has a low phase transition temperature. Therefore, the sintering temperature differs from that of conventional metal powder sintering processes, i.e., the sintering temperature is correspondingly lower. After extensive testing, the sintering temperature was set at 200-800℃. If the sintering temperature is too high, the material may soften and easily undergo microscopic plastic deformation under the action of the die head. If the sintering temperature is too low, the bonding between layers will be insufficient, leading to a decrease in material density.

[0027] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the preparation method of the present invention;

[0029] Figure 2 This is a scanning electron microscope image of the copper powder reinforced liquid metal alloy prepared by SPS sintering in the embodiments of the present invention;

[0030] Figure 3 The image shown is a scanning electron microscope (SEM) image of a copper powder-reinforced liquid metal alloy prepared using conventional processes in the comparative example. Detailed Implementation

[0031] The following description, through comparative examples and specific embodiments, illustrates the detailed implementation of the present invention. Those skilled in the art can easily understand the advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented in other different ways; that is, different modifications and changes can be made without departing from the scope disclosed in the present invention.

[0032] Example 1: A method for preparing liquid metal thermal conductive sheets using spark plasma sintering process, such as... Figure 1 and Figure 2 As shown, in this embodiment, bismuth, indium, and tin powders are selected as liquid metal raw materials, and copper powder is used as reinforcing particles. The process is carried out according to the following steps:

[0033] S1: Weigh 20.2g of bismuth with a purity of 99.99%, 60.3g of In, 19.5g of Sn, and 5.3g of copper powder with a particle size of 10μm as reinforcing particles;

[0034] S2: After mixing the above powders, use a high-energy ball mill to mechanically alloy the mixed powders. The ball milling parameters are: the ball milling media are hard alloy balls, the ball-to-material ratio is 10:1, the rotation speed is 2000 rpm / min, the ball milling time is 10 hours, and the ball milling jar is filled with argon gas for protection.

[0035] S3: The ball-milled powder is sieved to select powder with a particle size ≤74μm to ensure good compactness of the powder during sintering, and the powder is dried at 60℃ for 1 hour;

[0036] S4: The dried mixed powder is sintered by spark plasma to obtain a dense liquid metal billet. The sintering parameters are: sintering temperature 500℃, sintering mold is graphite mold, sintering pressure is 50MPa, and holding time is 8 minutes.

[0037] S5: The sintered liquid metal billet is rolled to the required thickness using a rolling mill, and then slit using a slicing machine to finally obtain a heat-conducting sheet with a size of 50x50x0.15mm.

[0038] Example 2: A method for preparing liquid metal thermal conductive sheets using spark plasma sintering process, such as... Figure 1 and Figure 2 As shown, in this embodiment, bismuth, indium, tin, and zinc powders are selected as liquid metal raw materials, and silicon carbide powder is used as reinforcing particles. The process is carried out according to the following steps:

[0039] S1: Weigh 35g of bismuth with a purity of 99.99%, 10g of indium, 50g of tin, 5g of zinc, and 1g of silicon carbide powder with a particle size of 10μm as reinforcing particles.

[0040] S2: After mixing the above powders, use a high-energy ball mill to mechanically alloy the mixed powders. The ball milling parameters are: the ball milling media are hard alloy balls, the ball-to-material ratio is 8:1, the rotation speed is 1500 rpm / min, the ball milling time is 12 hours, and the ball milling jar is filled with argon gas for protection.

[0041] S3: The ball-milled powder is sieved to select powder with a particle size ≤74μm to ensure good compactness of the powder during sintering, and the powder is dried at 40℃ for 2 hours.

[0042] S4: The dried mixed powder is sintered by spark plasma to obtain a dense liquid metal billet. The sintering parameters are: sintering temperature 200℃, sintering mold is graphite mold, sintering pressure is 40MPa, and holding time is 5 minutes.

[0043] S5: The sintered liquid metal billet is rolled to the required thickness using a rolling mill, and then slit using a slicing machine to finally obtain a heat-conducting sheet with a size of 50x50x0.15mm.

[0044] Example 3: A method for preparing liquid metal thermal conductive sheets using spark plasma sintering process, such as... Figure 1 and Figure 2 As shown, in this embodiment, indium, tin, and zinc powders are selected as liquid metal raw materials, and diamond powder is used as reinforcing particles. The process is carried out according to the following steps:

[0045] S1: Weigh 52g of indium with a purity of 99.99%, 46g of tin and 2g of zinc, and 10g of copper powder with a particle size of 10μm as reinforcing particles.

[0046] S2: After mixing the above powders, use a high-energy ball mill to mechanically alloy the mixed powders. The ball milling parameters are: the ball milling media is hard alloy balls, the ball-to-material ratio is 9:1, the rotation speed is 3000 rpm / min, the ball milling time is 8 hours, and the ball milling jar is filled with argon gas for protection.

[0047] S3: The ball-milled powder is sieved to select powder with a particle size ≤74μm to ensure good compactness of the powder during sintering, and the powder is dried at 50℃ for 1.2 hours;

[0048] S4: The dried mixed powder is sintered by spark plasma to obtain a dense liquid metal billet. The sintering parameters are: sintering temperature 300℃, sintering mold is graphite mold, sintering pressure is 30MPa, and holding time is 15 minutes.

[0049] S5: The sintered liquid metal billet is rolled to the required thickness using a rolling mill, and then slit using a slicing machine to finally obtain a heat-conducting sheet with a size of 50x50x0.15mm.

[0050] Example 4: A method for preparing liquid metal thermal conductive sheets using spark plasma sintering process, such as... Figure 1 and Figure 2 As shown, in this embodiment, indium gallium powder is selected as the liquid metal raw material, and copper powder is used as the reinforcing particles, and the process is carried out according to the following steps:

[0051] S1: Weigh 95g of indium gallium with a purity of 99.99% and 5g of graphene powder with a particle size of 10μm as reinforcing particles.

[0052] S2: After mixing the above powders, use a high-energy ball mill to mechanically alloy the mixed powders. The ball milling parameters are: the ball milling media are hard alloy balls, the ball-to-material ratio is 10:1, the rotation speed is 2800 rpm / min, the ball milling time is 6 hours, and the ball milling jar is filled with argon gas for protection.

[0053] S3: The ball-milled powder is sieved to select powder with a particle size ≤74μm to ensure good compactness of the powder during sintering, and the powder is dried at 80℃ for 1.5 hours;

[0054] S4: The dried mixed powder is sintered by spark plasma to obtain a dense liquid metal billet. The sintering parameters are: sintering temperature 800℃, sintering mold is graphite mold, sintering pressure is 35MPa, and holding time is 20 minutes.

[0055] S5: The sintered liquid metal billet is rolled to the required thickness using a rolling mill, and then slit using a slicing machine to finally obtain a heat-conducting sheet with a size of 50x50x0.15mm.

[0056] Comparative Example: This comparative example uses bismuth, indium, and tin powders as liquid metal raw materials and copper powder as reinforcing particles, and proceeds according to the following steps:

[0057] S1: Weigh 20.2g of bismuth with a purity of 99.99%, 60.3g of In, and 19.5g of Sn, and put them into a muffle furnace for melting. Set the melting temperature to 350℃ and hold for 30 minutes.

[0058] S2: Add 5.3g of copper powder with a particle size of 10μm to a beaker containing 50ml of 0.5mol / L sodium hydroxide solution and sonicate for 10 minutes.

[0059] S2: Pour the bismuth-indium-tin alloy after melting into a beaker and place it on a magnetic stirrer for stirring. The stirring temperature is 80℃ and the stirring time is 0.5-1h. Stop stirring after the copper powder is completely mixed into the alloy.

[0060] S3: The mechanically stirred liquid metal composite is cast into a mold, and the cast composite is rolled into a thin sheet with a thickness of 0.15mm to obtain a copper powder reinforced liquid metal heat-conducting sheet.

[0061] pass Figure 2 and Figure 3 As can be seen, the embodiment uses spark plasma sintering process and adds copper powder to modify the liquid metal heat-conducting sheet. The heat-conducting sheet prepared has uniform composition, good density, strong thermal conductivity, good toughness and wear resistance, and is suitable for high heat generation components. In contrast, the heat-conducting sheet prepared by the conventional process in the comparative example has uneven composition and lower density.

[0062] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structure made using the contents of the present invention specification and drawings, or directly or indirectly applied to other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing liquid metal thermal conductive sheets using spark plasma sintering, characterized in that: include: S1: Weigh the powder according to the composition of the heat-conducting sheet; S2: After mixing the above powders, use a high-energy ball mill to mechanically alloy the mixed powders; S3: Sift the ball-milled powder to select the particle size. The powder is dried at 40-80℃ for 1-2 hours. S4: The dried mixed powder is sintered by spark plasma to obtain a dense liquid metal billet; S5: The sintered liquid metal blank is machined to the required dimensions to obtain a liquid metal heat-conducting sheet that meets the dimensional accuracy requirements; In step S2, the balls in the high-energy ball mill are cemented carbide balls, the ball-to-material ratio is 12:1 to 8:1, the rotation speed is ≤3000 rpm / min, the ball milling time is greater than or equal to 6 hours, and the ball milling jar is filled with argon gas for protection. The powder composition of the heat-conducting sheet in step S1 includes liquid metal powder; The liquid metal powder is an alloy prepared from any one or at least two of gallium, indium, tin, zinc, lead, and bismuth; The powder composition of the heat-conducting sheet also includes reinforcing phase powder, which is at least one of copper powder, silicon carbide powder, diamond powder and graphene powder. The reinforcing phase powder accounts for 1-10 wt% of the total powder weight; The discharge plasma sintering process in step S4 is as follows: the sintering temperature is 200-800℃, the sintering mold is a graphite mold, the sintering pressure is 30-50MPa, and the holding time is 5-20 minutes.

2. The method for preparing liquid metal thermal conductive sheets using spark plasma sintering process according to claim 1, characterized in that: In step S4, the powder is coated with a layer of graphite film, and then the coated powder is placed in a sintering mold; or multiple layers of graphite pads are placed in the sintering mold, and the size of the graphite pads matches the cylindrical surface inside the sintering mold.

3. The method for preparing liquid metal thermal conductive sheets using spark plasma sintering process according to claim 1, characterized in that: In step S5, the machining process involves grinding the surface to the required dimensions using a grinding machine, and then slicing it to the required thickness using an internal cylindrical cutter. Alternatively, machining can be performed by rolling the sintered billet to the required thickness using a rolling mill, followed by slicing using a slicing machine.

4. The method for preparing liquid metal thermal conductive sheets using spark plasma sintering process according to claim 1, characterized in that: In step S5, after machining, the liquid metal heat-conducting sheet is ground and polished to obtain a liquid metal heat-conducting sheet that meets the dimensional accuracy requirements.

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