Electron beam additive manufacturing method for preparing diamond / copper composite material through step-by-step powder laying and surface printing

Abstract

The invention relates to the technical field of additive manufacturing, in particular to a method for preparing a diamond / copper composite material layer by layer through electron beam surface printing. The diamond / copper composite material is obtained by adopting the arrangement that odd-numbered layers are diamond layers and even-numbered layers are copper powder layers, and adopting an electron beam surface exposure printing strategy for printing on the copper powder layers every time. The diamond / copper composite material is prepared through electron beam surface exposure printing, layer-by-layer alternate powder laying and copper powder layer melting, the problems that in the solid-phase sintering process, diamond distribution is uneven, and copper is difficult to fill evenly are solved, the step of material mixing is omitted, uneven material mixing caused by large physical property difference in the material mixing process is avoided, and the service life of the diamond / copper composite material is prolonged. The high-density and high-uniformity diamond / copper composite material is achieved, and the heat conductivity of the composite material is improved; and the efficiency and range of electron beam powder bed melting forming are improved, and heat management application industrial production can be achieved easily.

Description

Technical Field

[0001] The invention relates to the technical field of additive manufacturing, and in particular to a method for preparing a diamond / copper composite material layer by layer by electron beam surface printing. Background Art

[0002] As the integration and power density of high-power electronic devices continue to increase, the heat dissipation problem becomes more and more critical, and traditional heat dissipation materials are difficult to meet the demand. Diamond-based composite materials combine the high thermal conductivity and low thermal expansion coefficient of diamond with the excellent thermal and electrical conductivity and good mechanical processing properties of metals. They have many advantages and have broad application prospects in high-end technology electronic packaging fields such as national defense, military industry, aerospace, etc. Diamond-based composite materials represented by diamond / copper can theoretically have a thermal conductivity of more than 1000 W / m·K, which is 5 times that of third-generation heat sink materials such as SiC / Al composite materials. However, there are great differences in physical properties such as density, surface morphology, and fluidity between diamond and copper. When diamond particles are mixed with copper powder in traditional solid-phase sintering methods such as hot pressing, high temperature and high pressure, and spark plasma sintering, problems such as uneven mixing, stratification, and particle agglomeration will occur. During the consolidation process, it is difficult for copper powder to be filled between diamond particles only through plastic deformation, which affects the density and thermal conductivity of the final composite material. Secondly, the thermal expansion coefficients of diamond and metal are very different. During the cooling process of solid-phase sintering, stress will be generated due to thermal expansion mismatch, affecting the interface bonding, resulting in defects such as gaps and cracks, affecting the overall density and thermal conductivity of the composite material.

[0003] As a key representative of near-net-shape forming technology, powder bed fusion forming technology (PBF) uses a unique method of melting powder materials layer by layer to successfully transform three-dimensional digital models into physical components. Compared with traditional manufacturing processes, PBF technology can manufacture complex structures that are difficult to achieve with traditional processes in an integrated manner. This not only greatly expands the design freedom of parts, but also significantly reduces the probability of joint defects in parts, thereby effectively improving the overall performance and reliability of the product. Powder bed fusion additive manufacturing methods based on different energy sources can be divided into laser powder bed fusion technology (L-PBF) and electron beam powder bed fusion technology (EB-PBF). However, copper has the characteristics of high reflectivity and extremely low absorption rate of lasers. Diamond composites produced by L-PBF usually show low relative density (about 80-87%) and a large number of pores, which brings great difficulties to the forming of high volume content diamond composites.

[0004] Compared with L-PBF, EB-PBF, which uses electron beam as energy source, has higher energy utilization, powder absorption rate and forming efficiency. This processing method provides excellent conditions for the processing of brittle metals, high-temperature alloys and high-reflective materials. However, the electron beam point-by-point scanning method currently used results in a low forming efficiency. At the same time, this technology is restricted by the deflection range of the electron gun, and the forming range is relatively limited. Especially when the focused beam spot is reduced to improve accuracy, the deflection range of the electron gun will be further restricted, which to a certain extent affects the application scope and efficiency of this technology.

[0005] At present, there is no patent or research on electron beam printing of diamond composite materials layer by layer, but there are related research on surface printing photopolymerization and selective laser melting and related device research on electron beam surface printing. Therefore, the present invention uses electron beam flow to prepare diamond / copper composite materials by layer by layer printing, which solves the problem of uneven mixing in traditional solid phase sintering and improves the efficiency of electron beam printing. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing diamond / copper composite materials by high-efficiency electron beam additive manufacturing. The present invention adopts electron beam surface exposure printing, layer-by-layer alternating powder laying, and melting copper powder layers to prepare diamond / copper composite materials, which solves the problems of uneven distribution of diamond and difficulty in uniform filling of copper during solid phase sintering, eliminates the mixing step, avoids uneven mixing caused by large differences in physical properties during the mixing process, realizes high-density and high-uniformity diamond / copper composite materials, and improves the thermal conductivity of the composite materials; improves the efficiency and range of electron beam powder bed melting forming, which is conducive to the industrial production of thermal management applications.

[0007] The present invention proposes for the first time the arrangement of using odd-numbered layers as diamond layers and even-numbered layers as copper powder layers, and adopting the strategy of electron beam surface exposure printing on the copper powder layer each time, thereby obtaining a product with extremely excellent performance. In particular, when the diamond particle size is the same, the performance of the product obtained by the present invention is far superior to that of the prior art.

[0008] The invention solves the problem of uneven distribution of diamond and difficulty in uniform filling of copper during solid phase sintering, and improves the efficiency and range of electron beam powder bed melting forming. At the same time, the invention has relatively loose requirements on raw materials.

[0009] Preferably, the diamond has a coating layer on the surface, the coating layer element is selected from one or more of W, Cr, and Ti, the coating thickness is 20 nm-5 μm, preferably 20-40 nm; the coated diamond particle size is 30-400 μm. In order to facilitate subsequent processing and achieve "high power density" and "high integration", preferably, in the present invention, the coated diamond particle size is preferably 50-80 μm, of course, other particle sizes within the scope of the present invention are also applicable to the present invention. In the process designed by the present invention, the diamond particle size is too large, the specific surface area is small, and the driving force for the interface bonding between diamond and copper is insufficient, which will affect the final performance of the product. In the present invention, the diamond particle size is too small, and agglomeration is likely to occur during the preheating process, which affects the melting and filling of copper powder between diamond particles.

[0010] Preferably, the copper powder used has a particle size of 20-40 μm and a purity of >99.95%.

[0011] Preferably, the electron beam powder bed melting device is first evacuated, and then the base plate is preheated at a temperature of 400-600° C. After preheating, a diamond layer is laid on the base plate, and then a copper powder layer is laid, and the copper powder layer is melted in its entirety by an electron beam surface exposure device, with an electron beam current of 10-18 mA and an electron beam current duration of 0.5-2 s, to form a first layer of diamond / copper composite material layer;

[0012] The above steps are repeated with the first diamond / copper composite material layer to prepare the next diamond / copper composite material layer until the desired thickness of the diamond / copper composite material is reached.

[0013] In the present invention, if the preheating temperature is too low and the cooling speed is too fast, the thermal expansion coefficients of diamond and copper will differ greatly, which will lead to a decrease in the interface bonding ability during the cooling process, resulting in defects such as cracks and gaps; if the preheating temperature is too high, a sintering neck will form between the copper powders, affecting the uniform powder spreading of the scraper.

[0014] The current used for baseplate preheating is 10-30 mA and the time is 5-10 s.

[0015] The thickness of the single-layer diamond powder is 30-100 μm, preferably 60-90 μm.

[0016] The thickness of the single-layer copper powder is 30-100 μm, preferably 60-90 μm. The present invention controls the thickness of the single-layer copper powder to be 30-100 μm in order to control the copper content in the diamond copper composite material, and to efficiently prepare a diamond copper composite material with good microstructure and uniform distribution of diamond particles and copper by cooperating with the electron beam surface exposure printing process parameters.

[0017] The electron beam surface exposure printing with appropriate parameters selected by the present invention can avoid uneven distribution of diamond and copper powder during solid phase sintering during the preparation process, and achieve high density and high thermal conductivity of the diamond / copper composite material. Secondly, compared with the traditional point-by-point scanning method, electron beam surface exposure printing greatly improves production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of the process designed for the present invention;

[0019] Figure 2 is the SEM image of the product obtained in Example 1;

[0020] Figure 3 This is the SEM image of the product obtained in Comparative Example 3;

[0021] Figure 4 This is the SEM image of the product obtained in Comparative Example 4. DETAILED DESCRIPTION

[0022] Example 1

[0023] 1. Material preparation

[0024] (1) Prepare high-purity copper powder: Select high-purity copper powder with a particle size range of 20-40 μm, purity > 99.95%, and high sphericity;

[0025] (2) Preparation of diamond powder: Select HFD-C diamond particles with a particle size range of 45-53 μm, and use magnetron sputtering to plate tungsten with a tungsten coating thickness of 20-40 nm;

[0026] 2. Electron beam surface printing

[0027] (1) Preheating: The substrate preheating temperature is 500°C, the substrate material is 316L stainless steel, the substrate preheating current is 15 mA, and the time is 10 min.

[0028] (2) Powder spreading: Double powder spreading device, first spread a layer of diamond powder with a thickness of 60 μm, then spread a layer of high-purity copper powder with a thickness of 60 μm;

[0029] (3) Forming: The electron beam surface exposure with a current of 15 mA and a holding time of 1 s is used for forming. The preparation steps of the first layer are repeated to prepare the next layer of diamond / copper composite material until the desired thickness of the diamond / copper composite material is about 3 mm.

[0030] 3. Sample characterization and analysis

[0031] The characterization diagram of the sample obtained in Example 1 is as follows: Figure 2The sample obtained in Example 1 has good macroscopic formability, a density of up to 99%, and in the microstructural morphology observation, the diamond is evenly distributed, the copper filling state is good, the interface bonding state of copper and diamond is good, and the thermal conductivity of the sample is as high as 700 W / mK.

[0032] Example 2

[0033] 1. Material Preparation

[0034] Prepare high-purity copper powder: Select high-purity copper powder with a particle size range of 20-40 μm, purity > 99.95%, and high sphericity;

[0035] Prepare diamond powder: select HFD-C diamond particles with a particle size range of 45-53 μm, and use magnetron sputtering to plate titanium with a titanium coating thickness of 20-40 nm;

[0036] 2. Electron beam surface printing

[0037] Preheating: The substrate preheating temperature is 500°C, the substrate material is 316L stainless steel, the substrate preheating current is 15mA, and the time is 10 min.

[0038] Powder spreading: Double powder spreading device, first spread a layer of diamond powder, layer thickness 50 μm, then spread a layer of high-purity copper powder, layer thickness 50 μm;

[0039] Forming: Electron beam surface exposure with a current of 15 mA and a holding time of 1 s is used for forming. Repeat the preparation steps of the first layer to prepare the next layer of diamond / copper composite material until the desired thickness of the diamond / copper composite material is about 3 mm.

[0040] 3. Sample Characterization and Analysis

[0041] The sample obtained in Example 2 has good macroscopic formability and a density of 98%. In the microstructural morphology observation, the diamond is evenly distributed, the copper filling state is good, the interface bonding state between copper and diamond is good, and the thermal conductivity of the sample is 654W / mK.

[0042] Example 3

[0043] 1. Material preparation

[0044] Prepare high-purity copper powder: Select high-purity copper powder with a particle size range of 20-40 μm, purity > 99.95%, and high sphericity;

[0045] Prepare diamond powder: select HFD-C diamond particles with a particle size range of 45-53 μm, and use magnetron sputtering to plate chromium with a chromium coating thickness of 20-40 nm;

[0046] 2. Electron beam surface printing

[0047] Preheating: The substrate preheating temperature is 500°C, the substrate material is 316L stainless steel, the substrate preheating current is 15mA, and the time is 10 min.

[0048] Powder spreading: Double powder spreading device, first spread a layer of diamond powder, layer thickness 55 μm, then spread a layer of high-purity copper powder, layer thickness 55 μm;

[0049] Forming: Electron beam surface exposure with a current of 15 mA and a holding time of 1 s is used for forming. Repeat the preparation steps of the first layer to prepare the next layer of diamond / copper composite material until the desired thickness of the diamond / copper composite material is about 3 mm.

[0050] 3. Sample characterization and analysis

[0051] The sample obtained in Example 3 has good macroscopic formability and a density of 99%. In the microstructural morphology observation, the diamond is evenly distributed, the copper filling state is good, the interface bonding state of copper and diamond is good, and the thermal conductivity of the sample is 687W / mK.

[0052] Comparative Example 1

[0053] The other conditions are the same as those in Example 1, except that the thickness of the copper powder in step 2 is 150 μm.

[0054] Sample characterization and analysis: Scanning electron microscopy showed that the diamond particles were dispersed, there was too much copper between the diamond particles, some copper powder was granular, there were a lot of pores, and the density of the composite material was about 84%. This indicates that the copper powder was too thick, and the copper powder at the bottom could not be melted during electron beam irradiation, affecting the density and performance of the diamond / copper composite material. Due to the poor organizational morphology and density of the sample, its thermal conductivity was not measured.

[0055] Comparative Example 2

[0056] Other conditions were the same as those in Example 1, except that the electron beam current was 20 mA during the electron beam surface printing process. The density of the obtained product was about 87%.

[0057] Sample characterization and analysis: Scanning electron microscopy showed that the sample had defects such as depressions and protrusions, and the diamonds were unevenly distributed and the interface was deformed, indicating that the diamonds may have graphitized. This indicates that the electron beam current is too large and the input energy density is too high, causing significant thermal damage to the diamonds and affecting the performance of the composite material. Due to the poor organizational morphology and density of the sample, its thermal conductivity was not measured.

[0058] Comparative Example 3

[0059] The other conditions are the same as those in Example 1, except that the thickness of the copper powder in step 2 is 15 μm.

[0060] The characterization diagram of the sample obtained in Comparative Example 3 is as follows: Figure 3 As shown. Sample characterization and analysis: Scanning electron microscopy showed that the diamond was exposed and the interface was deformed, graphitization may have occurred, and there were pores on the sample surface. The density of the composite material was about 81%. This indicates that the copper powder was too thin, and the electron beam irradiation caused certain thermal damage to the diamond, affecting the density and performance of the diamond / copper composite material. Due to the poor organizational morphology and density of the sample, its thermal conductivity was not measured.

[0061] Comparative Example 4

[0062] Other conditions are the same as those in Example 1, except that: high-purity copper powder and diamond powder are mixed evenly, the mixed powder is laid into a layer of 60 microns, and then electron beam surface exposure is performed with a current of 15 mA and a holding time of 1 second; the thermal conductivity of the obtained sample is less than 400 W / mK. The density of the obtained product is about 90%.

[0063] The characterization diagram of the sample obtained in Comparative Example 4 is as follows: Figure 4 Sample characterization and analysis: Scanning electron microscopy was used to observe the part close to the first layer, and it was found that the diamond was unevenly distributed, indicating that when the first layer of powder is a mixed powder, the same uneven mixing situation as in solid phase sintering will occur. This means that the first layer of powder can only be diamond powder.

Claims

1. An electron beam additive manufacturing method for preparing diamond / copper composite materials by step-by-step powder spreading and surface printing, characterized in that: From bottom to top, the odd-numbered layers are diamond layers and the even-numbered layers are copper powder layers. Each time printing is performed on the copper powder layer, an electron beam surface exposure printing strategy is adopted to obtain a diamond / copper composite material.

2. The electron beam additive manufacturing method for preparing diamond / copper composite materials by step-by-step powder spreading and surface printing according to claim 1, characterized in that: The diamond has a coating layer on the surface, the coating layer element is selected from one or more of W, Ti, and Zr, the coating thickness is 20 nm-5 μm, preferably 20-40 nm; the coated diamond particle size is 30-400 μm, preferably 50-80 μm.

3. The electron beam additive manufacturing method for preparing diamond / copper composite materials by step-by-step powder spreading and surface printing according to claim 1, characterized in that: The copper powder used has a particle size of 20-40 μm and a purity of >99.95%.

4. The electron beam additive manufacturing method for preparing diamond / copper composite materials by step-by-step powder spreading and surface printing according to claim 1, characterized in that: First, the electron beam powder bed melting equipment is evacuated, and then the base plate is preheated at a temperature of 400-600°C. After preheating, a diamond layer is laid on the base plate, and then a copper powder layer is laid. The copper powder layer is melted by an electron beam surface exposure device, with an electron beam current of 10-18 mA and an electron beam current duration of 0.5-2 s to form the first diamond / copper composite material layer; The above steps are repeated with the first diamond / copper composite material layer to prepare the next diamond / copper composite material layer until the desired thickness of the diamond / copper composite material is reached.

5. The electron beam additive manufacturing method for preparing diamond / copper composite materials by step-by-step powder spreading and surface printing according to claim 1, characterized in that: The current used for baseplate preheating is 10-30 mA and the time is 5-10 s.

6. The electron beam additive manufacturing method for preparing diamond / copper composite materials by step-by-step powder spreading and surface printing according to claim 1, characterized in that: The thickness of the single-layer diamond powder is 30-100 μm, preferably 60-90 μm.

7. The electron beam additive manufacturing method for preparing diamond / copper composite materials by step-by-step powder spreading and surface printing according to claim 1, characterized in that: The thickness of the single-layer copper powder is 30-100 μm, preferably 60-90 μm.

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