Functionally gradient composite material, power module and article having dissimilar material joining part, and method for producing functionally gradient composite material

Abstract

The functionally gradient composite material (111) is constituted by a plurality of at least two types of materials including a matrix (121). In the functionally gradient composite material (111), a second phase (122) of a material, that is different from the material constituting the matrix (121) which serves as a first phase, is present in the matrix (121). In a cross-sectional view, the functionally gradient composite material (111) includes a region in which the area ratio of the shape of the second phase (122) decreases in one direction (A), and the second phase (122) is mesh-shaped.

Description

Gradient functional composite material, power module and article having a joint of different materials, and method for producing gradient functional composite material 【0001】 The present disclosure relates to a gradient functional composite material, a power module and an article having a joint of different materials, and a method for producing a gradient functional composite material. 【0002】 In products such as power modules and artificial satellites that have heat generating parts and require heat control under constraints such as insulation and light weight, different materials are often joined and used together. In the vicinity of the joint of different materials, when a temperature change occurs, thermal stress is generated due to the difference in thermal expansion of the materials. When the thermal stress increases, peeling is likely to occur at the joint, so a technique for relaxing the thermal stress is required. 【0003】 For example, Patent Document 1 below discloses a technique for inclining the coefficient of thermal expansion in the vicinity of a joint by changing the mixing ratio of Al and SiC stepwise or continuously at the joint between an Al-based metal layer and a composite layer in which particles mainly composed of SiC are dispersed in an Al-based metal matrix. 【0004】 Patent Document 2 also discloses a technique for inclining physical properties by forming a porous body made of a metal in which voids gradually change in a specific direction in the production of a ceramics-metal-based gradient functional material, and press-fitting a slurry of ceramic powder into the voids. 【0005】 Japanese Patent Application Laid-Open No. 2001-335859, Japanese Patent Application Laid-Open No. 06-25775 【0006】 By using a gradient functional composite material with inclined physical properties, it is possible to reduce the difference in thermal expansion in the vicinity of the joint of different materials and relieve thermal stress. However, the gradient functional composite material has problems such as a decrease in thermal conductivity and strength. 【0007】For example, a graded functional composite material formed by mixing particles, as in Patent Document 1, has many heterogeneous interfaces, and these interfaces act as thermal resistance, resulting in low thermal conductivity and insufficient mitigation of the effects of temperature changes. Furthermore, if a graded functional composite material is formed using a component in which materials are joined on the order of mm or more, rather than using a graded material in which materials are mixed on the order of μm (for example, a component in which the distribution of holes in perforated metal is graded and those holes are filled with another material), the area of ​​heterogeneous interfaces can be reduced and thermal conductivity can be increased, but the strength is reduced because fracture due to differences in thermal expansion at the interfaces is more likely to occur. 【0008】 As described in Patent Document 2, a graded functional composite material formed using a porous material suffers from a decrease in thermal conductivity because unconnected pores remain as voids. Furthermore, since these voids can become fracture initiation points, a decrease in strength is also a concern. 【0009】 Thus, conventional technology has the challenge of not being able to achieve both thermal stress relief by reducing the difference in thermal expansion and a balance between thermal conductivity and strength. 【0010】 This disclosure is made to solve the above-mentioned problems and aims to provide a graded functional composite material that can relieve thermal stress while suppressing a decrease in thermal conductivity and strength. 【0011】 The functionally graded composite material according to this disclosure is a functionally graded composite material composed of at least two types of materials including a matrix, wherein a second phase of a material different from the materials constituting the matrix exists within the matrix as a first phase, and in a cross-sectional view, it includes a region in which the area ratio of the shape of the second phase decreases in one direction, and the second phase is mesh-like. 【0012】 The functionally graded composite material described herein can relieve thermal stress while suppressing a decrease in thermal conductivity and strength. 【0013】Figure 1 is a schematic diagram of a power module according to Embodiment 1. Figure 2 is an enlarged view of the dissimilar material joint in the power module according to Embodiment 1. Figure 3 is a schematic diagram of a cross-section in the thickness direction of the gradient functional composite material according to Embodiment 1. Figure 4 is a graph showing the change in the area ratio of the second phase in the thickness direction of the gradient functional composite material according to Embodiment 1. Figure 5 is a schematic diagram of a cross-section in the thickness direction of the gradient functional composite material according to Embodiment 2. 【0014】 <Embodiment 1> Figure 1 is a schematic diagram of a power module 1 according to Embodiment 1. The power module 1 comprises an insulating substrate 3 on which semiconductor elements 2 are mounted, and a base plate 4 on which the insulating substrate 3 is mounted. A case 5 for housing the semiconductor elements 2 and the insulating substrate 3 is bonded to the base plate 4, and a sealing resin 6 for sealing the semiconductor elements 2 and the insulating substrate 3 is filled inside the case 5. A heat sink 7 is also bonded to the lower surface of the base plate 4. 【0015】 Power module 1 is merely one example of an article to which the gradient function composite material according to Embodiment 1 is applied. In other words, the application of the gradient function composite material according to Embodiment 1 is not limited to power module 1, but can be applied to any other article. Furthermore, the structure of power module 1 to which the gradient function composite material according to Embodiment 1 is applied is not limited to that shown in Figure 1. 【0016】 In this embodiment, the joint between the base plate 4 and the insulating substrate 3 of the power module 1 becomes a dissimilar material joint 11 to which a gradient functional composite material is applied. Figure 2 shows an enlarged view of the dissimilar material joint 11. As shown in Figure 2, the dissimilar material joint 11 has a structure in which a metal plate 113, which is the base plate 4, and a ceramic plate 112, which is the insulating substrate 3, are joined via a gradient functional composite material 111. Direction A shown in Figure 2 indicates the thickness direction of the gradient functional composite material 111. In the dissimilar material joint 11, the metal plate 113, the gradient functional composite material 111, and the ceramic plate 112 are joined by brazing. In this embodiment, the metal plate 113 is made of aluminum alloy, and the ceramic plate 112 is made of alumina. 【0017】Figure 3 shows a schematic diagram of a cross-section of the gradient functional composite material 111 along the thickness direction (direction A). The gradient functional composite material 111 is a composite material composed of at least two types of materials, including a matrix 121. Inside the first phase, the matrix 121, there exists a second phase 122 made of a material different from the materials that make up the matrix 121. The gradient functional composite material 111 has a three-dimensional shape that includes a region in which the area ratio of the second phase 122 decreases in one direction. In addition, in the cross-section along direction A, the shape of the second phase 122 is mesh-like. 【0018】 In this embodiment, the gradient functional composite material 111 is composed of two types of materials: the first phase, the matrix 121, is made of an aluminum alloy, and the second phase 122 is made of alumina. In this case, the gradient functional composite material 111 includes a region in which the area ratio of the second phase 122 decreases from the ceramic plate 112 side towards the metal plate 113 side. The thickness of the gradient functional composite material 111 is 2 mm. 【0019】 Figure 4 is a graph showing the relationship between the position of the dissimilar material joint 11 in the thickness direction (direction A) and the area ratio of the second phase 122 in a cross section perpendicular to direction A. In Figure 4, the position in direction A is shown as a ratio to the thickness of the dissimilar material joint 11, with the interface between the dissimilar material joint 11 and the ceramic plate 112 set as 0. It can be seen that the amount of the second phase 122 decreases as the distance from the interface between the dissimilar material joint 11 and the ceramic plate 112 increases. 【0020】 The presence of voids in the graded functional composite material 111 causes a decrease in thermal conductivity and strength. Therefore, it is preferable that the area ratio of voids in the graded functional composite material 111 be less than 5%, including 0%. If the area ratio of voids is less than 5%, the decrease in thermal conductivity and strength can be suppressed. 【0021】 In the gradient functional composite material 111 according to this embodiment, the area ratio of the second phase 122 in a cross section perpendicular to direction A changes along direction A. Therefore, the thermal expansion coefficient of the dissimilar material joint 11 in the direction perpendicular to direction A changes along direction A. That is, the gradient functional composite material 111 has a thermal expansion coefficient that is gradient along direction A. 【0022】On the ceramic plate 112 side of the gradient-functional composite material 111, the area ratio of alumina is high, resulting in a small difference in thermal expansion with the ceramic plate 112. On the metal plate 113 side of the gradient-functional composite material 111, the area ratio of alumina is low, resulting in a small difference in thermal expansion with the metal plate 113. As a result, the gradient-functional composite material 111 can alleviate thermal stress by mitigating the difference in thermal expansion between the metal plate 113 and the ceramic plate 112. 【0023】 As described above, graded functional composite materials, which are made by mixing particles, have many heterogeneous interfaces, and these interfaces act as thermal resistance, resulting in low thermal conductivity and insufficient mitigation of the effects of temperature changes. In contrast, in the graded functional composite material 111 according to this embodiment, the shape of the second phase 122 is a continuous mesh shape, so the area of ​​heterogeneous interfaces where the aluminum alloy and ceramic are in contact is small, and high thermal conductivity can be obtained. Furthermore, because the matrix 121 and the second phase 122 are intertwined, the effect of shape constraint on deformation (hereinafter referred to as "deformation constraint effect") reduces thermal stress caused by differences in thermal expansion, and high strength can be obtained. 【0024】 These effects are due to the shapes of the matrix 121 and the second phase 122, and the influence of these shapes can be quantitatively demonstrated by the characteristics of the cross-section perpendicular to direction A and the characteristics of the cross-section along direction A. 【0025】 As described later, the second phase 122 is integrally formed by inserting the raw material for the second phase 122 into a mold, forming the second phase 122, and then removing the mold. The continuous shape of the second phase 122 can be confirmed by the presence of the second phase 122 in any cross-section (all cross-sections) in direction A. This can also be confirmed by the number of second phase 122 particles in a given volume. 【0026】The fact that the second phase 122 is mesh-like and provides high strength can be confirmed by two methods based on the characteristics of the cross section perpendicular to direction A and the cross section along direction A. The first method is to confirm this by examining the equivalent circular diameter of the second phase 122 in the cross section perpendicular to direction A where the area ratio of the second phase 122 is the median value. The second method is to confirm this by examining the average of the shortest distances from the point in the second phase 122 furthest from the matrix 121 to the matrix 121 in the cross section along direction A. 【0027】 The inventors of the technology relating to this disclosure confirmed the shape characteristics of the second phase 122 in the gradient functional composite material 111 according to this embodiment from secondary electron images obtained by a Scanning Electron Microscope (SEM). The gradient functional composite material 111 was cut to have a cross section perpendicular to direction A or a cross section along direction A, and the cross section was observed with an SEM after being finished by sanding and buffing. 【0028】 To confirm the presence of the second phase 122 in any cross-section in direction A, four samples were prepared, each obtained from a different cross-section along direction A, and 40 mm was measured for each sample. ２ This was done by observing the region. 【0029】 The confirmation that the second phase 122 is mesh-like was carried out using the first and second methods described above. 【0030】 In the first method, first, an observation image of the cross-section of the dissimilar material joint 11 along direction A was image-processed, and the matrix 121 of the observation image and the second phase 122 were binarized. The binarized observation image was divided into 10 parts along direction A, and the area ratio of the second phase 122 in each region was calculated, and the change in the area ratio of the second phase 122 in direction A was calculated. Then, at the position where the area ratio was the median value, the gradient functional composite material 111 was cut in a direction perpendicular to direction A, and the 100 mm of the cross-section was measured. ２Observation images of the region were obtained. These observation images were binarized by image processing between the matrix 121 and the second phase 122, and the equivalent circle diameter (the diameter of a true circle corresponding to the area of ​​the region) for each region of the second phase 122 was calculated, and the average value was taken as the equivalent circle diameter of the second phase 122 in that cross section. In the gradient functional composite material 111 according to this embodiment, the equivalent circle diameter of the second phase 122 was 212 μm in the cross section where the area ratio of the second phase 122 in direction A was the median value. 【0031】 The smaller the equivalent diameter of the second phase 122, the thinner the continuity of the second phase 122. When the equivalent diameter of the second phase 122 is 20 μm or less, the thermal conductivity decreases, so the lower limit of the equivalent diameter of the second phase 122 is set to 20 μm. Also, the larger the equivalent diameter of the second phase 122, the weaker the deformation restraint effect becomes. When the equivalent diameter of the second phase 122 is 5000 μm or more, the deformation restraint effect cannot be obtained, so the upper limit of the equivalent diameter of the second phase 122 is set to 5000 μm. More preferably, the lower limit of the equivalent diameter of the second phase 122 is 50 μm and the upper limit is 3000 μm. Even more preferably, the lower limit is 100 μm and the upper limit is 2000 μm. 【0032】 In the second method, first, the optical microscope image of the cross-section of the gradient functional composite material 111 along direction A is used to observe the 10 mm ２ The region was observed, and for each region of the second phase 122, the point where the shortest distance to the matrix 121 was largest was found, that distance was measured, and the average value of the distances measured in all regions was calculated. In the gradient functional composite material 111 according to this embodiment, in a cross section along direction A, the average value of the shortest distance from the point in the second phase 122 furthest from the matrix 121 to the matrix 121 was 188 μm. Since the thermal conductivity decreases when the average value of this distance is 10 μm or less, the lower limit of the average value of this distance is set to 10 μm. Also, since the deformation restraint effect cannot be obtained when the average value of this distance is 5000 μm or more, the upper limit of the average value of this distance is set to 5000 μm. More preferably, the lower limit of the average value of this distance is 30 μm and the upper limit is 3000 μm. Even more preferably, the lower limit is 50 μm and the upper limit is 1000 μm. 【0033】The continuity of the shape of the second phase 122 was confirmed by measuring the number of second phase 122 particles. First, the gradient functional composite material 111 was cut out so that the cross-section perpendicular to direction A was a 10 mm x 10 mm square. Then, using a method in which the matrix 121 was dissolved but the second phase 122 was not, the second phase 122 was extracted from the gradient functional composite material 111 by dissolving only the matrix 121. As in this embodiment, if the matrix 121 is an aluminum alloy and the second phase 122 is alumina, the iodine-methanol method can be used to dissolve only the matrix 121 and extract the second phase 122. The number of divisions of the second phase 122 is then calculated by counting the number of self-supporting extracted second phase 122 particles. For example, if 2 of the extracted second phase 122 particles are self-supporting, the number of second phase 122 particles is 2; if 10 particles are self-supporting, the number of second phase 122 particles is 10. In the gradient functional composite material 111 according to this embodiment, the number of second phases 122 was one. The fewer the number of second phases 122, the higher the thermal conductivity, with one being the lower limit. If the number of second phases 122 exceeds 15, the effect of improving thermal conductivity cannot be obtained, so the upper limit is set to 15. More preferably, the upper limit of the number of second phases 122 is 10, and even more preferably, the upper limit is 8. 【0034】 As described above, it is preferable that the area ratio of voids in the gradient-functional composite material 111 is less than 5%. The area ratio of voids in the gradient-functional composite material 111 can be confirmed by sanding and buffing a cross section of the gradient-functional composite material 111 along direction A, and observing the cross section with an optical microscope. In the observed image, black areas that are different from the matrix 121 and the second phase 122 are identified as voids, and the observed image is binarized into black areas and non-black areas by image processing, and the area ratio of the black areas is calculated to determine the area ratio of the voids. 【0035】 Here, we will describe the manufacturing method of the gradient function composite material 111 according to this embodiment. 【0036】First, the shape of the second phase 122 is designed so that it has a mesh-like structure and a three-dimensional shape that includes a region in which the area ratio of the second phase 122 decreases in one direction corresponding to direction A. Specifically, a three-dimensional shape electronic data, which is a CAD model of the mesh shape of the second phase 122, is created. 【0037】 Next, the CAD model of the second phase 122 is inverted using a Boolean operation to obtain the three-dimensional shape electronic data, which is the CAD model of the second phase 122 mold. Then, a mold is fabricated using a stereolithography type 3D printer and a UV-curing resin specifically for stereolithography. 【0038】 Alumina paste is poured into the molded shape, dried, and hardened to form a second phase 122 inside the mold. Then, the mold is dissolved by immersion in acetone and removed from the second phase 122 to obtain a second phase 122 made of alumina. Molten aluminum alloy is pressure-impregnated into the obtained second phase 122 to form a matrix 121, and the excess aluminum alloy region is removed by machining to obtain a gradient functional composite material 111. 【0039】 In the gradient-function composite material 111 according to this embodiment, the matrix 121 is an aluminum alloy and the second phase 122 is alumina, but the materials of the matrix 121 and the second phase 122 are not limited to these. The material of the matrix 121 may be a metal other than aluminum, such as copper or magnesium, or a thermoplastic resin such as nylon or PEEK, a thermosetting resin such as epoxy resin or cyanate resin, an elastomer, or a ceramic material such as silicon nitride or aluminum nitride. The material of the second phase 122 may be a ceramic material such as silicon nitride or aluminum nitride, or a metal such as aluminum or copper, a thermoplastic resin such as nylon or PEEK, a thermosetting resin such as epoxy resin or cyanate resin, or an elastomer, as long as it is a different material from the matrix 121. 【0040】When a light metal such as an aluminum alloy or a magnesium alloy is used for the matrix 121 and a ceramic is used for the second phase 122, the gradient functional composite material 111 can be given lightweight properties. Furthermore, when an aluminum alloy or a magnesium alloy is used for the matrix 121, in addition to improving the thermal conductivity of the gradient functional composite material 111, the molten metal temperature of the matrix 121 can be lowered, so that the productivity can be improved. 【0041】 In FIG. 3, the network-like second phase 122 has a periodic structure in the direction perpendicular to the direction A, but the structure of the second phase 122 does not have to be periodic. In the direction perpendicular to the direction A, the structure of the second phase 122 and the distribution of the area ratio of the second phase 122 may change. 【0042】 Also, in the manufacturing method of the gradient functional composite material 111 described above, the CAD of the mold of the second phase 122 was created by Boolean operation and shaped by a 3D printer to obtain a mold. However, for example, a mold may be manufactured from a shaped object of the shape of the second phase 122 using a sand mold or the like. Further, the 3D printer for shaping the mold is not limited to the stereolithography type, and may be a fused deposition modeling (FDM) type, a filament fused fabrication (FFF) type, a selective laser sintering (SLS) type, or the like. Also, instead of the UV curable resin, a resin cured by another method such as heat or magnetic field, or a thermoplastic resin may be used, and metal may be used as long as the mold can be removed. 【0043】 The step of impregnating the second phase 122 with the material of the matrix 121 was performed by pressure impregnation, but as long as the voids can be made less than 5%, the atmosphere during impregnation may be atmospheric pressure or a vacuum state. Also, since the outside of the region of the second phase 122 becomes a single-phase region of the matrix 121, this is removed by machining in the above manufacturing process. However, for the purpose of cost reduction by reducing machining costs, etc., as long as there are no problems in terms of characteristics, a single-phase region of the matrix 121 may partially remain in the gradient functional composite material 111. 【0044】In this embodiment, a power module is shown as an article to which the gradient functional composite material 111 is applied. However, the gradient functional composite material 111 can also be applied to other articles. For example, in the joint of mission equipment of a satellite, especially when lightweight is emphasized, the mission equipment is joined to a CFRP (Carbon Fiber Reinforced Plastics) structural member. Since CFRP has a lower coefficient of thermal expansion than the mission equipment, the gradient functional composite material 111 can be applied to the joint portion. 【0045】 The thermal stress at the joint of dissimilar materials may increase when the temperature gradient in the vicinity of the joint is large. For example, in the case of local heating or heating with a large amount of heat input such as combustion, its heat transfer, electric heating, induction heating, and aerodynamic heating, a large temperature distribution is formed at the dissimilar material joint, and in this case, the gradient functional composite material 111 can particularly exhibit its effect. 【0046】 <Embodiment 2> FIG. 5 is a schematic cross-sectional view of the gradient functional composite material 111 according to Embodiment 2 in the thickness direction (direction A). The gradient functional composite material 111 according to Embodiment 2 has a structure in which the second phase 122 is divided in the direction A. In FIG. 5, the second phase 122 is divided into three in the direction A. In FIG. 5, in order to emphasize that the second phase 122 is divided, the interval between the second phases 122 is widened for illustration, but actually, the gap between the second phases 122 is so small that it cannot be visually distinguished. Since other configurations of the gradient functional composite material 111 are the same as those in Embodiment 1, the description here is omitted. 【0047】 According to the gradient functional composite material 111 according to Embodiment 2, since the second phase 122 is divided into a plurality of parts, the destruction of the second phase 122 can be suppressed in the pressurization process for impregnating the matrix 121 material into the second phase 122. Therefore, the degree of freedom in setting conditions in the pressurization process can be improved. However, it should be noted that compared with the gradient functional composite material 111 of Embodiment 1, since the number of the second phases 122 increases, it is disadvantageous from the viewpoint of thermal conductivity. 【0048】In the production of the gradient-function composite material 111 according to Embodiment 2, an FDM type 3D printer was used to fabricate the mold for the second phase 122, PLA (Poly Lactic Acid) containing carbon fibers was used as the filament, and THF (Tetrahydrofuran) was used to dissolve the mold. By using a filament containing carbon fibers, the amount of resin to be dissolved can be reduced, and the second phase 122 can be easily extracted. 【0049】 Furthermore, it is possible to freely combine each embodiment, or to modify or omit each embodiment as appropriate. 【0050】 1 Power module, 2 Semiconductor element, 3 Insulating substrate, 4 Base plate, 5 Case, 6 Sealing resin, 7 Heat sink, 11 Dissimilar material joint, 111 Functionally graded composite material, 112 Ceramic plate, 113 Metal plate, 121 Matrix, 122 Second phase.

Claims

1. A functionally graded composite material comprising at least two types of materials including a matrix, wherein a second phase of a material different from the materials constituting the matrix exists within the matrix as a first phase, and in a cross-sectional view, it includes a region in which the area ratio of the shape of the second phase decreases in one direction, and the second phase is mesh-like.

2. The gradient functional composite material according to claim 1, comprising the second phase in any cross section perpendicular to the one direction.

3. The functionally graded composite material according to claim 1 or 2, wherein, in a cross-section along the one direction, the average value of the shortest distance between the point furthest from the matrix in the second phase and the matrix is ​​10 μm or more and 5000 μm or less.

4. A graded functional composite material according to any one of claims 1 to 3, wherein in a cross section perpendicular to the one direction, where the area ratio of the second phase is the median value, the average value of the equivalent circular diameter of the second phase is 20 μm or more and 5000 μm or less.

5. The gradient functional composite material according to any one of claims 1 to 4, wherein the number of second phases in a cross-sectional area of ​​10 mm × 10 mm perpendicular to one direction is 1 or more and 15 or less.

6. A graded functional composite material according to any one of claims 1 to 5, wherein the area ratio of voids is less than 5%, including 0%.

7. The functionally graded composite material according to any one of claims 1 to 6, wherein the matrix is ​​a light metal and the second phase is a ceramic.

8. A power module having a dissimilar material joint containing a gradient functional composite material as described in any one of claims 1 to 7.

9. An article having a dissimilar material joint containing a gradient functional composite material as described in any one of claims 1 to 7.

10. A method for manufacturing a functionally graded composite material comprising at least two types of materials including a matrix, wherein a second phase of a material different from the materials constituting the matrix exists within the matrix as a first phase, comprising: forming a mold for the second phase such that the second phase has a three-dimensional shape including a mesh-like structure and regions in which the area ratio decreases in one direction; forming the second phase inside the mold by inserting the material for the second phase into the mold; removing the mold from the second phase; and forming the functionally graded composite material by impregnating the second phase with the matrix in a molten state.

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