High-strength and high-thermal-conductivity copper alloy

Abstract

The invention discloses a high-strength and high-thermal-conductivity copper alloy. The copper alloy is composed of a copper matrix and a second phase. Wherein the copper matrix is composed of a plurality of copper grains close to pure copper, the size of the copper grains is smaller than 400 nm, and fine grain strengthening is formed; and the second phase is clamped among the copper grains in a thin film form to partially wrap the copper grains, and the thickness of the thin film is less than 10nm. The heat conductivity of the second-phase material is higher than that of pure copper, so that the heat transfer rate among copper grains is ensured, and the heat-conducting property of the copper alloy is improved; or the second-phase solid solution copper element forms a doped semiconductor, under the condition that the thickness of the thin film is limited, a semiconductor tunneling effect occurs, and hot electrons of a copper matrix effectively penetrate through the second-phase thin film to be injected into adjacent copper crystal grains in a degenerate energy level state, so that the interface thermal resistance is kept at a low level, and the high thermal conductivity is obtained. The high-strength and high-thermal-conductivity copper alloy disclosed by the invention can meet the use requirements of thermal management materials for important structures.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy materials, and particularly relates to a copper alloy with high strength and high thermal conductivity. Background Art

[0002] Copper and copper alloys are structural and functional materials with excellent mechanical and physical properties, and are widely used in the fields of power electronics, aerospace, national defense, and automobiles. High-strength and high-conductivity copper alloys, especially high-strength and high-thermal-conductivity copper alloys, are important thermal management materials for structural applications. The development of science and technology and industry has continuously put forward higher requirements for the comprehensive properties of high-strength and high-thermal-conductivity copper alloys, prompting materials designers to develop new copper alloys with more excellent properties.

[0003] However, there is often a contradiction between the strength and thermal conductivity of copper alloys, and it is difficult to have both. For alloy materials, the main ways to improve the strength of alloys include solid solution strengthening, fine grain strengthening, dislocation strengthening, and second-phase strengthening. These strengthening methods can significantly improve the strength of alloys and have been successful in many copper alloy systems.

[0004] For example, the patent with application number 201110023963.X discloses a solid solution deformation strengthening and aging strengthening process method for a beryllium bronze alloy. A large number of fine grains precipitate during the thermomechanical treatment process, thereby greatly improving the strength of the copper alloy. In particular, it solves the problem of low strength of some copper alloys, and a high-strength bulk copper alloy with a hardness of up to 423 HV can be obtained.

[0005] The patent with application number 201110297534.1 discloses a microalloy-strengthened copper alloy containing rare earths for an electric motor rotor and its preparation method. Pure microalloying strengthening elements such as silicon, iron, mixed rare earth alloy, and boron are added to copper. The silicon content is 0.18% - 2.0%, iron is 0.5% - 1.0%, the mixed rare earth alloy is 0.08% - 0.36%, boron is 0.001% - 0.01%, trace impurities, and the balance is copper. By adding microalloying strengthening elements such as silicon, iron, mixed rare earth alloy, and boron to the copper matrix, the comprehensive requirements for mechanical properties and electrical conductivity in material use are fully met.

[0006] The patent with the application number 202211408646.4 discloses an alumina dispersion strengthened copper alloy and its preparation method and application. The mass percentage composition of the alumina dispersion strengthened copper alloy is 0.45 - 1.5 wt% of Al2O3, and the balance is Cu; the average grain size of the alumina dispersion strengthened copper alloy is 10 - 50 μm, the average size of the Al2O3 particles contained in the microstructure is ≤ 50 nm, and the number of Al2O3 particles per unit area is (5 - 103) × 109 pieces / mm2. By controlling the size, distribution and standard deviation of the Al2O3 particles in the copper alloy, a fine and uniformly distributed microstructure is obtained. The hardness of the alumina dispersion strengthened copper alloy is 70 - 85 HRB, the yield strength is 400 - 520 MPa, the tensile strength is 450 - 580 MPa, the elongation after fracture is ≥ 16%, the reduction of area is ≥ 35%, the conductivity is 75 - 90% IACS, and it has excellent cold heading processability, high strength and conductivity, and can be used as an automotive welding material.

[0007] The patent with the application number 201510427513.5 discloses a preparation method of a nano-strengthened copper alloy. The copper alloy consists of the following components: 0.1 - 1.5% of nano-carbon by the total mass of the copper alloy, and the particle size of the carbon is < 70 nm; 0.1 - 5% of nano-chromium by the total mass of the copper alloy, and the particle size of the chromium is < 100 nm; 0.1 - 3% of nano-zirconia by the total mass of the copper alloy, and the particle size of the zirconia is < 70 nm; the balance is copper and other alloys. The nano-strengthened copper alloy prepared by this invention has a high finished product rate, low cost, stable performance and few internal defects, and can be widely used in the manufacture of various nano-strengthened copper alloys.

[0008] The above patents respectively adopt strengthening methods such as solid solution strengthening, fine grain strengthening, dislocation strengthening, and second phase strengthening to improve the strength of the alloy. However, while the above methods improve the strength of the copper alloy, they often damage the thermal conductivity of the copper alloy. This is because the heat conduction of the copper alloy basically follows the electron thermal conduction mechanism, and strengthening methods such as solid solution strengthening, fine grain strengthening, dislocation strengthening or second phase strengthening will all increase the thermal resistance of electron thermal conduction, resulting in a decrease in thermal conductivity, making it difficult to achieve both high strength and high thermal conductivity in copper alloys by using the above conventional methods of strengthening copper alloys. Summary of the Invention

[0009] Aiming at the problems in the above-mentioned prior art, in order to overcome the contradiction of the coexistence of high strength and high thermal conductivity in copper alloys, the present invention provides a copper alloy, and through the selection of the second phase and composition design of the copper alloy, as well as the microstructure design of the copper matrix and the second phase, a copper alloy capable of simultaneously having high strength and high thermal conductivity is obtained.

[0010] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions.

[0011] The present invention first provides a copper alloy, which has the characteristics of high strength and high thermal conductivity. The copper alloy includes a copper matrix and a second phase; wherein the copper matrix is composed of a number of copper grains, and the second phase is sandwiched between the copper grains in the form of a thin film, forming a partial wrapping state around the copper grains.

[0012] Furthermore, the content of the solid solution elements in the copper matrix is less than 0.02 at.%.

[0013] Furthermore, the solubility of the second phase in copper is less than 0.02 at.%.

[0014] It is inevitable for trace elements to enter copper. Due to the different characteristics of each element, some are insoluble in copper, some are slightly soluble, some are highly soluble or infinitely soluble, the solubility decreases sharply with the decrease of temperature, and there are complex phase changes under the solid phase, etc. Therefore, the influence of each external element on the properties of copper is also different. However, the heat conduction of copper alloys basically follows the electron heat conduction mechanism, and the addition of solid solution elements usually increases the thermal resistance of electron heat conduction, resulting in a decrease in thermal conductivity. Therefore, in the copper alloy provided by the present invention, to ensure that the copper alloy can inherit the high thermal conductivity of pure copper, the content of the solid solution elements in the copper matrix is limited to a low level, and the copper matrix is almost pure copper, ensuring that the copper matrix has the characteristic of high thermal conductivity like pure copper.

[0015] To achieve the purpose of limiting the content of solid solution elements in the copper matrix to a low level, this requires the inventor to also consider avoiding the second phase entering the copper matrix in the form of solid solution, etc. during the process of forming the copper alloy of the present invention, so as to reduce the thermal conductivity of the copper matrix; therefore, when selecting the second phase, the inventor considered the solid solution situation of the second phase and copper elements. For example, in Example 1, boron element is selected as the second phase: the solubility of boron in the copper matrix is extremely low: since the boron atomic radius (≈0.09 nm) is much smaller than that of copper (≈0.128 nm), it mainly exists in the form of interstitial atoms, but the interstitial positions in the face-centered cubic (FCC) structure of copper are limited, resulting in an extremely low solubility of boron in the copper matrix at room temperature, almost zero. Another example is that in other embodiments of the present invention, the second phase is boron nitride or graphene, both of which have extremely low solubility in the copper matrix and basically do not exist in the form of solid solution in the copper matrix.

[0016] Furthermore, the characteristic size of the copper grains constituting the copper matrix is in the range of 50 - 400 nm; wherein the characteristic size refers to the minimum size of the grain size of the copper grains in each direction; and more than 80% of the surface area of the copper grains constituting the copper matrix is wrapped by the second phase.

[0017] The size of the copper grains that make up the copper matrix is restricted in the copper alloy. The inventor mainly aims to construct an ultrafine-grained structure of the copper matrix to achieve the purpose of strengthening the copper matrix by grain refinement and improving its strength. Since the copper grains that make up the copper matrix are wrapped and separated by the second phase, and the characteristic size of these copper grains is less than 400 nm, the copper matrix composed of these copper grains is equivalent to having an ultrafine-grained structure. Therefore, it has high strength. For example, in one embodiment of the present invention, the size range of the copper grains that make up the copper matrix in the copper alloy is 60-180 nm; in another embodiment of the present invention, the copper grains are in a long strip shape, and its width, that is, the characteristic size, is less than 400 nm. At the same time, these copper grains that make up the copper matrix are separated by the second phase in the form of a thin film. While having strong grain refinement strengthening, it also has a second-phase strengthening effect, which makes the above copper alloy have high-strength characteristics.

[0018] Furthermore, the thermal conductivity of the second phase is higher than that of pure copper; or the second phase can dissolve copper elements to form a doped semiconductor.

[0019] The high thermal conductivity of the second phase can ensure the heat transfer effect between copper grains when combined with the copper matrix, and improve the thermal conductivity of the copper alloy. For example, in a certain embodiment of the present invention, the second phase uses graphene. As a single-layer honeycomb structure material composed of carbon atoms, graphene has excellent thermal conductivity characteristics, and its thermal conductivity can be as high as 2000-5000 W / (m·K), which is five to more than ten times that of copper (the thermal conductivity of copper is about 400 W / (m·K)). The high thermal conductivity of graphene enables it to effectively transfer heat, and at the same time, its interfacial thermal resistance with the copper matrix is low, ensuring the high thermal conductivity of the copper alloy. In another embodiment of the present invention, the second phase uses boron nitride, and the thermal conductivity of boron nitride can reach more than 2000 W / (m·K), which is 3-5 times or even higher than that of metals such as copper and aluminum, and is one of the best thermal conductors of metals and ceramics; at the same time, its interfacial thermal resistance with the copper matrix is also low. Therefore, the second phase boron nitride can significantly improve the thermal conductivity of the copper alloy.

[0020] However, in another embodiment of the present invention, the second phase is boron, and the intrinsic thermal conductivity of boron is only 5-6 W / (m·K), which is much lower than that of pure copper. But boron is used as the second phase in the copper alloy of the present invention. From the Cu-B phase diagram, it can be seen that B can dissolve copper elements and has a large solubility, that is, B can be doped with Cu, and the energy level changes after doping to form a doped semiconductor. The thermal activation at high temperature can promote the manifestation of the semiconductor tunneling effect; furthermore, since the second phase that wraps the copper grains is in the form of a thin film, and in the present invention, the thickness of the second-phase thin film is restricted to be less than 10 nm, the semiconductor tunneling effect naturally occurs. Under this effect, the hot electrons in the copper matrix can effectively cross the second-phase thin film and be injected into adjacent copper grains in the degenerate energy level state, so that the interfacial thermal resistance remains at a low level, thereby obtaining high thermal conductivity.

[0021] More specifically, the second phase is boron, boron nitride or graphene. However, it is obvious that the technical solution of the present invention is not limited to only three materials, i.e., boron, boron nitride or graphene, for the material that can satisfy the formation of the second phase in the copper alloy provided by the present invention as described above.

[0022] Furthermore, the second phase is sandwiched between pairs of copper grains in the form of a thin film, and the thickness range of the thin film is 2 - 10 nm. For example, in one embodiment of the present invention, the second phase - boron phase is sandwiched between copper grains in the form of a thin film with a thickness of about 10 nm. In another embodiment of the present invention, the copper grains constituting the copper matrix are separated by graphene, and the graphene is multi-layer graphene with a thickness of 2 - 8 nm.

[0023] Therefore, the copper alloy as described above in the present invention has comprehensive properties of both high strength and high thermal conductivity, and can meet the demanding property requirements of thermal management materials for important structures. For example, in one embodiment of the present invention, the prepared copper-boron alloy has an ultra-high strength of 1.0 GPa and a thermal conductivity of 160 W / (m·K); in another embodiment, the copper-graphene alloy has a high strength of 600 MPa and a thermal conductivity of 407 W / (m·K); in another embodiment of the copper-boron nitride alloy, it has a high strength of 780 MPa and a thermal conductivity of 350 W / (m·K).

[0024] Each embodiment of the present invention also provides the preparation of copper alloys that meet the above-mentioned microscopic morphology and organizational structure, where the second phases are boron, graphene, and boron nitride respectively, and form copper-boron, copper-graphene, and copper-boron nitride alloys with the copper matrix composed of copper grains. In one embodiment, a 3D printing technology of laser powder bed fusion is adopted. Utilizing the characteristics of rapid non-equilibrium solidification of the laser powder bed fusion printing technology, the copper melt pool is controlled at the micron level, enabling the boron phase to wrap around the copper grains in the form of a thin film, and finally forming a copper-boron alloy that meets the requirements of the above-mentioned tissue composition, microscopic morphology, etc. of the present invention, and obtaining comprehensive properties of high strength and high thermal conductivity. In another embodiment of the present invention, a graphene precursor material layer - glucose organic layer that forms the second phase is coated on the surface of nano-copper powder by a hydrothermal method, and a copper-graphene material is obtained through SPS hot pressing sintering, and then through drawing deformation, a copper-graphene alloy that meets the requirements of the above-mentioned tissue composition, microscopic morphology, etc. of the present invention is formed, and comprehensive properties of high strength and high thermal conductivity are obtained.

[0025] However, the copper alloy elucidated above in the present invention is not limited to the methods in the embodiments of the present invention for preparation. Under the condition of appropriate selection of the second-phase material, etc., other methods may also prepare the copper alloy described in the present invention. Description of the Drawings

[0026] Figure 1This is a transmission electron microscope photograph of the copper-boron alloy material prepared in Example 1 of the present invention. The arrow in the figure indicates the second-phase boron film that wraps and separates the copper grains.

[0027] Figure 2 This is the X-ray diffraction pattern of the copper-boron material prepared in Example 1 of the present invention. The diffraction peaks of the copper phase and the boron phase are clearly distinguishable, and the diffraction peak of the copper phase shows almost no shift.

[0028] Figure 3 This is a transmission electron microscope photograph of the copper-graphene material prepared in Example 2 of the present invention. The arrow indicates the graphene sheets that separate and wrap the copper grains. Detailed implementation manners

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0030] Example 1

[0031] In this embodiment, a copper alloy with both high strength and high thermal conductivity is prepared. The copper alloy is a copper-boron alloy of Cu-3w.t% B, which is composed of a copper matrix and a second-phase boron. In this embodiment, the 3D printing technology of laser powder bed melting is adopted. By using the characteristics of rapid non-equilibrium solidification of the 3D printing technology of laser powder bed melting, the copper melt pool is controlled in the micron order. The rapid non-equilibrium solidification of this method avoids the problem of the huge difference in melting points between copper and boron, and makes the boron phase wrap around the copper grains in the form of a thin film. The preparation process is as follows.

[0032] 1) The raw material of the copper matrix is selected as pure copper powder to ensure that the content of other elements dissolved in the formed copper matrix is less than 0.02 at.%. Pure copper powder and pure boron powder are mixed in proportion to form a mixed powder of Cu-3wt.% B, and this mixed powder is used as the raw material.

[0033] 2) Print the copper-boron alloy by using the laser powder bed melting method. The printing parameters are: a near-infrared laser with a laser power of 425 W and a scanning rate of 825 mm / s. The copper-boron alloy is obtained by using the rapid solidification characteristics of laser printing.

[0034] The prepared copper-boron alloy is tested: the results of the force-thermal performance test show that the material has an ultra-high strength of 1.0 GPa and a thermal conductivity of 160 W / (m·K).

[0035] The characterization results of the transmission electron microscope (TEM) are as shown in the appendix Figure 1As shown, it can be seen from the figure that the TEM characterization results show that the structure of the copper alloy prepared in this example is a copper-boron duplex structure, which includes a copper matrix composed of copper grains, and a second phase, i.e., boron phase, which is sandwiched between the copper grains and forms a separated and encapsulated state for the copper grains; as shown in the attached Figure 1 The arrow in the figure indicates the second phase boron phase that wraps and separates the copper grains. It can be seen from the figure that the boron phase is in a thin film state. The test results in the figure show that: the surface area of the copper grains is wrapped by the boron thin film by more than about 80%. The size range of the copper grains that make up the copper matrix is 60-180 nm, forming an ultrafine grain microstructure with a strong grain refinement strengthening function. The second phase boron phase is in a thin film state, and the thickness of the boron thin film is about 10 nm.

[0036] As shown in the attached Figure 2 This is the X-ray diffraction pattern of the copper-boron alloy material prepared in this example. The diffraction peaks of the copper phase and the boron phase are clearly distinguishable, and the diffraction peak of the copper phase shows almost no shift and is almost the same as the peak position of the standard card. This also indicates that there are almost no other elements such as solid solution in the copper matrix. This is also the result of choosing boron as the second phase because boron has almost no solid solubility in copper at room temperature and is close to pure copper. The X-ray diffraction results further confirm that the alloy material is composed of a copper phase and a boron phase. The weaker diffraction peak of the boron phase is due to the low boron content and the nano-thin film state.

[0037] Example 2

[0038] In this example, a copper alloy with both high strength and high thermal conductivity was prepared. This copper alloy is a copper-graphene alloy, which is composed of a copper matrix and a second phase graphene layer. The preparation process is as follows.

[0039] First, nano-copper powder was prepared by a wet chemical method.

[0040] After that, a layer of glucose organic layer was coated on the surface of the copper powder by a hydrothermal method; this glucose organic layer is the source material precursor layer for the subsequent formation of the second phase graphene layer in the copper alloy.

[0041] Then, a copper-graphene material was obtained by SPS hot pressing sintering;

[0042] Finally, the copper-graphene material was deformed by drawing. In this example, the deformation amount reached 70%, and a copper-graphene alloy was obtained.

[0043] The prepared copper-boron alloy was tested: the force-thermal performance test results show that this material has a high strength of 600 MPa and a thermal conductivity of 407 W / (m·K).

[0044] TEM characterization results: As shown in the attached Figure 3Transmission electron microscope photograph of the copper-graphene alloy prepared in this example, where the graphene sheets separating and wrapping the copper grains are indicated by the arrows. As can be seen from the figure, the copper grains grow in a strip shape, with a length exceeding 30 μm and a width less than 400 nm. The copper grains are separated by graphene, and the graphene is multi-layer graphene with a thickness of 2 - 8 nm. Since the copper grains are separated into long strip crystals with a width less than 400 nm by the graphene sheets in the vertically elongated direction, forming fine grain strengthening, its strength is significantly higher than that of pure copper. Also, since graphene is insoluble in copper, the copper grains can maintain the thermal conductivity properties of nearly pure copper. And the thermal conductivity of graphene itself is extremely high, so the composite structure of the two has good thermal conductivity properties.

[0045] Example 3

[0046] In this example, a copper alloy with both high strength and high thermal conductivity was prepared. The copper alloy is a copper boron nitride alloy, which consists of a copper matrix and a second-phase boron nitride layer. The preparation process is as follows.

[0047] Pure copper powder and pure boron powder were mixed in proportion to form a Cu-3wt.%B mixed powder, and this mixed powder was used as the raw material to print the copper boron nitride alloy by laser powder bed fusion. The printing parameters were: a near-infrared laser with a laser power of 425 W and a scanning rate of 825 mm / s. The copper boron alloy was obtained by utilizing the rapid solidification characteristics of laser printing. Then it was placed in a nitriding furnace for nitriding treatment, using ammonia gas as the nitrogen source, and nitriding at 560 °C for 7 h to nitride the copper boron alloy into a copper boron nitride alloy. The force-thermal performance test results of the copper boron nitride alloy prepared in this example show that the material has a high strength of 780 MPa and a thermal conductivity of 350 W / (m·K); the TEM characterization results show that the microstructure is a copper and boron nitride two-phase microstructure, and the copper grains are wrapped and separated by the boron nitride phase; among them, the characteristic size range of the copper grains is 200 - 400 nm, and the second-phase boron nitride phase is sandwiched between the copper grains in the form of a thin film, with a film thickness of 2 - 10 nm. Since the copper grains are separated into ultrafine grains, the material has excellent high-strength characteristics; at the same time, the thermal conductivity of boron nitride itself is extremely high, about 5 times that of pure copper, so the composite structure of the two has good thermal conductivity properties.

Claims

1. A high-strength and high-thermal-conductivity copper alloy, characterized in that: The copper alloy includes a copper matrix and a second phase; wherein the copper matrix is composed of a number of copper grains, and the second phase is sandwiched between the copper grains in the form of a thin film, forming a partial wrapping state around the copper grains.

2. The high-strength and high-thermal-conductivity copper alloy according to claim 1, wherein: The content of the solid solution elements in the copper matrix is less than 0.02 at.%.

3. The high-strength and high-thermal-conductivity copper alloy according to claim 2, wherein: The solubility of the second phase in copper is less than 0.02 at.%.

4. A high-strength and high-thermal-conductivity copper alloy according to claim 1, characterized in that: The characteristic size of the copper grains constituting the copper matrix is in the range of 50 to 400 nm.

5. The high-strength and high-thermal-conductivity copper alloy according to claim 1, wherein: The second phase sandwiched between the copper grains in the form of a thin film, the thickness range of the thin film is 2 to 10 nm.

6. The high-strength and high-thermal-conductivity copper alloy according to claim 5, wherein: The thermal conductivity of the second phase is higher than that of pure copper, or the second phase can dissolve copper elements to form a doped semiconductor.

7. The high-strength and high-thermal-conductivity copper alloy according to claim 6, characterized in that: The second phase is graphene, boron nitride, or boron.

8. A method for preparing a high-strength and high-thermal-conductivity copper alloy according to claim 7, characterized in that: The second phase is boron. The copper-boron alloy, namely the high thermal conductivity copper alloy, is formed by using the laser powder bed melting method and the rapid non-equilibrium solidification of the laser powder bed melting printing technology.

9. A method for preparing a high-strength and high-thermal-conductivity copper alloy according to claim 7, characterized in that: The second phase is graphene. A graphene precursor material layer, namely a glucose organic layer, which forms the second phase, is coated on the surface of the nano copper powder by the hydrothermal method. The copper-graphene material is obtained by SPS hot pressing sintering, and then the copper-graphene alloy, namely the high thermal conductivity copper alloy, is formed by drawing deformation.

10. A method for preparing a high-strength and high-thermal-conductivity copper alloy according to claim 7, characterized in that: The second phase is boron nitride. The copper-boron alloy is formed by using the laser powder bed melting method and the rapid non-equilibrium solidification of the laser powder bed melting printing technology, and then the copper boron nitride alloy, namely the high thermal conductivity copper alloy, is obtained by nitridation treatment.

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