High-strength and high-thermal-conductivity copper-boron alloy and preparation method thereof

Abstract

The invention discloses a high-strength and high-thermal-conductivity copper-boron alloy in a high-temperature environment, which comprises the following components in percentage by mass: 2.0-4.0% of boron element and the balance of Cu, the organization structure is composed of copper crystal grains and a boron film, and the boron film is clamped between the copper crystal grains to separate and wrap the copper crystal grains. The invention further discloses a method for preparing the high-strength and high-thermal-conductivity copper-boron alloy, a laser 3D printing technology is adopted, the characteristic of rapid non-equilibrium solidification of laser 3D printing is utilized, a molten pool is controlled at the micron dimension, and the periphery of copper grains is wrapped with a boron phase in a film form through rapid non-equilibrium solidification. The heat conductivity of the copper-boron alloy at 600 DEG C exceeds 200 W / (m.K), the tensile strength exceeds 300 MPa, and the comprehensive performance of the copper-boron alloy in the high-temperature environment is superior to that of a conventional copper alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloy materials, and in particular relates to a copper alloy having high strength and high thermal conductivity in a high-temperature environment and a preparation method thereof. Background Art

[0002] Copper and copper alloys are structural and functional materials with excellent mechanical and physical properties, finding widespread application in power electronics, aerospace, defense, automotive, and other fields. For example, in electromagnetic transmission, to withstand transient inputs of extremely high currents, guide rail materials must possess high strength, electrical conductivity, and thermal conductivity, especially under high temperatures. Another example is the inner wall of a rocket engine thrust chamber, which must withstand high chamber pressures and large heat fluxes, requiring high strength and thermal conductivity even under combustion conditions. To this end, much research has focused on the development of high-strength and high-conductivity copper alloys, with some progress achieved.

[0003] Patent application number 202010678959.6 discloses a high-strength, high-conductivity copper alloy material, its preparation method, and application. The material's weight percentage composition includes: 0.3-0.8 wt.% Cr, 0.05-0.5 wt.% Fe, 0.05-0.3 wt.% Ti, 0.01-0.1 wt.% Si, with the balance being Cu and unavoidable impurities. The high-strength, high-conductivity copper alloy is prepared through an alloying design of elements such as Cr, Fe, Ti, and Si, and a thermomechanical heat treatment process primarily based on two-stage aging. The patent strengthens the alloy and improves its electrical conductivity by controlling the size and density of the CrFe phase, (Cr,Fe)2Ti and Cr3Si composite precipitates, and the Cr elemental phase in the alloy's microstructure. The resulting strip exhibits a yield strength exceeding 650 MPa, a conductivity exceeding 65% IACS, and good resistance to high-temperature softening.

[0004] Patent application number 201710164079.5 discloses a composite-reinforced high-strength, high-conductivity copper alloy and its preparation method. The alloy is composed of Cr, at least one element selected from Ag and In, and at least one element selected from La, Ce, and Y, with the balance being Cu and unavoidable impurities. The component contents are (all in mass percentage): Cr 0.26-1.0%; Ag and In 0.05-0.4% combined; La, Ce, or Y 0.1-0.5% combined; unavoidable impurities no greater than 0.5%; and Cu as the balance. By combining and optimizing the composition of the high-strength, high-conductivity copper alloy, a copper alloy frame strip or wire with high strength, high conductivity, and high softening temperature resistance is produced.

[0005] The patent with application number 202010784254.2 discloses a high-strength and high-conductivity copper alloy wire. The wire contains raw materials with the following mass fractions: silver 0.1-1.5 wt%, cobalt 0.1-1 wt%, and the balance is copper and inevitable impurities. Among them, the purities of silver, copper, and cobalt are not less than 99.99%. The wire grain structure contains twins. The invention also discloses a preparation method of the high-strength and high-conductivity copper alloy wire, including melting, casting, and extruding copper, silver, and cobalt, and then drawing under a magnetic field of -300 to -100 °C and 0.5 to 5 T, and finally annealing to obtain a copper alloy conductive wire. Under the combined action of the magnetic field and low-temperature deformation, a large number of twins are induced to aggregate and grow, forming twin strengthening; at the same time, due to the extremely small electron scattering ability of coherent twin boundaries, the high conductivity of the copper alloy wire is maintained, and it also has high strength.

[0006] The patent with application number 202110599007.X discloses a preparation method of a high-strength and high-conductivity copper alloy, which includes the following steps: Step 1: Preparation of the precursor; Step 2: Calcination and reduction; Step 3: Spark plasma sintering. The preparation process of the invention is simple. Only pure copper powder and yttrium nitrate hexahydrate are required as raw materials to prepare a composite powder with Y2O3 dispersed on the surface of copper powder. After sintering, a dense block can be obtained. The distribution of Y2O3 is uniform, which can refine copper grains, and the strength and hardness of the copper alloy are improved, reaching 251.1 MPa to 303.9 MPa and 101.3 HV to 140.5 HV respectively. At the same time, the conductivity can be maintained at an extremely high level of 78-98% IACS, which can improve the performance of electrical materials such as electric contacts and extend their service life.

[0007] High strength and high thermal conductivity are inherently a pair of contradictory properties and are difficult to achieve simultaneously. As described in the above patents, solid solution strengthening, fine grain strengthening, dislocation strengthening, second phase strengthening and other strengthening methods are respectively adopted to improve the strength of the alloy. However, while improving the strength of the copper alloy, these methods often damage the thermal conductivity of the copper alloy. This is because the heat conduction of copper alloys 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 lead to a decrease in the thermal conductivity of the alloy. For example: alloying elements and precipitates will scatter electrons, increase the thermal resistance of electron heat conduction, and cause a decrease in thermal conductivity; fine grain strengthening increases the number of grain boundaries, hinders the movement of electrons and phonons, and reduces the thermal conductivity; the interface between the precipitate and the matrix will also scatter electrons and phonons, affecting the thermal conductivity. In short, it is difficult to achieve both high strength and high thermal conductivity in copper alloys by using the above conventional methods of strengthening copper alloys.

[0008] However, it is even more challenging to achieve both high strength and high thermal conductivity in copper alloys under high-temperature environments. Because there are problems such as thermal stability issues in high-temperature environments. The precipitated phases may coarsen or dissolve at high temperatures, reducing the strengthening effect; high temperatures exacerbate oxidation and corrosion, affecting the material properties; there are problems such as increased thermal stress at high temperatures, which may lead to cracks or deformation. Summary of the Invention

[0009] In view of the above technical problems, in order to overcome the contradiction between high strength and high thermal conductivity existing simultaneously in copper alloys, the present invention provides a copper-boron alloy and a preparation method thereof. This copper-boron alloy can be a copper alloy that simultaneously has high strength and high thermal conductivity, and can also have the comprehensive properties of high strength and high thermal conductivity under high-temperature environments.

[0010] To achieve the above invention object, the present invention provides the following technical solutions.

[0011] The present invention provides a high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environments. The copper-boron alloy, in terms of mass percentage content, includes the following elements: B: 2.0% - 4.0%, and the rest is Cu. The structure of this copper-boron alloy consists of copper grains and boron thin film structures. The boron thin films are sandwiched between the copper grains to form separation and encapsulation of the copper grains. Among them, the size of the copper grains is 100 - 300 nm, and the thickness of the boron thin films is 5 - 10 nm.

[0012] Further, the high-temperature environment refers to: the environmental temperature reaches 600 °C; the high strength means that under the test environment of 600 °C for the copper-boron alloy, the tensile strength is above 300 MPa; the high thermal conductivity means that under the test environment of 600 °C for the copper-boron alloy, its thermal conductivity is above 200 W / (m·K).

[0013] Boron has an extremely low solubility in copper. Since the boron atomic radius (≈0.09 nm) is much smaller than that of copper (≈0.128 nm), boron mainly exists in the form of interstitial atoms. However, the interstitial positions in the face-centered cubic (FCC) structure of copper are limited, resulting in an extremely low solubility of boron, almost zero at room temperature. On the other hand, the melting point difference between boron and copper is too large. The melting point of boron exceeds 2000 °C, almost twice that of pure copper. During the solidification process of the copper-boron melt, due to the huge melting point difference between the two, coarse primary boron phases are often formed. Therefore, when pure boron phases form copper alloys with copper, it is often difficult to effectively strengthen the copper alloy, and thus the strength of copper-boron alloys prepared by traditional casting methods is relatively low. In addition, although copper has excellent thermal conductivity (about 400 W / (m·K)), generally, the intrinsic thermal conductivity of boron is only 5 - 6 W / (m·K). In the copper alloy formed by pure boron phases and copper, the low thermal conductivity of boron and the fact that the boron phase is a coarse primary boron phase directly hinder the conduction of copper hot electrons, making it difficult for the copper-boron alloy composed of the two to achieve high thermal conductivity performance.

[0014] Therefore, when boron is used as an additive element to strengthen copper alloys, the strengthened copper alloys formed by boron and copper usually contain boron in the form of precipitated phases or compounds. For example, in copper alloys, boron acts as a strong deoxidizer, reacting with oxygen and other impurities (such as sulfur and phosphorus) in the copper melt to form stable compounds (such as B2O3), purifying the matrix, reducing brittle phases at grain boundaries, and improving electrical and thermal conductivities. Or, by adding trace amounts of boron (usually 0.001% - 0.1%) to copper, fine and dispersed borides are formed as heterogeneous nucleation cores to refine the casting structure, inhibit the growth of copper grains, and improve strength and hardness. Or, by adding a small amount of boron, hard borides are formed as second-phase particles to hinder dislocation movement and enhance the strength of copper alloys. However, excessive boron will lead to increased brittleness of copper alloys and decreased electrical and thermal conductivities. Therefore, in such strengthened copper alloys, the addition of boron often needs to be strictly controlled (usually <0.1 wt.%) to balance strengthening and properties such as electrical and thermal conductivities.

[0015] In the copper-boron alloy provided by the present invention, when boron is used as an element to strengthen copper alloys, its existence in the copper alloy is no longer in the form of the usual precipitated phases or compounds, but in the form of independent pure boron phases existing in the copper matrix. Moreover, these pure boron phases are not coarse primary boron phases, but exist in the copper matrix in the form of nano-thin films, separating and wrapping the copper grains that make up the copper matrix. Due to the different microscopic forms of their existence, the interaction mechanisms between them and copper are naturally different, and the effects on the properties of copper alloys are also different.

[0016] First of all, in the above-mentioned copper-boron alloy provided by the present invention, it is composed of two-phase structures of copper and boron. Copper forms a copper matrix in the form of copper grains, and boron exists in the form of a nano-thin film structure. Since the solubility of boron in copper is almost 0, the copper grains constituting the copper matrix remain close to the state of pure copper. Therefore, the copper matrix composed of these copper grains has an intrinsic high thermal conductivity. In addition, the pure boron phase separates and wraps the copper grains in the form of a nano-thin film; boron has a relatively large band gap (about 1.5 to 1.6 eV), and at room temperature, it is difficult for electrons to transition from the valence band to the conduction band, and its conductivity is relatively low. Therefore, boron is a semiconductor at room temperature. At this time, in the copper-boron alloy of the present invention, the boron phase in the form of a nano-thin film wraps the copper grains, forming a contact between a metal and a semiconductor; as the temperature increases, the conductivity of boron will increase. At high temperatures, more electrons obtain enough energy to transition to the conduction band, and the conductivity of boron rises. At this time, in the copper-boron alloy of the present invention, the boron in the form of a nano-thin film forms an ohmic contact with the copper grains. At room temperature, in the copper-boron alloy, since the thickness of the boron thin film is limited to the nano-thickness (5 - 10 nm), the contact between the semiconductor boron thin film and the metal copper grains undergoes a semiconductor tunneling effect. Under this effect, the heat-transfer electrons of the copper matrix can effectively penetrate the second-phase thin film and inject into adjacent copper grains in the degenerate energy level state, so that the interfacial thermal resistance remains at a low level, thereby obtaining a high thermal conductivity. When the temperature increases, the conductivity of boron will increase. At high temperatures, when more electrons obtain enough energy to transition to the conduction band and an ohmic contact is formed between the boron thin film and the copper grains, under the condition of high-temperature thermal activation, the hot electrons of copper can effectively penetrate the nano-boron thin film and inject into adjacent copper grains in the degenerate energy level state, so that the interfacial thermal resistance remains at a low level. Thus, the above-mentioned copper-boron alloy of the present invention can obtain high thermal conductivity in an environment from room temperature to high temperature (up to 600 °C). In the embodiments of the present invention, the thermal conductivity of the copper-boron alloy prepared in each embodiment is above 200 W / (m·K) in a test environment of 600 °C.

[0017] On the other hand, the size of the copper grains constituting the copper matrix in the copper-boron alloy is limited to 100 - 300 nm, constructing an ultrafine grain structure of the copper matrix to achieve the purpose of strengthening the strength of the copper matrix by fine grain strengthening; in addition, since the copper grains constituting the copper matrix are wrapped and separated by the second-phase boron thin film, therefore, while the copper-boron alloy has strong fine grain strengthening, it also has a second-phase strengthening effect, which makes the above-mentioned copper-boron alloy have high-strength characteristics. In a high-temperature environment reaching 600 °C, since the copper grains are separated by the high-melting-point boron thin film (the melting point of boron exceeds 2000 °C), therefore, the copper grains are difficult to grow even in a high-temperature environment, so that it still has high strength. In the embodiments of the present invention, the tensile strength of the copper-boron alloy prepared in each embodiment is above 300 MPa in a test environment of 600 °C.

[0018] Therefore, the above-mentioned copper-boron alloy of the present invention can achieve high strength and high thermal conductivity, especially high strength and high thermal conductivity can also be achieved in a high-temperature environment.

[0019] The present invention also provides a method for preparing the above-mentioned copper-boron alloy.

[0020] For the copper-boron alloy composed of a single boron phase and copper, it has traditionally been prepared by a casting method. Since the melting point of boron exceeds 2000 °C, almost twice that of pure copper, during the solidification of the copper-boron melt, due to the huge difference in melting points between the two, boron will form coarse primary boron phases. To ensure the realization of the copper-boron alloy as described above in the present invention, the present invention adopts a laser 3D printing technology. Utilizing the characteristics of rapid non-equilibrium solidification in laser 3D printing, the molten pool is controlled at the micron scale. The rapid non-equilibrium solidification avoids the problem of the huge difference in melting points between copper and boron, and enables the boron phase to wrap around the copper grains in the form of a thin film. Specifically, the present invention provides the following technical solutions.

[0021] The method for preparing the above-mentioned copper-boron alloy in the present invention adopts a laser powder bed fusion method, and includes the following steps.

[0022] Step 1: Using pure copper powder and pure boron powder as raw materials, mechanically mix them in proportion to form a composite powder. The addition ratio of the two powders is the same as the copper-boron component ratio in the finally obtained copper-boron alloy, and the addition ratio satisfies: the pure boron powder is 2.0 wt.% - 4.0 wt.% of the composite powder, and the rest is pure copper powder. Among them, the pure copper powder is spherical powder with a diameter of 15 - 53 μm, and the pure boron powder is irregular nano-powder with a particle size of 50 - 200 nm.

[0023] Step 2: Using the composite powder as the 3D printing raw material, perform 3D printing by the laser powder bed fusion method to obtain a copper-boron alloy. The laser 3D printing atmosphere condition is argon, and the oxygen content < 100 ppm. The substrate is a pure copper substrate, and the substrate is preheated to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 375 - 425 W, scanning speed 750 - 850 mm / s, scanning spacing 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°. Using pure copper as the substrate further increases the cooling rate. At the same time, the substrate preheating and the stripe scanning strategy with an interlayer rotation angle of 67° are adopted to reduce the risk of high laser reflection from the pure copper substrate burning out the laser.

[0024] The beneficial effects of the present invention are as follows:

[0025] 1. The copper-boron alloy provided by the present invention has a thermal conductivity exceeding 200 W / (m·K) at 600 °C, and a tensile strength exceeding 300 MPa. Its comprehensive performance in a high-temperature environment is superior to that of copper alloys such as CuCrZr.

[0026] 2. The preparation method provided by the present invention is simple and convenient, can directly produce component-level products on a large scale, and has good application prospects. Description of the Drawings

[0027] Figure 1 Transmission electron microscope photograph of the copper-boron alloy prepared in Example 1.

[0028] Figure 2 Transmission electron microscope photograph of the copper-boron alloy prepared in Example 2.

[0029] Figure 3 Transmission electron microscope photograph of the copper-boron alloy prepared in Comparative Example 2.

[0030] Figure 4 Metallographic structure photograph of the copper-boron alloy prepared in Comparative Example 4.

[0031] Figure 5 Photograph of the copper-boron alloy prepared in Comparative Example 5. Specific embodiments

[0032] 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 in 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.

[0033] Example 1

[0034] Step 1: According to 3 wt.% of B powder as the composite powder and the balance as Cu powder, select and weigh the corresponding raw materials. Among them, the Cu powder is gas-atomized copper powder with a purity of ≥99.99%, and the particle size is 15 - 53 μm; the B powder is nano-powder with a purity of ≥99.9%, and the particle size is in the range of 50 - 200 nm; mechanically mix the copper powder and boron powder for 0.2 hours to make the two fully mix to form a composite powder.

[0035] Step 2: Use the composite powder as the 3D printing raw material and perform 3D printing by the laser powder bed fusion method to obtain a copper-boron alloy. The laser 3D printing atmosphere condition is argon, and the oxygen content is 50 ppm. The substrate is a pure copper substrate. Preheat the substrate to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 400 W, scanning rate 800 mm / s, scanning spacing 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°.

[0036] Example 2

[0037] Step 1: According to 4 wt.% of B powder as the composite powder and the balance as Cu powder, select and weigh the corresponding raw materials. Among them, the Cu powder is gas-atomized copper powder with a purity of ≥99.99%, and the particle size is 15 - 53 μm; the B powder is nano-powder with a purity of ≥99.9%, and the particle size is in the range of 50 - 200 nm; mechanically mix the copper powder and boron powder for 0.2 hours to make the two fully mix to form a composite powder.

[0038] Step 2: Using the composite powder as the raw material for 3D printing, perform 3D printing by the laser powder bed fusion method to obtain a copper-boron alloy. The atmosphere condition for laser 3D printing is argon with an oxygen content of 50 ppm. The substrate is a pure copper substrate. Preheat the substrate to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 375 W, scanning rate 750 mm / s, scanning spacing 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°.

[0039] Example 3

[0040] Step 1: According to the proportion that B powder is 2 wt.% of the composite powder and the balance is Cu powder, select and weigh the corresponding raw materials. Among them, the Cu powder is gas-atomized copper powder with a purity of ≥99.99%, and the particle size is 15 - 53 μm; the B powder uses nano-powder with a purity of ≥99.9%, and the particle size is in the range of 50 - 200 nm; mechanically mix the copper powder and boron powder for 0.2 hours to make the two fully mix to form a composite powder.

[0041] Step 2: Using the composite powder as the raw material for 3D printing, perform 3D printing by the laser powder bed fusion method to obtain a copper-boron alloy. The atmosphere condition for laser 3D printing is argon with an oxygen content of 50 ppm. The substrate is a pure copper substrate. Preheat the substrate to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 425 W, scanning rate 850 mm / s, scanning spacing 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°.

[0042] Comparative Example 1

[0043] In this comparative example, the addition ratio of boron powder in the composite powder is reduced, and the B powder is 0.5 wt.% of the composite powder, to prepare a copper-boron alloy with a relatively low boron content.

[0044] Step 1: According to the proportion that B powder is 0.5 wt.% of the composite powder and the balance is Cu powder, select and weigh the corresponding raw materials. Among them, the Cu powder is gas-atomized copper powder with a purity of ≥99.99%, and the particle size is 15 - 53 μm; the B powder uses nano-powder with a purity of ≥99.9%, and the particle size is in the range of 50 - 200 nm; mechanically mix the copper powder and boron powder for 0.2 hours to make the two fully mix to form a composite powder.

[0045] Step 2: Using the composite powder as the raw material for 3D printing, perform 3D printing by the laser powder bed fusion method to obtain a copper-boron alloy. The atmosphere condition for laser 3D printing is argon with an oxygen content of 50 ppm. The substrate is a pure copper substrate. Preheat the substrate to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 400 W, scanning speed 800 mm / s, scanning spacing 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°.

[0046] Comparative Example 2

[0047] In this comparative example, the addition ratio of boron powder in the composite powder was increased, and the B powder was 10 wt.% of the composite powder, to obtain a copper-boron alloy with a relatively high boron content.

[0048] Step 1: According to the ratio that the B powder is 10 wt.% of the composite powder and the balance is Cu powder, select and weigh the corresponding raw materials. Among them, the Cu powder is gas-atomized copper powder with a purity of ≥99.99%, and the particle size is 15 - 53 μm; the B powder uses nano-powder with a purity of ≥99.9%, and the particle size is in the range of 50 - 200 nm; mechanically mix the copper powder and boron powder for 0.2 hours to make them fully mixed to form a composite powder.

[0049] Step 2: Using the composite powder as the raw material for 3D printing, perform 3D printing by the laser powder bed fusion method to obtain a copper-boron alloy. The atmosphere condition for laser 3D printing is argon with an oxygen content of 50 ppm. The substrate is a pure copper substrate. Preheat the substrate to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 400 W, scanning speed 800 mm / s, scanning spacing 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°.

[0050] Comparative Example 3

[0051] In this comparative example, during 3D printing, the substrate used is a stainless steel substrate, which is different from the pure copper substrates of each example.

[0052] Step 1: According to the ratio that the B powder is 3 wt.% of the composite powder and the balance is Cu powder, select and weigh the corresponding raw materials. Among them, the Cu powder is gas-atomized copper powder with a purity of ≥99.99%, and the particle size is 15 - 53 μm; the B powder uses nano-powder with a purity of ≥99.9%, and the particle size is in the range of 50 - 200 nm; mechanically mix the copper powder and boron powder for 0.2 hours to make them fully mixed to form a composite powder.

[0053] Step 2: Using the composite powder as the 3D printing raw material, perform 3D printing by the laser powder bed fusion method to obtain a copper-boron alloy. The atmosphere condition for laser 3D printing is argon with an oxygen content of 50 ppm. The substrate is a stainless steel substrate. Preheat the substrate to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 400 W, scanning rate 800 mm / s, scanning spacing 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°.

[0054] Comparative Example 4

[0055] Compared with each example, this comparative example performs 3D printing with a low laser power.

[0056] Step 1: According to the proportion that B powder is 3 wt.% of the composite powder and the balance is Cu powder, select and weigh the corresponding raw materials. Among them, the Cu powder is gas atomized copper powder with a purity of ≥99.99%, and the particle size is 15 - 53 μm; the B powder is nano powder with a purity of ≥99.9%, and the particle size is in the range of 50 - 200 nm; mechanically mix the copper powder and boron powder for 0.2 hours to make them fully intermix to form a composite powder.

[0057] Step 2: Using the composite powder as the 3D printing raw material, perform 3D printing by the laser powder bed fusion method to obtain a copper-boron alloy. The atmosphere condition for laser 3D printing is argon with an oxygen content of 50 ppm. The substrate is a pure copper substrate. Preheat the substrate to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 200 W, scanning rate 800 mm / s, scanning spacing of 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°.

[0058] Comparative Example 5

[0059] Compared with each example, this comparative example increases the laser scanning rate.

[0060] Step 1: According to the proportion that B powder is 3 wt.% of the composite powder and the balance is Cu powder, select and weigh the corresponding raw materials. Among them, the Cu powder is gas atomized copper powder with a purity of ≥99.99%, and the particle size is 15 - 53 μm; the B powder is nano powder with a purity of ≥99.9%, and the particle size is in the range of 50 - 200 nm; mechanically mix the copper powder and boron powder for 0.2 hours to make them fully intermix to form a composite powder.

[0061] Step 2: Using the composite powder as the 3D printing raw material, 3D printing is carried out by the laser powder bed fusion method to obtain a copper-boron alloy. The laser 3D printing atmosphere condition is argon with an oxygen content of 50 ppm. The substrate is a pure copper substrate. The substrate is preheated to 50 °C before printing. The laser used is a near-infrared fiber laser with a wavelength of 1060 nm. The printing parameters are: laser power 400 W, scanning speed 1200 mm / s, scanning spacing 90 μm, and the scanning strategy is stripe scanning with an interlayer rotation angle of 67°.

[0062] Comparative Example 6

[0063] Compared with each of the examples, in this comparative example, when performing 3D printing in Step 2, the pure copper substrate is not preheated. The other process procedures and parameters are the same as those in the examples.

[0064] Comparative Example 7

[0065] Compared with each of the examples, in this comparative example, when performing 3D printing, the scanning strategy in Step 2 is stripe scanning with an interlayer rotation angle of 90°. The other process procedures and parameters are the same as those in the examples.

[0066] The copper-boron alloys obtained in the above examples and comparative examples are subjected to various tests.

[0067] The internal structures of the copper-boron alloys are observed by a transmission electron microscope. The test results show that for the copper-boron alloys prepared in each of the examples, the tissue characteristics of boron thin films wrapping and separating copper grains are shown; as shown in Figure 1 and Figure 2 , which are the transmission electron microscope photos of the copper-boron alloys prepared in Example 1 and Example 2 respectively. It can be seen from the figures that the copper-boron alloy is composed of copper grains and boron thin films. Among them, the boron thin film has a nanoscale thickness, and the boron thin film is sandwiched between the copper grains, forming a state of dividing and wrapping the copper grains; among them, the size of the copper grains is 100 - 300 nm, and the thickness of the boron thin film is 5 - 10 nm.

[0068] When the boron content in the copper-boron alloy increases, such as in Comparative Example 2 where the boron content reaches 10 wt.%, even when using the 3D printing rapid non-equilibrium solidification preparation method, while forming boron thin films, there will still be the formation of coarse primary boron particles, thus affecting the thermal conductivity of the alloy. As shown in Figure 3 which is the transmission electron microscope photo of the copper-boron alloy sample prepared in Comparative Example 2, showing the tissue characteristics of boron thin films wrapping and separating copper grains and relatively coarse boron particles (as indicated by the arrows in the figure), which are boron particles formed due to excessive boron.

[0069] In the 3D printing preparation process, inappropriate parameters will directly affect the quality of the copper-boron alloy and the final properties such as strength and thermal conductivity, as shown in Figure 4The metallographic structure photograph of the copper-boron alloy sample prepared in Comparative Example 4 shows that there are a large number of pores inside the sample, which is caused by too low laser power during 3D printing. Similarly, as shown in the attached Figure 5 The photograph of the copper-boron alloy sample prepared in Comparative Example 5 shows that there are a large number of pores inside the sample, which is caused by too high laser scanning rate. The influence of other parameter adjustments on the formation and results of the copper-boron alloy is summarized in Table 1 below.

[0070] The tensile strength of the copper-boron alloys prepared in each example and comparative example was tested using a mechanical testing machine at 600 °C; in addition, a thermal conductivity testing system was used to test the thermal conductivity of each copper-boron alloy at 600 °C. The test results are shown in Table 1 below.

[0071] Table 1 Test results of the performance of the samples obtained in each example

[0072]

[0073] From the data in Table 1, it can be seen that:

[0074] The samples of Examples 1 to 3 all show excellent comprehensive performance of high strength and high thermal conductivity in the test environment at 600 °C, indicating that within the technical parameter range of the technical solution of the present invention, a copper-boron alloy material with high strength, high thermal conductivity and other high performance at high temperature can be obtained.

[0075] Comparing the test results of Example 1 and Comparative Example 1, it can be seen that if the boron content is too low, it is impossible to generate enough boron film to separate copper grains, resulting in insufficient high-temperature strength of the material.

[0076] Comparing the test results of Example 1 and Comparative Example 2, it can be seen that if the boron content is too high, although the material strength is relatively high, due to the formation of primary boron particles by excessive boron, the thermal conductivity is damaged, resulting in a relatively low thermal conductivity of the material.

[0077] Comparing the test results of Example 1 and Comparative Example 3, it can be seen that if a stainless steel substrate is used, due to the low thermal conductivity and slow cooling rate of stainless steel, the non-equilibrium rapid cooling effect cannot be achieved, and the tissue characteristics of separating copper grains by boron film as in each example are not formed. Therefore, both the strength and thermal conductivity data of the alloy material are relatively low.

[0078] Comparing and analyzing the test results of Example 1 and Comparative Examples 4 and 5, it can be seen that if the laser power or scanning rate is not within the parameter range of the technical solution provided by the present invention, it is impossible to obtain a dense and high-quality copper-boron alloy, and it is difficult to achieve material forming.

[0079] Comparing and analyzing the test results of Example 1 with Comparative Examples 6 and 7, it can be seen that if the pure copper substrate is not preheated or the strip scanning strategy with an interlayer corner of 67° is not adopted, it will cause the laser to reflect back to the laser. In the lightest case, the laser will alarm and stop, and in the worst case, the laser will be burned out.

Claims

1. A high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environment, characterized in that: The copper-boron alloy, by mass percentage, comprises the following elements: B: 2.0% - 4.0%, and the rest is Cu; The structure of the copper-boron alloy consists of copper grains and boron thin film structure; the boron thin film is sandwiched between the copper grains to form separation and encapsulation of the copper grains; The high-temperature environment refers to: the environmental temperature reaches 600 °C.

2. The high-strength and high-thermal-conductivity copper-boron alloy in a high-temperature environment according to claim 1, wherein: The size range of the copper grains is 100 - 300 nm, and the thickness range of the boron thin film is 5 - 10 nm.

3. A high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environment according to claim 1, characterized in that: Under the test environment of 600 °C, the copper-boron alloy has a tensile strength of more than 300 MPa and a thermal conductivity of more than 200 W / (m·K).

4. A method for preparing a high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environment according to any one of claims 1-3, characterized in that, The laser powder bed fusion method is adopted, including the following steps: Step 1, using pure copper powder and pure boron powder as raw materials, mechanically mixing them in proportion to form a composite powder; Step 2, using the composite powder as the 3D printing raw material, and adopting the laser powder bed fusion method for 3D printing to obtain the copper-boron alloy; Among them, in Step 2, the substrate is a pure copper substrate, and the substrate is preheated before printing; Among them, in Step 2, the laser scanning strategy is non-vertical scanning.

5. The preparation method of a high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environment according to claim 4, wherein, In Step 1, the addition ratio of the two powders of pure copper powder and pure boron powder satisfies: the pure boron powder is 2.0 wt.% - 4.0 wt.% of the composite powder, and the rest is pure copper powder.

6. The preparation method of a high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environment according to claim 4, wherein, In Step 1, the pure copper powder is spherical powder with a diameter of 15 - 53 μm, and the pure boron powder is irregular nano-powder with a particle size of 50 - 200 nm.

7. The preparation method of a high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environment according to claim 4, characterized in that: In Step 2, the laser used is a near-infrared fiber laser with a wavelength of 1060 nm; the atmosphere condition for laser 3D printing is argon, and the oxygen content < 100 ppm.

8. The preparation method of a high-strength and high-thermal conductivity copper-boron alloy under high-temperature environment according to claim 4, characterized in that: In Step 2, the substrate is preheated to 50 °C before printing.

9. The preparation method of a high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environment according to claim 4, wherein: In Step 2, the laser power is 375 - 425 W, and the scanning speed is 750 - 850 mm / s.

10. The preparation method of a high-strength and high-thermal-conductivity copper-boron alloy under high-temperature environment according to claim 4, characterized in that: In Step 2, the laser scanning spacing is 90 μm, and the scanning strategy is strip scanning with an interlayer rotation angle of 67°.

Images