Preparation method of boron nitride reinforced copper-based composite material based on in-situ synthesis

Abstract

The invention relates to a preparation method of a boron nitride reinforced copper-based composite material based on in-situ synthesis, and belongs to the technical field of composite material preparation and powder metallurgy. Freezing a solution containing boric acid and urea to a solid state, and performing freeze drying to obtain BN precursor powder; the BN precursor powder and copper powder are evenly mixed and then calcined, and in-situ BN / Cu composite powder is obtained; the in-situ BN / Cu composite powder is sintered, and a consolidated in-situ BN / Cu composite block is obtained; and finally, the in-situ BN / Cu composite block is subjected to hot rolling treatment. According to the method, the BN can be directly generated on the surface of the copper powder, the BN agglomeration phenomenon is effectively avoided, the size of the synthesized BN is easily controlled, the reinforcing effect of the BN can be played to the maximum extent, the interface bonding strength between the BN and copper is improved, and the method has great significance in improving the strength and wear resistance of the copper-based composite material and has good application prospects. The breakthrough of a high-performance contact wire material is expected to be realized.

Description

Technical Field

[0001] The invention relates to a preparation method of a copper-based composite material reinforced by in-situ synthesis of boron nitride, and belongs to the technical field of composite material preparation and powder metallurgy. Background Art

[0002] As the core component of the high-speed railway contact network, the contact wire provides power for the train. It is not only required to have high tensile strength and excellent electrical conductivity, but also excellent wear resistance. Currently, most of the contact wires used are copper alloys with low electrical conductivity (about 62% IACS), resulting in high energy consumption. It is urgent to develop contact wire materials with better comprehensive performance. Copper-based composite materials (CMCs) are not only high in strength and have electrical conductivity similar to pure copper, but also have good wear resistance, and are expected to become a new generation of contact wire materials.

[0003] The performance of CMCs depends largely on the inherent properties of the reinforcement. Boron nitride (BN) has been considered as an ideal two-dimensional reinforcement in copper-based composites due to its excellent physical and chemical properties: ultra-high strength and modulus (tensile strength: 61GPa; Young's modulus: 900GPa), excellent thermal conductivity (750W / m·k), excellent chemical inertness (resistant to high temperatures of 1800℃), low friction coefficient (0.16), and good performance complementarity with the copper matrix.

[0004] At present, the preparation of BN-reinforced copper-based (BN / Cu) composites has developed in a diversified manner, including ball milling, molecular mixing, chemical plating, etc. However, these methods still have some shortcomings: first, due to the high specific surface area of ​​BN, it is easy to agglomerate under the action of van der Waals force, and it is difficult to disperse evenly in the copper matrix, resulting in uneven local performance of the composite material; secondly, agglomeration will affect the size of BN, and then affect its intrinsic properties; thirdly, BN has poor wettability with the copper matrix and does not react chemically, so it is difficult to form a strong interface bond, which will reduce the reinforcement effect. Summary of the invention

[0005] In view of this, the present invention provides a preparation method of a copper-based composite material based on in-situ synthesis of boron nitride, wherein the method uses boric acid and urea as raw materials to synthesize a BN precursor, then generates BN in-situ on the surface of copper powder through a calcination process to obtain an in-situ BN / Cu composite powder, then sinters the in-situ BN / Cu composite powder into a block, and finally obtains a uniformly distributed high-performance in-situ boron nitride reinforced copper-based composite material through hot rolling. Compared with the traditional preparation process, the in-situ synthesis method adopted by the present invention can directly generate BN on the surface of copper powder. This method not only effectively avoids the BN agglomeration phenomenon, but also easily controls the size of the synthesized BN, can maximize the enhancement effect of BN, and also improves the interface bonding strength between copper and copper, which is of great significance for improving the strength and wear resistance of copper-based composite materials, and is expected to achieve a breakthrough in high-performance contact line materials.

[0006] The objectives of the present invention are achieved through the following technical solutions.

[0007] A method for preparing a copper-based composite material reinforced with boron nitride based on in-situ synthesis comprises the following steps:

[0008] (1) Preparation of BN precursor

[0009] First, boric acid and urea are dissolved in water to prepare a solution, then the solution is frozen to a solid state, and then the solid state is freeze-dried to obtain a BN precursor powder;

[0010] Preferably, the content of urea is greater than the content required by the stoichiometric ratio; more preferably, the molar ratio of boric acid to urea is 1:20 to 1:30;

[0011] Preferably, the freeze-drying temperature is -50°C to -30°C, and the time is 24h to 48h;

[0012] (2) Preparation of in-situ boron nitride reinforced copper-based (BN / Cu) composite powders

[0013] The BN precursor powder and the copper powder are mixed evenly and transferred to a sintering furnace, and calcined under a reducing protective gas atmosphere, so that the BN precursor powder generates BN in situ on the surface of the copper powder, that is, an in-situ BN / Cu composite powder is obtained;

[0014] The copper powder may be in the shape of a sphere, a flake, or other regular shapes, or any irregular shape; preferably, the copper powder is in the shape of a sphere;

[0015] Preferably, the particle size of the copper powder is 20 μm to 50 μm;

[0016] Preferably, the reducing protective gas is a mixed gas of nitrogen and hydrogen; more preferably, the volume ratio of nitrogen to hydrogen is 5:1 to 9:1;

[0017] Preferably, the calcination temperature is 800°C to 1000°C, and the calcination time is 2h to 5h; more preferably, the heating rate during the calcination process is 50°C / min to 100°C / min;

[0018] Preferably, in the in-situ BN / Cu composite powder, the mass fraction of BN is 0.1% to 0.5%;

[0019] (3) Preparation of in-situ BN / Cu composite bulk

[0020] Sintering the in-situ BN / Cu composite powder to obtain a consolidated in-situ BN / Cu composite block;

[0021] Preferably, the in-situ BN / Cu composite powder is sintered by rapid hot pressing (FHP); ​​more preferably, the parameters of the rapid hot pressing sintering include: a sintering temperature of 600°C to 900°C, a sintering pressure of 30MPa to 50MPa, and a sintering time of 10min to 30min; more preferably, the heating rate of the rapid hot pressing sintering is 50°C / min to 100°C / min;

[0022] Preferably, the in-situ BN / Cu composite powder is further subjected to a ball milling step before being sintered, namely, the in-situ BN / Cu composite powder is placed in a ball milling jar, a stearic acid control agent is added to inhibit the cold welding behavior of the powder, the ball milling is performed under a nitrogen or inert gas protective atmosphere to avoid oxidation of the powder, and the sintering is performed after the ball milling;

[0023] The ball milling parameters include: a ball milling speed of 200 rpm to 400 rpm, a ball milling time of 4 h to 8 h, a ball-to-material ratio of 10:1 to 20:1, and a mass of stearic acid of 0.5% to 2% of the mass of the in-situ BN / Cu composite powder;

[0024] (4) Thermal deformation processing

[0025] The in-situ BN / Cu composite block is subjected to hot rolling treatment to further optimize its structure and performance, thereby completing the preparation of the copper-based composite material reinforced by in-situ synthesized boron nitride;

[0026] The hot rolling treatment has a rolling temperature of 350°C to 650°C and a total rolling deformation of ≥80%;

[0027] Preferably, the specific operation of hot rolling the in-situ BN / Cu composite block is as follows: first, the in-situ BN / Cu composite block is heated at 350°C to 650°C, and then the heated in-situ BN / Cu composite block is hot rolled, wherein the hot rolling passes are 3 to 6 passes, the deformation in each pass is ≤30%, the total rolling deformation is ≥80%, and the return furnace temperature of the hot rolling process is 350°C to 650°C.

[0028] Beneficial effects:

[0029] (1) The present invention uses urea and boric acid as raw materials to first synthesize a BN precursor, and then synthesizes BN in situ on the surface of copper powder by calcination. This method can regulate the size of the synthesized BN by the raw material ratio, and can also effectively avoid the BN agglomeration phenomenon, thereby achieving uniform distribution of BN in the copper powder. Moreover, the BN generated in situ on the surface of the copper powder can significantly improve the interface bonding strength between BN and the copper matrix. In addition, the use of excess urea is conducive to improving the completeness of the generated BN, reducing the generation of other by-products, and improving the purity of BN.

[0030] (2) The hot rolling process can eliminate some microscopic defects, improve the density of the material, and promote grain refinement and obtain a uniform grain structure, thereby further improving the strength and toughness of the material.

[0031] In summary, the preparation method described in the present invention is highly universal and practical, the process flow is simple and easy to operate, and the prepared boron nitride reinforced copper-based composite material has excellent mechanical properties and wear resistance, which provides effective guidance for the development of high-performance copper-based composite materials and has good application prospects in high-performance contact line materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a scanning electron microscope (SEM) image of the in-situ generation of BN on copper particles after calcination in step (2) of Example 1.

[0033] Figure 2 The transmission electron microscope (TEM) images and inverse fast Fourier transform images of BN generated after calcination in step (2) of comparative example 1 at different magnifications.

[0034] Figure 3 This is a comparison chart of the conductivity-hardness bar graphs of the in-situ BN / Cu composite material prepared in Example 1 and the externally added BN / Cu composite material prepared in Comparative Example 1.

[0035] Figure 4 3 is a comparison diagram of stress-strain curves of the in-situ BN / Cu composite material prepared in Example 1 and the externally added BN / Cu composite material prepared in Comparative Example 1.

[0036] Figure 5 This is a comparison chart of the friction coefficient change curves of the in-situ BN / Cu composite material prepared in Example 1 and the external BN / Cu composite material prepared in Comparative Example 1.

[0037] Figure 6 This is a comparison diagram of the wear track profiles of the in-situ BN / Cu composite material prepared in Example 1 and the externally added BN / Cu composite material prepared in Comparative Example 1.

[0038] Figure 7 This is a comparison of the fracture scanning electron microscope images of the in-situ BN / Cu composite material prepared in Example 1 and the external BN / Cu composite material prepared in Comparative Example 1.

[0039] Figure 8 This is a comparison chart of the conductivity-hardness bar graphs of the in-situ BN / Cu composite material prepared in Example 2 and the Pure Cu material prepared in Comparative Example 2.

[0040] Fig. 9 It is a comparison diagram of stress-strain curves of the in-situ BN / Cu composite material prepared in Example 2 and the Pure Cu material prepared in Comparative Example 2.

[0041] Fig.10 This is a comparison chart of the friction coefficient change curves of the in-situ BN / Cu composite material prepared in Example 2 and the Pure Cu material prepared in Comparative Example 2.

[0042] Fig.11 This is a comparison diagram of the wear track profiles of the in-situ BN / Cu composite material prepared in Example 2 and the Pure Cu material prepared in Comparative Example 2. DETAILED DESCRIPTION

[0043] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments, wherein the methods are conventional methods unless otherwise specified, and the raw materials can be obtained from public commercial channels unless otherwise specified.

[0044] In the following embodiments:

[0045] Urea purity is 99%, Shanghai McLean Biochemical Technology Co., Ltd.;

[0046] Boric acid was analytically pure (≥99.5%) and was obtained from Shanghai MacLean Biochemical Technology Co., Ltd.

[0047] Pure copper powder is nearly spherical aerosolized copper powder, with a particle size of 20μm to 50μm and a purity of 99.9%, produced by Shanghai Naio Nano Technology Co., Ltd.

[0048] Scanning electron microscope: Nova Nano-450, FEI, USA;

[0049] Transmission electron microscope: Talos F200C, FEI, USA;

[0050] Mechanical properties characterization: The tensile test was carried out at room temperature using a universal tensile testing machine (AUTOGRAPH AG-I, Shimadzu Corporation, Japan). 4 s -1 ;

[0051] Friction performance characterization: The test was carried out using a multifunctional friction tester (MS-M9000, Lanzhou Huahui Instrument Technology Co., Ltd.).

[0052] Example 1

[0053] A method for preparing a copper-based composite material reinforced with boron nitride based on in-situ synthesis comprises the following steps:

[0054] (1) Preparation of BN precursor

[0055] First, 0.15 g (0.0024 mol) of boric acid and 2.9 g (0.048 mol) of urea were added to 100 mL of deionized water and ultrasonically treated for 5 min to ensure complete dissolution to obtain a solution; then the solution was placed in a refrigerator to freeze it to a solid state; and then a freeze dryer was used to dry the frozen solid state at -50 ° C for 36 h to finally obtain a white BN precursor powder;

[0056] (2) Preparation of in-situ boron nitride reinforced copper-based composite powders

[0057] 2.5 g of BN precursor powder and 49.95 g of copper powder were mixed evenly, and then the mixed powder was placed in a tube furnace and calcined in a mixed gas atmosphere of 85 vol.% N2 and 15 vol.% H2 to generate BN in situ on the surface of the copper powder, thereby obtaining an in-situ boron nitride reinforced copper-based composite powder, which is referred to as an in-situ BN / Cu composite powder.

[0058] The calcination process parameters include: initial vacuum degree ≤ 10Pa (e.g., it can be 10Pa), heating rate 50°C / min, calcination temperature 900°C, calcination time 3h, and cooling with the furnace after calcination;

[0059] (3) Preparation of in-situ BN / Cu composite bulk

[0060] The in-situ BN / Cu composite powder is added into a ball mill, and a stearic acid control agent is added according to 1% of the mass of the in-situ BN / Cu composite powder, and ball milling beads are added according to a ball-to-material ratio of 15:1. The ball milling speed is set to 350 rpm, and the ball milling is carried out for 6 hours under a N2 protective atmosphere. After the ball milling is completed, the ball-milled in-situ BN / Cu composite powder is loaded into a cylindrical graphite mold with a diameter of 20 mm (Φ20 mm), and then the graphite mold is transferred to a rapid hot pressing sintering furnace (FHP, FHP-828, Suzhou Hateng Technology Co., Ltd.) for sintering to obtain a consolidated in-situ BN / Cu composite block;

[0061] The process parameters of FHP include: initial vacuum degree in the furnace chamber ≤ 10Pa (e.g., it can be 10Pa), initial pressure ≤ 1.5MPa (e.g., it can be 1.5MPa), heating rate 50℃ / min, sintering pressure also increases to 50MPa when sintering temperature rises to 800℃, and heat and pressure are maintained at 800℃ and 50MPa for 20min, and cooled with the furnace after sintering is completed;

[0062] (4) Thermal deformation

[0063] The in-situ BN / Cu composite block is heated at 500°C for 15 minutes, and then the heated in-situ BN / Cu composite block is hot-rolled by a hot rolling processing device, thereby completing the preparation of the in-situ synthesized boron nitride reinforced copper-based composite material, and the corresponding product is abbreviated as an in-situ BN / Cu composite material;

[0064] The process parameters of the hot rolling treatment include: 4 hot rolling passes, 25% rolling deformation in each pass, and returning to the furnace at 500° C. for 5 minutes after each rolling.

[0065] Figure 1 The morphology of in-situ synthesized BN on the copper powder surface is shown. According to the SEM characterization results, BN is successfully generated in-situ on the copper powder surface after calcination (see the arrow), and BN is evenly covered on the copper powder surface, ensuring a good dispersion effect of BN in the copper matrix.

[0066] Comparative Example 1

[0067] (1) First, 0.15 g of boric acid and 2.9 g of urea were added to 100 mL of deionized water and ultrasonically treated for 5 min to ensure complete dissolution to obtain a solution; then the solution was placed in a refrigerator to freeze it to a solid state; and then a freeze dryer was used to dry the frozen solid state at -50 ° C for 36 h to finally obtain a white BN precursor powder;

[0068] (2) placing 2.5 g of BN precursor powder in a tube furnace and calcining it in a mixed gas atmosphere of 85 vol.% N2 and 15 vol.% H2 to obtain BN powder;

[0069] The calcination process parameters include: initial vacuum degree ≤ 10Pa (e.g., it can be 10Pa), heating rate 50°C / min, calcination temperature 900°C, calcination time 3h, and cooling with the furnace after calcination;

[0070] (3) 0.05 g of BN powder and 49.95 g of copper powder obtained in step (2) were added to a ball mill, and a stearic acid control agent was added according to 1% of the sum of the mass of the BN powder and the copper powder, and ball milling beads were added according to a ball-to-material ratio of 15:1. The ball milling speed was set to 350 rpm, and the ball milling was carried out for 6 h under a N2 protective atmosphere. After the ball milling was completed, an external BN / Cu composite powder was obtained; the external BN / Cu composite powder was loaded into a cylindrical graphite mold with a diameter of 20 mm (Φ20 mm), and the graphite mold was transferred to a rapid hot pressing sintering furnace (FHP, FHP-828, Suzhou Hateng Technology Co., Ltd.) for sintering to obtain a consolidated external BN / Cu composite block;

[0071] The process parameters of FHP include: initial vacuum degree in the furnace chamber ≤ 10Pa (e.g., it can be 10Pa), initial pressure ≤ 1.5MPa (e.g., it can be 1.5MPa), heating rate 50℃ / min, sintering pressure also increases to 50MPa when sintering temperature rises to 800℃, and heat and pressure are maintained at 800℃ and 50MPa for 20min, and cooled with the furnace after sintering is completed;

[0072] (4) heating the external BN / Cu composite block at 500° C. for 15 min, and then hot rolling the heated external BN / Cu composite block using a hot rolling processing device to obtain an external BN reinforced copper-based composite material, which is referred to as an external BN / Cu composite material;

[0073] The process parameters of the hot rolling treatment include: 4 hot rolling passes, 25% rolling deformation in each pass, and returning to the furnace at 500° C. for 5 minutes after each rolling.

[0074] Figure 2 (a) shows the morphology of BN synthesized in step (2) of comparative example 1. According to the characterization results of TEM, the thickness of BN is relatively thin, with a sheet diameter of about 10 μm. Thin layer BN can better form a close interface contact with the copper substrate, increase the contact area, and enhance the interface bonding force, which is conducive to stress transfer and the improvement of the overall mechanical properties of the material. High-resolution transmission electron microscopy of BN ( Figure 2 (b), HRTEM) shows that the synthesized BN has good crystallinity. By inverse fast Fourier transform ( Figure 2 (b) Inset), the two diffraction rings of BN are marked, confirming that the synthesized BN is hexagonal.

[0075] The conductivity, hardness and stress-strain tests were performed on the in-situ BN / Cu composite material prepared in Example 1 and the external BN / Cu composite material prepared in Comparative Example 1. The test results are as follows: Figure 3 and Figure 4As shown. Compared with the added BN / Cu composite material, the conductivity, hardness and strength of the in-situ BN / Cu composite material are significantly improved. This is because in the added BN / Cu composite material, there is an interface discontinuity between the copper matrix and BN, which leads to the scattering of electrons at the interface, reducing the overall conductivity of the material; while in the in-situ BN / Cu composite material, the in-situ generated BN and the copper matrix can form a strong interface bond, reducing the interface electron scattering, thereby maintaining a high conductivity. In addition, the in-situ BN is small in size, evenly distributed and has a strong interface bonding force, which can more effectively enhance the hardness of the composite material; while the added BN has limited improvement in the hardness of the composite material due to its uneven dispersion and weak interface bonding force. Furthermore, in the added BN / Cu composite material, the interface bonding between copper and BN is weak, and interface debonding is prone to occur under stress, which in turn affects the strength of the composite material; while in the in-situ BN / Cu composite material, BN is directly generated in situ on the surface of copper particles, which significantly enhances the interface bonding between the copper matrix and BN, improves the load transfer capacity of the composite material, and thus enhances the strength of the composite material.

[0076] The friction performance of the in-situ BN / Cu composite material prepared in Example 1 and the external BN / Cu composite material prepared in Comparative Example 1 were tested respectively. Figure 5 The friction coefficient test results show that the friction coefficient of the in-situ BN / Cu composite material is 0.45, and the friction coefficient of the external BN / Cu composite material is 0.52. The friction coefficient of the in-situ BN / Cu composite material is lower than that of the external BN / Cu composite material. This is mainly attributed to the strong bond between BN and the Cu matrix in the in-situ BN / Cu composite material, which reduces the peeling and shedding of BN, thereby improving the wear resistance of the material and the stability of the friction coefficient. In addition, the uniformly distributed BN in the in-situ BN / Cu composite material provides uniform support during the friction process, making the stress distribution on the friction surface more uniform, reducing the wear rate and enhancing the wear resistance, thereby further improving the wear resistance of the material. In addition, from Figure 6 The wear track profile shows that the wear track of the in-situ BN / Cu composite is shallower (area wear volume 1.7×10 -3 mm 2 ), indicating that its wear resistance is better than that of the BN / Cu composite material (area wear loss 2.7×10 -3 mm 2 ).

[0077] The fracture morphologies of the in-situ BN / Cu composite material prepared in Example 1 and the externally added BN / Cu composite material prepared in Comparative Example 1 were characterized. Figure 7The SEM characterization results of the fracture show that in the added BN / Cu composite, BN and the copper matrix were delaminated and pulled out, proving that the interface bonding between the two is weak, which can easily lead to interface failure and fracture during deformation; on the contrary, in the in-situ BN / Cu composite, BN is firmly embedded in the copper matrix without obvious delamination, which indicates that the load may have been effectively transferred from the copper matrix to BN, and the strong interface bonding provides good load transfer capacity, thereby improving the strength of the composite.

[0078] Example 2

[0079] A method for preparing a copper-based composite material reinforced with boron nitride based on in-situ synthesis comprises the following steps:

[0080] (1) Preparation of BN precursor

[0081] First, 0.35 g (0.0057 mol) of boric acid and 10 g (0.17 mol) of urea were added to 200 mL of deionized water and ultrasonically treated for 8 min to ensure complete dissolution to obtain a solution; then the solution was placed in a refrigerator to freeze it to a solid state; then a freeze dryer was used to dry the frozen solid state at -40 ° C for 48 h, and finally a white BN precursor powder was obtained;

[0082] (2) Preparation of in-situ boron nitride reinforced copper-based composite powders

[0083] 9 g of BN precursor powder and 30 g of copper powder were mixed evenly, and then the mixed powder was placed in a tube furnace and calcined in a mixed gas atmosphere of 85 vol.% N2 and 15 vol.% H2 to generate BN in situ on the surface of the copper powder, thereby obtaining an in-situ boron nitride reinforced copper-based composite powder, which was abbreviated as in-situ BN / Cu composite powder;

[0084] The calcination process parameters include: initial vacuum degree ≤ 10Pa (e.g., it can be 10Pa), heating rate 100°C / min, calcination temperature 850°C, calcination time 4h, and cooling with the furnace after calcination;

[0085] (3) Preparation of in-situ BN / Cu composite bulk

[0086] The in-situ BN / Cu composite powder is added into a ball mill, and a stearic acid control agent is added according to 0.5% of the mass of the in-situ BN / Cu composite powder, and ball milling beads are added according to a ball-to-material ratio of 10:1. The ball milling speed is set to 400 rpm, and the ball milling is carried out for 4 hours under a N2 protective atmosphere. After the ball milling is completed, the ball-milled in-situ BN / Cu composite powder is loaded into a cylindrical graphite mold with a diameter of 20 mm (Φ20 mm), and then the graphite mold is transferred to a rapid hot pressing sintering furnace (FHP, FHP-828, Suzhou Hateng Technology Co., Ltd.) for sintering to obtain a consolidated in-situ BN / Cu composite block;

[0087] The process parameters of FHP include: initial vacuum degree in the furnace chamber ≤ 10Pa (e.g., it can be 10Pa), initial pressure ≤ 1.5MPa (e.g., it can be 0.5MPa), heating rate 100℃ / min, sintering pressure also increases to 30MPa when sintering temperature rises to 900℃, and heat and pressure are maintained at 900℃ and 30MPa for 30min, and cooled with the furnace after sintering is completed;

[0088] (4) Thermal deformation

[0089] The in-situ BN / Cu composite block is heated at 650°C for 10 minutes, and then the heated in-situ BN / Cu composite block is hot-rolled by a hot rolling processing device, thereby completing the preparation of the in-situ synthesized boron nitride reinforced copper-based composite material, and the corresponding product is abbreviated as an in-situ BN / Cu composite material;

[0090] The process parameters of the hot rolling treatment include: 5 hot rolling passes, 20% rolling deformation in each pass, and returning to the furnace at 650° C. for 5 minutes after each rolling.

[0091] Comparative Example 2

[0092] (1) 30 g of copper powder was added to a ball mill, and a stearic acid control agent was added according to 0.5% of the mass of the copper powder, and ball milling beads were added according to a ball-to-material ratio of 10:1. The ball milling speed was set to 400 rpm, and the ball milling was carried out for 4 h under a N2 protective atmosphere. After the ball milling was completed, the copper powder after ball milling was loaded into a cylindrical graphite mold with a diameter of 20 mm (Φ20 mm), and then the graphite mold was transferred to a rapid hot pressing sintering furnace (FHP, FHP-828, Suzhou Hateng Technology Co., Ltd.) for sintering to obtain a consolidated pure copper (Pure Cu) block;

[0093] The process parameters of FHP include: initial vacuum degree in the furnace chamber ≤ 10Pa (e.g., it can be 10Pa), initial pressure ≤ 1.5MPa (e.g., it can be 0.5MPa), heating rate 100℃ / min, sintering pressure also increases to 30MPa when sintering temperature rises to 900℃, and heat and pressure are maintained at 900℃ and 30MPa for 30min, and cooled with the furnace after sintering is completed;

[0094] (2) The pure copper block is heated at 650° C. for 10 min, and then the heated pure copper block is hot-rolled using a hot rolling processing device to obtain a pure copper material, which is abbreviated as Pure Cu;

[0095] The process parameters of the hot rolling treatment include: 5 hot rolling passes, 20% rolling deformation in each pass, and returning to the furnace at 650° C. for 5 minutes after each rolling.

[0096] The conductivity, hardness and stress-strain tests were performed on the in-situ BN / Cu composite material prepared in Example 2 and the Pure Cu material prepared in Comparative Example 2. The test results are as follows: Figure 8 and Fig. 9 As shown. Since BN has high hardness and high modulus, the introduced BN can effectively improve the hardness of the in-situ BN / Cu composite material compared to the Pure Cu material. At the same time, the lattice mismatch between BN and the Cu matrix will cause electron scattering during the conduction process. Compared to the Pure Cu material, the in-situ BN / Cu composite material after the introduction of BN will lead to a decrease in conductivity. Fig. 9 The stress-strain test results show that the ultimate tensile strength of the in-situ BN / Cu composite material is significantly increased by 200MPa compared with Pure Cu, an increase of about 75%. This improvement is mainly due to the high hardness and high strength of BN, whose addition significantly enhances the rigidity and strength of the composite material; in addition, the interaction between BN and the copper matrix further improves the mechanical properties of the composite material.

[0097] The friction performance tests were performed on the in-situ BN / Cu composite material prepared in Example 2 and the Pure Cu material prepared in Comparative Example 2, respectively. Fig.10 The friction coefficient test results show that the friction performance of the in-situ BN / Cu composite material is significantly better than that of the PureCu material, and its friction coefficient is reduced from about 0.7 to 0.43. This is because BN has a solid lubricating effect, which can significantly reduce friction during the friction process; and the in-situ generated BN is closely combined with the copper matrix, so its lubrication effect is more effective and lasting, thereby further reducing the friction coefficient. Fig.11 The wear track profile test results show that the area wear loss of the in-situ BN / Cu composite material is 1.5×10 -3 mm2 , which is significantly lower than 4.3×10 -3 mm 2 , indicating that the prepared in-situ BN / Cu composite material has excellent wear resistance.

[0098] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a copper-based composite material based on in-situ synthesis of boron nitride, characterized in that: The following steps are involved: (1) first dissolving boric acid and urea in water to prepare a solution, then freezing the solution to a solid state, and then freeze-drying the solid state to obtain a BN precursor powder; (2) mixing the BN precursor powder and the copper powder uniformly and transferring them to a sintering furnace, and calcining them under a reducing protective gas atmosphere, so that the BN precursor powder generates BN in situ on the surface of the copper powder, that is, obtaining an in-situ BN / Cu composite powder; (3) sintering the in-situ BN / Cu composite powder to obtain a consolidated in-situ BN / Cu composite block; (4) hot rolling the in-situ BN / Cu composite block to complete the preparation of the in-situ synthesized boron nitride reinforced copper-based composite material; The hot rolling treatment has a rolling temperature of 350° C. to 650° C. and a total rolling deformation of ≥80%.

2. The method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 1, characterized in that: In step (1), the molar ratio of boric acid to urea is 1:20 to 1:30; and / or, In step (1), the freeze-drying temperature is -50°C to -30°C, and the time is 24h to 48h.

3. The method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 1, characterized in that: In step (2), the particle size of the copper powder is 20 μm to 50 μm; and / or, In step (2), the copper powder has a spherical shape.

4. The method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 1, characterized in that: In step (2), the reducing protective gas is a mixed gas of nitrogen and hydrogen; and / or, In step (2), the calcination temperature is 800° C. to 1000° C., and the calcination time is 2 h to 5 h.

5. The method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 4, characterized in that: The volume ratio of nitrogen to hydrogen in the reducing protective gas is 5:1 to 9:

1. and / or, The heating rate during the calcination process is 50°C / min to 100°C / min.

6. The method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 1, characterized in that: In the in-situ BN / Cu composite powder, the mass fraction of BN is 0.1% to 0.5%.

7. The method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 1, characterized in that: In-situ BN / Cu composite powders were sintered by rapid hot pressing.

8. The method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 7, characterized in that: The parameters of the rapid hot pressing sintering include: a sintering temperature of 600° C. to 900° C., a sintering pressure of 30 MPa to 50 MPa, and a sintering time of 10 min to 30 min.

9. A method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 1, 7 or 8, characterized in that: The in-situ BN / Cu composite powder is subjected to a ball milling step before being sintered, that is, the in-situ BN / Cu composite powder is placed in a ball milling jar, a stearic acid control agent is added, and ball milling is performed under a nitrogen or inert gas protective atmosphere, and then sintering is performed after ball milling; The ball milling parameters include: ball milling speed of 200 rpm to 400 rpm, ball milling time of 4 h to 8 h, ball-to-material ratio of 10:1 to 20:1, and the mass of stearic acid of 0.5% to 2% of the mass of the in-situ BN / Cu composite powder.

10. The method for preparing a copper-based composite material based on in-situ synthesis of boron nitride according to claim 1, characterized in that: The specific operation of hot rolling treatment of the in-situ BN / Cu composite block is as follows: The in-situ BN / Cu composite block is first heated at 350°C to 650°C, and then the heated in-situ BN / Cu composite block is hot rolled, wherein the hot rolling passes are 3 to 6 passes, the deformation in each pass is ≤30%, the total rolling deformation is ≥80%, and the return furnace temperature in the hot rolling process is 350°C to 650°C.

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