Nanocrystalline copper and preparation method thereof

Abstract

The invention provides nanocrystalline copper and a preparation method thereof, and relates to the technical field of nanocrystalline material preparation, and the preparation method comprises the following steps: preparing deposited nano-copper by adopting an electro-deposition method, and then performing high-pressure torsion treatment on the deposited nano-copper to obtain the nanocrystalline copper. Initially uniform block nanocrystalline copper is obtained through an electro-deposition method, then high-pressure torsion treatment is conducted on the initial nanocrystalline copper, the grain size of the nanocrystalline copper is further cut, a small-angle grain boundary is introduced, and high-stability uniform nanocrystalline block copper is obtained. Wherein the grain size of the initial nanocrystalline copper is small, the initial nanocrystalline copper is uniformly distributed and presents isometric crystals, the fine initial grain means that the grain boundary proportion is high and the dislocation storage capacity is low, the stable nanocrystalline copper can be obtained by refining the grain through relatively mild high-pressure torsion treatment, the grain boundary energy can be reduced, and the grain boundary energy can be uniformly sheared and deformed; on one hand, the nanostructure is densified, and on the other hand, after the grain boundary energy is reduced, the nanostructure is more stable at high temperature.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanocrystalline material preparation, and particularly relates to a nanocrystalline copper and a preparation method thereof. BACKGROUND

[0002] Nanocrystalline metal materials have a wide application prospect in the fields of aerospace, microelectronics, energy and structural materials due to their excellent mechanical properties such as high strength, high hardness, good wear resistance and corrosion resistance. Among them, nanocrystalline copper (Cu) becomes an important component of high-end electronic devices, wear-resistant parts and high-performance composite materials due to its excellent electrical conductivity, thermal conductivity and mechanical properties. However, how to prepare a nanocrystalline Cu bulk material with high purity, uniform and fine grains, excellent mechanical properties and high thermal stability has been a research focus and challenge in the field of material science.

[0003] At present, the methods for preparing nanocrystalline Cu mainly include two categories: one is severe plastic deformation (SPD) method, such as high-pressure torsion (HPT), equal-channel angular pressing (ECAP) and high-energy ball milling (HEBM); the other is electrodeposition method. However, the SPD method has the following problems: (1) only suitable for preparing small-size samples; (2) the prepared nanocrystalline Cu has more defects and higher grain boundary energy, which is prone to grain growth at high temperature, resulting in poor thermal stability and difficulty in maintaining nanocrystalline structure for a long time; (3) the SPD technology usually requires special equipment and high processing cost, and is not easy to mass-produce; the electrodeposition method has the following problems: (1) the grain of nanocrystalline Cu is prone to grow at high temperature, and has poor thermal stability, thereby reducing its mechanical properties; (2) some electrodeposited nanocrystalline Cu samples may have pores, cracks or uneven deposition, which affects the final mechanical properties. SUMMARY

[0004] Therefore, the application provides a nanocrystalline copper and a preparation method thereof, which can solve the problem of poor thermal stability of nanocrystalline copper in the prior art.

[0005] In order to solve the above problems, the application provides a preparation method of nanocrystalline copper, which comprises the following steps:

[0006] Step 1): preparing a deposited-state nanocrystalline copper alloy by using an electrodeposition method;

[0007] Step 2): performing high-pressure torsion treatment on the deposited-state nanocrystalline copper alloy to obtain nanocrystalline copper.

[0008] Further, in the step 1), the step of preparing the as-deposited nanometer copper alloy by electrodepositing specifically comprises:

[0009] Preparation of plating solution: preparing a plating solution containing copper sulfate and concentrated sulfuric acid;

[0010] Electrodepositing: electrodepositing the plating solution to obtain the as-deposited nanometer copper alloy; wherein the anode is pure copper and the cathode is a zirconium-based amorphous plate.

[0011] Further, in the step of preparing the plating solution, the copper sulfate is CuSO4·5H2O; the concentration of CuSO4·5H2O is 200-240 g / L; the concentration of the sulfuric acid is 40-60 g / L; and / or

[0012] The pH value of the plating solution is ≤1.

[0013] Further, the step of preparing the plating solution specifically comprises: dissolving the CuSO4·5H2O and the concentrated sulfuric acid in deionized water, filtering after stirring and dissolving to obtain a filtrate; and then performing pre-plating treatment to obtain the plating solution.

[0014] Further, the pre-plating treatment uses the filtrate as the electrolyte, a copper plate as the anode and a copper sheet as the cathode; the pre-plating treatment time is 20-30 h.

[0015] Preferably, an additive is added to the filtrate after the pre-plating treatment; further preferably, the additive is thiourea; the concentration of the thiourea is ≤0.02 g / L.

[0016] Further, the temperature of the plating solution is 10-20℃; and / or

[0017] The current density is 50-200 mA / cm 2 .

[0018] Further, in the step 1), the structure of the as-deposited nanometer copper alloy is FCC structure; the grain size of the as-deposited nanometer copper alloy is 20-200 nm.

[0019] Further, in the step 2), the pressure of the high-pressure torsion treatment is 0.5-1 GPa; and / or

[0020] The torsion angle of the high-pressure torsion treatment is 5-10°; and / or

[0021] The torsion frequency of the high-pressure torsion treatment is 1-5 Hz; and / or

[0022] The torsion frequency of the high-pressure torsion treatment is 1-5 Hz; and / or

[0023] The cycle number of the high-pressure torsion treatment is 1000-3000.

[0024] Further, in the high-pressure torsion treatment of the step 2):

[0025] The as-deposited nanometer copper is subjected to liquid nitrogen cooling treatment.

[0026] Further, after the step 1), the as-deposited nanometer copper is subjected to stacking treatment.

[0027] In another aspect, the application provides a nanocrystalline copper, wherein the grain size of the nanocrystalline copper is 20-50 nm, and the grain size of the nanocrystalline copper is 19-21 nm after heat treatment at 300℃ for 0.5 h.

[0028] Preferably, the nanocrystalline copper is obtained by the preparation method of any one of the above.

[0029] The nanocrystalline copper and the preparation method thereof have the following beneficial effects:

[0030] 1. In one aspect, the application provides a preparation method of nanocrystalline copper, comprising the following steps: preparing as-deposited nanometer copper by electrodeposition; and then subjecting the as-deposited nanometer copper to high-pressure torsion treatment to obtain nanocrystalline copper. It should be noted that the initial nanocrystalline copper is obtained by electrodeposition, and then the initial nanocrystalline copper is subjected to high-pressure torsion treatment to further refine, densify and stabilize the grain size of the nanocrystalline copper, thereby obtaining high-stability nanocrystalline copper. Since the grain size of the initial nanocrystalline copper is small and uniformly distributed, the small initial grain size means a high proportion of grain boundaries and a low dislocation storage capacity. Therefore, the grain size can be refined to obtain nanocrystalline copper by relatively mild high-pressure torsion treatment (e.g., smaller pressure and torsion number of high-pressure torsion treatment). The relatively mild high-pressure torsion treatment generates continuous shear stress by low-speed shearing, promotes coordinated rotation of nanocrystalline grains, gradually reduces the orientation difference between adjacent grains, converts high-angle grain boundaries into low-angle grain boundaries, directly reduces the grain boundary energy, and reduces the thermodynamic driving force for grain growth after the grain boundary energy is reduced, thereby making the nanometer structure more stable at high temperatures.

[0031] 2. Further, liquid nitrogen cooling treatment is performed during the high-pressure torsion treatment, which can reduce the thermal effect during plastic deformation, thereby slowing down the grain self-growth effect caused by heat release during deformation and further improving the thermal stability. In addition, the stacking treatment is performed on multiple initial nanocrystalline coppers (as-deposited nanometer copper alloy), which facilitates subsequent high-pressure torsion (HPT) treatment of the samples. Moreover, the HPT is applied after stacking, which can increase the rolling friction effect between bulk Cu (initial nanocrystalline copper) and make the shearing effect between the layers better, thereby increasing the structural deformation effect caused by shearing deformation, which is beneficial to further refining the grain size.

[0032] 3. In another aspect, the present invention provides nanocrystalline copper obtained by any of the preparation methods described above, wherein the nanocrystalline copper has a lamellar structure and a grain size of 20-50 nm. When the grain size is smaller, the motion of full dislocations is suppressed, and the coordinated deformation is mainly caused by the emission of partial dislocations from the grain boundaries, resulting in relaxation in the grain boundary region and reduced grain boundary energy, thereby improving thermal stability and having excellent comprehensive mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. The drawings described below are merely exemplary. Those skilled in the art can, without inventive effort, derive other implementation drawings based on the provided drawings.

[0034] Figure 1 is a macroscopic image of nanocrystalline copper in Example 1 of the present invention;

[0035] Figure 2 is the X-ray diffraction pattern of nanocrystalline copper in Example 1 of the present invention;

[0036] Figure 3 Middle: a, b, c, d are respectively TEM bright field image, TEM dark field image, diffraction ring image, and grain size statistical diagram of the nanocrystalline copper in Example 1 of the present invention;

[0037] Figure 4 Middle: a, b, c, and d are respectively a TEM bright field image, a TEM dark field image, a diffraction ring image, and a grain size statistical diagram of the nanocrystalline copper after heat treatment in Example 1 of the present invention;

[0038] Figure 5 Middle: a, b, c, and d are respectively a TEM bright field image, a TEM dark field image, a diffraction ring image, and a grain size statistical diagram of the nanocrystalline copper in Example 2 of the present invention;

[0039] Figure 6 Middle: a, b, c, and d are respectively a TEM bright field image, a TEM dark field image, a diffraction ring image, and a grain size statistical diagram of the nanocrystalline copper after heat treatment in Example 2 of the present invention;

[0040] Figure 7 is an SEM image of nanocrystalline copper in Example 3 of the present invention;

[0041] Figure 8 is an SEM image of the nanocrystalline copper after heat treatment in Example 3 of the present invention;

[0042] Figure 9is a SEM image of the nanocrystalline copper in Example 4 of the present application;

[0043] Figure 10 is a SEM image of the nanocrystalline copper in Example 4 of the present application after heat treatment;

[0044] Figure 11 is a SEM image of the nanocrystalline copper in Comparative Example 1 of the present application;

[0045] Figure 12 is a SEM image of the nanocrystalline copper in Comparative Example 1 of the present application after heat treatment;

[0046] Figure 13 In the figure, a, b, c, and d are respectively a TEM bright field image, a TEM dark field image, a diffraction ring image, and a grain size statistical diagram of the nanocrystalline copper in Comparative Example 1 of the present application after heat treatment;

[0047] Figure 14 In the figure, a, b, c, and d are respectively a TEM bright field image, a TEM dark field image, a diffraction ring image, and a grain size statistical diagram of the nanocrystalline copper in Comparative Example 2 of the present application after heat treatment;

[0048] Figure 15 is a SEM image of the nanocrystalline copper in Comparative Example 3 of the present application;

[0049] Figure 16 is a SEM image of the nanocrystalline copper in Comparative Example 4 of the present application;

[0050] Figure 17 is a SEM image of the nanocrystalline copper in Comparative Example 4 of the present application after heat treatment. DETAILED DESCRIPTION

[0051] To further clarify the technical means and effects taken by the present application to achieve the predetermined purposes, the specific embodiments, structures, features, and effects thereof according to the present application are described in detail below in combination with the drawings and preferred embodiments. In the following description, different "an embodiment" or "embodiments" do not necessarily refer to the same embodiment. In addition, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0052] The present application provides a preparation method of nanocrystalline copper, comprising the following steps:

[0053] Step 1): preparing a deposited-state nanocrystalline copper alloy by using an electrodeposition method;

[0054] This step is specifically: dissolving copper sulfate pentahydrate CuSO4·5H2O and concentrated sulfuric acid in deionized water, filtering after stirring and dissolving to obtain a filtrate; then performing pre-plating treatment to obtain a plating solution;

[0055] Then the above plating solution is subjected to electrodeposition to obtain the as-deposited nanometer copper; wherein the anode is pure copper and the cathode is a zirconium-based amorphous plate.

[0056] The concentration of CuSO4'5H2O is 200-240 g / L; the concentration of H2SO4 is 40-60 g / L; and the pH value of the plating solution is ≤1. Since trace elements have a great influence on the purity of the electrodeposited sample, the plating solution needs to be pre-plated to further purify the plating solution; the pre-plating treatment uses the filtrate as the electrolyte, uses a 60x60x5 mm 3 copper plate as the anode, and uses a 25x25x1 mm 3 copper sheet as the cathode; the pre-plating treatment time is 20-30 h, and the current density is 50-200 A / cm 2 ; preferably, an additive is added to the filtrate after the pre-plating treatment; further preferably, the additive is thiourea; the concentration of the thiourea is ≤0.02 g / L; on the one hand, thiourea has a significant grain refinement effect on electrodeposited Cu, and on the other hand, controlling the amount can avoid introducing impurities;

[0057] During the electrodeposition, the temperature of the plating solution is 10-20℃; the current density is 50-200 mA / cm 2 ; the anode is a pure copper plate with a purity of 99.999%, and the cathode is a zirconium-based amorphous plate; wherein the anode consumes Cu, and the cathode and the anode are two parallel plates, which make the electric field lines between the plates more uniform, thus being more conducive to depositing a uniform alloy sample; preferably, before electrodeposition, the amorphous plate is polished by using 400#, 1000#, 2000#, and 5000# sandpaper in sequence; the amorphous plate is selected in order to make the crystal grains as randomly oriented as possible during deposition to obtain equiaxed grains;

[0058] The structure of the obtained as-deposited nanometer copper alloy is FCC structure; the grain size of the as-deposited nanometer copper is 20-200 nm.

[0059] Step 2): subjecting the as-deposited nanometer copper to high-pressure torsion treatment to obtain nanocrystalline copper;

[0060] This step specifically includes: stacking multiple as-deposited nanometer copper alloys, and then subjecting them to high-pressure torsion treatment in a liquid nitrogen environment to obtain nanocrystalline copper.

[0061] In this step, the as-deposited nanometer copper alloy is cut into thin blocks with an area of 4x4 mm 2 ; preferably, two blocks are stacked together for high-pressure torsion deformation to increase the deformation degree of the sample, thereby obtaining better grain refinement effect;

[0062] The parameters of the high-pressure torsion treatment are as follows: the pressure is 0.3-1 GPa, the torsion angle is 5-10°, the frequency is 1-5 Hz, and the cycle number is 500-3000. The parameters of the high-pressure torsion treatment are relatively mild in terms of load and rotation speed, which helps to maintain the bulk properties of the electrodeposited sample without forming fragments. The anvil and the pad of the high-pressure torsion treatment are made of high-speed steel, which has high strength and hardness and can withstand high load.

[0063] In some embodiments, before the high-pressure torsion treatment, the as-deposited nano-copper alloy is polished by using 400#, 1000# and 2000# sandpaper in sequence to remove the oxide film on the surface of the as-deposited nano-copper alloy.

[0064] It should be noted that the initial nanocrystalline copper is obtained by the electrodeposition method, and the initial nanocrystalline copper is subjected to high-pressure torsion treatment to further refine the grain size of the nanocrystalline copper. Since the initial nanocrystalline copper has small and uniform grain size, the small initial grain size means a high proportion of grain boundaries and low dislocation storage capacity. The relatively mild high-pressure torsion treatment (e.g., smaller pressure and torsion number) can refine the grain size to obtain nanocrystalline copper. The relatively mild high-pressure torsion treatment generates continuous shear stress through low-speed shearing, promotes coordinated rotation of nanocrystalline grains, gradually reduces the orientation difference between adjacent grains, converts high-angle grain boundaries into low-angle grain boundaries, directly reduces the grain boundary energy, and reduces the thermodynamic driving force for grain growth after the grain boundary energy is reduced. The nanometer structure is more stable at high temperature.

[0065] Meanwhile, pores, micro-cracks or dendritic defects may be generated in the electrodeposition process due to parameter fluctuations. After superposition, the interface of the two samples can be tightly fitted through polishing treatment (removal of surface oxide layer and rough structure). Under the high-pressure effect of subsequent high-pressure torsion, the defects of the bulk sample can be closed by extrusion, thereby improving the overall density of the material.

[0066] In addition, the high-pressure torsion treatment is performed in a liquid nitrogen environment. On the one hand, the liquid nitrogen environment prevents the possibility of Cu oxidation during deformation and prevents the introduction of impurities. On the other hand, since heat is generated during deformation due to friction, the liquid nitrogen environment can prevent grain growth caused by heat generation, which helps to obtain smaller grains.

[0067] By superimposing a plurality of initial nanocrystalline coppers (as-deposited nano-copper), a sample suitable for subsequent high-pressure torsion (HPT) treatment is obtained. The application of HPT after superposition can increase the rolling friction effect between the bulk Cu (initial nanocrystalline copper), so that the shearing effect between the layers is better, thereby increasing the structural deformation effect caused by shear deformation, which is beneficial to further refining the grain size.

[0068] In another aspect, the present application provides a nanocrystalline copper prepared by any of the above-mentioned methods, wherein the nanocrystalline copper has a grain size of 20-50 nm in a lamellar structure. The grain size is the thickness of the lamellar structure. When the grain size is small, full dislocation movement is inhibited, and deformation is mainly coordinated by partial dislocations emitted from the grain boundary, resulting in relaxation of the grain boundary region, reduction of the grain boundary energy, and thus improved thermal stability, thereby having excellent comprehensive mechanical properties.

[0069] The present application is further illustrated below with reference to specific examples and comparative examples.

[0070] Example 1

[0071] The present example provides a method for preparing nanocrystalline copper, comprising the following steps:

[0072] Step 1): Dissolve 240 g / L of copper sulfate pentahydrate CuSO4·5H2O and 60 g / L of concentrated sulfuric acid in deionized water, stir using a magnetic stirring heating table, and control the temperature at 25±1℃. After stirring and dissolving, filter with filter paper. Perform 24 h pre-plating treatment on the filtrate after filtering with filter paper. The pre-plating treatment uses a pure copper plate as an anode and a coarse-grained copper sheet as a cathode, and the current density is 50 mA / cm 2 After pre-plating treatment, a plating solution is obtained.

[0073] Then place the plating solution in a low-temperature constant-temperature tank, use water as a cooling liquid, and control the temperature of the plating solution to be 15℃. Use direct current deposition to obtain a deposited nanocrystalline copper alloy.

[0074] The process parameters for direct current deposition are as follows: use a pure copper plate as a sacrificial anode, use a zirconium-based amorphous plate as a cathode, control the current density to be constant at 100 mA / cm 2 , and the deposition time is 2 h. The thickness of the obtained deposited nanocrystalline copper alloy is 120-150 μm.

[0075] Step 2): Cut the above-mentioned deposited nanocrystalline copper alloy into blocks with a size of 4×4 mm 2 . Stack two blocks together and place them on a pad. After liquid nitrogen environmental cooling, perform high-pressure torsion treatment to obtain a nanocrystalline copper.

[0076] The pressure for high-pressure torsion treatment is 1 GPa, the torsion angle is 5°, the frequency is 1 Hz, and the cycle number is 3000 times.

[0077] Figure 1 The surface macroscopic picture of the nanocrystalline copper prepared in this example can be seen. The surface of the nanocrystalline copper sample is bright and has no signs of oxidation, indicating that it has excellent corrosion resistance. From the Figure 2It can be seen that the X-ray diffraction pattern of the nanocrystalline copper of the embodiment is a typical FCC structure, and the nanocrystalline copper alloy has a random orientation distribution, and it is found that the grain size of the nanocrystalline copper prepared by the two-step method is reduced to 15 nm from 64 nm of the nanocrystalline copper obtained by only the first step of electrodeposition according to the half-height width of the (111) peak position of the X-ray diffraction pattern; Figure 3 The TEM bright-dark field image and diffraction pattern of the embodiment are shown, the grain size distribution is obtained according to the dark field image, the grain size of the nanocrystalline copper of the embodiment is 19 nm, which is similar to the grain size obtained by the Scherrer formula, proving the reliability of the XRD data; the nanocrystalline copper of the embodiment is heat-treated at 300℃ / 0.5h, Figure 4 The bright-dark field image and diffraction pattern of the heat-treated sample are shown, and the grain size is 21 nm, which shows that the grain size of the sample does not grow substantially, and exhibits high thermal stability.

[0078] Embodiment 2

[0079] The embodiment provides a preparation method of nanocrystalline copper, comprising the following steps:

[0080] Step 1): 240g / L of copper sulfate pentahydrate CuSO4·5H2O and 60g / L of concentrated sulfuric acid are dissolved in deionized water, magnetic stirring is used to stir with a magnetic stirring heating table, and the temperature is controlled at 25±1℃; after stirring and dissolving, filtration is performed with filter paper; 24h pre-plating treatment is performed on the filtrate after filtration with filter paper, pure copper plate is used as an anode, coarse-grained copper sheet is used as a cathode, and the current density is 50mA / cm 2 ; after pre-plating treatment, 0.02g / L of thiourea is added, and after complete dissolution under electromagnetic stirring, a plating solution is obtained;

[0081] Then the plating solution is placed in a low-temperature constant-temperature tank, water is used as a cooling liquid, the temperature of the plating solution is adjusted to 15℃, and a deposited nanocrystalline copper alloy is obtained by direct current electrodeposition;

[0082] 2 The process parameters of direct current electrodeposition are as follows: pure copper plate is used as a sacrificial anode, zirconium-based amorphous plate is used as a cathode, the current density is controlled to be constant at 100mA / cm 2 , and the deposition time is 2h.

[0083] Step 2): the deposited nanocrystalline copper alloy is cut into a block with a size of 4×4mm 2 , two blocks are stacked and placed on a pad, and after liquid nitrogen environmental cooling, high-pressure torsion treatment is performed to obtain nanocrystalline copper;

[0084] The pressure of the high-pressure torsion treatment is 1GPa, the torsion angle is 5°, the frequency is 1Hz, and the cycle number is 3000 times.

[0085] Figure 5 For the TEM bright-dark field image and diffraction pattern of the nanocrystalline copper of the present example, the grain size distribution is obtained by counting the grain size according to the dark field image, which shows that the grain size of the nanocrystalline copper of the present example is 12 nm; the nanocrystalline copper of the present example is heat treated at 300℃ / 0.5h, Figure 6 For the bright-dark field image and diffraction pattern of the heat treated sample, and the grain size is counted in turn to be 20 nm, the grain structure with small size is still maintained, which shows high thermal stability.

[0086] Example 3

[0087] The present example provides a preparation method of nanocrystalline copper, which comprises the following steps:

[0088] Step 1): Dissolve 240g / L of copper sulfate pentahydrate CuSO4·5H2O and 60g / L of concentrated sulfuric acid in deionized water, stir with a magnetic stirring heating table, and control the temperature at 25±1℃. After stirring and dissolving, filter with filter paper; perform 24h pre-plating treatment on the filtrate after filtering with filter paper, use pure copper plate as anode and coarse-grained copper sheet as cathode, and the current density is 50mA / cm 2 ; obtain the plating solution after pre-plating treatment;

[0089] Then place the plating solution in a low-temperature constant temperature tank, use water as cooling liquid, control the temperature of the plating solution to be 15℃, and obtain the deposited nanocrystalline copper alloy by direct current deposition;

[0090] The process parameters of direct current deposition are as follows: use pure copper plate as sacrificial anode and zirconium-based amorphous plate as cathode, control the current density to be constant at 100mA / cm 2 , and the deposition time is 2h. The thickness of the obtained deposited nanocrystalline copper alloy is 120-150μm.

[0091] Step 2): Cut the above-mentioned deposited nanocrystalline copper alloy into blocks with a size of 4×4mm 2 , stack two blocks together and place them on a pad, perform high-pressure torsion treatment after liquid nitrogen environmental cooling, and obtain nanocrystalline copper;

[0092] The pressure of high-pressure torsion treatment is 0.5GPa, the torsion angle is 5°, the frequency is 1Hz, and the cycle number is 1500 times.

[0093] It is found by SEM observation that the grain size of the nanocrystalline copper prepared by the two-step method meets the expectation (such as Figure 7 ), and the grain does not grow after heat treatment at 300℃ for 0.5h (such as Figure 8 ), which shows high thermal stability.

[0094] Example 4

[0095] The present embodiment provides a method for preparing nanocrystalline copper, comprising the following steps:

[0096] Step 1): 240 g / L of copper sulfate pentahydrate CuSO4·5H2O and 60 g / L of concentrated sulfuric acid are dissolved in deionized water, and a magnetic stirring heating table is used for stirring while controlling the temperature at 25±1℃. After stirring and dissolving, the solution is filtered with filter paper; 24h pre-plating treatment is performed on the filtrate after filtering with filter paper, and the pre-plating treatment uses a pure copper plate as an anode and a coarse-grained copper sheet as a cathode, with a current density of 50 mA / cm 2 ; a plating solution is obtained after pre-plating treatment;

[0097] Then the plating solution is placed in a low-temperature constant temperature tank, and water is used as a cooling liquid to control the temperature of the plating solution to 15℃. A direct current deposition is used to obtain a deposited nanocrystalline copper alloy.

[0098] The process parameters of the direct current deposition are as follows: a pure copper plate is used as a sacrificial anode, a zirconium-based amorphous plate is used as a cathode, the current density is controlled to be constant at 100 mA / cm 2 , and the deposition time is 2h. The thickness of the deposited nanocrystalline copper alloy obtained is 120-150μm.

[0099] Step 2): The deposited nanocrystalline copper alloy is cut into blocks of 4×4mm 2 , and two blocks are stacked and placed on a pad. After liquid nitrogen environmental cooling, high-pressure torsion treatment is performed to obtain nanocrystalline copper.

[0100] The pressure of the high-pressure torsion treatment is 0.7GPa, the torsion angle is 5°, the frequency is 1Hz, and the cycle number is 3000 times.

[0101] Figure 9 The SEM image of the nanocrystalline copper of the present embodiment is shown in FIG. 1. It is observed that the present embodiment successfully obtains nanocrystalline copper with a smaller grain size. After heat treatment at 300℃ for 0.5h, Figure 10 The SEM image of the present embodiment after heat treatment is shown in FIG. 2. It is found that the grain size does not change significantly, indicating that it also has good thermal stability.

[0102] Comparative Example 1

[0103] The present comparative example provides a method for preparing nanocrystalline copper, comprising the following steps:

[0104] 240g / L of copper sulfate pentahydrate CuSO4·5H2O, 60g / L of concentrated sulfuric acid are dissolved in deionized water, and a magnetic stirring heating table is used for stirring while controlling the temperature at 25±1℃, and after stirring and dissolving, filter paper is used for filtration; 24h pre-plating treatment is carried out in the filtrate after filtration with filter paper, and the pre-plating treatment uses a pure copper plate as an anode and a coarse-grained copper sheet as a cathode, and the current density is 100mA / cm 2 ; the plating solution is obtained after pre-plating treatment;

[0105] Then the plating solution is placed in a low-temperature constant-temperature tank, water is used as a cooling liquid, the temperature of the plating solution is regulated to 15℃, and direct current deposition is used to obtain deposited nano-copper alloy;

[0106] The process parameters of direct current deposition are as follows: a pure copper plate is used as a sacrificial anode, a zirconium-based amorphous plate is used as a cathode, the current density is controlled to be constant at 100mA / cm 2 , and the deposition time is 2h.

[0107] Figure 11 The SEM image of the electrodeposited sample of the present comparative example shows that the grain size is about 150nm, and there are abnormally grown grains (grain size is 1-2μm). This method cannot realize grain refinement because the second step of high-pressure torsion is not performed. In addition, the electrodeposited nanocrystalline copper of the present comparative example is heat-treated at 300℃ / 0.5h, Figure 12 The SEM image of the sample after heat treatment shows that the grains have been obviously coarsened, and the grain size is uniformly distributed at about 2-5μm, and there are annealing holes, indicating that the nano-copper in the present comparative example has poor thermal stability.

[0108] Comparative Example 2

[0109] The present comparative example provides a preparation method of nanocrystalline copper, comprising the following steps:

[0110] 240g / L of copper sulfate pentahydrate CuSO4·5H2O, 60g / L of concentrated sulfuric acid are dissolved in deionized water, and a magnetic stirring heating table is used for stirring while controlling the temperature at 25±1℃, and after stirring and dissolving, filter paper is used for filtration; 24h pre-plating treatment is carried out in the filtrate after filtration with filter paper, and the pre-plating treatment uses a pure copper plate as an anode and a coarse-grained copper sheet as a cathode, and the current density is 100mA / cm 2 ; 0.02g / L of thiourea is added after pre-plating treatment, and after complete dissolution by electromagnetic stirring, the plating solution is obtained;

[0111] Then the plating solution is placed in a low-temperature constant-temperature tank, water is used as a cooling liquid, the temperature of the plating solution is regulated to 15℃, and direct current deposition is used to obtain nanocrystalline copper;

[0112] The process parameters of direct current electrodeposition are as follows: taking pure copper plate as a sacrificial anode, taking zirconium-based amorphous plate as a cathode, controlling the current density to be constant at 100 mA / cm 2 , and the deposition time is 2 h.

[0113] The nano-crystalline copper prepared by electrodeposition in the present comparative example, Figure 13 The TEM bright-field image, diffraction pattern and grain size distribution diagram of the present comparative example show that the microstructure presents an equiaxed crystal morphology, and the grain size is 20 nm. However, the nano-crystalline copper in the present comparative example is subjected to heat treatment at 300℃ / 0.5h, Figure 14 The bright-field image of the sample after heat treatment shows that the grains have been obviously coarsened, the grain size is 500nm-2μm, and micrometer-sized holes are presented, indicating that the nano-crystalline copper has not only poor thermal stability, but also very low density. This is because the nano-crystalline copper prepared by electrodeposition presents an equiaxed grain (as shown in the TEM image), which is different from the grain of the nano-crystalline copper subjected to high-pressure torsion in the embodiment (lamellar structure). The grain boundary energy of the equiaxed grain is higher than that of the lamellar structure, so the stability of the equiaxed grain is poor.

[0114] Comparative example 3

[0115] The present comparative example provides a preparation method of nano-crystalline copper, comprising the following steps:

[0116] Step 1): 240g / L of copper sulfate pentahydrate CuSO4·5H2O and 60g / L of concentrated sulfuric acid are dissolved in deionized water, and a magnetic stirring heating table is used for stirring while the temperature is controlled at 25±1℃. After stirring and dissolving, the solution is filtered with filter paper; 24h pre-plating treatment is performed on the filtrate after filtration, the pre-plating treatment takes a pure copper plate as an anode, takes a coarse-grained copper sheet as a cathode, and the current density is 100mA / cm 2 ; the plating solution is obtained after pre-plating treatment;

[0117] Then the plating solution is placed in a low-temperature constant-temperature tank, water is used as a cooling liquid, the temperature of the plating solution is regulated to 15℃, and a direct current electrodeposition is adopted to obtain a deposited nano-crystalline copper alloy;

[0118] The process parameters of direct current electrodeposition are as follows: taking pure copper plate as a sacrificial anode, taking zirconium-based amorphous plate as a cathode, controlling the current density to be constant at 100 mA / cm 2 , and the deposition time is 2 h.

[0119] Step 2): the deposited nano-crystalline copper alloy is cut into a block with a size of 4×4mm 2 , two blocks are stacked and placed on a pad, subjected to high-pressure torsion treatment after liquid nitrogen environmental cooling, and a nano-crystalline copper is obtained;

[0120] Among them, the pressure of high-pressure torsion treatment is 0.3GPa, the torsion angle is 5°, the frequency is 1Hz, and the cycle number is 1500 times.

[0121] In this comparative example, a load smaller than the specified range and fewer cycles were used for high-pressure torsion. Figure 15 For the final nanocrystalline copper, the load is too small to achieve further shear refinement of the grains, and the grains do not have structural evolution characteristics. Therefore, high-pressure torsion does not change the structure and improve its structural stability.

[0122] Comparative Example 4

[0123] This comparative example provides a method for preparing nanocrystalline copper, comprising the following steps:

[0124] Step 1): 240 g / L of copper sulfate pentahydrate CuSO4·5H2O and 60 g / L of concentrated sulfuric acid are dissolved in deionized water, stirred using a magnetic stirring heating table while controlling the temperature at 25±1°C, stirred and dissolved, and filtered with filter paper; the filtrate after filtration with filter paper is pre-plated for 24 hours, with a pure copper plate as the anode and a coarse-grained copper sheet as the cathode, and a current density of 100 mA / cm 2 ; After pre-plating treatment, a plating solution is obtained;

[0125] The plating solution was then placed in a low-temperature constant temperature bath, and water was used as a coolant to adjust the temperature of the plating solution to 15°C, and a deposited nano-copper alloy was obtained by direct current electrodeposition.

[0126] The process parameters of DC electrodeposition are: pure copper plate as sacrificial anode, zirconium-based amorphous plate as cathode, and the current density is controlled to be constant at 100 mA / cm 2 , the deposition time is 2h.

[0127] Step 2): Cut the deposited nano-copper alloy into blocks of 4×4 mm2, stack two blocks and place them on a pad, cool them in a liquid nitrogen environment, and then perform a high-pressure torsion treatment to obtain nanocrystalline copper;

[0128] The pressure of the high-pressure torsion treatment is 0.5 GPa, the torsion angle is 5°, the frequency is 1 Hz, and the number of cycles is 500.

[0129] In this comparative example, a load smaller than the specified range and fewer cycles were used for high-pressure torsion. Figure 16 The SEM image of the nanocrystalline copper obtained in this comparative example shows that although a certain grain refinement effect is achieved, the overall material is not uniform and some grains are still larger in size. Figure 17 This is the SEM image of the comparative example after heat treatment at 300°C for 0.5h. It is observed that the grains have grown to the micron level, indicating that its thermal stability is poor.

[0130] Those skilled in the art can easily understand that the advantageous technical features of the above-mentioned modes can be freely combined and superimposed without conflict.

[0131] The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application. The above merely describes the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing nanocrystalline copper, characterized in that: The following steps are involved: Step 1): preparing deposited nano-copper by electrodeposition; Step 2): performing high-pressure twisting treatment on the deposited nano-copper to obtain nano-crystalline copper.

2. The method for preparing nanocrystalline copper according to claim 1, wherein: In step 1), the step of preparing the deposited nano-copper alloy by electrodeposition specifically includes: Plating solution preparation: prepare plating solution containing copper sulfate and concentrated sulfuric acid; Electrodeposition: Electrodepositing the plating solution to obtain the deposited nano-copper alloy; wherein the anode is pure copper metal and the cathode is a zirconium-based amorphous plate.

3. The method for preparing nanocrystalline copper according to claim 2, wherein: In the step of preparing the plating solution: The copper sulfate is copper sulfate pentahydrate CuSO4.5H2O; the concentration of copper sulfate pentahydrate CuSO4'5H2O is 200-240 g / L; the concentration of sulfuric acid is 40-60 g / L; and / or The pH value of the plating solution is less than 1.

4. The method for preparing nanocrystalline copper according to claim 3, wherein: The steps of preparing the plating solution specifically include: dissolving the copper sulfate pentahydrate CuSO4·5H2O and concentrated sulfuric acid in deionized water, stirring and dissolving, and then filtering to obtain a filtrate; and then performing a pre-plating treatment to obtain the plating solution; The pre-plating treatment uses the filtrate as the electrolyte, the copper plate as the anode, and the copper sheet as the cathode; the pre-plating treatment time is 20-30 hours; Preferably, an additive is added to the filtrate after the pre-plating treatment; further preferably, the additive is thiourea; and the concentration of thiourea is ≤0.02 g / L.

5. The method for preparing nanocrystalline copper according to claim 2, wherein: In the step of electroplating: the temperature of the plating solution is 10-20°C; and / or Current density is 50-200mA / cm 2 .

6. The method for preparing nanocrystalline copper according to claim 1, wherein: In the step 1), the structure of the deposited nano-copper is an FCC structure; and the grain size of the deposited nano-copper is 20-200 nm.

7. The method for preparing nanocrystalline copper according to claim 1, wherein: In the step 2), the pressure of the high-pressure torsion treatment is 0.5-1 GPa; and / or The twisting angle of the high-pressure twisting treatment is 5-10°; and / or The torsion frequency of the high-pressure torsion treatment is 1-5 Hz; and / or The high-pressure torsion treatment has a cycle number of 1000-3000 times.

8. The method for preparing nanocrystalline copper according to claim 1, wherein: In the high-pressure twisting process of step 2): The deposited nano-copper alloy is subjected to liquid nitrogen cooling treatment.

9. The method for preparing nanocrystalline copper according to any one of claims 1 to 8, characterized in that: After step 1), the method further includes: subjecting the plurality of deposited nano-coppers to a superimposed high-pressure torsion treatment.

10. A nanocrystalline copper, characterized in that: The nanocrystalline copper has a lamellar structure and a grain size of 12-20 nm. After the nanocrystalline copper is heat-treated at 300° C. for 0.5 h, the grain size is 19-21 nm. Preferably, the nanocrystalline copper is obtained by the preparation method according to any one of claims 1 to 9.

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