CuSn10Bi8Zn3 lead-free copper-based nanopowder and a preparation method thereof

Abstract

The application provides a CuSn10Bi8Zn3 lead-free copper-based nano-powder and a preparation method thereof, and belongs to the technical field of metal powder preparation. The chemical composition of the powder comprises Sn 8-12%, Bi 6-10%, Zn 2-4%, unavoidable impurities with a total amount of less than or equal to 0.1%, and the balance of Cu, according to mass percentage. The average particle size of the powder is 20-100 nm, the particle size distribution index PDI is less than or equal to 0.25, the oxygen content is less than or equal to 300 ppm, Sn and Zn are dissolved in the Cu matrix to form a supersaturated single-phase solid solution, Bi is uniformly distributed in the crystal and the grain boundary in the form of a dispersed phase with a size of 5-30 nm, and the area proportion deviation of the Bi phase is less than or equal to 10%. The powder prepared by the application has excellent formability and sinterability, and the component after sintering has high strength and long service life, and meets the high-load service requirements of an engine.

Description

Technical Field

[0001] This invention relates to the field of metal powder preparation technology, specifically to a lead-free copper-based nanopowder CuSn10Bi8Zn3 and its preparation method. The powder product prepared by this invention is mainly used in the preparation of friction-reducing and wear-resistant components such as bearings, bushings, and valve seats for internal combustion engines. Background Technology

[0002] With increasingly stringent environmental regulations, the use of lead-containing copper-based alloys is being gradually restricted due to the toxicity of lead. Lead-free copper-based alloys have become the core development direction for engine friction-reducing and wear-resistant materials. CuSnBi-based lead-free copper-based alloys use Bi instead of Pb as the soft lubricating phase, combining good friction-reducing and mechanical properties, making them the most promising lead-free copper-based material system for engines.

[0003] However, existing CuSnBi-based copper-based powders and their preparation technologies have the following core defects: First, Bi has extremely low solid solubility in the Cu matrix, and under conventional preparation processes, it is prone to macroscopic segregation and coarsening, forming a continuous network Bi phase. This leads to stress concentration, a significant decrease in fatigue performance and wear resistance, and fails to meet the service requirements of engines under high load conditions. Second, CuSnBi powders prepared by conventional gas atomization processes have coarse particle sizes and wide particle size distributions, making it difficult to achieve nano-scale production. In room-temperature high-energy ball milling processes, Bi is prone to softening and agglomeration due to its low melting point, making it impossible to prepare nano-scale powders with uniformly dispersed Bi phases. At the same time, the ball milling process easily introduces impurities and increases oxygen content, leading to a deterioration in powder sintering performance. Third, existing CuSnBi powders have insufficient formability and sintering activity, resulting in low density and poor interfacial bonding in sintered components. It is difficult to achieve both high strength and excellent friction reduction and wear resistance, thus failing to meet the requirements of long service life and high reliability of engines.

[0004] To this end, a lead-free copper-based nanopowder CuSn10Bi8Zn3 with uniform nano-dispersion of Bi phase, low oxygen content, and excellent formability and sintering performance is proposed, along with its industrially producible preparation method. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of easy segregation and coarsening of the Bi phase in CuSnBi lead-free copper-based powder, difficulty in nano-sizing, high oxygen content, poor molding and sintering performance, and insufficient wear and friction reduction performance in the prior art. The invention provides a CuSn10Bi8Zn3 lead-free copper-based nanopowder with uniform composition, stable structure, and excellent performance, as well as a matching preparation method, to achieve large-scale preparation of the powder and meet the application requirements of friction-reducing and wear-resistant components for engines.

[0006] The specific technical solution is as follows: A lead-free copper-based nanopowder CuSn10Bi8Zn3, the chemical composition of the powder by mass percentage includes Cu, Sn, Bi and Zn, wherein Sn is 8-12%, Bi is 6-10%, Zn is 2-4%, the total amount of unavoidable impurities is ≤0.1%, and the balance is Cu; The powder has an average particle size of 20-100 nm and a particle size distribution index (PDI) ≤ 0.25. Sn and Zn are dissolved in a Cu matrix to form a supersaturated single-phase Cu-based solid solution. Bi is uniformly distributed as a nano-scale elemental dispersed phase within the Cu-based solid solution and at the grain boundaries. The particle size of the Bi dispersed phase is 5-30 nm, and the area ratio deviation of the Bi phase is ≤ 10%. The oxygen content of the powder is ≤ 300 ppm, and the loose packing density is 1.2-2.5 g / cm³. 3 The tap density is 2.8-4.2 g / cm³. 3 .

[0007] The reasonable component ratio in this scheme can provide stable basic properties for the matrix and adapt to the usage requirements of the target service scenario. The uniform fine grain structure can endow the powder with good forming and processing performance and sintering activity. The solid solution structure can avoid the formation of harmful brittle phases and prevent the material properties from deteriorating. The uniformly dispersed soft phase can continuously play a lubricating role during the material service process, while avoiding material failure caused by local stress concentration. The low oxygen content can reduce the interfacial bonding obstacles during the powder sintering process and improve the overall bonding strength and long-term service stability of the sintered component.

[0008] The aforementioned CuSn10Bi8Zn3 lead-free copper-based nanopowder contains a Bi dispersed phase with a near-spherical structure and a Cu-based solid solution grain size of 15-80 nm. The near-spherical soft phase structure further reduces the risk of stress concentration under load, improves the fatigue resistance of components, and the suitable matrix grain size balances the material's strength and plasticity, avoiding the imbalance between strength and plasticity caused by mismatched grain sizes, thus further optimizing the material's overall mechanical properties.

[0009] The aforementioned CuSn10Bi8Zn3 lead-free copper-based nanopowder has a sphericity ≥0.85 and a Hall flowability of 12-18 s / 50g. Good particle sphericity further optimizes the powder's filling performance and flow characteristics. Stable flow performance ensures uniform powder filling during molding, avoiding localized density inconsistencies in the molded green body, and providing a stable foundation for obtaining components with uniform performance during subsequent sintering.

[0010] The aforementioned CuSn10Bi8Zn3 lead-free copper-based nanopowder, by mass percentage, further contains 0.01-0.05% La-Ce mixed rare earth alloy, wherein the mass ratio of La to Ce in the La-Ce mixed rare earth alloy is (1-2):1. The addition of trace rare earth elements can purify the matrix structure, reduce the adverse effects of harmful impurities on material properties, further refine the grain structure, optimize the material's forming properties and stability during service, and improve the overall performance of the material.

[0011] This invention also provides a method for preparing lead-free copper-based nanopowder CuSn10Bi8Zn3, comprising the steps of master alloy smelting, atomization powder preparation, ball milling, annealing, and surface modification; specifically including the following steps: S1 Vacuum Induction Melting for Master Alloy Preparation: Weigh the raw materials according to the chemical composition ratio, place them in a vacuum induction melting furnace, and evacuate to 1×10⁻⁶. -3 Pa ~ 5 × 10 -2 Pa, after being filled with a protective atmosphere, is smelted, held at a temperature and then cast to obtain a master alloy ingot; S2 Ultrasonic Coupled Inert Gas Atomization for Pre-alloyed Powder Preparation: The master alloy ingot is reheated and melted, and then atomized into powder using an ultrasonic coupled inert gas atomization process with an ultrasonic transducer built into the nozzle. After sieving, the pre-alloyed powder is obtained. S3 Cryogenic High-Energy Ball Milling for Nanopowder Precursors: Pre-alloyed powder and process control agent are loaded into a ball mill jar and subjected to high-energy ball milling in a cryogenic environment with high-purity protective atmosphere and liquid nitrogen cooling throughout the process to obtain nanopowder precursors. S4 Low-temperature vacuum annealing: The nanopowder precursor is placed in a vacuum annealing furnace for low-temperature vacuum annealing, and then cooled in the furnace to obtain annealed nanopowder. S5 Plasma-enhanced vapor deposition surface passivation modification: Annealed nanopowder was subjected to plasma-enhanced vapor deposition treatment, and a graphene passivation layer was coated on the powder surface to obtain the final CuSn10Bi8Zn3 lead-free copper-based nanopowder.

[0012] The end-to-end process design enables quality control across the entire chain, from raw material preparation to finished product output. Vacuum melting ensures uniform mixing of alloy components and prevents the introduction of impurities through raw material oxidation. Ultrasonic coupling atomization refines powder particles from the source and inhibits the formation of microstructure segregation. Cryogenic ball milling achieves uniform particle refinement and prevents the softening and agglomeration of low-melting-point phases. Low-temperature vacuum annealing eliminates internal stress generated during processing and stabilizes the microstructure of the material. Surface modification treatment improves the storage stability and compatibility of the powder with subsequent processing.

[0013] In the above preparation method, in step S1, the melting temperature is 1050-1200℃, the holding time is 15-45 min, the protective atmosphere is high-purity argon gas with a purity ≥99.999%, and the casting temperature is 1100-1200℃. The La-Ce mixed rare earth alloy is added to the melt under argon protection 5-10 min before the end of the melting and holding period. The appropriate melting temperature and holding time ensure that the alloy raw materials are fully melted, achieving uniform mixing of components. The timing of rare earth element addition ensures that its modifying effect is fully realized, avoiding oxidation and burn-off of rare earth elements, and further improving the metallurgical quality of the alloy melt.

[0014] In the above preparation method, in step S2, the atomizing medium is high-purity argon gas with a purity ≥99.999%, the atomizing pressure is 3-8 MPa, the ultrasonic power is 2-5 kW, the ultrasonic frequency is 20-40 kHz, and the atomizing temperature is 1100-1250℃; the particle size of the pre-alloyed powder obtained after sieving is 10-50 μm. Suitable atomizing process parameters can ensure that the alloy melt is fully broken down, obtaining pre-alloyed powder with uniform particle size, providing a qualified raw material basis for subsequent refining processing, and further suppressing the generation of microstructure segregation, ensuring the compositional uniformity between different particles of the powder.

[0015] In the above preparation method, in step S3, the ambient temperature of the cryogenic high-energy ball mill is -196℃ to -150℃, the ball-to-powder ratio is (10-20):1, the ball milling speed is 300-600 rpm, and the ball milling time is 4-12 h; the process control agent is stearic acid, and the addition amount is 0.2-1.0% of the pre-alloyed powder mass; the oxygen content in the tank during the entire ball milling process is ≤50ppm. The suitable ball milling process parameters enable controllable refinement of powder particles, the addition of the process control agent prevents cold welding and agglomeration of powder particles during ball milling, and the low-oxygen ball milling environment prevents oxidation of the powder during the refinement process, ensuring the processing quality of the powder.

[0016] In the above preparation method, in step S4, the vacuum degree of the low-temperature vacuum annealing is ≥5×10⁻⁶. -3 The annealing temperature is 120-200℃, the holding time is 2-6h, and the heating rate is 2-5℃ / min. Suitable annealing process parameters can effectively eliminate internal processing stress in the powder, stabilize the powder's grain structure, avoid grain growth and coarsening during annealing, and further reduce the oxygen content in the powder, thus optimizing the powder's sintering activity.

[0017] In the above preparation method, in step S5, the carbon source for plasma-enhanced vapor deposition is acetylene, the deposition temperature is 80-150℃, and the ambient vacuum degree is ≥1×10⁻⁶. -2The deposition time is 10-30 min, with a RF power of 50-200 W. The coated graphene passivation layer has a continuous, pinhole-free structure and a thickness of 0.5-2 nm. Suitable surface modification process parameters enable the formation of a uniform and continuous passivation layer on the powder surface. This passivation layer effectively improves the powder's oxidation resistance and long-term storage stability, while also optimizing the interfacial bonding performance during sintering, thus enhancing the density and overall performance of the sintered components.

[0018] In the above preparation method, during the entire process of steps S1 to S5, the oxygen content in the contact atmosphere of the solid raw materials and powders is controlled at ≤50ppm, and the oxygen partial pressure in the furnace during the smelting stage is ≤1×10⁻⁶. -3 Pa. Controlling the oxygen content throughout the entire process can prevent powder oxidation at each processing stage, consistently ensuring the low oxygen content requirement of the powder, and providing a full-chain quality assurance for the powder to achieve good sintering and service performance.

[0019] The present invention has the following beneficial effects: 1. The reasonable composition and structural design solves the technical problem of easy segregation and coarsening of Bi phase in CuSnBi system: Through the alloying design of Zn element and precise control of nanoscale dispersion structure, Bi phase is uniformly distributed in Cu matrix without macro segregation and local aggregation. It not only retains the friction-reducing and lubricating effect of Bi phase, but also avoids the performance degradation caused by Bi phase coarsening. The fatigue performance and wear resistance of the material are greatly improved.

[0020] 2. The preparation process is highly innovative, realizing the controllable nano-sizing of lead-free copper-based powder: Through the cryogenic high-energy ball milling process, the technical bottleneck of easy agglomeration of low-melting-point Bi phase during room temperature ball milling has been overcome, and nano-powder with an average particle size of 20-100nm and a Bi phase particle size of 5-30nm has been prepared. The particle size distribution is uniform and the oxygen content is ≤300ppm, which is far superior to existing similar products.

[0021] 3. Excellent overall performance of the powder, suitable for engine service requirements: The prepared powder has high sphericity, good flowability, and its loose and tap densities are suitable for powder metallurgy forming processes. It has excellent sintering activity, and the density of the components after hydrogen-protected sintering is ≥98%, hardness ≥180HB, friction coefficient ≤0.12, and wear rate ≤3.5×10⁻⁶. -14 m 3 With a strength of / (N·m), it combines high strength, high toughness and excellent friction reduction and wear resistance, which can meet the high load and long service life requirements of engines.

[0022] 4. The entire process is controllable, with no toxic or harmful substances added, meeting environmental protection requirements. The process parameters are adapted to industrial production, and it has good prospects for industrial application. Attached Figure Description

[0023] Figure 1 This is a process flow diagram for preparing CuSn10Bi8Zn3 lead-free copper-based nanopowder according to the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0025] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual images. They should not be construed as limiting the scope of this application. To better illustrate the embodiments of the present invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0026] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0027] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] Reference Figure 1 In this embodiment of the invention, the parameter detection method is uniformly as follows: Powder average particle size and PDI: Detected using dynamic light scattering (DLS) method, according to GB / T 19627-2005. Bi phase particle size, distribution, and graphene layer thickness: Detected using transmission electron microscopy (TEM). Bi phase area ratio deviation was calculated by statistical analysis of TEM image fields of view, with at least 5 non-repeating fields of view included. Phase structure: X-ray diffraction (XRD) was used to detect the phase structure using a Cu target with Kα radiation, and the scanning range was 10°-90°. Oxygen content: Detected using an oxygen, nitrogen, and hydrogen analyzer, with the testing standard being GB / T 5158-2018; Loose packing density and tapped density: The testing standards are GB / T 1479.1-2011 and GB / T 5162-2006; Sphericity: Calculated statistically using scanning electron microscope (SEM) images, with at least 200 powder particles counted; Hall effect flowability: The testing standard is GB / T 1482-2010; Post-sintering performance: Sintering was carried out under hydrogen protection at a temperature of 820℃ and a holding time of 2h, followed by furnace cooling; hardness was tested using a Brinell hardness tester, and friction and wear performance was tested using a ring-block friction and wear tester with a load of 200N, a rotation speed of 200rpm, and a wear time of 30min. Example

[0029] The CuSn10Bi8Zn3 lead-free copper-based nanopowder of this embodiment has the following chemical composition by mass percentage: Sn 10%, Bi 8%, Zn 3%, La-Ce mixed rare earth 0.03%, unavoidable impurities 0.05%, and the balance being Cu, wherein the mass ratio of La to Ce in the La-Ce mixed rare earth is 1.5:1.

[0030] The preparation method of this embodiment includes the following steps: S1 Vacuum Induction Melting Preparation of Master Alloy: Weigh electrolytic Cu, pure Sn, pure Bi, pure Zn, and La-Ce mixed rare earth raw materials according to the above chemical composition ratio, place them in a vacuum induction melting furnace, and evacuate to 2×10⁻⁶. -3 Pa, fill with 99.999% high-purity argon gas to a slightly positive pressure, heat to 1150℃ for melting, hold for 30 minutes, add La-Ce mixed rare earth under argon protection 8 minutes before the end of the holding, continue to hold for 8 minutes, and then cast at 1180℃ to obtain the master alloy ingot. S2 Ultrasonic Coupled Inert Gas Atomization for Pre-alloy Powder Preparation: The master alloy ingot is placed in an atomization furnace and reheated to 1200℃. The powder is prepared by ultrasonic coupled inert gas atomization process with an ultrasonic transducer built into the nozzle. The atomization medium is high-purity argon gas with a purity of 99.999%, the atomization pressure is 5MPa, the ultrasonic power is 3kW, and the ultrasonic frequency is 30kHz. After atomization, the pre-alloy powder with a particle size of 10-50μm is obtained by sieving. S3 Cryogenic High-Energy Ball Milling for Nanopowder Precursor Preparation: Pre-alloyed powder and stearic acid were loaded into a ball mill jar, with the amount of stearic acid added being 0.5% of the mass of the pre-alloyed powder. After sealing the ball mill jar, a vacuum was drawn, and high-purity argon gas was introduced. The oxygen content inside the jar was controlled to be ≤50ppm. The ball mill jar was immersed in a cryogenic device cooled by liquid nitrogen throughout the process, with the ambient temperature controlled at -196℃, the ball-to-powder ratio at 15:1, the ball milling speed at 450rpm, and the ball milling time at 8h, to obtain the nanopowder precursor. S4 Low-Temperature Vacuum Annealing: The nanopowder precursor is placed in a vacuum annealing furnace and evacuated to a vacuum level of 1×10⁻⁶. -2 Pa was heated to 150°C at a heating rate of 3°C / min, held at that temperature for 4 hours, and then cooled to room temperature in the furnace to obtain annealed nanopowder. S5 Plasma-Enhanced Vapor Deposition Surface Passivation Modification: Annealed nanopowder is placed in a PECVD apparatus and vacuumed to 1×10⁻⁶. -2 Pa, heated to 120℃, using acetylene as the carbon source, RF power 100W, deposition time 20min, coated the powder surface with a 1nm thick continuous pinhole-free graphene passivation layer, to obtain the final CuSn10Bi8Zn3 lead-free copper-based nanopowder.

[0031] Testing revealed that the powder prepared in this embodiment had an average particle size of 50 nm, a PDI of 0.18, a Bi dispersed phase particle size of 10-20 nm, a Bi phase area ratio deviation of 6%, and XRD analysis showed only diffraction peaks of the Cu-based solid solution with no diffraction peaks of any second phase other than Bi. The sphericity was 0.90, the Hall flowability was 15 s / 50 g, the loose packing density was 1.8 g / cm³, the tap density was 3.5 g / cm³, and the oxygen content was 180 ppm. After hydrogen-protected sintering, the component exhibited a density of 98.5%, a hardness of 195 HB, a coefficient of friction of 0.10, and a wear rate of 2.8 × 10⁻⁶. -14 m³ / (N·m). Example

[0032] The CuSn10Bi8Zn3 lead-free copper-based nanopowder of this embodiment has the following chemical composition by mass percentage: Sn 8%, Bi 6%, Zn 2%, La-Ce mixed rare earth 0.01%, total unavoidable impurities 0.08%, and the balance being Cu, wherein the mass ratio of La to Ce in the La-Ce mixed rare earth is 1:1.

[0033] The preparation method of this embodiment includes the following steps: S1 Preparation of master alloy by vacuum induction melting: Weigh the raw materials according to the above chemical composition ratio, place them in a vacuum induction melting furnace, and evacuate to 5×10⁻⁶. -2Pa, high-purity argon gas is introduced to a slightly positive pressure, the temperature is raised to 1050℃ for melting, and the temperature is held for 45 minutes. 10 minutes before the end of the holding, La-Ce mixed rare earth is added under argon protection. After holding for another 10 minutes, the master alloy ingot is cast at 1100℃. S2 Ultrasonic coupling inert gas atomization to prepare pre-alloyed powder: The master alloy ingot is reheated and melted to 1100℃, and powder is prepared by ultrasonic coupling inert gas atomization process with an ultrasonic transducer built into the nozzle. The atomization pressure is 3MPa, the ultrasonic power is 2kW, the ultrasonic frequency is 20kHz, and the pre-alloyed powder with a particle size of 10-50μm is obtained by sieving. S3 Cryogenic High-Energy Ball Milling for Preparation of Nanopowder Precursors: Pre-alloyed powder and stearic acid were loaded into a ball mill jar. The amount of stearic acid added was 0.2%. The oxygen content in the jar was controlled to be ≤50ppm. The ball mill jar was immersed in liquid nitrogen cooling equipment throughout the process. The ambient temperature was -150℃. The ball-to-powder ratio was 10:1. The ball milling speed was 300rpm. The ball milling time was 12h to obtain nanopowder precursors. S4 Low-Temperature Vacuum Annealing: Vacuum drawn to 5×10 -3 Pa was heated to 120°C at a heating rate of 2°C / min, held at that temperature for 6 hours, and then cooled in the furnace to obtain annealed nanopowder. S5 Plasma-Enhanced Vapor Deposition Surface Passivation Modification: Annealed nanopowder is placed in a PECVD apparatus and vacuumed to 1×10⁻⁶. -2 Pa, heated to 80℃, using acetylene as the carbon source, RF power 50W, deposition time 30min, to coat a 0.5nm thick continuous non-porous graphene passivation layer, to obtain the final powder.

[0034] Testing revealed that the powder prepared in this embodiment had an average particle size of 100 nm, a PDI of 0.25, a Bi dispersed phase particle size of 20-30 nm, a Bi phase area ratio deviation of 9%, and XRD analysis showed it to be a single-phase Cu-based supersaturated solid solution with a sphericity of 0.85, a Hall flowability of 18 s / 50 g, a loose packing density of 1.2 g / cm³, a tapped density of 2.8 g / cm³, and an oxygen content of 280 ppm. The sintered component exhibited a density of 98.1%, a hardness of 182 HB, a coefficient of friction of 0.12, and a wear rate of 3.4 × 10⁻⁶. -14 m³ / (N·m). Example

[0035] The CuSn10Bi8Zn3 lead-free copper-based nanopowder of this embodiment has the following chemical composition by mass percentage: Sn 12%, Bi 10%, Zn 4%, La-Ce mixed rare earth 0.05%, unavoidable impurities 0.06%, and the balance being Cu, wherein the mass ratio of La to Ce in the La-Ce mixed rare earth is 2:1.

[0036] The preparation method of this embodiment includes the following steps: S1 Vacuum Induction Melting for Master Alloy Preparation: Weigh the raw materials according to the above chemical composition ratio, place them in a vacuum induction melting furnace, and evacuate to 1×10⁻⁶. -3 Pa, high-purity argon gas is introduced to a slightly positive pressure, the temperature is raised to 1200℃ for melting, and the temperature is held for 15 minutes. 5 minutes before the end of the holding period, La-Ce mixed rare earth is added under argon protection. After holding for another 5 minutes, the master alloy ingot is cast at 1200℃. S2 Ultrasonic Coupled Inert Gas Atomization for Pre-alloy Powder Preparation: The master alloy ingot is reheated and melted to 1250℃, and powder is prepared by ultrasonic coupled inert gas atomization process with an ultrasonic transducer built into the nozzle. The atomization pressure is 8MPa, the ultrasonic power is 5kW, the ultrasonic frequency is 40kHz, and the pre-alloy powder with a particle size of 10-50μm is obtained by sieving. S3 Cryogenic High-Energy Ball Milling for Nanopowder Precursors: Pre-alloyed powder and stearic acid were loaded into a ball mill jar. The amount of stearic acid added was 1.0%, and the oxygen content in the jar was controlled to be ≤50ppm. The ball mill jar was immersed in liquid nitrogen cooling equipment throughout the process. The ambient temperature was -180℃, the ball-to-powder ratio was 20:1, the ball milling speed was 600rpm, and the ball milling time was 4h to obtain nanopowder precursors. S4 Low-Temperature Vacuum Annealing: Vacuum drawn to 1×10 -2 Pa was heated to 200℃ at a heating rate of 5℃ / min, held for 2 hours, and then cooled in the furnace to obtain annealed nanopowder. S5 Plasma-Enhanced Vapor Deposition Surface Passivation Modification: Annealed nanopowder is placed in a PECVD apparatus and vacuumed to 1×10⁻⁶. -2 Pa, heated to 150℃, using acetylene as the carbon source, RF power 200W, deposition time 10min, coated with a 2nm thick continuous pinhole-free graphene passivation layer to obtain the final powder.

[0037] Testing revealed that the powder prepared in this embodiment had an average particle size of 20 nm, a PDI of 0.20, a Bi dispersed phase particle size of 5-15 nm, a Bi phase area ratio deviation of 7%, and XRD analysis showed it to be a single-phase Cu-based supersaturated solid solution with a sphericity of 0.88, a Hall flowability of 16 s / 50 g, and a bulk density of 2.5 g / cm³. 3 Tap density 4.2 g / cm³ 3 The oxygen content is 220 ppm; the density of the sintered component is 98.8%, the hardness is 210 HB, the coefficient of friction is 0.11, and the wear rate is 3.0 × 10⁻⁶. -14 m³ / (N·m).

[0038] Comparative Example 1 The only difference between this comparative example and Example 1 is that step S3 uses room temperature high-energy ball milling with a ball milling environment temperature of 25°C. All other parameters are completely consistent with Example 1.

[0039] Testing revealed that the powder prepared in this comparative example had an average particle size of 220 nm, a PDI of 0.65, and exhibited severe agglomeration and coarsening of the Bi phase, with particle sizes ranging from 100 to 500 nm. Significant segregation was observed, and the oxygen content was 850 ppm. The sintered component had a density of 92.3%, a hardness of 125 HB, a coefficient of friction of 0.18, and a wear rate of 8.2 × 10⁻⁶. -14 m³ / (N·m), the performance is far lower than that of Example 1.

[0040] Comparative Example 2 The only difference between this comparative example and Example 1 is that step S2 uses conventional inert gas atomization without ultrasonic coupling assistance; the other parameters are completely consistent with Example 1.

[0041] Testing revealed that the pre-alloyed powder prepared in this comparative example had uneven composition and localized segregation of the Bi phase. The final nanoparticles also exhibited uneven Bi phase distribution and locally formed continuous network structures. Consequently, the fatigue performance of the sintered component significantly decreased, with a friction coefficient of 0.16 and a wear rate of 6.7 × 10⁻⁶. -14 m³ / (N·m).

[0042] Comparative Example 3 The only difference between this comparative example and Example 1 is that Zn is not added to the chemical composition; all other parameters are exactly the same as in Example 1.

[0043] Testing revealed severe Bi phase segregation in the powder prepared in this comparative example. XRD analysis showed Cu6Sn5 intermetallic compound diffraction peaks, a wide particle size distribution, and decreased corrosion resistance of the sintered component, with a wear rate of 7.5 × 10⁻⁶. -14 The N·m³ / (N·m) is insufficient to meet the engine's service requirements.

[0044] Table 1 Comparison of Designed and Measured Values ​​of Sample Chemical Composition Unit: mass percentage (wt%) 1 Example 1 Design value margin 10.0 8.0 3.0 0.03 ≤0.1 Measured value 78.92 9.97 8.03 3.00 0.03 0.05 2 Example 2 Design value margin 8.0 6.0 2.0 0.01 ≤0.1 Measured value 83.91 8.02 5.98 2.00 0.01 0.08 3 Example 3 Design value margin 12.0 10.0 4.0 0.05 ≤0.1 Measured value 73.89 11.98 10.02 4.00 0.05 0.06 4 Comparative Example 1 Design value margin 10.0 8.0 3.0 0.03 ≤0.1 Measured value 78.87 9.96 8.02 3.00 0.03 0.12 5 Comparative Example 2 Design value margin 10.0 8.0 3.0 0.03 ≤0.1 Measured value 78.90 9.95 8.04 3.00 0.03 0.08 6 Comparative Example 3 Design value margin 10.0 8.0 0 0.03 ≤0.1 Measured value 81.91 9.98 8.03 0 0.03 0.05 Remark: Detection method: Spark source atomic emission spectrometry, detection standard GB / T5121.27-2008; The unavoidable impurities are mainly Pb, Fe, S, and P, with the content of each individual impurity ≤0.03%; All measured components in the embodiments fully comply with the component limits defined in this application.

[0045] Table 2. Measured data of comprehensive performance of sintered samples. 1 Example 1 98.5 195 320 8.5 0.10 2.8 2 Example 2 98.1 182 280 7.2 0.12 3.4 3 Example 3 98.8 210 350 6.8 0.11 3.0 4 Comparative Example 1 92.3 125 180 2.2 0.18 8.2 5 Comparative Example 2 94.5 140 210 3.5 0.16 6.7 6 Comparative Example 3 93.8 135 200 3.0 0.17 7.5 Remark: Unified sintering process: hydrogen protective atmosphere, sintering temperature 820℃, holding time 2h, and furnace cooling; Friction and wear test conditions: ring-block friction and wear test machine, grinding parts are GCr15 bearing steel, load is 200N, speed is 200rpm, wear time is 30min, dry friction condition; Mechanical property testing standards: GB / T228.1-2021 (tensile properties), GB / T231.1-2018 (Burl hardness), GB / T19077.1-2003 (density). The performance of the sintered samples in the embodiments of the present invention fully meets the high-load service requirements of friction-reducing and wear-resistant components such as engine bearings and bushings.

[0046] In step S3, during the cryogenic high-energy ball milling process, the average particle size of the Bi dispersed phase after ball milling is controlled by a quantitative control equation, which is:

[0047] In the formula: The average particle size of the Bi dispersed phase after cryogenic ball milling is expressed in nm. The initial average particle size of the Bi phase in the pre-alloyed powder prepared in step S2 is given in nm. The ambient thermodynamic temperature of cryogenic high-energy ball milling is expressed in K. Let be the aggregation inhibition coefficient of Zn, which is dimensionless and satisfies . ,in This represents the mass percentage of Zn in the powder. The ball-to-material ratio for cryogenic high-energy ball milling is dimensionless. The spindle speed of the cryogenic high-energy ball mill is expressed in rpm. The effective ball milling time for cryogenic high-energy ball milling is expressed in hours (h). This is the inherent correction factor for cryogenic ball milling in the CuSn10Bi8Zn3 system, in units of... The fixed value is .

[0048] Taking Example 1 as an example, the engineering application of the equation is demonstrated, and the calculated values ​​are in high agreement with the measured values: Step 1: Obtain input parameters Measured initial Bi phase particle size of pre-alloyed powder ; Cryogenic ball milling temperature (-196℃); Zn mass fraction Calculated ; Ball ratio ; Ball mill speed ; Effective ball milling time ; System correction coefficient

[0049] Step 2: Substitute into the equation to calculate Step 3: Result Verification In Example 1, the measured average particle size of the Bi phase was 10-20 nm, with an average of 15 nm. The calculated value from the equation was completely consistent with the measured value, with an error of 0, which verified the accuracy and reliability of the equation.

[0050] Technical Benefits: This equation enables precise quantitative control of the Bi dispersed phase particle size, resolving the batch performance fluctuations caused by relying on experience-based process adjustments in existing technologies. It can stably control the particle size and distribution of the Bi phase, ensuring the consistency of the powder's microstructure from the process source and improving the performance stability between powder batches. Furthermore, it allows for rapid matching of corresponding process parameters based on target service requirements, shortening the process development and debugging cycle and reducing the difficulty of quality control in industrial production.

[0051] Working principle and process: After completing the original step S2 ultrasonic coupling atomization, the initial average particle size of the Bi phase in the pre-alloyed powder was measured. ; Determine the target particle size of the Bi dispersed phase based on the target service scenario of the powder. ; By combining the range of process parameters defined in the original claims and substituting them into the control equation, a matching combination of cryogenic ball mill process parameters is calculated. Perform the original step S3 cryogenic high-energy ball milling according to the calculated parameters to obtain a Bi dispersed phase that meets the target particle size requirements; Annealing and surface modification were then carried out in the original steps S4 and S5 to obtain lead-free copper-based nanopowder with the target properties.

[0052] The above are merely preferred embodiments of the present invention and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A lead-free copper-based nanopowder, CuSn10Bi8Zn3, characterized in that, The chemical composition of the powder, by mass percentage, includes Cu, Sn, Bi, and Zn, with Sn 8-12%, Bi 6-10%, Zn 2-4%, unavoidable impurities ≤0.1%, and the balance being Cu. The powder has an average particle size of 20-100 nm and a particle size distribution index (PDI) ≤ 0.

25. Sn and Zn are dissolved in a Cu matrix to form a supersaturated single-phase Cu-based solid solution. Bi is uniformly distributed as a nano-scale elemental dispersed phase within the Cu-based solid solution and at the grain boundaries. The particle size of the Bi dispersed phase is 5-30 nm, and the area ratio deviation of the Bi phase is ≤ 10%. The oxygen content of the powder is ≤ 300 ppm, and the loose packing density is 1.2-2.5 g / cm³. 3 The tap density is 2.8-4.2 g / cm³. 3 .

2. The CuSn10Bi8Zn3 lead-free copper-based nanopowder according to claim 1, characterized in that, The Bi dispersed phase has a near-spherical structure, and the grain size of the Cu-based solid solution is 15-80 nm.

3. The CuSn10Bi8Zn3 lead-free copper-based nanopowder according to claim 1, characterized in that, The powder has a sphericity ≥0.85 and a Hall flowability of 12-18s / 50g.

4. The CuSn10Bi8Zn3 lead-free copper-based nanopowder according to claim 1, characterized in that, The powder also contains, by mass percentage, 0.01-0.05% of a La-Ce mixed rare earth alloy, wherein the mass ratio of La to Ce in the La-Ce mixed rare earth alloy is (1-2):

1.

5. A method for preparing CuSn10Bi8Zn3 lead-free copper-based nanopowder according to any one of claims 1 to 4, characterized in that, The process includes steps such as master alloy smelting, atomization powder preparation, ball milling, annealing, and surface modification; specifically, it includes the following steps: S1 Vacuum Induction Melting for Master Alloy Preparation: Weigh the raw materials according to the chemical composition ratio, place them in a vacuum induction melting furnace, and evacuate to 1×10⁻⁶. -3 Pa ~ 5 × 10 -2 Pa, after being filled with a protective atmosphere, is smelted, held at a temperature and then cast to obtain a master alloy ingot; S2 Ultrasonic Coupled Inert Gas Atomization for Pre-alloyed Powder Preparation: The master alloy ingot is reheated and melted, and then atomized into powder using an ultrasonic coupled inert gas atomization process with an ultrasonic transducer built into the nozzle. After sieving, the pre-alloyed powder is obtained. S3 Cryogenic High-Energy Ball Milling for Nanopowder Precursors: Pre-alloyed powder and process control agent are loaded into a ball mill jar and subjected to high-energy ball milling in a cryogenic environment with high-purity protective atmosphere and liquid nitrogen cooling throughout the process to obtain nanopowder precursors. S4 Low-temperature vacuum annealing: The nanopowder precursor is placed in a vacuum annealing furnace for low-temperature vacuum annealing, and then cooled in the furnace to obtain annealed nanopowder. S5 Plasma-enhanced vapor deposition surface passivation modification: Annealed nanopowder was subjected to plasma-enhanced vapor deposition treatment, and a graphene passivation layer was coated on the powder surface to obtain the final CuSn10Bi8Zn3 lead-free copper-based nanopowder.

6. The preparation method according to claim 5, characterized in that, In step S1, the melting temperature is 1050-1200℃, the holding time is 15-45min, the protective atmosphere is high-purity argon with a purity ≥99.999%, and the casting temperature is 1100-1200℃. The La-Ce mixed rare earth alloy is added to the melt under argon protection 5-10min before the end of the melting and holding period.

7. The preparation method according to claim 5, characterized in that, In step S2, the atomizing medium is high-purity argon gas with a purity ≥99.999%, the atomizing pressure is 3-8MPa, the ultrasonic power is 2-5kW, the ultrasonic frequency is 20-40kHz, and the atomizing temperature is 1100-1250℃; the particle size of the pre-alloyed powder obtained after sieving is 10-50μm.

8. The preparation method according to claim 5, characterized in that, In step S3, the ambient temperature of the cryogenic high-energy ball mill is -196℃ to -150℃, the ball-to-material ratio is (10-20):1, the ball milling speed is 300-600 rpm, and the ball milling time is 4-12 h; the process control agent is stearic acid, and the amount added is 0.2-1.0% of the mass of the pre-alloyed powder; the oxygen content in the tank during the entire ball milling process is ≤50ppm.

9. The preparation method according to claim 5, characterized in that, In step S4, the vacuum degree of the low-temperature vacuum annealing is ≥5×10⁻⁶. -3 Pa, annealing temperature is 120-200℃, holding time is 2-6h, and heating rate is 2-5℃ / min.

10. The preparation method according to claim 5, characterized in that, In step S5, the carbon source for plasma-enhanced vapor deposition is acetylene, the deposition temperature is 80-150℃, and the ambient vacuum degree is ≥1×10⁻⁶. -2 Pa, RF power of 50-200W, deposition time of 10-30min; the coated graphene passivation layer has a continuous, pinhole-free structure with a thickness of 0.5-2nm.

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