A method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate

Abstract

The application discloses a method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride base material, which comprises the following steps: performing composite acid liquid micro-etching and roughening treatment on the base material; preparing a gradient transition layer with gradually changed phosphorus content; performing electroplating in a plating solution containing modified Fe2O3 particles and PTFE by adopting a periodic reverse current and intermittent ultrasonic coupling process; and finally performing two-stage heat treatment. By constructing a unique structure of a PTFE lubricating network and Fe2O3 interface pinning, the application synchronously realizes strong combination (Lc2> 50 N) of the plating layer and the base material, high hardness (HV> 400), low friction (μ< 0.12) and excellent wear resistance, effectively solves the problem of the contradiction between poor combination of the metal lubricating layer on the surface of the aluminum nitride and performance, and the process is stable and controllable and suitable for complex-shaped parts.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride substrate surface modification technology, and in particular to a method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate. Background Technology

[0002] Aluminum nitride (AlN) ceramics, due to their superior thermal conductivity (theoretically up to 320 W / m·K), excellent electrical insulation, low coefficient of thermal expansion matching that of silicon, and good mechanical strength, have become a key fundamental material in fields such as third-generation semiconductor packaging, high-power LED heat dissipation substrates, and high-temperature, high-frequency circuit substrates. In recent years, as high-end equipment has developed towards high temperature, high speed, and high reliability, the application scenarios of aluminum nitride ceramics are expanding from static thermally conductive / insulating components to dynamic tribological components, such as rolling elements in high-performance bearings, sealing rings in special pumps and valves, or sliding guides. In these applications, aluminum nitride substrates (such as bearing balls, bushings, sliders, and other specifically shaped components) not only need to maintain their inherent thermal conductivity and insulation advantages, but their surfaces must also possess excellent wear resistance, friction reduction, and anti-galling properties.

[0003] However, aluminum nitride, as a typical covalent ceramic, has high surface chemical inertness and low surface energy, making it a "difficult-to-plate" material. This poses a severe challenge to preparing high-performance metallic lubricating coatings on its surface, specifically in the following ways:

[0004] 1. Weak adhesion between the coating and the substrate: Traditional surface roughening methods (such as sandblasting and alkaline etching) have limited effectiveness on aluminum nitride, making it difficult to form an effective mechanical interlock. Conventional activation processes (such as sensitization-activation) result in uneven adsorption on the aluminum nitride surface, leading to blistering and peeling of subsequent chemical plating. The significant difference in thermal expansion coefficients between the coating and the substrate generates substantial interfacial stress during temperature changes or service life, further deteriorating the adhesion strength. For moving aluminum nitride components subjected to alternating loads or impacts, insufficient adhesion will directly lead to premature coating failure.

[0005] 2. The coating itself struggles to achieve both wear resistance and friction reduction: Current technology typically involves electroless plating of nickel-phosphorus (Ni-P) onto aluminum nitride, followed by electroplating of hard chromium or nickel-based alloys to improve hardness and wear resistance, but this results in a high coefficient of friction (>0.5). To reduce friction, solid lubricants such as polytetrafluoroethylene (PTFE) can be electroplated to form a Ni-P-PTFE composite layer. However, the introduction of PTFE significantly softens the coating matrix, sacrificing wear resistance and creating a performance contradiction of "high wear resistance and low friction reduction." For precision moving parts requiring both long lifespan and low power consumption, a single-function coating cannot meet the requirements.

[0006] 3. Poor uniformity and stability of multi-component composite coatings: To synergistically improve performance, researchers have attempted to co-deposit hard particles (such as SiC and Al2O3) and soft lubricating particles (such as PTFE and MoS2) in the coating. However, due to the significant differences in surface properties, density, and charge among the different particles, selective adsorption, agglomeration, or sedimentation easily occur during conventional electroplating, resulting in uneven distribution of coating components and a loose structure. This inhomogeneity leads to large fluctuations in coating performance (such as coefficient of friction and wear rate), poor batch repeatability, and an inability to meet the stringent reliability and consistency requirements of high-end industrial applications.

[0007] Therefore, developing a novel coating preparation method that can firmly adhere to the surface of aluminum nitride substrates and achieve a stable and uniform composite of high-hardness, wear-resistant phases and low-friction lubricating phases is of paramount importance for expanding the application of aluminum nitride ceramics in high-end tribology. Current technologies lack comprehensive solutions that systematically address the three major challenges of interfacial bonding, performance synergy, and structural uniformity. Summary of the Invention

[0008] The main objective of this invention is to provide a method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate, thereby overcoming the shortcomings of the prior art.

[0009] This invention provides a method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate, comprising the following steps: S1, interface strengthening pretreatment: after degreasing the aluminum nitride substrate, micro-etching and roughening are performed using a composite acid solution containing hydrofluoric acid to form a composite rough surface with nano-scale grooves and micron-scale pits; subsequently, the substrate is immersed in a palladium-containing activation solution to uniformly adsorb nano-palladium catalytic centers on the surface; S2, gradient transition layer preparation: the substrate treated in step S1 is immersed in a first electroless nickel-phosphorus plating solution and plated at 80-85°C for 20-40 minutes to form a first nickel-phosphorus layer; then, without removing the substrate, the plating solution temperature is lowered to 65-75°C, and a complexing agent is added to adjust the solution composition, and plating continues for 30-50 minutes to form a second nickel-phosphorus layer with a gradually decreasing phosphorus content; the phosphorus content of the first nickel-phosphorus layer is 10-12 wt%, and the phosphorus content of the second nickel-phosphorus layer is 7-9 wt%. wt%, total thickness is 5-10μm; S3, preparation of composite electroplating solution: the formula of the composite electroplating solution is as follows:

[0010] Nickel sulfamate 250-320 g / L, nickel chloride 10-15 g / L, boric acid 35-45 g / L, sodium dodecyl sulfate 0.1-0.3 g / L, alkynyl alcohol inhibitor 0.05-0.15 g / L, Fe2O3 composite nanoparticles modified with stearic acid and silane coupling agent 15-50 g / L, PTFE concentrated dispersion containing fluorinated surfactant 30-80 mL / L; S4, multi-field coupling plating and composite lubricating layer co-deposition process: using the substrate treated in step S2 as the cathode, it is placed in the composite electroplating solution for multi-field coupling plating, controlling the plating solution temperature at 50-60℃, pH value at 3.8-4.5, and cathode current density at 1-4 A / dm³. 2 During plating, forward and reverse periodic commutation currents and intermittent ultrasonic waves are applied simultaneously, along with circulating filtration of the plating solution; S5, Post-treatment and structural stabilization: After electroplating, the workpiece is removed, cleaned and dried, and then subjected to two-stage heat treatment under an inert atmosphere: the first stage is held at 250-280℃ for 1 hour, and the second stage is held at 320-380℃ for 0.5 hours.

[0011] Further, the composition of the composite acid solution in step S1 is: 40wt% hydrofluoric acid 50-100 mL / L, 98wt% sulfuric acid 50-100 mL / L, 65wt% nitric acid 20-50 mL / L, and corrosion inhibitor benzotriazole 1-3 g / L; the temperature of the micro-etching-roughening treatment is 25-35℃, and the time is 3-8 minutes.

[0012] Furthermore, in step S2, the formation of the second nickel-phosphorus layer is achieved by uniformly pumping a replenishing solution composed of sodium hypophosphite, sodium citrate, and deionized water into the first electroless nickel-phosphorus plating solution. The flow rate of the replenishing solution causes the concentration of sodium hypophosphite in the plating solution to decrease linearly by 25%-35% within 30-50 minutes.

[0013] Furthermore, the preparation method of the double-modified Fe2O3 composite nanoparticles in step S3 is as follows: first, the Fe2O3 nanoparticles are refluxed in an ethanol solution of stearic acid, and then dispersed in an acetone solution of KH-560 silane coupling agent for secondary modification. The particles are hydrophobic in the plating solution and have a partial positive charge on their surface.

[0014] Furthermore, in step S3, the average particle size of the Fe2O3 composite nanoparticles is 50 nm; the solid content of the PTFE concentrated dispersion is 60%, and the average particle size of the solid particles is 0.2 μm.

[0015] Furthermore, the composite electroplating solution in step S3 also contains 0.5-2 g / L sodium saccharin as a stress modifier and 0.01-0.1 g / L rare earth cerium nitrate as a co-deposition promoter.

[0016] Furthermore, in step S4, the frequency of the periodic commutation current is 100-1000Hz, and the time ratio of the forward current to the reverse current is 10:1 to 20:1.

[0017] The frequency of the intermittent ultrasound applied is 28kHz, the power is 150-300W, the working cycle is 2 seconds of operation followed by 1 second of rest, and the direction of application of the intermittent ultrasound is at an angle of 45-75° to the cathode surface.

[0018] According to another aspect of the present invention, an aluminum nitride substrate component is also provided, the surface of which is prepared with a Ni-P-Fe2O3-PTFE composite lubricating layer by any of the above methods.

[0019] Furthermore, in the Ni-P-Fe2O3-PTFE composite lubricating layer, PTFE is distributed in a continuous network or island structure within the Ni-P matrix, while Fe2O3 nanoparticles are embedded at the phase boundary between PTFE and Ni-P. The thickness of the Ni-P-Fe2O3-PTFE composite lubricating layer is 20-50 μm, the Fe2O3 content is 4-8 vol%, the PTFE content is 18-28 vol%, and the remainder is a Ni-P alloy. The surface friction coefficient of the coating is less than 0.12, and the wear rate is less than 5.0 × 10⁻⁶. -6 mm 3 / (N·m).

[0020] Compared with the prior art, the present invention provides a method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate:

[0021] 1. Achieved ultra-high and stable interfacial bonding strength between the coating and the aluminum nitride substrate.

[0022] By employing a selective micro-etching and roughening process using an HF-H2SO4-HNO3 composite acid system, a composite morphology combining "nanogrooves" and "micro-pits" was constructed on the substrate surface. This not only significantly increases the contact and anchoring area of ​​the coating, but the resulting multi-layered interlocking structure also effectively dissipates interfacial stress, fundamentally solving the problem of "difficult-to-coat" ceramics.

[0023] The in-situ constructed "high-phosphorus-low-phosphorus" dual-layer gradient transition layer achieves a smooth transition in chemical composition and microstructure from aluminum nitride (low coefficient of thermal expansion) to the metallic coating (high coefficient of thermal expansion). This structure significantly buffers internal stress caused by thermal mismatch, preventing peeling and flaking of the coating due to stress concentration under thermal cycling or temperature changes. For the aluminum nitride substrate as a moving part, this robust interface ensures the reliability of the coating under complex loads such as shearing and impact.

[0024] The performance contradiction between "high hardness / wear resistance" and "low coefficient of friction" of the coating was successfully resolved, achieving synergistic optimization.

[0025] This invention creatively constructs a unique microscopic composite structure of "soft phase (PTFE) continuous lubrication network + hard phase (Fe2O3) interface pinning reinforcement". The PTFE-formed main lubrication network ensures an extremely low steady-state coefficient of friction (below 0.12); while the doubly modified Fe2O3 nanoparticles are not randomly distributed, but preferentially enriched and anchored at the phase interface between the PTFE network and the Ni-P matrix. This structure allows the Fe2O3 particles to act as hard support points, bearing the main load and improving the macroscopic hardness (above HV400) and anti-ploughing ability of the coating, and also to fix the PTFE phase like "rivets", preventing it from being torn and extruded over a large area and rapidly during friction. The synergy of these two aspects gives the composite coating both excellent wear resistance (low wear rate) and durable and stable low friction characteristics, with performance far exceeding that of simple blended composite coatings.

[0026] 3. It ensures highly uniform and stable composite of multi-component heterogeneous particles in the coating, significantly improving the consistency of coating quality and process reproducibility.

[0027] Targeted dual surface modification of particles (stearic acid hydrophobization + silane coupling agent functionalization) makes the surface properties of Fe2O3 nanoparticles highly compatible with PTFE microparticles and the plating bath environment, which reduces the tendency of agglomeration thermodynamically and promotes the co-adsorption of the two on the cathode surface.

[0028] The multi-field coupling process of periodic commutating current and intermittent directional ultrasound enables precise control of the electrodeposition process from a dynamic perspective. The commutating current suppresses dendrite growth and smooths the coating; while the intermittent ultrasound prevents particle agglomeration and sedimentation, its directional characteristics enhance particle transport and embedding into the cathode. The synergistic effect of the two ensures the uniform distribution of Fe2O3 and PTFE throughout the three-dimensional space of the coating, eliminating defects such as component segregation, nodules, or porosity commonly found in conventional processes. This results in minimal batch-to-batch variation in coating properties (such as thickness, composition, and tribological properties) and excellent repeatability.

[0029] 4. It broadens the high-end application scenarios of aluminum nitride substrates and has significant engineering practical value.

[0030] The method provided by this invention has a high degree of technological maturity and is easy to upgrade based on existing electroplating equipment. It is suitable for the uniform surface treatment of aluminum nitride components with complex geometries (such as components with internal holes, curved surfaces, and grooves).

[0031] By successfully imparting this high-performance composite lubricating layer to the surface of aluminum nitride substrate, it can function stably as a key moving component in harsh tribological environments with high temperature, high speed, and low maintenance requirements (such as vacuum environments, corrosive media, or situations where liquid lubricants cannot be used). This significantly improves the overall lifespan and reliability of components with aluminum nitride as the core material, and has important engineering applications and economic benefits. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0033] Figure 1 This is a process flow diagram of electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate, provided in an embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the idealized microstructure of the aluminum nitride substrate surface after composite acid micro-etching and roughening treatment, provided in an embodiment of the present invention.

[0035] Figure 3 This is a schematic diagram illustrating the particle modification effect provided in an embodiment of the present invention;

[0036] Figure 4 A process synergy diagram provided for embodiments of the present invention.

[0037] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Please see Figure 1-4 A method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on an aluminum nitride substrate, comprising the following steps:

[0040] S1. Interface Strengthening Pretreatment: Take the aluminum nitride substrate to be treated (e.g., a disc with dimensions of Φ30mm×5mm, used for a precision bearing cage), and first ultrasonically clean it for 10 minutes in an alkaline degreasing solution (a mixed solution of 50g / L Na3PO4 and 50g / L NaOH, 60℃), then rinse it thoroughly with deionized water. Roughening and Activation: Prepare a composite acid solution with the following composition: hydrofluoric acid (40wt%) 70mL / L, sulfuric acid (98wt%) 80mL / L, nitric acid (65wt%) 30mL / L, and benzotriazole 2g / L. Immerse the cleaned substrate in this acid solution and allow it to stand at 30℃ for 6 minutes. HF effectively corrodes AlN grains, while the addition of H2SO4 and HNO3 synergistically promotes selective etching of grain boundaries, and benzotriazole, as a corrosion inhibitor, suppresses excessive corrosion of the grain surface. This process creates micron-sized pits approximately 0.5-2 μm deep on the surface, while simultaneously generating numerous nano-sized (approximately 50-200 nm) groove-like rough structures on the pit walls and planar areas, providing excellent mechanical anchoring points for subsequent coatings. After treatment, the surface is washed with water and then rapidly immersed in an activation solution composed of PdCl2 (0.2 g / L) and HCl (10 mL / L) at 45°C for 5 minutes, allowing the palladium nanoparticles to be uniformly adsorbed onto the rough surface.

[0041] S2, Gradient transition layer fabrication:

[0042] The activated substrate was rapidly transferred to the first electroless nickel-phosphorus plating solution. The solution composition was: 25 g / L nickel sulfate, 30 g / L sodium hypophosphite, 15 g / L sodium citrate, 10 mL / L lactic acid, and the pH was adjusted to 4.8 with ammonia. Plating was performed in an 82°C water bath for 30 minutes, forming a first nickel-phosphorus layer approximately 3 μm thick with a phosphorus content of approximately 11.2 wt%, exhibiting an amorphous structure. Subsequently, without removing the workpiece, the water bath temperature was lowered to 70°C. A replenishing solution (containing 10 g / L sodium hypophosphite and 5 g / L sodium citrate) was uniformly pumped into the plating solution at a rate of 1.5 mL / min using a constant flow pump for 40 minutes. The cooling slowed the reaction rate, while the addition of the replenishing solution diluted the relative concentration of sodium hypophosphite in the plating solution (linearly decreasing from an initial 30 g / L to approximately 20 g / L), while the replenishment of sodium citrate maintained the complexing ability. Under these conditions, the phosphorus content of the deposited nickel-phosphorus layer gradually decreased to approximately 8.1 wt%. This step ultimately forms a gradient transition layer with a total thickness of approximately 8 μm and a phosphorus content that continuously decreases from the inside to the outside. The lower phosphorus content in the outer layer means that microcrystals begin to appear, resulting in a denser structure, higher hardness, and better compatibility with the subsequently electroplated crystalline Ni matrix, achieving a smooth transition in thermal expansion coefficient and mechanical properties.

[0043] S3. Preparation of composite electroplating solution:

[0044] 1. Preparation of Fe2O3 composite nanoparticles: 20g of α-Fe2O3 powder with an average particle size of 50nm was dispersed in 200mL of ethanol solution containing 5g of stearic acid and refluxed at 80℃ for 2 hours. After filtration, washing, and drying, the resulting hydrophobic powder was dispersed in acetone solution containing 3% KH-560 silane coupling agent and stirred at room temperature for 4 hours. After drying, double-modified Fe2O3 particles were obtained. In this way, the long chain of stearic acid endows the particles with hydrophobicity, making them easily approachable with PTFE; the hydrolysis product (Si-OH) of KH-560 can form -Si-O- chemical bonds with the coating matrix during subsequent heat treatment, greatly enhancing the interfacial bonding.

[0045] 2. Preparation of the composite electroplating solution: Dissolve 280g of nickel aminosulfonate, 12g of nickel chloride, and 40g of boric acid sequentially in 1L of deionized water. Add 1g of sodium saccharin, 0.05g of rare earth cerium nitrate, 0.2g of sodium dodecyl sulfate, and 0.1g of propargyl alcohol, and stir to dissolve. Add 30g of double-modified Fe2O3 particles and stir vigorously for 1 hour to pre-disperse them. Finally, slowly add 50mL of a concentrated PTFE dispersion (60% solid content) stabilized with a fluorinated surfactant under low-speed stirring. Adjust the pH to 4.2 with aminosulfonic acid. The fluorinated surfactant can be perfluorooctyl sulfonate, perfluoropolyether surfactant, etc. Fluorinated chains have lower surface energy and stronger compatibility with PTFE.

[0046] S4. Multi-field coupled plating and co-deposition process of composite lubricating layer:

[0047] Using the workpiece processed in step S2 as the cathode and a high-purity nickel plate as the anode, the workpiece is placed in the prepared electroplating solution. The plating solution temperature is maintained at 55°C, and a circulating filtration system (filter cartridge precision 5μm) is used to keep the plating solution clean.

[0048] Enabling a multi-field coupled system:

[0049] Electrical parameters: A periodic commutation pulse power supply is used, with the forward current density set at 2.5 A / dm. 2 Forward time is 15ms; reverse current density is 0.5 A / dm³. 2 The reverse time is 1.5ms (forward:reverse time ratio = 10:1, frequency approximately 61Hz).

[0050] Ultrasonic field: Install an ultrasonic probe (frequency 28kHz) at a 60° angle to the cathode plane, set the ultrasonic power to 200W, and the working mode is: turn on for 2 seconds and turn off for 1 second (intermittent operation).

[0051] Mechanical stirring: Gentle mechanical stirring at 250 rpm.

[0052] Electroplating was performed for 60 minutes under this combined field. The periodic commutation current effectively dissolved the microscopic protrusions formed during the deposition process, resulting in a denser and smoother coating, while also promoting particle embedding. The intermittent directional ultrasound not only powerfully broke up particle agglomerations and ensured their uniform suspension, but its "on-off" mode also prevented the detachment of adsorbed particles due to continuous cavitation. The synergy of these two methods enabled dynamic and precise control of the mass transfer, nucleation, and growth processes.

[0053] By controlling the particle concentration (Fe2O3 nanoparticles and solid particles of concentrated PTFE dispersion) and plating parameters in the composite electroplating solution, the final composite lubricating layer is formed in which PTFE is distributed in a continuous network or island structure within the Ni-P matrix, while the Fe2O3 nanoparticles are preferentially embedded at the phase boundary between PTFE and Ni-P. The thickness of the composite lubricating layer is 20-50 μm, the Fe2O3 content is 4-8 vol%, the PTFE content is 18-28 vol%, and the remainder is Ni-P alloy. The surface friction coefficient of the coating is less than 0.12, and the wear rate is less than 5.0 × 10⁻⁶. -6 mm 3 / (N·m).

[0054] S5. Post-processing and structural stabilization:

[0055] After electroplating, the workpiece is removed, ultrasonically cleaned with deionized water, and dried with hot air. It is then placed in a tube furnace under argon protection for a two-stage heat treatment: in the first stage, the temperature is increased to 260°C at a rate of 5°C / min and held for 1 hour; in the second stage, the temperature is further increased to 350°C and held for 0.5 hours, followed by furnace cooling. Thus, the first stage of low-temperature heat treatment primarily eliminates internal stress in the plating layer and partially crystallizes the Ni-P matrix, increasing its hardness; the second stage of higher temperature treatment promotes an interfacial reaction between the silane coupling agent on the surface of the modified Fe2O3 particles and the Ni matrix, forming stronger chemical bonds. Simultaneously, it induces partial thermal flow in the PTFE particles, promoting a more stable network distribution within the matrix.

[0056] Result characterization:

[0057] The total thickness of the composite lubricating layer was approximately 35 μm. Scanning electron microscopy (SEM) observation showed that the coating was dense, with Fe2O3 nanoparticles and PTFE particles evenly distributed and without obvious agglomeration. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) surface scanning analysis confirmed that PTFE tended to form interconnected island or network structures, while Fe2O3 particles were significantly enriched in the phase boundary region between PTFE and the Ni-P matrix, forming a "pinned" structure. The microhardness of the coating was HV520. Under ball-disc friction and wear testing (GCr15 steel balls as the grinding material, load 5 N, speed 0.2 m / s), the average steady-state friction coefficient was 0.10, and the wear rate was 3.8 × 10⁻⁶.- 6 mm 3 / (N·m). The adhesion between the coating and the substrate was tested by the scratch method. The critical load (Lc2) was greater than 50N, which showed excellent interfacial bonding strength.

[0058] The present invention also provides an aluminum nitride substrate component, the surface of which is prepared with a Ni-P-Fe2O3-PTFE composite lubricating layer by the above method.

[0059] Example 1

[0060] Step 1: Interface Enhancement Preprocessing

[0061] 1. Take a commercially available hot-pressed sintered aluminum nitride substrate (grade: HCP-170, thermal conductivity ≥170 W / m·K, size Φ30mm×5mm round sheet), and after standard degreasing and cleaning, process it according to the following steps:

[0062] 2. Composite acid roughening: A mixture of HF (40wt%) 70 mL / L + H2SO4 (98wt%) 80 mL / L + HNO3 (65wt%) 30 mL / L + benzotriazole 2 g / L was used to immerse the substrate at 30±2℃ for 6 minutes. After removal, the substrate surface changed from a glossy grayish-white to a uniform matte gray.

[0063] 3. Morphology and Roughness Characterization: The surface profile before and after treatment was measured using laser confocal microscopy (CLSM). The results showed that the arithmetic mean roughness (Ra) of the treated surface increased from the original 0.05 μm to 1.28 μm, and uniformly distributed micron-sized pits (depth 1–3 μm) and nanoscale textures on the pit walls were observed. Scanning electron microscopy (SEM) images confirmed the formation of a composite structure of "micropits-nanogrooves".

[0064] Activation: Then immerse in PdCl2 (0.2 g / L) + HCl (10 mL / L) activation solution and soak at 45°C for 5 minutes.

[0065] Step 2: The gradient transition layer is prepared using a two-step chemical plating method.

[0066] First layer (high phosphorus): Plated in a chemical plating bath at 82℃ (nickel sulfate 25 g / L, sodium hypophosphite 30 g / L, sodium citrate 15 g / L, lactic acid 10 mL / L, pH=4.8) for 30 minutes, with a deposition thickness of approximately 3.2 μm (measured using a thickness gauge). Glow discharge spectroscopy (GDS) analysis showed that the phosphorus content of this layer was 11.5 wt%.

[0067] Second layer (low phosphorus): With the workpiece in the plating bath, the temperature was lowered to 70°C, and replenishment solution was pumped in at a rate of 1.5 mL / min for 40 minutes. The final gradient transition layer had a total thickness of 8.5 μm. GDS depth profile analysis showed that the phosphorus content smoothly transitioned from 11.5 wt% to 7.9 wt% from the interface to the outer layer.

[0068] Step 3: Preparation of Composite Electroplating Solution

[0069] 1. Particle modification: Prepare double-modified Fe2O3 nanoparticles as described above.

[0070] 2. Plating solution preparation: Prepare a composite plating solution containing 30 g / L modified Fe2O3 and 50 mL / L PTFE dispersion (other components are the same as before).

[0071] Step 4: Multi-field coupled plating and co-deposition of composite lubricating layer

[0072] Electroplating was performed for 60 minutes under multi-field coupling conditions, with the following specific values ​​for PRC (Periodic Reverse Current): 2.5 A / dm² × 15 ms forward and 0.5 A / dm² × 1.5 ms reverse; intermittent ultrasound: 200 W, 2 s working time / 1 s intermittent time; 55℃, pH = 4.2.

[0073] Step 5: Post-treatment and structural stabilization. Two-stage heat treatment is carried out under argon protection: 260℃ / 1h + 350℃ / 0.5h.

[0074] Step 6: Performance Testing and Data Analysis: Systematic testing was conducted on the prepared "Sample A (of this invention)".

[0075] 1. Coating structure and composition:

[0076] Thickness: The total coating thickness (transition layer + composite layer) is 35.8 ± 1.5 μm (measured at 5 points, average and standard deviation).

[0077] Microstructure: SEM cross-sectional images show that the coating is dense and crack-free, with no visible gaps at the interface with the substrate. TEM and EDS surface scanning analyses confirm that the PTFE phase (F elemental mapping) is distributed in a continuous network, and Fe2O3 particles (Fe elemental mapping) are significantly enriched at the phase boundary between PTFE and the Ni-P matrix, forming a "pinned" structure.

[0078] Volume fraction of components: SEM images were calculated using Image-Pro Plus and combined with EDS quantitative analysis to determine the following in the composite lubricating layer: PTFE ≈ 22 ± 3 vol%, Fe2O3 ≈ 6.5 ± 1 vol%, and the remainder was Ni-P matrix.

[0079] 2. Mechanical and tribological properties:

[0080] Bond strength: A scratch test was conducted (scratch tester, diamond indenter, radius 200 μm, loading rate 100 N / min). The critical failure load Lc2 (complete peeling of the coating) was measured to be 52.4 N. The acoustic emission signal was stable, and no early peeling peak was observed, indicating a strong bond.

[0081] Microhardness: The hardness of the coating section was measured to be HV 518 ± 25 using a Vickers microhardness tester (load 25g).

[0082] Friction and wear performance: A ball-disc friction and wear tester was used (the wear part was a Φ6 mm GCr15 steel ball, the load was 5 N, the sliding speed was 0.2 m / s, the total stroke was 1000 m, and the environment was dry air at room temperature).

[0083] Average steady-state friction coefficient: 0.098 ± 0.012.

[0084] Wear rate: The wear rate was calculated by measuring the cross-sectional area of ​​the wear track using a white light interferometer, and was determined to be 3.5 × 10⁻⁶. -6 mm 3 / (N·m).

[0085] Wear track morphology: SEM observation showed that the wear track surface was smooth, with a continuous PTFE transfer film visible, and no obvious furrows or peeling pits.

[0086] Comparative Example 1: Traditional single-particle composite coating

[0087] The substrate and pretreatment are the same as in Example 1, up to the chemical plating underlayer (using single-component chemical plating of Ni-P, thickness ~8μm, phosphorus content ~9%).

[0088] Plating solution and process: A conventional Watt's nickel plating solution (NiSO4·6H2O 250g / L, NiCl2·6H2O 45g / L, H3BO3 40g / L) was used, with only 40g / L PTFE dispersion added. Fe2O3 was not added. PRC and ultrasound were not used; only mechanical stirring (250 rpm) was employed at 55℃, pH=4.0, and a current density of 2 A / dm³. 2 Electroplating for 60 minutes.

[0089] Post-treatment: Heat treatment at 200℃ for 1 hour only.

[0090] Sample label: Sample B.

[0091] Test results:

[0092] Bond strength: Scratch test Lc2 = 20.1 N, the first coating crack acoustic emission signal appears at about 15 N.

[0093] Microhardness: HV 210 ± 35.

[0094] Friction and wear: The initial coefficient of friction was low (~0.13), but it fluctuated sharply and increased as the test progressed. The average coefficient of friction was 0.31 over a 1000m journey, and the wear rate was as high as 22.4 × 10⁻⁶. -6 mm 3 / (N·m). The wear marks are wide and deep, indicating severe plastic deformation and PTFE membrane rupture.

[0095] Comparative Example 2: Simple co-deposition of unmodified mixed particles

[0096] The substrate and pretreatment are the same as in Example 1, followed by chemical plating for the underlayer.

[0097] Plating solution and process: A plating solution formulation similar to that of Example 1 was used, but unmodified ordinary Fe2O3 nanoparticles (30 g / L) and PTFE dispersion (50 mL / L) were added. The electroplating process was carried out using only ordinary DC power (2.5 A / dm²) and continuous ultrasound (200 W), at a temperature of 55°C, pH=4.2, and a time of 60 minutes.

[0098] Post-processing: Same as in Example 1.

[0099] Sample label: Sample C.

[0100] Test results:

[0101] Coating morphology: SEM showed that the coating surface was rough and contained a large number of micron-sized nodules. Particle agglomeration and pores were visible in the cross section.

[0102] Compositional analysis: EDS surface scanning showed that the distribution of Fe and F elements was extremely uneven, with obvious enrichment and depletion areas.

[0103] Bond strength: Lc2 = 28.7 N.

[0104] Microhardness: HV 380 ± 45 (large fluctuation).

[0105] Friction and wear: The coefficient of friction fluctuated drastically throughout the test (0.15~0.45), with an average of 0.29, and the wear rate was 15.8×10⁻⁶. -6 mm 3 / (N·m). The surface of the wear track shows delamination pits formed by the shedding of hard particle aggregates.

[0106] The performance comparison is shown in the table below:

[0107]

[0108] As shown in the table above, the technical solution of this invention (sample A) has undergone systematic testing, and its performance is comprehensive and significantly surpasses that of traditional processes. Regarding interface bonding, the critical scratch load of sample A reaches 52.4 N, far exceeding that of comparative example 1 (20.1 N) and comparative example 2 (28.7 N), proving that the "composite roughening + gradient undercoating" design achieves superior adhesion. In terms of coating structure and mechanical properties, sample A achieves a microhardness of HV 518, and SEM / TEM analysis shows that it forms a unique "PTFE continuous lubrication network + Fe2O3 interface pinning" composite structure. In contrast, comparative example 1 (HV 210) softens due to the lack of a hard phase, while comparative example 2 (HV 380) exhibits uneven structure and large hardness fluctuations due to particle agglomeration. Regarding core tribological properties, sample A exhibits an extremely low average coefficient of friction (0.098) and wear rate (3.5 × 10⁻⁶). -6 mm 3 / (N·m)), possessing both excellent friction reduction and wear resistance; in contrast, Comparative Example 1, due to its poor wear resistance, had a wear rate as high as 22.4×10. -6 Comparative Example 2, due to structural defects, exhibited drastic fluctuations in its friction coefficient, with an average value of 0.29, and a wear rate as high as 15.8 × 10⁻⁶. -6 Experimental data fully demonstrate that the technical solution of this invention, through systematic innovation, successfully solved three major technical problems: weak bonding force, contradiction between wear resistance and friction reduction performance, and uneven particle co-deposition, achieving a qualitative leap in comprehensive performance.

[0109] In summary, the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any changes, modifications, and evolutions made by those skilled in the art without departing from the scope of the present invention based on the disclosed technical content shall be considered equivalent embodiments of the present invention. Furthermore, any changes, modifications, and evolutions made to the above embodiments based on the essential technology of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate, characterized in that, Includes the following steps: S1. After degreasing the aluminum nitride substrate, a composite acid solution containing hydrofluoric acid is used for micro-etching and roughening to form a composite rough surface with nano-scale grooves and micro-scale pits; then, it is immersed in a palladium-containing activation solution to make the surface uniformly adsorb nano-palladium catalytic centers. S2. Immerse the substrate in the first electroless nickel-phosphorus plating solution and plate at 80-85°C for 20-40 minutes to form a first nickel-phosphorus layer; then, without removing the substrate, lower the plating solution temperature to 65-75°C, add a complexing agent to adjust the solution composition, and continue plating for 30-50 minutes to form a second nickel-phosphorus layer with a gradually decreasing phosphorus content; the phosphorus content of the first nickel-phosphorus layer is 10-12 wt%, the phosphorus content of the second nickel-phosphorus layer is 7-9 wt%, and the total thickness is 5-10 μm; S3. Prepare a composite electroplating solution, wherein the formula of the composite electroplating solution is as follows: Nickel sulfamate 250-320 g / L, nickel chloride 10-15 g / L, boric acid 35-45 g / L, sodium dodecyl sulfate 0.1-0.3 g / L, alkynyl alcohol inhibitor 0.05-0.15 g / L, Fe2O3 composite nanoparticles modified with stearic acid and silane coupling agent 15-50 g / L, and concentrated PTFE dispersion containing fluorinated surfactant 30-80 mL / L; S4. Using the substrate as the cathode, perform multi-field coupling plating in a composite electroplating solution, controlling the solution temperature at 50-60℃, pH value at 3.8-4.5, and cathode current density at 1-4 A / dm³. 2 During plating, forward and reverse periodic commutation currents and intermittent ultrasonic waves are applied simultaneously, along with the plating solution circulation and filtration. S5. After electroplating, remove the workpiece, clean and dry it, and then perform a two-stage heat treatment under an inert atmosphere: the first stage is held at 250-280℃ for 1 hour, and the second stage is held at 320-380℃ for 0.5 hours.

2. The method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on an aluminum nitride substrate as described in claim 1, characterized in that, The composite acid solution in step S1 consists of: 40wt% hydrofluoric acid 50-100 mL / L, 98wt% sulfuric acid 50-100 mL / L, 65wt% nitric acid 20-50 mL / L, and corrosion inhibitor benzotriazole 1-3 g / L; the temperature for micro-etching-roughening treatment is 25-35℃, and the time is 3-8 minutes.

3. The method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on an aluminum nitride substrate as described in claim 1, characterized in that, In step S2, the formation of the second nickel-phosphorus layer is achieved by uniformly pumping a replenishing solution composed of sodium hypophosphite, sodium citrate and deionized water into the first electroless nickel-phosphorus plating solution. The flow rate of the replenishing solution causes the concentration of sodium hypophosphite in the plating solution to decrease linearly by 25%-35% within 30-50 minutes.

4. The method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate as described in claim 1, characterized in that, The preparation method of the double-modified Fe2O3 composite nanoparticles in step S3 is as follows: first, the Fe2O3 nanoparticles are refluxed in an ethanol solution of stearic acid, and then dispersed in an acetone solution of KH-560 silane coupling agent for secondary modification.

5. The method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate as described in claim 1, characterized in that, In step S3, the average particle size of the Fe2O3 composite nanoparticles is 50 nm; the solid content of the PTFE concentrated dispersion is 60%, and the average particle size of the solid particles is 0.2 μm.

6. The method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on the surface of an aluminum nitride substrate as described in claim 1, characterized in that, In step S3, the composite electroplating solution is replaced by nickel sulfamate 250-320 g / L, nickel chloride 10-15 g / L, boric acid 35-45 g / L, sodium dodecyl sulfate 0.1-0.3 g / L, alkynyl alcohol inhibitor 0.05-0.15 g / L, Fe2O3 composite nanoparticles modified by stearic acid and silane coupling agent 15-50 g / L, concentrated PTFE dispersion containing fluorinated surfactant 30-80 mL / L, sodium saccharin 0.5-2 g / L as stress modifier, and rare earth cerium nitrate 0.01-0.1 g / L as co-deposition promoter.

7. The method for electroplating a Ni-P-Fe2O3-PTFE composite lubricating layer on an aluminum nitride substrate as described in claim 1, characterized in that, In step S4, the frequency of the periodic commutation current is 100-1000Hz, and the time ratio of the forward current to the reverse current is 10:1 to 20:

1. The frequency of the intermittent ultrasound applied is 28kHz, the power is 150-300W, the working cycle is 2 seconds of operation followed by 1 second of rest, and the direction of application of the intermittent ultrasound is at an angle of 45°-75° to the cathode surface.

8. An aluminum nitride substrate component, characterized in that, Its surface is prepared with a Ni-P-Fe2O3-PTFE composite lubricating layer by the method described in any one of claims 1-7.

9. The aluminum nitride substrate component as described in claim 8, characterized in that, In the Ni-P-Fe2O3-PTFE composite lubricating layer, PTFE is distributed in a continuous network or island structure within the Ni-P matrix, while Fe2O3 nanoparticles are embedded at the phase boundary between PTFE and Ni-P. The thickness of the Ni-P-Fe2O3-PTFE composite lubricating layer is 20-50 μm, the Fe2O3 content is 4-8 vol%, the PTFE content is 18-28 vol%, and the remainder is a Ni-P alloy. The surface friction coefficient of the coating is less than 0.12, and the wear rate is less than 5.0 × 10⁻⁶. -6 mm 3 / (N·m).

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