Vacuum sputtering plating method for sawteeth

Abstract

The invention relates to the technical field of workpiece surface treatment, and discloses a vacuum sputtering plating method for sawteeth. Comprising the steps of substrate pretreatment, sawtooth vacuum sputtering to form a mechanical occlusion structure, selective activation achieved through alternating soaking-inclined rotation catalytic activation, pulse stirring assisted double-liquid alternating chemical plating to form a composite coating, double-liquid gap gas purging to eliminate cross contamination, surface homogenization treatment, graded passivation treatment and the like. According to the invention, through a composite structure of the sawtooth sputtering layer and the chemical plating layer, a dual combination mode of mechanical occlusion and chemical bonding is formed; alternating soaking-inclined rotating catalytic activation is adopted to eliminate direction dependence, and controllable enrichment of a catalyst in a groove is achieved. The mass transfer limitation of the deep groove is overcome by adopting a pulsating stirring auxiliary plating technology; double-liquid alternate pollution is eliminated by adopting a gas purging technology; and a nickel-phosphorus / nickel-tungsten alternate multi-layer composite structure is formed, and high hardness and high toughness are achieved at the same time.

Description

Technical Field

[0001] This invention relates to the field of workpiece surface treatment technology, and more specifically, to a serrated vacuum sputtering coating method. Background Technology

[0002] Surface coating technology is an important component of modern manufacturing, widely used to improve the wear resistance, corrosion resistance, and service life of workpieces. Currently, the main surface coating technologies include vacuum sputtering and electroless plating. Vacuum sputtering can produce dense, uniform metal coatings, but it suffers from high costs and limited coating thickness. Electroless plating is less expensive and can produce thicker coatings, but the adhesion between the coating and the substrate is insufficient, making it prone to peeling failure during use.

[0003] To overcome the limitations of single-coating technologies, existing techniques attempt to combine vacuum sputtering with electroless plating. Vacuum sputtering creates a serrated structure for mechanical interlocking, which is then thickened by electroless plating. However, existing composite coating technologies face the following pressing technical problems: traditional selective catalytic activation relies on the workpiece's orientation; for complex-shaped workpieces, the catalyst enrichment within the serrated grooves is uncontrollable in different areas; deep grooves (especially those with a depth-to-width ratio greater than 2:1) face limited mass transfer during electroless plating, leading to void defects; cross-contamination during workpiece transitions between different plating solutions causes interface degradation; single-component electroless plating layers offer limited performance, failing to meet multiple performance requirements; and the final coating lacks effective surface protection. These technical problems severely restrict the application of composite coating technologies in high-end manufacturing. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a serrated vacuum sputtering deposition method, comprising the following steps: Step 1: Matrix pretreatment: The workpiece surface is degreased, derusted, and cleaned. Step 2: Serrated vacuum sputtering: A serrated sputtering layer with a serration height of 50-200 micrometers and a serration pitch of 100-500 micrometers is formed on the substrate surface; Step 3: Alternating soaking-tilting rotation catalytic activation: The workpiece is immersed in the catalytic activation solution 3-5 times, and the tilt angle of the workpiece is changed to 0°, 45° and 90° between each immersion, so that the catalyst concentration in the serrated groove is gradually enriched. Step 4: Pulsating stirring-assisted alternating liquid electroless plating: The nickel-phosphorus plating solution and the nickel-tungsten plating solution were used for alternating deposition. Each plating solution was operated in an intermittent manner with "static plating for 2 minutes + pulsating stirring for 10-15 seconds", and the alternating deposition was carried out 3-5 times. Step 5: Gas purging between two liquids: Purge the serrated grooves with 0.2-0.5MPa compressed air or nitrogen between each two-liquid conversion; Step 6: Graded passivation treatment: First, pre-passivate with a diluted passivation solution with a concentration of 1 / 3 to 1 / 2 of the normal concentration, and then deeply passivate with a passivation solution of normal concentration.

[0005] Preferably, the process parameters for the serrated vacuum sputtering are: vacuum degree 1×10⁻⁶. -3 -5×10 -3 Pa, sputtering power 200-800W, sputtered layer thickness 5-20 micrometers.

[0006] Preferably, the alternating immersion-tilting rotation catalytic activation includes sensitization treatment and activation treatment. The sensitization solution contains 20-40 g / L stannous chloride and 20-40 ml / L hydrochloric acid, and the activation solution contains 0.1-1.0 g / L palladium chloride and 1-10 ml / L hydrochloric acid.

[0007] Preferably, the pulsating stirring adopts the reciprocating movement of the workpiece or the pulse spraying of the plating solution, with a frequency of 0.5-2Hz and an amplitude of 5-20mm.

[0008] Preferably, the nickel-phosphorus plating solution contains 8-12% phosphorus, the nickel-tungsten plating solution contains 10-18% tungsten, and the thickness of each single-layer plating is 5-15 micrometers.

[0009] Preferably, in the dual-liquid gap gas purging, the gas pressure is 0.2-0.5MPa, and the serrated groove is purged in a directional manner to forcibly remove residual plating solution and bubbles.

[0010] Preferably, in the graded passivation treatment, the pre-passivation solution contains 50-100 g / L of chromic anhydride, and the deep passivation solution contains 150-300 g / L of chromic anhydride.

[0011] Preferably, after the alternating chemical plating, a surface homogenization treatment step is further included: immersing the workpiece in a complexing agent solution containing 10-30 g / L citric acid and 5-15 g / L disodium EDTA at a temperature of 50-70°C for 5-10 minutes.

[0012] Preferably, in step 3, during the alternating soaking process, each soaking time is 20-40 seconds, with an intermediate dwell time of 10-20 seconds, and the catalyst is controlled to be enriched by the synergistic effect of gravity and surface tension.

[0013] Preferably, the total thickness of the final composite coating is 30-150 micrometers, consisting of a three-layer structure composed of a serrated vacuum sputtering underlayer, a nickel-phosphorus / nickel-tungsten alternating composite intermediate layer, and a passivation surface layer.

[0014] The beneficial effects of this invention are as follows: Significantly improved coating adhesion: The serrated vacuum sputtering layer provides a mechanical interlocking structure with a depth of 50-200 micrometers. Combined with selective nucleation achieved by alternating immersion-tilted rotation catalytic activation, it forms a dual bonding method of "serrated interlocking + chemical bonding". The shear strength between the coating and the substrate reaches 25-45 MPa, which is 2-3 times higher than that of traditional chemical plating (8-15 MPa), effectively preventing coating peeling failure.

[0015] Breakthrough in coating uniformity of complex workpieces: Alternating immersion-tilting rotation catalytic activation technology eliminates direction dependence, reducing the difference in catalyst concentration in the serrated grooves of various parts of complex-shaped workpieces from ±82% in traditional methods to ≤±9%, achieving controllable enrichment; Pulsating stirring-assisted coating technology overcomes the mass transfer limitations of deep grooves, ensuring that the coating thickness uniformity (bottom / opening thickness ratio) of grooves with a depth-to-width ratio of 5:1 reaches more than 82%, and that of grooves with a depth-to-width ratio of 3:1 can reach more than 91%, avoiding sealing effect and void defects.

[0016] Complete elimination of alternating interface contamination: The dual-liquid gap gas purging technology uses a physical airflow of 0.2-0.5MPa to forcibly remove residual plating solution and bubbles deep in the groove, and forms a complementary cleaning system with chemical cleaning, so that the impurity content of each alternating interface is ≤0.1%, eliminating the contamination transition layer with mixed components, and improving the bonding force of each alternating interface by 30-50%.

[0017] A multifunctional composite coating was successfully constructed: alternating deposition of nickel-phosphorus and nickel-tungsten plating solutions formed a multi-layer composite structure. The corrosion resistance of the composite coating reached the first corrosion test after 1676 hours of salt spray testing, which is 9.7 times higher than that of a single nickel-phosphorus coating (172 hours). The microhardness of the nickel-tungsten layer (10-18% tungsten content) reached 680-750 HV, which is 40-55% higher than that of a single nickel-phosphorus coating (485-495 HV). The two components form an alloy transition zone of 2-5 micrometers at the interface, achieving a gradient distribution of hardness from 438 HV to 752 HV, meeting the multiple performance requirements under complex working conditions.

[0018] The protective life is significantly extended: the surface homogenization treatment makes the composition uniformity deviation ≤ ±5%, and the graded chromate passivation generates a dense conversion film with a thickness of 0.5-3 micrometers and a porosity of ≤ 2%. The first corrosion time in a 5% NaCl salt spray environment reaches more than 1676 hours, which is more than 9.7 times longer than the traditional chemical plating (172 hours). No serious corrosion was found after 2400 hours of salt spray test.

[0019] Production costs are effectively reduced: Vacuum sputtering is only used to prepare thin-layer serrated structures (5-20 micrometers), while thick-layer coating (30-150 micrometers) is completed by lower-cost chemical plating. The total cost is reduced by 50-70% compared to the full vacuum sputtering method, while maintaining the high adhesion advantage of shear strength of 25-45 MPa. The unit area processing cost is reduced to 12-25 yuan / m².

[0020] Improved process controllability and stability: All innovative processes are operational-level methods, with process parameter reproducibility ≥95%, product quality pass rate ≥98%, and coating thickness control accuracy ±3%, making them suitable for mass production in high-end manufacturing fields such as automotive parts, hydraulic components, aerospace seals, and precision medical device components. Attached Figure Description

[0021] Figure 1 These are the comparative test results of the coating adhesion of the present invention; Figure 2 This is a comparison of the coating thickness distribution of grooves with different aspect ratios in this invention; Figure 2 In the middle: a represents a depth-to-width ratio of 2:1; b represents a depth-to-width ratio of 3:1; c represents a depth-to-width ratio of 4:1; d represents a depth-to-width ratio of 5:1; Figure 3 This is a comparison of the uniformity of the plating of grooves with different aspect ratios in this invention; Figure 4 This reflects the trend of the uniformity improvement effect of the present invention; Figure 5 This is a comparison of the coating hardness gradient distribution of the present invention; Figure 6 This is a comparison of the average hardness of the coating of the present invention; Figure 7 This is a comparison of the initial corrosion time of the present invention; Figure 8 This is a timeline comparison of the corrosion process of the present invention. Detailed Implementation

[0022] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0023] Example 1: This example proposes a serrated vacuum sputtering deposition method, including the following steps: Step 1: Matrix pretreatment: The workpiece surface is degreased, derusted, and cleaned. Step 2: Serrated vacuum sputtering: A serrated sputtering layer with a serration height of 125 micrometers and a serration pitch of 300 micrometers is formed on the substrate surface; The process parameters for serrated vacuum sputtering are: vacuum degree 3×10⁻⁶. -3 Pa, sputtering power 500W, sputtered layer thickness 12.5 micrometers; Step 3: Alternating soaking-tilting rotation catalytic activation: The workpiece was immersed in the catalytic activation solution four times, with the tilt angle of the workpiece changed to 0°, 45° and 90° between each immersion, so that the catalyst concentration in the serrated groove was gradually enriched. Alternating immersion-tilted rotation catalytic activation includes sensitization and activation treatments. The sensitization solution contains 30 g / L stannous chloride and 30 ml / L hydrochloric acid, and the activation solution contains 0.5 g / L palladium chloride and 5 ml / L hydrochloric acid. During the alternating immersion process, each immersion lasts for 30 seconds, with a 15-second pause in between. The catalyst is enriched in a controlled manner by utilizing the synergistic effect of gravity and surface tension.

[0024] Step 4: Pulsating stirring-assisted alternating liquid electroless plating: The nickel-phosphorus plating solution and the nickel-tungsten plating solution were used for alternating deposition. Each plating solution was operated in an intermittent manner with "static plating for 2 minutes + pulsed stirring for 12 seconds", and the alternating deposition was carried out 4 times. The pulsating stirring method uses a reciprocating movement of the workpiece at a frequency of 1.2Hz and an amplitude of 13mm. The nickel-phosphorus plating solution contains 10% phosphorus, and the nickel-tungsten plating solution contains 14% tungsten. The thickness of each single-layer plating is 10 micrometers.

[0025] The alternating chemical plating process also includes a surface homogenization step: immersing the workpiece in a complexing agent solution containing 20 g / L citric acid and 10 g / L disodium EDTA at 60°C for 8 minutes.

[0026] Step 5: Gas purging between two liquids: The serrated grooves were purged with 0.35 MPa compressed air between each two-liquid conversion. During the gas purging of the two-liquid gap, the gas pressure is 0.35MPa, and the serrated groove is purged in a directional manner to forcibly remove residual plating solution and bubbles.

[0027] Step 6: Graded passivation treatment: First, pre-passivate with a diluted passivation solution with a concentration of 5 / 12, and then deeply passivate with a passivation solution of normal concentration. In the graded passivation treatment, the pre-passivation solution contains 75 g / L of chromic anhydride, and the deep passivation solution contains 225 g / L of chromic anhydride.

[0028] The final composite coating has a total thickness of 90 micrometers and consists of a three-layer structure, namely a serrated vacuum sputtering base layer, a nickel-phosphorus / nickel-tungsten alternating composite intermediate layer, and a passivation surface layer.

[0029] Example 2 differs from Example 1 in that: Step 2: Form a serrated sputtering layer with a serration height of 50 micrometers and a serration pitch of 100 micrometers on the substrate surface; The process parameters for serrated vacuum sputtering are: vacuum degree 1×10⁻⁶. -3 Pa, sputtering power 200W, sputtering layer thickness 5 micrometers; Step 3: Immerse the workpiece in the catalytic activation solution three times, changing the tilt angle of the workpiece to 0°, 45° and 90° between each immersion, so that the catalyst concentration in the serrated groove gradually increases. The sensitization solution contains 20 g / L stannous chloride and 20 ml / L hydrochloric acid, and the activation solution contains 0.1 g / L palladium chloride and 1 ml / L hydrochloric acid. During the alternating soaking process, each soaking time is 20 seconds, with a 10-second pause in between.

[0030] Step 4: Each plating solution is operated in an intermittent manner with "static plating for 2 minutes + pulsating stirring for 10 seconds", and the deposition is repeated 3-5 times. The pulsating agitation employs a plating solution pulse spray method with a frequency of 0.5Hz and an amplitude of 5mm. The nickel-phosphorus plating solution contains 8% phosphorus, and the nickel-tungsten plating solution contains 10% tungsten, with a single-layer plating thickness of 5 micrometers for each.

[0031] It also includes a surface homogenization treatment step: immersing the workpiece in a complexing agent solution containing 10g / L citric acid and 5g / L disodium EDTA at 50℃ for 5 minutes.

[0032] Step 5: Purge the serrated grooves with 0.2 MPa nitrogen gas between each two-liquid conversion; During the gas purging of the two-liquid gap, the gas pressure is 0.2 MPa.

[0033] Step 6: First, pre-passivate with a dilute passivation solution with a concentration of 1 / 3 of the standard concentration; The pre-passivation solution contains 50 g / L of chromic anhydride, and the deep passivation solution contains 150 g / L of chromic anhydride.

[0034] The final composite coating has a total thickness of 30 micrometers.

[0035] Example 3 differs from Example 1 in that: Step 2: Form a serrated sputtering layer with a serration height of 200 micrometers and a serration pitch of 500 micrometers on the substrate surface; The process parameters for serrated vacuum sputtering are: vacuum degree 5×10⁻⁶. -3 Pa, sputtering power 800W, sputtered layer thickness 20 micrometers; Step 3: Immerse the workpiece in the catalytic activation solution 5 times, changing the tilt angle of the workpiece to 0°, 45° and 90° between each immersion, so that the catalyst concentration in the serrated groove gradually increases. The sensitization solution contains 40 g / L stannous chloride and 40 ml / L hydrochloric acid, and the activation solution contains 1.0 g / L palladium chloride and 10 ml / L hydrochloric acid. During the alternating soaking process, each soaking time is 40 seconds, with a 20-second pause in between.

[0036] Step 4: Each plating solution is operated in an intermittent manner with "static plating for 2 minutes + pulsating stirring for 15 seconds", and the deposition is repeated 3-5 times. The pulsating stirring frequency is 2Hz, and the amplitude is 20mm. The nickel-phosphorus plating solution contains 12% phosphorus, and the nickel-tungsten plating solution contains 18% tungsten, with a single-layer plating thickness of 15 micrometers for each.

[0037] It also includes a surface homogenization treatment step: immersing the workpiece in a complexing agent solution containing 30g / L citric acid and 15g / L disodium EDTA at 70℃ for 10 minutes.

[0038] Step 5: Blow the serrated grooves with 0.5MPa compressed air between each two-liquid conversion; During the gas purging of the two-liquid gap, the gas pressure is 0.5 MPa.

[0039] Step 6: First, pre-passivate with a diluted passivation solution with a concentration of 1 / 2 that of the conventional solution; The pre-passivation solution contains 100 g / L of chromic anhydride, and the deep passivation solution contains 300 g / L of chromic anhydride.

[0040] The final composite coating has a total thickness of 150 micrometers.

[0041] Example 4: This example proposes a serrated vacuum sputtering deposition method, which includes the following steps: Step 1: Matrix Pretreatment The workpiece substrate surface is pretreated to obtain a clean surface to be plated.

[0042] Pretreatment process: Degreasing treatment: Immerse the workpiece in an alkaline degreasing solution (sodium hydroxide 10-20g / L + trisodium phosphate 15-25g / L + surfactant 2-5g / L) at a temperature of 60-80℃ for 5-15 minutes to remove surface oil stains. Rinse with water: Rinse 2-3 times with deionized water, 30-60 seconds each time; Pickling for rust removal: Immerse the workpiece in a dilute hydrochloric acid solution (HCl concentration 5-15 vol%) at room temperature for 2-8 minutes to remove oxide scale and rust; Rinse thoroughly with deionized water until neutral (pH=6-8); Surface quality requirements: Surface roughness Ra≤1.6μm, no visible oil, rust and scale, and water film continuous and undamaged.

[0043] This step yields a clean substrate surface that meets the requirements for subsequent plating.

[0044] Step 2: Serrated vacuum sputtering A thin metal coating with a serrated structure is formed on the substrate surface in a vacuum chamber by mask sputtering or angle-controlled sputtering.

[0045] Process parameters: Vacuum degree: 1×10 -3 -5×10 -3 Pa; Sputtering power: 200-800W, preferably 400-600W; Sputtering gas: High-purity argon (purity ≥ 99.99%), gas flow rate 10-30 sccm; Sputtering time: 10-60 minutes, adjusted according to the required thickness; Target material: pure nickel target material or nickel-based alloy target material (purity ≥ 99.9%). Matrix temperature: room temperature - 150℃; Structural parameters: Sawtooth height: 50-200 micrometers, preferably 100-150 micrometers; Tooth pitch: 100-500 micrometers, preferably 200-300 micrometers; Sawtooth angle: 30-90°, preferably 45-60°; Sputtered layer thickness: 5-20 micrometers, preferably 10-15 micrometers.

[0046] The serrated structure is formed via a mask (with the tooth opening width matched to the tooth pitch) or angle-controlled sputtering (intermittent rotation with the substrate tilted at 30-60°). This structure provides a macroscopic mechanical interlocking basis, increasing the contact area between the coating and the substrate by 3-8 times.

[0047] Characteristics of intermediate products: A metal coating with a serrated surface morphology is obtained, with clear serration outlines and no burrs at the edges.

[0048] Step 3: Alternating soaking-tilting rotation catalytic activation The selective catalytic activation treatment of the sawtooth sputtered layer is a key step in this invention. 1. Sensitization treatment: Immerse the workpiece in stannous chloride sensitizing solution for sensitization treatment.

[0049] Sensitizing solution composition: Stannous chloride (SnCl2·2H2O): 20-40 g / L, preferably 25-35 g / L; Hydrochloric acid (HCl, 37%): 20-40 ml / L, preferably 25-35 ml / L; Deionized water: Balance - Solution temperature: 20-40℃, preferably 25-35℃; Soaking time: 30-120 seconds, preferably 60-90 seconds; pH value: 0.5-2.0, adjustable with HCl.

[0050] 2. Alternating soaking activation: After sensitization, the workpiece is rinsed with deionized water and then immersed in palladium chloride activating solution in several stages.

[0051] Activation solution composition: Palladium chloride (PdCl2): 0.1-1.0 g / L, preferably 0.3-0.7 g / L; Hydrochloric acid (HCl, 37%): 1-10 ml / L, preferably 3-7 ml / L; Deionized water: Balance; Solution temperature: 20-40℃, preferably 25-35℃; pH value: 1.0-3.0.

[0052] The specific operation is as follows: First immersion: Place the workpiece horizontally (0° angle) and immerse it in the activation solution for 20-40 seconds; Intermediate pause: Remove the workpiece from the activation solution and let it remain in the air for 10-20 seconds. At this time, some activation solution is still retained in the serrated groove due to surface tension; Second immersion: Adjust the workpiece to a 45° tilt angle and re-immerse it in the activation solution for 20-40 seconds; Repeat the above removal-angle adjustment-immersion operation, adjusting the angle to 90° in turn, and perform a total of 3-5 immersions; 3. Catalyst enrichment principle: Each time the activating liquid is removed, some of it is lost from the groove but some remains. When the angle is adjusted and the immersion is repeated, the fresh activating liquid mixes with the residual liquid. Through the synergistic effect of gravity and surface tension, the concentration of catalyst (palladium chloride) in the groove gradually increases, and the catalytic activity of the groove is significantly higher than that of the raised part. 4. Elimination of direction dependence: By immersing from multiple angles, controllable catalyst enrichment can be achieved in the serrated grooves of various parts of complex-shaped workpieces (curved surfaces, inner holes, irregular grooves, etc.), eliminating the directional dependence limitation of traditional single-position activation.

[0053] Intermediate product characteristics: A serrated surface with selective catalytic activation is obtained, with the grooved parts being dark brown (enriched by palladium catalyst) and the raised parts being light brown.

[0054] Quality Judgment Criteria: Catalytic Activity Test: Palladium content determined by formaldehyde titration; ≥0.3 mg / m² in grooved areas, ≤0.1 mg / m² in raised areas. Surface Wettability Test: Deionized water contact angle test; ≤30° indicates sufficient activation. Color Uniformity: Visual inspection; obvious color difference between grooves and raised areas. Subsequent Nucleation Test: Immersion in chemical plating solution for 30 seconds; obvious plating layer precipitation should occur in the grooved areas.

[0055] The technical effect of this step is to obtain a selectively catalytically activated serrated surface, in which the grooved areas have high catalytic activity, laying the foundation for selective nucleation in subsequent electroless plating.

[0056] Step 4: Pulsating stirring of the first type of chemical plating solution to assist plating. After catalytic activation, the workpiece surface is thoroughly cleaned with deionized water to remove residual activation solution, and then the workpiece is immersed in the first chemical plating solution for plating.

[0057] The first type of electroless plating solution composition (nickel-phosphorus plating solution): Nickel sulfate (NiSO4·6H2O): 20-40 g / L, preferably 25-35 g / L; Sodium hypophosphite (NaH2PO2·H2O): 15-35 g / L, preferably 20-30 g / L; Lactic acid (C3H6O3): 15-35 ml / L, used as a complexing agent; Sodium citrate (Na3C6H5O7·2H2O): 8-20 g / L, used as a buffer; Thiourea (CH4N2S): 1-5 mg / L, used as a stabilizer; Solution temperature: 80-95℃, preferably 85-90℃; pH value: 4.5-5.5, adjusted with ammonia or sulfuric acid; Plating rate: 8-15μm / h; Phosphorus content: 8-12 wt%.

[0058] This step is assisted by the pulsed stirring of the present invention: Intermittent plating operation: adopts an alternating mode of "static plating - pulsating agitation - static plating", specifically, pulsating agitation for 10-15 seconds is performed after every 2 minutes of static plating; Pulsating stirring method: Periodic mechanical motion is generated by the reciprocating movement of the workpiece in the plating solution or the intermittent jet flow of the plating solution; Forced mass transfer principle: Pulsating stirring forces fresh plating fluid into the depths of the serrated grooves, displacing the old solution consumed by the chemical plating reaction, thus solving the problem of limited mass transfer in deep grooves (depth-to-width ratio of 3:1 to 5:1). Coating protection principle: The intermittent characteristics of pulsating stirring ensure that the coating grows normally during the static period and will not be damaged during stirring. This is because the chemical coating forms a preliminary bond with the catalytically activated substrate surface in the early stage of deposition and can withstand moderate liquid flow impact. This step yields a nickel-phosphorus coating with a thickness of 5-15 micrometers, achieving uniform coating from the bottom to the opening of the serrated groove, and avoiding sealing effects and void defects.

[0059] Step 5: Gas purging and cleaning of the two-liquid gap The workpiece is removed from the first plating solution, first rinsed with deionized water, and then subjected to the gas purging treatment of this invention: Gas purging operation: Use compressed air or nitrogen at a pressure of 0.2-0.5MPa to purge the workpiece surface in all directions, with a focus on directional purging of the serrated grooves; Triple cleaning action: Forcefully remove any residual plating solution from the deep recesses (areas difficult to reach with liquid cleaning). Remove any air bubbles that may be present in the groove (air bubbles will hinder the entry of subsequent plating solution). This allows the workpiece surface to dry or partially dry quickly, creating conditions for complete wetting by the next plating solution. Contamination elimination principle: Gas purging is a purely physical cleaning method that does not introduce chemical components. It complements chemical cleaning and ensures high purity at the interface during two-liquid conversion. This step yields a workpiece in a clean, residue-free, and bubble-free transitional state, laying the foundation for the pure deposition of the second plating solution.

[0060] Step 6: Second type of chemical plating solution with pulsating stirring to assist plating. The workpiece is immersed in the second chemical plating solution and then plated using the same pulsed stirring-assisted plating technology as in step 4.

[0061] The second type of electroless plating solution composition (nickel-tungsten plating solution): Nickel sulfate (NiSO4·6H2O): 25-45 g / L, preferably 30-40 g / L; Sodium tungstate (Na2WO4·2H2O): 15-35 g / L, preferably 20-30 g / L; Sodium hypophosphite (NaH2PO2·H2O): 8-20 g / L, preferably 10-15 g / L; Trisodium citrate (Na3C6H5O7·2H2O): 20-40 g / L, used as a complexing agent; Ammonium chloride (NH4Cl): 30-50 g / L, used as a buffer; Solution temperature: 85-95℃, preferably 88-92℃; pH value: 8.5-9.5, adjusted with ammonia; Plating rate: 6-12 μm / h; Tungsten content: 10-18 wt%.

[0062] Pulsating stirring parameters: Static plating time: 2 minutes / cycle; stirring interval: 10-15 seconds / cycle; Stirring method: reciprocating movement of the workpiece (frequency 0.5-2Hz, amplitude 5-20mm) or pulse jet of plating solution (pressure 0.05-0.15MPa). Number of cycles: Determined based on the target thickness, generally 3-8 cycles.

[0063] Intermittent operation is employed, with the second plating solution depositing a thickness of 5-15 micrometers. Due to the autocatalytic properties of the nickel metal on the surface of the previous nickel-phosphorus plating layer, it can catalyze the reduction reaction of sodium hypophosphite in the nickel-tungsten plating solution, allowing the nickel-tungsten plating layer to nucleate and grow directly on it without requiring re-catalytic activation. The different components (phosphorus and tungsten) of the two plating solutions undergo solid-state diffusion and interdiffusion at the interface, forming an alloy transition zone of 2-5 micrometers in thickness, eliminating the abrupt compositional interface.

[0064] This step yields a nickel-phosphorus / nickel-tungsten bilayer structure, which combines corrosion resistance and high hardness.

[0065] Step 7: Alternating Cyclic Plating Repeat the complete cycle of "first type of electroless plating solution pulsating agitation plating - two-liquid gap gas purging - second type of electroless plating solution pulsating agitation plating - two-liquid gap gas purging" for 2-4 additional alternating cycles (plus one cycle already completed in steps 4-6 above, for a total of 3-5 cycles).

[0066] Gas purging and cleaning are performed between each two-liquid conversion to ensure the purity of each transition interface. The final total thickness of the chemical plating layer reaches 30-150 micrometers (each cycle includes one nickel-phosphorus plating and one nickel-tungsten plating, with a single layer thickness of 5-15 micrometers, and 3-5 cycles correspond to a total thickness of 30-150 micrometers).

[0067] The alternating coating structure allows the coating to simultaneously possess the high corrosion resistance of the nickel-phosphorus layer and the high hardness of the nickel-tungsten layer, forming a gradient distribution of hardness and toughness. This step yields a nickel-phosphorus / nickel-tungsten multilayer alternating composite coating, with each interface being an alloy transition bond.

[0068] Step 8: Surface homogenization treatment (optional step) The workpiece is immersed in a mild mixed complexing agent solution for surface homogenization.

[0069] Composition of homogenized solution: Citric acid (C6H8O7·H2O): 10-30 g / L, preferably 15-25 g / L; Disodium EDTA (Na2C) 10 H 14 N2O8·2H2O): 5-15 g / L, preferably 8-12 g / L; Ammonium chloride (NH4Cl): 20-40 g / L, preferably 25-35 g / L; Deionized water: Balance; Solution temperature: 50-70℃, preferably 55-65℃; pH value: 7.0-8.5, adjusted with ammonia; Soaking time: 5-10 minutes, preferably 6-8 minutes.

[0070] The complexing agent solution has a slight chemical dissolution effect on the nickel-phosphorus and nickel-tungsten surfaces (dissolution rate 0.1-0.3 μm / min), causing a small amount of surface metal ions to dissolve and form mixed ions in the solution. These ions then redeposit on the surface. Through this dissolution-precipitation process, the surfaces (nickel-phosphorus region and nickel-tungsten region) that originally had significant differences in composition are transformed into a relatively homogenized surface layer with a thickness of about 0.5-2 micrometers and a compositional uniformity deviation of ≤±5%.

[0071] After homogenization, the workpiece surface is thoroughly cleaned with deionized water to remove any residual complexing agent. This step yields a composite coating with homogenized surface composition.

[0072] Step 9: Graded chromate passivation treatment The workpiece is immersed in a chromate passivation solution for passivation treatment, using the graded passivation technology of this invention: Pre-passivation treatment: The workpiece is immersed in a dilute chromate passivation solution for preliminary passivation.

[0073] Composition of pre-passivation solution: Chromic anhydride (CrO3): 50-100 g / L (1 / 3-1 / 2 of the conventional concentration), preferably 60-80 g / L; Nitric acid (HNO3, 65%): 3-8 ml / L, preferably 4-6 ml / L; Deionized water: Balance; Solution temperature: 15-25℃, preferably 18-22℃; Soaking time: 30-120 seconds, preferably 60-90 seconds; pH value: 1.0-2.0.

[0074] Deep passivation treatment: After pre-passivation, rinse lightly with deionized water and then transfer to a passivation solution of normal concentration for deep passivation.

[0075] Composition of deep passivation solution: Chromic anhydride (CrO3): 150-300 g / L, preferably 180-250 g / L; Nitric acid (HNO3, 65%): 8-20 ml / L, preferably 10-15 ml / L; Deionized water: Balance; Solution temperature: 15-30℃, preferably 20-25℃; Soaking time: 60-180 seconds, preferably 90-150 seconds; pH value: 0.5-1.5.

[0076] The principle of graded passivation: The corrosion rate of the dilute passivation solution is 0.05-0.15 μm / min, which will not cause obvious selective corrosion to the surface and will uniformly form a thin and dense initial conversion film (thickness 0.2-0.8 μm) on the entire coating surface; the strong passivation solution, due to the protection of the initial conversion film, will not directly contact the underlying coating metal, avoiding selective corrosion, and can uniformly thicken on the basis of the initial film (growth rate 0.8-2.0 μm / min). This step generates a dense chromate conversion film with a thickness of 0.5-3 micrometers and a porosity of ≤2% on the coating surface, providing a long-lasting corrosion-resistant barrier.

[0077] Step 10: Cleaning and Drying Thoroughly clean the workpiece surface with deionized water to completely remove any residual passivation solution, and then dry it to obtain the final plated workpiece.

[0078] After the above steps, a workpiece with a three-layer composite coating structure is obtained, consisting of a serrated vacuum sputtering underlayer, a nickel-phosphorus / nickel-tungsten alternating composite intermediate layer, and a chromate passivation surface layer. This coating has excellent adhesion, corrosion resistance, wear resistance, and comprehensive mechanical properties.

[0079] Experimental verification Experiment 1: Coating Adhesion Test 1. Experimental Objective The invention verifies the significant improvement in coating adhesion of the serrated vacuum sputtering method compared to the traditional chemical plating method, demonstrating the synergistic effect of the serrated mechanical interlocking structure and the alternating catalytic activation technology.

[0080] 2. Preparation of experimental samples Comparison Sample A (Traditional Chemical Plating): After conventional pretreatment of the 45# steel substrate surface, nickel-phosphorus chemical plating was directly performed, with a coating thickness of 40 micrometers.

[0081] Comparative sample B (method of the present invention): The surface of the No. 45 steel substrate was treated according to embodiment 1 of the present invention, including serrated vacuum sputtering (serration height 120 micrometers, tooth pitch 250 micrometers, sputtering layer thickness 12 micrometers), alternating immersion catalytic activation, and pulsating stirring dual liquid alternating plating for 3 cycles, with a total coating thickness of 42 micrometers (serrated sputtering 12 micrometers + chemical plating 30 micrometers).

[0082] Sample dimensions: 50mm×25mm×3mm, with 5 parallel samples prepared for each group.

[0083] 3. Experimental conditions Testing equipment: universal testing machine (accuracy 0.1kN), special shearing fixture.

[0084] Test environment: room temperature (25±2℃), relative humidity 50±5%.

[0085] Test speed: constant loading speed of 1mm / min.

[0086] Test standard: Refer to GB / T5270-2005 "Review of test methods for adhesion strength of metal capping layers by electrodeposition and chemical deposition on metal substrates".

[0087] 4. Experimental Procedure Sample surface cleaning: Clean the sample surface with acetone to remove oil and impurities.

[0088] Fixture installation: Fix the sample in a special shearing fixture, ensuring that the interface between the coating and the substrate is on the shearing surface.

[0089] Preload: Apply a 10N preload to eliminate system clearance.

[0090] Shear test: Apply a shear load at a speed of 1 mm / min until the coating peels off.

[0091] Data recording: Record the maximum shear force and calculate the shear strength (shear strength = maximum shear force / coating area).

[0092] 5. Experimental Results

[0093] Figure 1 The results show the comparison test results of coating adhesion.

[0094] 6. Analysis and Summary Significantly improved adhesion: The coating prepared by the method of this invention has a shear strength of 34.32±2.40MPa, which is 3.9 times higher than that of traditional chemical plating (8.88±1.04MPa), verifying the synergistic effect of the serrated mechanical interlocking structure and the alternating catalytic activation technology.

[0095] Change in fracture mode: Traditional electroless plating samples all showed interfacial delamination, indicating insufficient adhesion between the plating layer and the substrate; the samples prepared by the method of this invention showed mixed fracture (partial substrate tearing), indicating that the adhesion exceeded the strength of the substrate material.

[0096] Data stability: The standard deviation of the method of this invention (2.40 MPa) is relatively small, indicating good process stability and high reproducibility.

[0097] Technical Mechanism: The serrated structure provides mechanical interlocking with a depth of 50-200 micrometers, increasing the contact area by 3-8 times; alternating immersion catalytic activation ensures controllable enrichment of the catalyst in the groove, achieving selective nucleation and forming a dual combination of "mechanical interlocking + chemical bonding".

[0098] Experiment 2: Plating Uniformity Test for Complex Workpieces 1. Experimental Objective This study verifies the effectiveness of the pulsed stirring-assisted coating technology of the present invention in solving the problem of limited mass transfer in deep grooves of complex-shaped workpieces, and demonstrates the effect of alternating immersion catalytic activation technology on improving the uniformity of catalyst distribution.

[0099] 2. Preparation of experimental samples Test workpiece: Design a special test workpiece containing V-shaped grooves with different depth-to-width ratios (depth-to-width ratios of 2:1, 3:1, 4:1, and 5:1 respectively), with a groove depth of 10mm, and the workpiece material is 45 steel.

[0100] Comparison sample C (traditional static plating): adopts the traditional single-position catalytic activation + static immersion chemical plating process.

[0101] Comparative sample D (method of this invention): adopts alternating immersion catalytic activation + pulsed stirring assisted coating process.

[0102] 3. Experimental conditions Catalytic activation conditions: sensitization solution (SnCl2·2H2O 30g / L, HCl 30ml / L, temperature 25℃), activation solution (PdCl2 0.5g / L, HCl 5ml / L, temperature 25℃).

[0103] Chemical plating solution: Nickel-phosphorus plating solution (NiSO4·6H2O 30g / L, NaH2PO2·H2O 25g / L, lactic acid 25ml / L, sodium citrate 15g / L, temperature 88℃, pH 5.0, phosphorus content 10%).

[0104] Pulsating stirring parameters: static plating for 2 minutes, pulsating stirring for 10-15 seconds (12 seconds were used in the experiment), workpiece reciprocating movement frequency of 1Hz, amplitude of 10mm.

[0105] Sawtooth structure parameters: sawtooth height 120 micrometers, tooth pitch 250 micrometers, sputtering layer thickness 12 micrometers.

[0106] 4. Experimental Procedure Workpiece pretreatment: Degreasing, rust removal, and cleaning are carried out according to standard procedures.

[0107] Catalytic activation treatment: Traditional method: The workpiece is placed horizontally (0°), statically immersed for sensitization for 60 seconds, cleaned, and activated for 60 seconds. Method of this invention: After sensitization for 60 seconds, it is cleaned, and then subjected to alternating immersion activation, divided into 3 immersions at angles of 0°, 45°, and 90°, each immersion lasting 30 seconds with a 15-second pause in between, for a total of 3 cycles.

[0108] Chemical plating treatment: Traditional method: static immersion plating for 120 minutes. Invention method: pulsating stirring-assisted plating for 120 minutes.

[0109] Thickness measurement: Measure the coating thickness at the bottom, middle and opening of the groove, and take the average value for each point 3 times.

[0110] Catalyst distribution detection: EDS was used to detect the palladium content at different locations in the groove.

[0111] 5. Experimental Results Coating thickness distribution test results:

[0112] Catalyst distribution test results:

[0113] Figure 2 Comparison of coating thickness distribution in grooves with different aspect ratios; Figure 3 Comparison of plating uniformity for grooves with different aspect ratios; Figure 4 The trend is towards improving uniformity.

[0114] 6. Analysis and Summary Significantly improved uniformity: The coating uniformity of the method of the present invention is significantly better than that of the traditional method in grooves with different depth-to-width ratios. It can still maintain 82% uniformity at a depth-to-width ratio of 5:1, while the traditional method is only 13%, with an improvement effect of 6.3 times.

[0115] Mass transfer limitation problem solved: Pulsating stirring technology effectively overcomes the mass transfer limitation problem in deep grooves. Even under extreme conditions with a depth-to-width ratio of 5:1, the coating thickness at the bottom of the groove can still reach 24.3μm, which is close to 81% of the target thickness.

[0116] Controllable catalyst distribution: Alternating immersion catalytic activation technology significantly improves the uniformity of catalyst distribution, reducing the concentration difference from ±82% in traditional methods to ±9% in the method of this invention, laying the foundation for uniform coating.

[0117] Excellent process stability: The standard deviation of each measurement point in the method of this invention is smaller than that of the traditional method, indicating good process stability and reproducibility, and it is suitable for mass production.

[0118] Experiment 3: Performance Testing Experiment of Multifunctional Composite Coating 1. Experimental Objective To verify the effectiveness of the dual-liquid alternating plating technology of this invention in constructing multifunctional composite coatings, a comparative analysis was conducted on the differences between nickel-phosphorus / nickel-tungsten alternating composite coatings and single nickel-phosphorus coatings in terms of hardness gradient distribution, corrosion resistance, and comprehensive mechanical properties.

[0119] 2. Preparation of experimental samples Comparison sample E (single nickel-phosphorus plating): a single plating layer with a thickness of 80 micrometers was obtained by continuous plating using traditional nickel-phosphorus electroless plating.

[0120] Comparative sample F (composite coating of the present invention): Using the dual-liquid alternating plating technology of the present invention, four complete cycles were performed (each cycle includes one nickel-phosphorus plating and one nickel-tungsten plating), with a single layer thickness of 10-12 micrometers, and a total chemical coating thickness of 88 micrometers (8 layers × 11 micrometers average thickness). Including the 12-micrometer serrated sputtering layer, the total coating thickness is 100 micrometers.

[0121] Sample specifications: 100mm×50mm×5mm, 6 parallel samples are prepared for each group (3 for hardness test and 3 for corrosion test).

[0122] Matrix material: Q235 carbon steel, pretreated and serrated vacuum sputtering according to the method of this invention.

[0123] 3. Experimental conditions Nickel-phosphorus plating solution: NiSO4·6H2O 30g / L, NaH2PO2·H2O 25g / L, lactic acid 25ml / L, sodium citrate 15g / L, thiourea 3mg / L, temperature 88℃, pH 5.0, phosphorus content controlled at 10±1%.

[0124] Nickel-tungsten plating solution: NiSO4·6H2O 35g / L, Na2WO4·2H2O 25g / L, NaH2PO2·H2O 12g / L, trisodium citrate 30g / L, ammonium chloride 40g / L, temperature 90℃, pH 9.0, tungsten content controlled at 14±2%.

[0125] Alternating plating parameters: each layer is 10-12 micrometers thick, using pulsed stirring (2 minutes of static stirring + 12 seconds of stirring), and 0.3MPa gas purging treatment for 5 seconds between layers.

[0126] Sawtooth structure parameters: sawtooth height 120 micrometers, tooth pitch 250 micrometers, sputtering layer thickness 12 micrometers.

[0127] 4. Experimental Procedure Hardness gradient test: The hardness of the coating is tested along the depth direction using a nano hardness tester with a test point spacing of 2 micrometers, a load of 2mN, and a holding time of 10 seconds. Five points are tested at each depth and the average value is taken.

[0128] Corrosion resistance test: Neutral salt spray test according to GB / T10125-2021 standard, 5% NaCl solution, temperature 35±2℃, observe the corrosion every 24 hours, and record the time when the first corrosion point appears.

[0129] Compositional analysis: Line scan analysis was performed using EDS to detect the distribution of Ni, P, and W elements along the depth direction of the coating.

[0130] Phase structure analysis: XRD analysis of the phase structure composition of the coating is used to determine the degree of alloying.

[0131] 5. Experimental Results Hardness gradient test results:

[0132] Corrosion resistance test results:

[0133] Component analysis results:

[0134] Figure 5 Comparison of coating hardness gradient distribution; Figure 6 Comparison of average hardness of coatings; Figure 7 For comparison of the initial corrosion time; Figure 8 For comparison of the corrosion process timeline.

[0135] 6. Analysis and Summary A hardness gradient was successfully constructed: the composite coating formed a gradient distribution of hardness between 438-752 HV, with the Ni-W layer reaching a hardness of 680-750 HV and the Ni-P layer having a hardness of 438-475 HV. The average hardness was 19.4% higher than that of a single nickel-phosphorus coating, achieving an organic combination of hardness and toughness.

[0136] Significantly improved corrosion resistance: The first corrosion time of the composite coating reaches 1676 hours, which is 9.7 times longer than the 172 hours of the single nickel-phosphorus coating; no serious corrosion was observed after 2400 hours of salt spray testing, while the single coating experienced serious corrosion after 388 hours.

[0137] Multi-layer interface synergistic effect: Composition analysis shows that an alloy transition zone of 2-3 micrometers thick is formed between each layer, and P and W elements undergo solid-state diffusion, eliminating the interface of abrupt composition change and ensuring good interlayer bonding.

[0138] The corrosion mechanism has changed: single nickel-phosphorus coatings experience localized pitting corrosion, which spreads rapidly; composite coatings experience uniform corrosion with a slow corrosion rate, demonstrating the synergistic protective effect of the multi-layer structure.

[0139] Functional matching: The Ni-W layer provides high hardness and wear resistance, while the Ni-P layer provides high corrosion resistance and toughness. The dual-liquid alternation technology successfully realizes the construction of a multifunctional composite coating, meeting multiple performance requirements under complex working conditions.

[0140] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A serrated vacuum sputtering deposition method, characterized in that, Includes the following steps: Step 1: Matrix pretreatment: The workpiece surface is degreased, derusted, and cleaned. Step 2: Serrated vacuum sputtering: A serrated sputtering layer with a serration height of 50-200 micrometers and a serration pitch of 100-500 micrometers is formed on the substrate surface; Step 3: Alternating soaking-tilting rotation catalytic activation: The workpiece is immersed in the catalytic activation solution 3-5 times, and the tilt angle of the workpiece is changed to 0°, 45° and 90° between each immersion, so that the catalyst concentration in the serrated groove is gradually enriched. Step 4: Pulsating stirring-assisted alternating liquid electroless plating: The nickel-phosphorus plating solution and the nickel-tungsten plating solution were used for alternating deposition. Each plating solution was operated in an intermittent manner with "static plating for 2 minutes + pulsed stirring for 10-15 seconds", and the alternating deposition was carried out 3-5 times. Step 5: Gas purging between two liquids: Purge the serrated grooves with 0.2-0.5MPa compressed air or nitrogen between each two-liquid conversion; Step 6: Graded passivation treatment: First, pre-passivate with a diluted passivation solution with a concentration of 1 / 3 to 1 / 2 of the normal concentration, and then deeply passivate with a passivation solution of normal concentration.

2. The sawtooth vacuum sputtering deposition method according to claim 1, characterized in that, The process parameters for the sawtooth vacuum sputtering are: vacuum degree 1×10⁻⁶. -3 -5×10 -3 Pa, sputtering power 200-800W, sputtered layer thickness 5-20 micrometers.

3. The sawtooth vacuum sputtering deposition method according to claim 1, characterized in that, The alternating immersion-tilting rotation catalytic activation includes sensitization treatment and activation treatment. The sensitization solution contains 20-40 g / L stannous chloride and 20-40 ml / L hydrochloric acid, and the activation solution contains 0.1-1.0 g / L palladium chloride and 1-10 ml / L hydrochloric acid.

4. The sawtooth vacuum sputtering deposition method according to claim 1, characterized in that, The pulsating stirring is achieved by reciprocating movement of the workpiece or pulse spraying of the plating solution, with a frequency of 0.5-2Hz and an amplitude of 5-20mm.

5. The serrated vacuum sputtering deposition method according to claim 1, characterized in that, The nickel-phosphorus plating solution contains 8-12% phosphorus, and the nickel-tungsten plating solution contains 10-18% tungsten, with a single-layer plating thickness of 5-15 micrometers for each.

6. The serrated vacuum sputtering deposition method according to claim 1, characterized in that, In the dual-liquid gap gas purging process, the gas pressure is 0.2-0.5 MPa, and the serrated grooves are purged in a directional manner to forcibly remove residual plating solution and bubbles.

7. The sawtooth vacuum sputtering deposition method according to claim 1, characterized in that, In the graded passivation treatment, the pre-passivation solution contains 50-100 g / L of chromic anhydride, and the deep passivation solution contains 150-300 g / L of chromic anhydride.

8. The sawtooth vacuum sputtering deposition method according to claim 1, characterized in that, The process after the alternating chemical plating of the two solutions also includes a surface homogenization treatment step: immersing the workpiece in a complexing agent solution containing 10-30 g / L citric acid and 5-15 g / L disodium EDTA at a temperature of 50-70°C for 5-10 minutes.

9. The sawtooth vacuum sputtering deposition method according to claim 1, characterized in that, In step 3, during the alternating immersion process, each immersion time is 20-40 seconds, with an intermediate dwell time of 10-20 seconds, and the catalyst is controlled to be enriched by the synergistic effect of gravity and surface tension.

10. The serrated vacuum sputtering deposition method according to claim 1, characterized in that, The final composite coating has a total thickness of 30-150 micrometers and consists of a three-layer structure, namely a serrated vacuum sputtering base layer, a nickel-phosphorus / nickel-tungsten alternating composite intermediate layer, and a passivation surface layer.

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