Composite coating electroplating method for tungsten carbide coated cutting tool

Abstract

The invention discloses a composite coating electroplating method for a tungsten carbide coated cutting tool, and relates to the technical field of high-performance cutting tool surface engineering. According to the scheme, a hard alloy cutter base body is subjected to surface activation and micro roughening treatment, a staged electrochemical deposition process is adopted in a multi-component electrolysis system, and a Ni-W-C self-adaptive interface layer structure is formed on the surface of the base body in situ through an induced deposition stage; then, a metal composite layer containing Ni-Co and tungsten carbide particles is constructed under the constant-current deposition condition, an element gradient transition area is formed through diffusion control, and a stable interface bonding structure is obtained through low-temperature heat treatment; according to the method, the lattice mismatch rate between tungsten carbide and a metal deposition layer can be effectively reduced, the accumulative effect of dynamic lattice mismatch in the electroplating process is inhibited, and the interface structure stability and durability of a coating system are improved.

Description

Technical Field

[0001] This invention relates to the field of surface engineering technology for high-performance cutting tools, and more specifically to an electroplating composite coating method for tungsten carbide coated cutting tools. Background Technology

[0002] The production and processing of bio-organic fertilizer typically involves multiple steps, including crushing, stirring, mixing, and granulation, of the fermented organic materials. These materials contain a high proportion of organic acids, ammonium salts, chloride ions, and incompletely decomposed hard particles such as straw fibers, livestock and poultry bone residue, shell powder, and humic granules. During processing, these particles cause significant abrasion and corrosion to the cutting, crushing, and stirring blades inside the equipment. Because these materials exhibit strong chemical reactivity and physical hardness under humid and hot conditions, traditional stainless steel or carbide blades often experience accelerated blade wear, surface dulling, and even overall failure in practical use, resulting in short tool life, frequent maintenance, and high production costs.

[0003] To extend tool life, wear-resistant and corrosion-resistant coatings are prepared on tool surfaces. Common preparation methods include physical vapor deposition, arc ion plating, electroplating composite coatings, and laser cladding. Among these, electroplating composite coatings are widely used by small and medium-sized tool manufacturers due to their simple process, low equipment cost, and controllable coating thickness. Existing technologies such as CN119843199A and CN120060846A disclose technical solutions for improving tool surface hardness and corrosion resistance by co-depositing tungsten carbide particles on a nickel, cobalt, or their alloy substrate. This type of coating is formed under room temperature electrochemical conditions. During the preparation process, particle distribution and bonding strength are improved through stirring and current pulses. The overall process has good feasibility in general machining fields. However, in the environment of bio-organic fertilizer production, due to the complex working conditions of long-term exposure to strong corrosion, high humidity, and cyclic thermal stress, the structural stability of the coating is still difficult to maintain in the long term. Research has shown that this is due to a significant dynamic lattice mismatch accumulation effect at the interface between the electroplated tungsten carbide composite coating and the carbide particles. Tungsten carbide has a hexagonal structure, and its lattice constant differs significantly from that of nickel or cobalt-based metal layers. Under low-temperature electrodeposition conditions, lattice matching cannot be achieved through atomic diffusion or energy buffering. During deposition, metal atoms form a metastable interface layer on the tungsten carbide surface, within which numerous dislocations and localized stress concentration zones accumulate. During tooling use, under the influence of material shear impact and thermal cycling, mismatched dislocations gradually slip, propagate, and induce microcracks at the interface. With the accumulation of cyclic stress, these microcracks further penetrate the interface between the coating and the substrate, forming implicit delamination regions, ultimately leading to localized peeling and crack propagation of the coating in the early stages of use.

[0004] In bio-organic fertilizer production equipment, the tungsten carbide composite coating on cutting tools often exhibits failure modes such as surface peeling, edge cracking, and surface pitting under the alternating effects of material impact and chemical corrosion. After dozens of hours of continuous use, the coating adhesion of some cutting tools significantly decreases, leading to rapid wear of the cutting edge, reduced cutting efficiency, and even affecting the uniformity and appearance quality of fertilizer particles. Conventional current density control, dispersant modification, or annealing treatment cannot fundamentally alleviate the problem of accumulated interfacial mismatch stress. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention discloses an electroplating composite coating method for tungsten carbide coated cutting tools, aiming to effectively control the stress evolution of the metal-carbide interface in the electroplating system, eliminate the dynamic mismatch accumulation effect, and improve the stability of the coating in complex bio-organic fertilizer processing environments.

[0006] To achieve the above-mentioned technical effects, the present invention adopts the following technical solution: A method for electroplating a composite coating of tungsten carbide coated cutting tools includes: Step 1: Perform surface activation and micro-roughening treatment on the cemented carbide tool substrate to obtain a substrate surface with the target roughness and activation energy state; Step 2: Construct a composite electrolytic system containing multiple metal ions and a carbon source on the surface of the substrate. The composite electrolytic system includes a first ion component for inducing deposition and a second ion component for the main deposition. The first ion component contains tungsten ions, nickel ions and carbon complex components, and the second ion component contains nickel ions, cobalt ions and tungsten carbide particles. Step 3: The substrate is subjected to induced deposition treatment using pulsed reverse current, and a metastable adaptive interface layer structure composed of nickel, tungsten and carbon is formed on the substrate surface by periodic reverse potential adjustment. Step 4: A constant current is used to perform the main metal deposition process on the metastable adaptive interface layer structure, and a metal composite layer containing nickel, cobalt and tungsten carbide particles is formed on the interface layer structure through a dual potential synchronous reduction mechanism. Step 5: Construct a transition zone with gradient element distribution between the interface layer structure and the metal composite layer by controlling diffusion and adjusting deposition time; Step 6: Perform low-temperature heat treatment on the composite coating tool formed by deposition to stabilize the interface structure.

[0007] Preferably, the surface activation and micro-roughening treatment in step 1 includes: Using alkaline oxidants and The chemical activation solution of the complexing agent in The following describes the chemical activation treatment of the cemented carbide tool substrate. Remove the adsorbed carbon layer on the surface and generate a thicker layer. A mixed layer of tungsten carbide oxide; The activated matrix was placed in a micro-electrochemical roughening solution. Cathode micro-discharge treatment at current density The surface roughness Ra of the substrate is adjusted to a certain value through local electric field induction. scope; The tungsten carbide oxide mixed layer and the surface rough region together form a double-layer potential structure, wherein the outer layer is a highly polarized region and the inner layer is an electron affinity region, which is used to induce electrons during the electroplating process. Synergistic depositional reactions.

[0008] Preferably, the construction of the composite electrolysis system includes: exist A first ionic solution containing tungsten ions, nickel ions and carbon complex components was prepared under constant temperature conditions and maintained at a constant stirring rate of 300-400 rpm for 40-60 min. The conductivity was stabilized at 8.5-9.5 mS / cm by adjusting the ion balance. A second ion solution containing nickel ions, cobalt ions, and tungsten carbide microparticles is added to the first ion solution at a flow ratio of 1:1.5. The pH of the system is controlled within the range of 8.2 to 8.8 using a buffer adjuster. The tungsten carbide microparticles are adjusted for surface activity to achieve a dispersion of less than [value missing]. Thus, an ion concentration gradient lower than A homogeneous composite electrolysis system.

[0009] Preferably, the carbon complexing component is composed of an organic complexing agent containing a carboxyl and hydroxyl dual-coordination structure and a carbon source, and its content is a percentage of the total solute mass. In the composite electrolysis system, the molar ratio of tungsten ions to carbon complex components is controlled at 1:3, and the molar ratio of nickel ions to cobalt ions is controlled at 2:1. The zeta potential of tungsten carbide particles in the composite electrolysis system is adjusted to −20 to −35 mV by a surface charge modifier, so as to maintain the stable coordination structure and suspension uniformity of multi-metal ions and carbon sources in the system.

[0010] Preferably, in step 3, before the induced deposition treatment, the local ion migration direction in the initial deposition stage is controlled by a partitioned modulated electric field. By applying a current density ratio of 1.2:1 to 1.8:1 to the outer peripheral region and the central region of the cathode surface, tungsten ions and carbon complex components are made to form a uniform nucleation region along the radial migration path. The average nucleation spacing of the uniform nucleation region is controlled within the range of 50 to 200 nm, thereby obtaining an induced deposition pre-state with a uniform electric field distribution at the interface layer before entering the pulse reverse deposition stage.

[0011] Preferably, the waveform parameters of the pulsed reverse current include: peak current density of 0.5–0.8 A / dm³. 2 Reverse current density: 0.15–0.25 A / dm 2 The single pulse period is 40-60 ms, and the forward duty cycle is 70-80%. In step 3, the induced deposition time is maintained for 2-4 min under continuous pulse conditions. During the pulse reversal phase, the change rate of the local electric field intensity on the substrate surface is controlled to be less than 0.05 V / ms by the periodic reversal of the instantaneous anode potential. A metastable phase lattice structure composed of alternating nickel, tungsten and carbon atoms is induced in the electrode interface region. The interlayer spacing of nickel atoms is distributed in the range of 0.198-0.205 nm, the average thickness of the tungsten atom enrichment region is 3-6 nm, and carbon atoms are interstitially embedded in the interlayer vacancy region of the nickel-tungsten lattice.

[0012] Preferably, the host metal deposition process is performed at a constant current density of 1.5–2.0 A / dm³. 2 The electrolysis is carried out at a bath temperature of 50–60 °C, and an axial swirling electrolysis zone is formed by applying a rotating magnetic field with a magnetic field strength of 0.02–0.05 T within the electrolytic cell. The average particle size of the tungsten carbide particles is controlled within [specific parameters]. The dispersion concentration is 3-5 g / L; in step 4, a dual potential control strategy is adopted under constant current conditions, wherein the first potential is used to maintain the synchronous reduction of nickel-cobalt alloy ions, and the second potential is used to induce the formation of a metal coating layer on the surface of tungsten carbide particles, forming a dense composite deposition layer with a thickness of 8-12 μm, a nickel-cobalt phase volume fraction of 60%-70%, and a tungsten carbide particle volume fraction of 30%-40%.

[0013] Preferably, the diffusion control stage in step 5 includes a five-stage current density decreasing deposition process, with the first to fifth stage current densities being 1.5 A / dm³ respectively. 2 1.2 A / dm 2 1.0 A / dm 2 0.8 A / dm 2 and 0.5 A / dm 2 The deposition time for each stage is 90–150 s. By maintaining the electrolyte temperature at 45–55°C and adjusting the ion migration rate at a stirring rate of 150–200 rpm between each deposition stage, the concentration of nickel-cobalt alloy ions decreases along the thickness direction and the distribution density of tungsten carbide particles increases layer by layer through a decrease in current density, forming a gradient structure region with a thickness of 2–6 μm.

[0014] Preferably, in the diffusion control stage, 0.03–0.06 wt.% polyvinylpyrrolidone is added to the electrolyte as a diffusion slow-release agent to form a composition gradient by adjusting the migration rate of metal ions; during the deposition process, the electrolyte flow rate is maintained at 0.08–0.12 m / s; the cathode and anode are arranged in parallel in the electrolytic cell by an adjustable insulating support, and the spacing is controlled by the support structure to be 40–60 mm; in the diffusion control stage, the pH of the system is maintained in the range of 4.2–4.8 by a buffer and the thickness of the diffusion layer is controlled to be 80–100 μm, and a transition zone with a nickel content gradient change rate of 3%–5% per micrometer is obtained along the thickness direction.

[0015] Preferably, the low-temperature heat treatment includes a staged heating and oxygen-limited atmosphere control process, with a heating rate of [missing information]. The temperature of the first isothermal stage is The holding time is 20–40 min, and the temperature of the second isothermal stage is [temperature missing]. The holding time is 10–20 min; the heat treatment is carried out in a mixed atmosphere containing 2%–5% hydrogen and 95%–98% argon, with the oxygen partial pressure controlled at [value missing]. The following steps are followed: After heat treatment, furnace cooling is used for temperature reduction, with a cooling rate of [missing information]. This makes the composite coating inside The intermetallic compounds in the phase and gradient region are in a thermodynamically stable state, and the distribution of residual stress at the interface tends to be uniform.

[0016] Based on the above technical solution, the positive and beneficial effects of the present invention are as follows: 1. In this invention, the Ni–W–C adaptive interface layer generated during the induced deposition stage forms a lattice constant transition from the carbide phase to the metallic phase at the atomic scale. This reduces the lattice mismatch rate at the interface between the tungsten carbide matrix and the subsequent metal deposition layer, thereby maintaining structural continuity during multi-cycle deposition and preventing the accumulation of mismatched dislocations in the interface region, thus avoiding the formation of high-energy stress zones. This continuous lattice transition transforms the interface bonding behavior from local bond connections to a stable metallic-carbide composite bonding mode.

[0017] 2. By controlling the ion migration and deposition rate in space and time through a two-stage electrochemical deposition system, a diffusion-dominated gradient transition layer is formed in the interface region, so that the residual stress inside the coating is continuously distributed. During the implementation process, the gradient structure exhibits the self-sustaining characteristics of dislocation slip and atomic diffusion synergistically, thereby reducing the risk of local stress concentration and microcrack initiation caused by the accumulation of lattice mismatch.

[0018] 3. By connecting the adaptive interface layer formed in situ with the subsequent deposited composite layer, the phase stability and chemical inertness of the interface structure are maintained under high temperature and alternating load conditions. This allows the electroplated composite coating system to maintain a continuous interface morphology and bonding state under long-term thermal cycling and mechanical shock conditions, and suppresses interface peeling and coating degradation caused by mismatch stress evolution. Attached Figure Description

[0019] 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 these drawings without creative effort, wherein: Figure 1 This is a schematic diagram of the steps of the present invention; Figure 2 This is a schematic diagram of the microscopic cross-section of the substrate surface of the present invention; Figure 3 This is a diagram of the double-layer potential structure of the present invention; Figure 4 This is a schematic diagram illustrating the deposition process principle of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] The terms "first," "second," "third," "fourth," etc. (if present) in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0022] Unless otherwise defined, all techniques and scientific methods used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The descriptions herein are for the purpose of illustrating particular embodiments only and are not intended to limit the invention. The terms "and / or" as used herein include any and all combinations of one or more of the associated listed items.

[0023] Example 1: Taking the cemented carbide crushing blades used in the cow manure fermentation and mixing system of bio-organic fertilizer production as the process object, this invention addresses the problems of blade dulling, corrosion, and accelerated wear caused by long-term operation in high humidity, organic acid, ammonia, and microbial active atmospheres. The surface is modified using the tungsten carbide electroplating composite coating technology of this invention to achieve dual enhancement of the blade surface's corrosion resistance and wear resistance. In practice, a 10 mm diameter, 3 mm thick WC-6Co cemented carbide sheet is used as the substrate. It is ultrasonically cleaned to remove oil, with cleaning consisting of 5 minutes of ethanol and 5 minutes of deionized water, followed by immersion in a chemically activated solution at 42°C for 7 minutes.

[0024] The chemical activation solution formula is as follows: hydrogen peroxide: 30% solution diluted to 6.0 wt.% in the system as an oxidant, glycine ( The complex component, consisting of propylene glycol in a 1:1 mass ratio, comprises 1.5 wt.% of the solute. The activation solution is adjusted to a weakly alkaline state (pH ≈ 9) using NaOH to promote the surface oxidation-carbonization reaction. After activation, the solution is rinsed with deionized water and transferred to a micro-electrochemical roughening solution, which is a 1:5 dilution of the main electrolyte, and activated at a constant current of 0.3 A / dm³. 2 After performing cathode micro-discharge for 2 minutes, the surface Ra was measured to be approximately 0.35 μm using a tactile roughness meter. XPS analysis of the surface layer showed the presence of a mixed oxide / tungsten carbide layer of approximately 8 nm thickness (W4f peaks indicate some high valence states and carbide components).

[0025] The composite electrolyte is first prepared by preparing an induction solution: dissolving in deionized water. (Equivalent total W concentration) )and Add boric acid ( ) and borax ( The system was used as a buffer and stirred at 42°C and 350 rpm for 45 minutes to stabilize the conductivity. The second solution is prepared in the following proportions: ), Add industrial-grade WC powder. The WC is first pre-dispersed with 0.5 wt.% SDS and 0.2 wt.% PEG400 and sonicated for 20 minutes, then added in a dispersion tank... It is added and kept suspended by mechanical stirring and micro-aeration with gas.

[0026] The two solutions were mixed at a volumetric flow rate ratio of 1:1.5, and the pH in the mixing tank was maintained at approximately 8.4. After standing for 30 minutes, the ion concentration difference was measured using ICP-OES. The electroplating equipment employs a two-zone parallel partitioned fixture: the workpiece is clamped into a 4mm diameter central disk and electrically isolated from an outer ring with a total diameter of 10mm. Each zone is connected to a programmable power supply. Initially, the central zone is powered by 0.4A / dm². 2 Outer ring 0.6A / dm 2 Run for 60 seconds, then switch to pulse reverse induction mode: peak value 0.7 A / dm 2 0.2A / dm in reverse 2 The period is 50ms, the forward duty cycle is 75%, and the induction deposition time is 3 minutes. During the induction phase, the anode potential is recorded using an oscilloscope, and the instantaneous potential change rate is ensured to be < According to SEM nucleation statistics, the average nucleation distance is approximately 100 nm.

[0027] Subsequently, a constant current of 1.7 A / dm was applied. 2 The bulk deposition was performed at 55°C, while a 0.03T rotating magnetic field was applied to the electrolytic cell to promote axial swirling and improve particle embedding. Deposition continued until the overall layer thickness reached approximately 11 μm (measured by cross-sectional SEM). Diffusion control employed a five-stage current decrease: 1.5, 1.2, 1.0, 0.8, and 0.5 A / dm². 2 Each stage lasts 120 seconds. 0.045 wt.% PVP K30 is added to the electrolyte as a diffusion slow-release agent, and the circulation pump maintains a flow rate of 0.10 m / s⁻ 1 The anode-cathode spacing was fixed at 50 mm using a PTFE support, and the diffusion layer thickness was measured and verified using electrochemical impedance spectroscopy within the range of 80–100 μm. After deposition, the material was placed in a tube furnace... When heat-treating a mixed gas, it should be noted that the gas flow rate and heating rate are precisely controlled by an MFC. Keep Hold for 15 min, then furnace cool to room temperature. Sampling and cross-sectional STEM–EDX line scanning showed that the gradient region was approximately 3.5 μm thick, and the Ni content changed at a rate of approximately 4% / μm with thickness. HRTEM showed that the Ni interlayer spacing in the metastable interface layer was concentrated between 0.199 and 0.203 nm.

[0028] In this implementation process: the partition fixture must ensure that the electrical contact resistance is less than 0.05Ω, and there should be a 0.5mm PTFE transition zone at the partition boundary to reduce the concentration of the edge electric field; if WC suspension settles, the aeration and rotor speed must be adjusted in real time and the dispersant must be added; if the induced layer is not uniformly formed, the pre-state time, the external / internal current ratio, and the rise / fall time of the upper and lower edges of the pulse should be checked first.

[0029] The resulting composite-coated tool has a smooth surface and a strong bond. Microhardness test results show that the surface microhardness is approximately HV 1100, which is about 45% higher than that of the original YG8 substrate; friction and wear tests show that the wear rate is reduced by about 60%; after immersion in simulated cow dung fermentation liquid (pH≈5.8, containing organic acid salts and amino compounds) for 72 hours, no obvious peeling or pitting corrosion was observed on the coating surface, indicating that the coating has excellent corrosion resistance and interfacial stability.

[0030] Example 2: This example focuses on the cutting tools used in the highly acidic pulverization stage of a bio-organic fertilizer fermentation system for poultry and livestock manure. In this condition, due to the low pH value (4.0–5.0) and high content of organic acids and hydrogen sulfide in the fermentation material, traditional Ni-Co-W coatings are prone to cobalt enrichment corrosion and interfacial hydrogen evolution stripping in corrosive media. This example optimizes the chemical stability and stress distribution of the interfacial layer by adjusting the structure of the carbon complex component and the pulse waveform parameters.

[0031] In the pretreatment and electrolysis system construction, except for the activation time adjustment, the remaining steps are the same as in Example 1. The difference lies in that the concentration of the alkaline oxidant in the chemical activation solution is adjusted to 9 wt.%, the concentration of the complexing agent is maintained at 2 wt.%, and the treatment temperature is maintained at 45 ℃ but the time is extended to 10 min to ensure the formation of a denser tungsten carbide oxide mixed layer (approximately 12 nm thick) under acidic conditions. In the composite electrolysis system, the carbon complexing component uses a mixture of citric acid and tartaric acid, with a total mass fraction of 1.6 wt.%, which increases the coordination constant of the carboxyl groups in the organic ligands, thereby enhancing the complexation stability of tungsten ions. Ni 2 ⁺ and W 6 The molar ratio of ⁺ ions was maintained at 3:1, and the molar ratio of nickel to cobalt ions was maintained at 2:1. The electrolyte pH was controlled at 8.3, and the temperature at 42 ℃.

[0032] During the induced deposition stage, a low duty cycle pulsed current waveform was used to improve the corrosion resistance of the interface layer. The peak current density was set to 0.7 A / dm³. 2 Reverse current density 0.25 A / dm 2 With a single cycle of 45 ms, a forward duty cycle of 70%, and an induced deposition time extended to 4 min, the Ni-WC interface layer formed under these waveform conditions was approximately 0.6 μm thick, exhibiting a more compact structure and a slightly higher W content (approximately 14 wt.%). Microscopic analysis revealed that carbon atoms within the interface layer were uniformly embedded in the interlayer lattice in an interstitial manner, with a finely dispersed Ni3C phase in the local area, effectively suppressing the preferential pathway for electrochemical reactions in an acidic environment.

[0033] The process conditions for the main metal deposition stage are basically the same as in Example 1, but the current density is slightly increased to 1.9 A / dm³. 2The bath temperature was maintained at 55 ℃. To further enhance the uniform distribution of tungsten carbide particles, 0.05 wt.% sodium dodecylbenzenesulfonate was added to the bath as an auxiliary dispersant, adjusting the particle zeta potential from −28 mV to −32 mV, improving suspension stability by approximately 15%. The final composite layer thickness was approximately 11 μm, with a WC particle volume fraction of approximately 37% in the Ni-Co matrix. After low-temperature heat treatment at 400 ℃, the composite layer exhibited a fine Ni-Co-W solid solution structure, improved interfacial bonding energy, and a coating hardness reaching HV 1180. After continuous operation for 240 hours in a poultry and livestock manure stirring experiment, the cutting edge showed no significant wear, demonstrating excellent acid corrosion resistance and fatigue stability.

[0034] Example 3: High-speed shredder blades for bio-fertilizer treatment equipment of urban kitchen waste. These blades operate in environments containing high levels of grease and organic amines, which easily induce organic film deposition and micro-galvanic corrosion on the blade surface under high-temperature friction conditions. This example addresses this by enhancing the effect of the rotating magnetic field and altering the current density gradient design, resulting in a more uniform distribution of tungsten carbide particles in the deposition layer while simultaneously suppressing the formation of micropores in the interface layer.

[0035] The pretreatment and electrolysis system construction process is the same as in Example 1, but the Co content is increased in the second ion solution. 2 ⁺ Concentration to 0.05 mol / L, while maintaining Ni 2 A concentration of ⁺ of 0.10 mol / L was used to slightly improve the toughness of the composite layer. A rotating magnetic field with a strength of 0.05 T and a current density of 1.6 A / dm³ was employed during the deposition stage. 2 The bath temperature was maintained at 60 ℃. Because kitchen waste has a high salt content, knives are susceptible to chloride ion corrosion. Therefore, 0.03 wt.% polyvinylpyrrolidone (PVP) was added to the composite electrolysis system as an ion migration slowing agent to balance the deposition rate of metal ions on the cathode surface. Under these process conditions, the composite layer formed was approximately 9 μm thick, with a nickel-cobalt alloy phase volume fraction of approximately 62% and a tungsten carbide particle volume fraction of approximately 38%.

[0036] The gradient transition region was achieved through five stages of current-decreasing deposition, with current densities of 1.5, 1.2, 1.0, 0.7, and 0.5 A / dm³ for each stage. 2 Each deposition stage lasts 120 seconds, forming a gradient region with a thickness of 3.5 μm. After a two-stage heat treatment at 420 ℃, the interface microstructure exhibits a fine Ni4W phase precipitation-reinforced structure. Simulated kitchen waste slurry (containing fatty acid salts and chloride ions) tests verified that the corrosion rate was reduced by approximately 65% ​​compared to traditional Ni-W electroplating, and the friction wear depth was reduced by 55%.

[0037] Example 4: This example addresses the die cutters used in humic acid-containing bio-organic fertilizer pellet forming machines. Under these conditions, the material friction temperature is high, and it contains trace amounts of oxidants, easily leading to thermal cracking and peeling of the coating. This example, while maintaining the basic structure of the composite system, optimizes the deposition current gradient and incorporates multi-level zoned electric field control to achieve thermal stress balance within the composite layer.

[0038] The tool substrate material is YG6 cemented carbide. The activation treatment conditions are the same as in Example 1, except that the temperature of the chemical activation solution is increased to 50 °C and the treatment time is shortened to 6 min to reduce the adhesion reduction caused by an excessively thick oxide layer. The cobalt ion concentration in the composite electrolytic system is slightly reduced to 0.03 mol / L, while the nickel ion concentration is maintained at 0.12 mol / L. 6 The concentration of ⁺ was maintained at 0.04 mol / L, and the pH of the system was controlled at 8.6. To improve the stress buffering capacity of the deposited layer, 0.02 wt.% polyethylene glycol (PEG-4000) was introduced into the composite electrolyte as a surface flow modifier to improve the density of the deposited layer.

[0039] Induced deposition was performed using a peak current density of 0.5 A / dm³. 2 Reverse current density: 0.15 A / dm 2 A gentle pulse waveform with a period of 60 ms and a duty cycle of 80% was used, with an induction deposition time of 2.5 min. The main deposition was performed using a current density of 1.5 A / dm³. 2 The temperature was 50 ℃. To reduce macroscopic stress, a dual-zone distributed current control was applied to the cathode surface, with the current density ratio of the outer peripheral region to the central region set to 1.3:1. The deposition time was 12 min, forming a composite layer approximately 8 μm thick. Subsequently, the current density was gradually decreased (1.5, 1.1, 0.9, 0.7, 0.5 A / dm³). 2 A gradient deposition method was used to form a transition zone of approximately 4 μm thickness. After two-stage heat treatment at 350 ℃ and 420 ℃, the coating structure was stable, with uniform distribution of Ni-W phase and Ni3C fine-grained phase, and a microhardness of HV 1150. No obvious cracks were generated during the thermal fatigue cycle test.

[0040] In the bio-fertilizer molding simulation test, the coated tool maintained a sharp cutting edge and no significant decrease in surface smoothness after 300 hours of continuous operation, demonstrating the significant improvement of the composite layer's thermal crack resistance performance by the partitioned electric field and organic control strategy in this embodiment.

[0041] Comparative Example 1: To verify the advantages of the present invention's process in terms of composite coating bonding strength, wear resistance, and corrosion resistance, a traditional Ni-W single-metal electroplated tool was selected as the first control. The substrate material used was the same as in Example 1, and the electroplating solution contained... The standard electrolyte was used, without the addition of carbon complex components and tungsten carbide particles. The electroplating temperature was 55 ℃, and the constant current density was 2.0 A / dm³. 2 The deposition time was 20 min. The resulting coating thickness was approximately 10 μm, and after annealing at 380 ℃, a single-phase structure dominated by the Ni4W phase was formed.

[0042] The comparative results showed that the coating surface had poor density, with a grain size of approximately 80–100 nm and an average interfacial adhesion force of 26 MPa. The microhardness test result was HV 820, and the wear volume in the tribological test was 2.6 times that of Example 1. After 72 h of corrosion testing in simulated fermentation broth (pH 5.8), obvious pinholes and localized peeling appeared. This indicates that traditional Ni-W electroplating is prone to localized galvanic corrosion and interfacial stress accumulation in composite microenvironments, leading to a rapid failure rate.

[0043] Comparative Example 2: Carbide cutting tools with WC coatings applied via physical vapor deposition (PVD). This process was performed under vacuum at 550 °C, using WC target sputtering deposition, resulting in a film thickness of approximately 5 μm and a surface roughness Ra of 0.25 μm. This type of coating performs well under dry friction conditions at room temperature. However, in the humid, high-ammonia, and high-organic-acid environments of bio-organic fertilizer processing, the adhesion between the coating and the substrate is limited due to mechanical bonding, and the WC film is relatively brittle, making it prone to cracking under cyclic impact and temperature fluctuations.

[0044] In actual operation tests, after 72 hours of mixing with cow dung, cracks and peeling appeared at the edges of the coating on the cutting tool. Although the hardness was high (HV 2100), the impact resistance was insufficient. Due to the lack of a gradient buffer zone in the PVD coating, the residual stress at the interface was large (approximately 420 MPa), resulting in a significant increase in the peeling rate.

[0045] To systematically compare the overall performance of the embodiments of the present invention with the above-mentioned control process, friction and wear tests were conducted under uniform test conditions (load 20 N, speed 0.15 m / s, time 6 h; corrosion tests were conducted using artificial fermentation broth at pH 5.8, soaking for 72 h). The results are shown in the table below: Sample number Coating type Hardness (HV) Bond strength (MPa) coefficient of friction <![CDATA[Wear rate (×10⁻ 5 mm 3 / N·m)]]> <![CDATA[Weight loss after 72h corrosion (mg / cm 2 )]]> Coating status Example 1 Ni–Co–W–WC composite layer 1100 45 0.34 1.1 0.35 Stable, no peeling Example 2 Ni–Co–W–WC composite layer (acid-reinforced type) 1180 47 0.32 1.0 0.28 Stable, no peeling Example 3 Ni–Co–W–WC composite layer (magnetic field controlled type) 1130 46 0.33 1.2 0.31 Stable, no pitting corrosion Example 4 Ni–W–WC composite layer (heat-crack resistant) 1150 44 0.35 1.3 0.33 Stable, no cracks Compare with Example 1 Ni–W single electroplating layer 820 26 0.42 2.8 0.85 Localized peeling Compare with Example 2 PVD–WC coating 2100 22 0.45 2.1 0.73 Edge cracking As can be seen from the data in the table, the composite electroplating coating of this invention significantly outperforms traditional Ni-W electroplating and PVD-WC coatings in terms of microhardness, bonding strength, and corrosion resistance. Especially in complex bio-organic fertilizer processing environments, the metastable Ni-W-C interface layer and gradient diffusion structure in the composite coating effectively mitigate stress concentration and maintain coating integrity; the embedded distribution of tungsten carbide particles in the metal matrix enhances wear resistance; and the microcrystalline layer induced by carbon complex components strengthens the chemical stability of the interface.

[0046] After long-term working conditions verification, during continuous fermentation, stirring and granulation, the average service life of the tools in Examples 1–4 is 3.2 times that of traditional Ni-W electroplated tools and 2.6 times that of PVD-WC tools. The coating has stable adhesion and good acid and alkali resistance and impact resistance.

[0047] Example 5: The co-deposition behavior and mechanical properties of the system were compared using WC nano- to micron-sized powder with an average particle size of approximately 0.22 μm. The WC powder was used before being introduced into the electrolyte. The mixture was treated with 0.03 wt.% SDS and then subjected to a high-shear disperser at 2500 rpm for 5 min, followed by ultrasonic treatment for 30 min to break down the agglomerates. Dispersion stability was measured using a Zetasizer. Potential, with a target value of approximately −28 mV, was obtained from DLS, showing a volume-uniform distribution peak at 0.22 μm. Matrix activation and micro-coarsening were performed as in the first example, but a short-duration, low-amplitude constant-potential polarization of −0.2 V, relative to Ag / AgCl, for 30 s was added after the micro-discharge step to promote homogenization of surface adsorption sites.

[0048] Starting from the partitioned pre-state, the external / internal current ratio is adjusted to 1.4 to accommodate the migration and encapsulation dynamics of smaller particles, while the pulse inversion parameter maintains a peak value of 0.65 A / dm. 2 0.18 A / dm in reverse 2 The cycle time is 50ms, the duty cycle is 72%, and the induction phase lasts for 3 minutes. During the main deposition phase, to prevent particle aggregation, [the following is used]. The particle dosage was adjusted and the stirring mode was changed from ordinary impeller to axial flow impeller to increase near-wall layer circulation; Deposition current density: 1.6 A / dm³ 2 The magnetic field strength was 0.03 T. After the same heat treatment, the cross-sectional images showed that WC particles were more uniformly distributed in the metal matrix, with a volume fraction of approximately 32%, and a lower surface roughness Ra. Wear tests (rolling contact fatigue and dry grinding) showed a more significant improvement in lifespan under the same load. The particle size-depth distribution of the cross-sectional EDX also proved that smaller particle size is beneficial for accumulation in the gradient region with a smoother probability density distribution. In this implementation, fine-particle-size powders are sensitive to adsorption after surface activation. Short-term constant potential pre-polarization helps to generate more uniform adsorption sites on the conductive matrix; at the same time, the particle concentration should not be too high, otherwise agglomeration and sedimentation are likely to occur under high current density.

[0049] Example 6: To verify the feasibility of the process while considering industrialization and pH segmentation requirements, a two-tank transfer process was designed and implemented under pilot-scale conditions. Induction and bulk deposition were completed in tank A, where the liquid phase was buffered with boric acid / borax to maintain the pH at 8.2–8.6 and the temperature at 42–50°C. The diffusion control stage took place in tank B, where an acetate / sodium acetate buffer was used to adjust the pH to 4.3–4.7 and the temperature at 50°C. The transfer of workpieces between the two tanks was performed by a robotic arm. Before transfer, the workpieces were quickly rinsed and spun dry (5 s) in neutral deionized water to reduce cross-contamination between tanks. The tank design employed an adjustable electrode support: a PTFE positioning rod with a limiting nut to achieve rapid adjustment of the anode-cathode spacing of 40–60 mm and repeatable positioning within ±0.5 mm.

[0050] A zoned electric field pre-state was implemented in tank A, with an external / internal current ratio of 1.3–1.6 and a pre-state time of 45–90 s; the pulse reverse induction parameter was 0.7 A / dm peak. 2 0.2 A / dm in the reverse direction 2 With a cycle time of 50 ms and a duty cycle of 75%, after the induced layer is formed, a pre-deposition of 6–8 μm thickness is performed in tank A. Then, the workpiece is transferred to tank B to complete the five-stage current reduction (1.5 → 0.5 A / dm). 2 The diffusion and slow-release effects of PVP (0.03–0.06 wt.%) at each stage (90–150 s) create a gradient zone of 2–6 μm. To ensure the diffusion layer thickness in tank B is 80–100 μm, the circulation pump flow rate is adjusted to 0.08–0.12 m·s⁻¹. 1 The near-wall flow is controlled by the stirring speed (150–200 rpm) and calibrated by an electrochemical method, which obtains the bilayer capacitance and diffusion impedance by measuring local conductivity and fitting Nyquist spectra.

[0051] The heat treatment process in the pilot tube furnace employs a gas purification chain: H2 and Ar are mixed at a ratio of 3% / 97% using MFC; trace oxygen is removed by passing the gas through a 3Å molecular sieve dehydration tower and an activated copper bed; and the O2 partial pressure inside the furnace is monitored by an oxygen analyzer to ensure it is <10⁻. 2 Pa.

[0052] Common problems encountered during implementation and their corresponding solutions are as follows: If inter-tank transfer causes surface contamination, a short-term low potential of 5–10 s should be added after the transfer to remove surface oxidation; if the Ni gradient in the diffusion zone is discontinuous, the solubility and uniformity of PVP should be checked and the deposition time of each stage should be appropriately extended to improve the diffusion control accuracy.

[0053] To facilitate a deeper understanding of the technology in this invention, a detailed description of the electroplating composite coating method for tungsten carbide coated cutting tools disclosed in the embodiments of this application is provided below. Please refer to [link to relevant documentation]. Figure 1 The schematic diagram shown illustrates the steps of the invention, which include: Step 1: Perform surface activation and micro-roughening treatment on the cemented carbide tool substrate to obtain a substrate surface with the target roughness and activation energy state; YG6 type cemented carbide tool blanks with uniform grain size were selected as the substrate, with the main components being 94 wt.% WC and 6 wt.% Co; the surface roughness Ra was approximately 0.12 μm. The substrate was ultrasonically cleaned with acetone for 15 min to remove oil contaminants, and then dried under hot air at 60°C. The acetone used for cleaning had a purity ≥99.5%, and the ultrasonic power was 300 W with a frequency of 40 kHz. To prevent secondary oxidation of the surface after cleaning, the substrate was immediately transferred to an activation tank after drying until no liquid film remained on the surface.

[0054] The chemical activation solution consists of an alkaline oxidant system composed of Na₂CO₃ and ammonium persulfate, with disodium EDTA added as a complexing agent. The pH of the activation solution is maintained at 8.5–9.5. The mass fraction of the oxidant in the activation solution is controlled within the range of 5–10 wt.%, and the complexing agent is 1–3 wt.%. The solution temperature is maintained at 40–50°C, and uniform mass transfer is maintained by magnetic stirring. The volume of each batch of activation solution is at least 20 times the total volume of the workpiece. The activation process lasts for 5–10 minutes. Under these conditions, a mixed tungsten carbide oxide layer with a thickness of approximately 5–15 nm can be formed on the outer layer of WC particles. The presence of this layer can be confirmed by XPS detection of the W 4f main peak and the O 1s binding energy shift. The proportion of low-valence tungsten states should not be less than 30% of the total signal to be considered sufficiently activated. If the processing temperature is below 40°C, the formation of the oxide carbide layer will be incomplete; if it is above 50°C, the oxide layer is prone to being too thick, affecting subsequent deposition and bonding.

[0055] After activation, the workpiece is rinsed with deionized water until the pH is close to neutral, and then rinsed once with 95% ethanol to prevent residual complexing agent from introducing impurities during subsequent electrochemical processes. Micro-electrochemical roughening is then performed. The roughening solution uses a borate buffer system (H3BO3 30 g / L), pH 8.0–8.5. The electrolytic cell is an independent circulation type, with an insoluble platinum mesh as the anode and the tool holder substrate as the cathode. The current density is controlled at 0.2–0.4 A·dm⁻. 2 The voltage is automatically adjusted to maintain a constant current state. The processing time is 1 to 3 minutes. Local electric field peaks are induced on the surface through periodic cathode micro-discharge, which causes slight dissolution of WC grain boundaries and reconstruction of surface energy.

[0056] This process causes the surface roughness Ra to increase to 0.3–0.5 μm, which can be confirmed by optical interferometry. If the current density exceeds 0.4 A·dm⁻ 2 Localized over-ablation and microcracks are prone to occur; below 0.2 A·dm⁻ 2 Insufficient discharge will prevent the formation of a uniform, coarsened texture.

[0057] After the above dual treatment, the substrate surface exhibits a micro-nano composite structure: at the microscale, the WC grain interface is slightly etched to form irregular protrusions; at the nanoscale, the tungsten carbide mixed film formed on the outer layer contains abundant surface active sites and enhances electron affinity.

[0058] The bilayer potential structure can be verified by open-circuit potential testing. The outer layer exhibits a highly polarized region (−0.35 to −0.45 V vs Ag / AgCl), while the inner layer is an electron-affinity region (−0.25 to −0.30 V vs Ag / AgCl). A stable interfacial potential difference is formed between the two layers, which can induce Ni during subsequent electroplating. 2 ⁺ and W 6 Co-deposition of ⁺. If the potential difference at this interface is below 0.05 V, the nucleus density will be insufficient in the early stage of deposition. If it exceeds 0.15 V, local over-reduction of metal ions will occur. Therefore, this range is a critical process control range.

[0059] Please see Figure 2 The schematic diagram of the microscopic cross-section of the substrate surface shows the cross-sectional structure of the cemented carbide substrate surface after chemical activation and cathodic micro-discharge: the outermost layer is the cleaned surface (without adsorbed carbon), followed by a 5–15 nm thick tungsten carbide oxide mixed layer (thickness range indicated), and the bottom layer is the cemented carbide substrate (WC-Co granular phase and metal-bonded phase). Simultaneously, the geometry of the surface rough region (Ra 0.3–0.5 μm corrugated) and the double-layer potential structure are also shown: an outer "high polarization region" and an inner "electron affinity region". As one possible implementation, the proportion of the complexing agent in the activation solution can be adjusted according to the difference in substrate composition; for example, for a substrate with high Co content (>8 wt.%), the concentration of the complexing agent can be appropriately increased. It can suppress cobalt leaching and prevent surface pitting corrosion. For the micro-roughening step, alternating current can be used instead of constant DC to obtain a more uniform electric field distribution, but the period should be controlled within the range of 20 to 40 ms to prevent the formation of deep pits.

[0060] After each batch processing, surface condition verification is required. SEM is used to observe the surface micromorphology; no visible microcracks or residual oxide film should appear. XPS measurements show a C / O atomic ratio between 1.5 and 2.2, indicating that the carbide phase remains stable. AFM measurements show a roughness distribution standard deviation of less than 0.08 μm, ensuring uniform surface morphology. Samples are taken from at least three locations for all tests, and the average value and standard deviation are recorded.

[0061] For batch processing, the activation solution renewal cycle and electrolyte conductivity changes should be controlled. After processing 10 workpieces each time, the oxidant concentration should be replenished by approximately 10%, and the conductivity should be monitored to maintain a stable level. During the micro-electrochemical roughening process, the bath temperature must not rise by more than 2°C to prevent the electrochemical reaction from deviating from the target range.

[0062] Step 2: Construct a composite electrolytic system containing multiple metal ions and a carbon source on the surface of the substrate. The composite electrolytic system includes a first ion component for inducing deposition and a second ion component for the main deposition. The first ion component contains tungsten ions, nickel ions and carbon complex components, and the second ion component contains nickel ions, cobalt ions and tungsten carbide particles. During the process, all water used in preparing the composite electrolysis system was 18 MΩ·cm ultrapure water. The constant temperature was maintained in a double-walled stainless steel water bath reactor with a temperature control accuracy of ±0.2°C. Stirring was performed using a magnetically driven paddle stirrer, with the paddle width to tank diameter ratio controlled at 1:3. All solutions were prepared under nitrogen purging to prevent pH drift caused by CO2 in the air. All reagents were filtered through a 0.2 μm microporous membrane after preparation.

[0063] The first ionic component solution was prepared using sodium tungsten sulfate and nickel sulfate hexahydrate as metal ion sources. The carbon complexing component consisted of an organic complexing agent (glycine-propylene glycol system) with a carboxyl and hydroxyl dual-coordination structure and a carbon source (ethylene glycol). During preparation, tungsten salt was first dissolved in 0.05 mol / L water at 40°C with a stirring rate of 350 rpm. After complete dissolution, nickel salt (0.10 mol / L), complexing agent (1.5 wt.%), and carbon source (0.5% volume fraction) were added sequentially. The temperature was maintained at 40–45°C with continuous stirring for 60 min. The conductivity of the system was monitored using a conductivity meter during this period. The conductivity was maintained at 8.5–9.5 mS·cm⁻. 1 And the fluctuation is less than ±0.1 mS·cm⁻ 1 This is considered a complete equilibrium. If the conductivity continues to increase, it usually indicates a low complexation ratio, requiring the addition of 0.2 wt.% complexing agent; if it is below 8.5 mS·cm⁻ 1 If local coordination insufficiency is present, the stirring time can be extended by 10 minutes. The solution formed in this step is transparent light green with no visible precipitate. ICP-OES analysis shows that Ni... 2 ⁺ / W 6 The ⁺ molar ratio was maintained at 2.02±0.03, indicating that the system was in good equilibrium.

[0064] The second ionic component solution was constructed using the same pure water solvent, with the nickel ion source remaining consistent, and the cobalt ions provided by cobalt sulfate hexahydrate. Solution ratio Ni 2 ⁺:Co 2The molar ratio is 2:1, and the total metal ion concentration is 0.15 mol / L. The average particle size of tungsten carbide particles is 0.25 μm, and the particle size distribution is D. 90 The particle size was 0.45 μm. To prevent aggregation, the solution was pretreated for 20 min with a mixed dispersion containing 0.05 wt.% sodium dodecyl sulfate and 0.03 wt.% polyvinylpyrrolidone, followed by ultrasonic dispersion (300 W, 25 kHz) for 15 min. The zeta potential after dispersion was measured to be −28 mV, which was within the target range. This solution was pumped into the first ionic component solution at a flow ratio of 1:1.5, and the mixing rate was controlled using a mass flow meter (accuracy ±0.05 L / h). During mixing, stirring was maintained at 300 rpm, and the pH was gradually adjusted to 8.5 ± 0.1 by adding a weakly alkaline buffer (borate system). Continuous pH monitoring was performed using an automatic titrator, and fluctuations were controlled to not exceed 0.02.

[0065] The mixing equilibrium period is approximately 20 minutes. When the system color changes from light green to light blue without any stratification, it indicates that the metal ion coordination and suspension system is stable. After centrifuging 3 mL of the sample at 10000 rpm, the metal ion concentration in the supernatant is analyzed. The ion concentration difference ΔC is controlled within 3 × 10⁻⁻⁻⁶. 4 mol·cm⁻ 3 If the detected value exceeds this range, it indicates insufficient mixing or stirring. Stirring should be extended by 5 minutes or the stirring speed increased to 400 rpm. At this point, the system is in a homogeneous suspension state, the average particle size detected by DLS is 0.32 μm, the PDI (polydispersity index) is less than 0.25, and the zeta potential remains at −31±2 mV.

[0066] During implementation, insufficient stirring can cause tungsten carbide particles to settle, increasing the ion concentration gradient, which is reflected in ICP detection. At this point, stirring should be intensified or the mixture redispersed. If the pH drifts above 8.9, the complex dissociates, potentially producing a blue-green precipitate; adjusting back to 8.5 will restore transparency. If the absolute value of the zeta potential is below −20 mV, micro-agglomerates will form in the system; 0.01 wt.% PVP should be added to readjust the surface charge. During implementation, three repeated experiments were conducted under different batch preparation conditions to detect fluctuations in key system parameters, as shown in the table below: parameter target value Measured average Standard deviation Qualification Criteria <![CDATA[Conductivity / mS·cm⁻ 1 > 8.5–9.5 8.92 ±0.07 ≤±0.1 pH 8.2–8.8 8.48 ±0.05 ≤±0.1 ζ potential / mV −20～−35 −31.4 ±1.8 ±3 <![CDATA[Ionic concentration difference / mol·cm⁻ 3 > <![CDATA[≤3×10⁻ 4 ]]> <![CDATA[2.6×10⁻ 4 ]]> <![CDATA[±0.3×10⁻ 4 ]]> <![CDATA[≤3×10⁻ 4 ]]> <![CDATA[Particle size D 50 / μm]]> <0.5 0.32 ±0.02 ≤0.5 After a 24-hour static stability test, no visible sedimentation was observed, indicating good suspension uniformity and coordination stability. This composite electrolysis system can provide a stable supply of metal ions and carbon source concentration distribution in the subsequent induced deposition stage, laying the foundation for constructing a gradient metal composite layer.

[0067] It should be noted that the conductivity in this invention refers to the specific conductivity of the composite electrolysis system at 25±0.5°C, measured by a conductivity meter and converted to the standard temperature of 25°C. To ensure the stability of the metal ion coordination and carbon complexation system, the conductivity is controlled between 8.5 and 9.5 mS·cm⁻. 1 Within the range, when below 8.3 mS·cm⁻ 1 When the ionic strength of the solution is insufficient, the tungsten complex does not dissociate completely, which can easily cause fluctuations in the subsequent deposition current density; when it is higher than 9.7 mS·cm⁻ 1 This indicates that free Ni 2 ⁺ If too high, the deposition rate becomes unbalanced. Validation has shown that the optimal range is 8.8–9.2 mS·cm⁻ 1 This method yields stable and fine deposition layers. The pH value is the solution acidity / alkalinity measured using a glass electrode method at a constant temperature of 40–45°C. Calibration with standard buffer solutions of pH 7.00 and 9.18 is performed before measurement. A pH range of 8.2–8.8 is acceptable, with 8.4–8.6 being the recommended range. Within this range, the complex is stable, and tungsten ions are distributed as... It exists in a form that prevents hydroxide precipitation.

[0068] Zeta potential refers to the surface potential of tungsten carbide particles measured by a dynamic light scattering instrument, with -20 to -35 mV as the effective suspension range. If the absolute value is below -18 mV, the electrostatic repulsion between particles weakens, leading to agglomeration; if it exceeds -38 mV, it indicates excessive dispersant, which will weaken the deposition bonding force. The optimal range is -30 ± 3 mV, where the particle dispersion is stable and does not affect the diffusion of metal ions. Tungsten carbide particle dispersion refers to the particle size distribution. The value was determined by dynamic light scattering. A dispersion of <0.5 μm was required, with an optimal distribution range of 0.25–0.35 μm, enabling uniform embedding into the metal matrix during deposition to form a composite structure.

[0069] The method for calculating the ion concentration difference is as follows: under static conditions (after stopping stirring and maintaining a constant temperature for 10 min), the difference in the total molar concentration of the solute in the solution measured at different sampling locations within the same electrolytic cell, with the range controlled. To stabilize the system, exceeding this value will result in uneven local ion concentrations in the solution, leading to component segregation in the deposition layer. Optimal range. The recommended sampling locations are defined as follows: 0.5 mm from the cathode surface, 10 mm from the horizontal projection of the cathode at the center of the tank, and 50 mm above the tank; each location should be sampled at least three times and three parallel measurements should be performed to calculate the average and standard deviation. The determination method uses ion chromatography or a calibrated conductivity conversion curve to determine the main metal cations in the solution (…). The total solute molar concentration is calculated based on the concentration of the dominant anion (in the form of the dissolved substance) and the concentration of the dominant anion.

[0070] In addition, the content of the carbon complex component is 1.2 to 1.8 wt.% of the total solute mass fraction of the organic carbon source and complexing agent system, with a recommended value of 1.5 wt.%; the molar ratio of tungsten ions to carbon complex components is controlled at 1:3 to achieve stable coordination. When the ratio deviates from the range of 1:2.5 to 1:3.5, coordination unsaturation or free carbon deposition will occur in the system; the molar ratio of nickel ions to cobalt ions is centered at 2:1, with an allowable deviation of ±0.1 to ensure the stability of the alloy composition ratio.

[0071] Step 3: A pulsed reverse current is used to induce deposition on the substrate. A metastable, adaptive interface layer structure composed of nickel, tungsten, and carbon is formed on the substrate surface through periodic reverse potential adjustment. In this process, a constant-temperature circulating electroplating tank with a PTFE-lined stainless steel structure and a volume of 8 L is used. The tank is equipped with an independent cathode rotation mechanism and a programmable pulse power supply module. After treatment in Step 2, the tool substrate is immediately clamped in the cathode fixture. The cathode fixture employs a multi-zone current distribution plate structure, with independent power channels leading out from the central and outer peripheral zones. A current density ratio of 1.2:1 to 1.8:1 is controlled through an independent adjustable resistor unit. The contact resistance between the current distribution plate and the workpiece is 0.02–0.05 Ω, calibrated using the four-wire method.

[0072] Before induced deposition treatment, a zoned electric field pre-adjustment stage is first performed, with a constant DC current density of 0.3 A / dm³. 2 The process is maintained for 30 s to stabilize the interfacial ion layer. This stage primarily promotes the formation of a radial migration gradient between tungsten ions and carbon complex components on the cathode surface. By adjusting the current density ratio between the central and peripheral regions, the local electric field intensity distribution can be controlled, thereby forming a uniform nucleation region. The nucleation spacing was measured using AFM and SEM cross-section observations, with a target range of 50–200 nm. When the current ratio is below 1.2:1, the nucleation density is insufficient, while above 1.8:1, excessive aggregation occurs.

[0073] After completing the pre-adjustment phase, switch to pulsed reverse current mode. The pulse waveform uses a rectangular modulation wave, with a forward peak current density of 0.5–0.8 A / dm. 2 Reverse current density: 0.15–0.25 A / dm 2 The cycle time is 40–60 ms, and the positive duty cycle is 70–80%. The current waveform is monitored in real time using a digital oscilloscope, and the output deviation is controlled within ±2%. The induction deposition time is controlled between 2 and 4 minutes, with the optimal value being approximately 3 minutes. The bath temperature is maintained at 45 ± 1°C and regulated by a thermostatic circulating pump.

[0074] During the pulse reversal phase, the instantaneous rate of change of the anode potential, measured by an electrochemical workstation, should be less than 0.05 V / ms. Exceeding this threshold will induce local hydrogen evolution and lattice distortion, leading to interface layer inhomogeneity. The response rates of the rising and falling edges are adjusted in real time through a software feedback loop to keep the output potential waveform within the allowable rate of change.

[0075] The induced layer was characterized by XRD and HRTEM, revealing the formation characteristics of the Ni–W–C ternary metastable phase: the interlayer spacing of nickel atoms was concentrated in the range of 0.198–0.205 nm, the thickness of the tungsten atom-rich region was 3–6 nm, and carbon atoms were distributed in interstitial vacancies in the Ni–W lattice. EDS line scanning showed that the W element content gradient along the thickness direction varied by 2.5–3.5 at.% / nm, indicating the formation of a self-strained metastable layer structure.

[0076] During device scaling-up, if the increased number of blades results in an electrode spacing greater than 50 mm, the stirring flow rate should be increased by 10–15% simultaneously to maintain a constant ion concentration gradient at the cathode interface. If the pulse waveform distortion exceeds ±5%, the power supply module and grounding circuit need to be recalibrated. If a decrease in nucleation density or the appearance of a non-uniform region is detected, the reverse current density can be reduced to 0.12 A / dm³. 2 Alternatively, the pulse period can be shortened to 40 ms for compensation.

[0077] Key control points in this step include: current density ratio, potential change rate, nucleation spacing, and temperature stability; key quality attributes are the Ni–W–C interface layer thickness, elemental distribution, and lattice spacing. The current density ratio refers to the ratio of the measured current density in the central region to the outer region of the cathode fixture under steady-state output conditions. It is determined using the four-electrode method on an electrochemical workstation, with a measurement time of no less than 5 s and the steady-state average value taken. Its control range is 1.2:1 to 1.8:1, with an optimal value of 1.5:1. When it is below 1.2:1, the deposition rate in the outer region is low and the nucleation density is uneven; when it is above 1.8:1, stress concentration in the central region leads to increased interface roughness.

[0078] In this invention, the pulse period is adjustable within a range of 40–60 ms, with an optimal value of approximately 50 ms. A period below 40 ms results in insufficient ion diffusion and incomplete grain rearrangement; a period above 60 ms is detrimental to the formation of fine metastable lattices. The forward duty cycle ranges from 70–80%, with an optimal value of 75%. A low duty cycle leads to a decrease in the forward deposition rate and insufficient W content; a high duty cycle weakens the reverse trimming effect.

[0079] Peak current density and reverse current density were measured using a reference electrode placed in the thermostatic bath. The recommended value for peak current density is 0.6 A / dm³. 2 (Range 0.5~0.8 A / dm)2 The recommended reverse current density is 0.2 A / dm³. 2 (Range 0.15~0.25A / dm) 2 The instantaneous anodic potential change rate was recorded in real time by an electrochemical workstation with a sampling frequency ≥10 kHz. Maintaining it below 0.05 V / ms ensures that no local hydrogen evolution or abrupt lattice strain occurs at the interface; a range of 0.035 ± 0.005 V / ms is recommended.

[0080] It should be noted that the nucleation spacing refers to the average center-to-center distance of primary nuclei formed after the pre-deposition phase of induced deposition. This is calculated by averaging at least 100 nuclei samples using AFM scanning or SEM cross-sectional statistics. The spacing is controlled within the range of 50–200 nm, with an optimal nucleation spacing of approximately 100 nm, which yields a uniform electric field distribution and a stable interface structure. The nickel atom interlayer spacing and the tungsten enrichment layer thickness are determined using HRTEM lattice imaging and EDS surface scanning methods, respectively. The interlayer spacing should be between 0.198 and 0.205 nm, and the tungsten enrichment layer thickness should be controlled between 3 and 6 nm. Below this range, the strain self-adjustment characteristics are insufficient; above this range, interlayer slip tends to increase, affecting the interfacial bonding.

[0081] The optimal combination of parameters in the above parameter system is: current density ratio 1.5:1, peak current density 0.6 A / dm³. 2 Reverse current density 0.2 A / dm 2 The deposition time was 3 min, the period was 50 ms, the duty cycle was 75%, the deposition time was 3 min, the anodic potential change rate was approximately 0.035 V / ms, and the bath temperature was 45°C. After experimental testing, the metastable Ni–W–C interface layer obtained under these conditions had the narrowest lattice spacing distribution, the smoothest element transition, and the best overall bonding strength and wear resistance.

[0082] Step 4: A constant current is used to deposit the main metal on the metastable adaptive interface layer structure. A metal composite layer containing nickel, cobalt, and tungsten carbide particles is formed on the interface layer structure through a dual-potential synchronous reduction mechanism. Specifically, the substrate that forms a uniform metastable Ni–W–C interface layer through step 3-induced deposition is then rinsed with anhydrous ethanol and... After drying, the material is immediately transferred to the main deposition tank. This tank is made of alkali-resistant polypropylene, has a volume of 20 L, and is equipped with a water-jacketed constant temperature control system (temperature control accuracy ±0.5 ℃), a rotating magnetic field generator, and a dual-output constant current power supply. The cathode clamp is a zoned electrical connection conductive clamp, and the anode uses high-purity nickel plates (99.95% purity) and cobalt plates arranged symmetrically in a 1:1 ratio to reduce the ion concentration gradient.

[0083] The main electrolyte consists of the following components: The solution contained 60 g / L sodium citrate, 3–5 g / L WC particles, and 0.15–0.25 g / L total concentration of surface conditioner (sodium dodecylbenzenesulfonate and polyvinylpyrrolidone in a 1:3 mass ratio). After premixing the solution by mechanical stirring at 300 rpm for 60 min, the homogeneity within the tank was maintained using a circulating pump. The magnetic field was generated by rotating magnetic poles driven by a permanent magnet synchronous motor, with the magnetic induction intensity controlled between 0.02 and 0.05 T, optimally 0.035 T, corresponding to a rotation frequency of 20–25 Hz.

[0084] Please see Figure 3 The diagram shows a double-layer potential structure. A thin layer of tungsten carbide mixed with oxide, approximately 5–15 nm thick, is formed on the surface of the cemented carbide tool substrate. This layer possesses both the high polarization characteristics of oxides and the conductivity of carbides, forming an inner and outer double-layer potential structure in the electrochemical system. The outer layer is a highly polarized region, primarily responsible for electric field enhancement and ion adsorption; the inner layer is an electron-affinity region with high electron-donating capacity, serving as the preferential nucleation region for subsequent metal ions.

[0085] In a composite electrolysis system, when a pulsed reverse current is applied to the cathode substrate, the outer highly polarized region first induces Ni… 2 ⁺ and W 6 ⁺ ions undergo synergistic adsorption and reduction reactions to form a metastable primary layer composed of alternating Ni, W, and C atoms. Simultaneously, the carbon complex component partially dissociates under the influence of a transient anodic potential reversal, allowing carbon atoms to intercalate into vacancies in the Ni–W lattice, thereby suppressing lattice strain accumulation and stabilizing the local energy state distribution. The resulting metastable lattice structure exhibits a nanoscale periodic layered arrangement, with Ni atom interlayer spacing maintained at 0.198–0.205 nm, W atom-rich regions approximately 3–6 nm thick, and carbon atoms uniformly distributed in the interlayer regions. This metastable structure possesses significant electronic coupling characteristics and adaptive stress release capabilities, resulting in high nucleation density and bonding strength at the interface bonding region during subsequent metal composite layer deposition.

[0086] The main deposition stage employed a constant current mode with a current density of 1.5–2.0 A / dm³. 2 The bath temperature is 50–60℃. To ensure… and To achieve synchronous restoration, a dual-potential control strategy is employed: the first potential region is maintained at -0.95 to -1.05 V (vs. SCE), corresponding to the Ni-Co alloy deposition reaction; the second potential region is maintained at -1.10 to -1.20 V, used to induce the formation of a Ni-Co metal coating layer on the surface of WC particles. The switching between the two potentials is controlled in real-time by feedback from the power supply's partitioned output, with a switching cycle of 10–15 s and a duty cycle of approximately 60:40.

[0087] The deposition process lasts approximately 10–12 minutes. During this period, the system is kept stable by online conductivity and pH monitoring. The conductivity should be between 8.0 and 9.0 mS / cm, and the pH should be controlled at 8.4 ± 0.1. If the pH drops by more than 0.2, a buffer (0.1 mol / L sodium citrate solution) should be added immediately. The axial swirling electrolysis zone formed by the magnetic field causes WC particles to move spirally along the electrode surface. Dynamic light scattering monitoring shows that the peak position of the WC particle distribution remains at 0.25–0.35 μm, indicating uniform deposition.

[0088] To prevent particle agglomeration or stress-induced interlayer separation, a short reverse cleaning is performed every 2 minutes (reverse current density 0.05 A / dm³). 2 The deposition process lasted for 2 seconds. After deposition, the material was washed with deionized water and dried. The resulting metal composite layer was approximately 10 ± 0.5 μm thick, with a Ni–Co alloy phase volume fraction of 65% and a WC particle volume fraction of 35%. The elemental distribution within the layer, as shown by EDS linear scanning, exhibited fluctuations of less than ±2 at.%. Three batches of data were randomly selected during the process and are analyzed as follows: Batch number <![CDATA[Current density (A / dm 2 )]]> Magnetic field strength (T) Layer thickness (μm) WC volume fraction (%) Ra (μm) Peel strength (MPa) 1 1.6 0.035 9.8 34.7 0.36 167 2 1.8 0.035 10.2 35.3 0.34 169 3 1.7 0.04 10.1 34.9 0.35 168 average — — 10.0±0.2 35.0±0.3 0.35±0.01 168±1 Cross-sectional observation of the deposited layer showed that WC particles were uniformly distributed without obvious aggregation or porosity; XRD detection confirmed the formation of Ni–Co solid solution, with a slight leftward shift of the (111) crystal plane peak, indicating sufficient solid solution strengthening. Failure analysis showed that when the magnetic field strength was below 0.02 T, particle sedimentation intensified, and a localized particle-depleted region formed in the composite layer; while above 0.05 T, the excessive Lorentz force disrupted ion migration, leading to increased surface roughness. Similarly, when the current density was below 1.5 A / dm³, 2 This will result in insufficient deposition rate and low Co content, exceeding 2.0 A / dm³. 2 This will trigger hydrogen evolution and increase interfacial stress. If the switching lag between the two potentials exceeds 3 seconds, a potential dead zone will form at the electrode interface, resulting in discontinuous coating.

[0089] It should be noted that in this invention, dual potential control refers to a potential adjustment method that alternates between the reduction of the nickel-cobalt alloy and the coating reaction of tungsten carbide particles under constant current conditions by programmably switching the output potential level of the power supply; the switching cycle is 10-15 s, and the duty cycle is 60:40. Magnetic field strength refers to the instantaneous magnetic induction intensity in the normal direction of the cathode surface within the deposition tank, measured by a gaussmeter during the deposition process, with a recommended value of 0.035 T. The volume fraction of tungsten carbide particles is statistically calculated using the cross-sectional EDS integral method, taking the average value from five different locations. The recommended range is 30-40%, with an optimal value of 35%, at which point the intralayer porosity is lowest and the interfacial bonding force is highest. Layer thickness is defined as the vertical thickness from the metal composite layer to the Ni–W–C interface layer, measured by SEM cross-sectional thickness measurement, with an optimal average value of 10 ± 0.5 μm. Peel strength is tested using a micro-tensile tester at 25 ℃ with a loading rate of 0.1 MPa / s, with an optimal value of approximately 168 MPa.

[0090] Step 5: Construct a transition zone with gradient element distribution between the interface layer structure and the metal composite layer by controlling diffusion and adjusting deposition time; Please see Figure 4 The schematic diagram of the deposition process shows that after the main metal deposition is completed, the process immediately switches to the diffusion control stage, maintaining the same electrolytic cell and electrode assembly. The tank temperature is maintained at 50±2°C, and the electrolyte is stirred by a mechanical impeller with a diameter of 80 mm and a rotation speed of 170 rpm. The electrode spacing is fixed at 50 mm by an insulating support, and the electrolyte flow rate is controlled at 0.1 m / s. The cathode is a tool substrate with a Ni–Co–WC composite layer already formed, and the anode is a Ni–Co hybrid plate.

[0091] Before gradient deposition begins, 0.04 wt.% polyvinylpyrrolidone (PVP, molecular weight ≈40000) is added to the bath to regulate the effective migration rate of metal ions within the diffusion layer. PVP acts as a slow-release agent at this stage, allowing Ni... 2 ⁺、Co 2 The diffusion rate of ⁺ was reduced by approximately 12%, while local aggregation of WC particles was inhibited. The pH of the system was maintained at 4.5 ± 0.1 using a buffer, monitored in real time and compensated for by titration. A five-stage decreasing current deposition process was then performed, with each stage maintaining a stable current density and time. The data are as follows: series <![CDATA[Current density (A / dm 2 )]]> Deposition time (s) Expected layer thickness (μm) Stirring speed (rpm) Temperature (°C) 1 1.5 120 1.2 170 50 2 1.2 120 0.9 170 50 3 1.0 120 0.7 180 50 4 0.8 120 0.5 180 50 5 0.5 120 0.4 200 50 The current switching time between each stage does not exceed 2 seconds, and the automatic switching is achieved through program-controlled power supply. This graded current setting allows the deposition rate of nickel ions on the cathode surface to gradually decrease, while WC particles concentrate on the surface due to Brownian motion and swirling effects, resulting in a gradual decrease in the metal component and a gradual increase in the proportion of ceramic phase in the composite layer.

[0092] During this process, the thickness of the electrolyte diffusion layer is maintained at approximately 90 μm, calculated using electrochemical impedance spectroscopy (EIS). If the diffusion layer thickness is too low (<80 μm), the gradient region tends to abruptly change; if it is too high (>100 μm), the gradient layer thickness is insufficient, which can easily lead to component stratification.

[0093] After deposition, a gradient transition region with a thickness of approximately 4 ± 0.5 μm was obtained through cleaning and drying. EDS linear scanning showed that the Ni content decreased along the thickness direction from 68 at.% on the interface layer side to 52 at.% on the composite layer side, with an average gradient of approximately 4.0% per micrometer. The WC particle volume fraction increased continuously from 28% to 38%. This gradient region exhibited a significant elemental diffusion bandwidth of approximately 60–80 nm under high-resolution TEM, with continuous grain boundaries and no interlayers.

[0094] Microscopic analysis during implementation showed no significant abrupt changes in composition or concentrated pore areas in the diffusion zone. XPS depth profiling revealed a continuous shift in the Ni 2p peak along the depth direction, indicating good elemental diffusion continuity. EIS curves showed a smooth change in interfacial impedance with no obvious charge transport breakpoints. If the PVP addition was below 0.03 wt.%, the metal ion migration rate was too fast, and the compositional gradient was not obvious; if it exceeded 0.06 wt.%, the electrolyte viscosity increased, and the deposition rate became unstable. If the stirring rate was below 150 rpm, localized nickel-rich zones were easily formed; if it was above 200 rpm, particle segregation may occur.

[0095] It should be noted that the diffusion layer thickness in this invention refers to the distance between the cathode surface and the ion concentration stabilization region, obtained through electrochemical impedance spectroscopy fitting. The recommended value is 90 μm, with an allowable range of 80–100 μm. The nickel element gradient change rate is obtained by dividing the change in Ni content measured by EDS line scan by the gradient region thickness. The optimal range is 3.5%–4.5% / μm. The PVP mass fraction refers to the percentage of polyvinylpyrrolidone added during the diffusion control stage relative to the total solute mass. The recommended value is 0.04 wt.%. The total deposition thickness is the gradient region thickness between the Ni–W–C interface layer and the Ni–Co–WC composite layer, with a recommended range of 4 ± 0.5 μm. The current density gradient switching time is ≤2 s. The system flow rate is the average linear velocity of the electrolyte between the electrodes measured by a flow meter, with a recommended value of 0.1 m / s.

[0096] In addition, the process described in this invention can be implemented in two equivalent ways to achieve two types of pH conditions: A) independent tank liquid partitioning process; B) same tank sequential adjustment process.

[0097] In Implementation A (i.e., the example), induced deposition and bulk deposition are carried out in a first tank, which is maintained at a constant temperature of 40–45 °C and a pH of 8.2–8.8, and is equipped with online pH, conductivity, and temperature sensors. After bulk deposition is completed and the workpiece is characterized for the necessary thickness and composition, it is transferred to a second tank for diffusion-controlled deposition. The second tank is maintained at a constant temperature of 45–55 °C and a pH of 4.2–4.8, and is also equipped with an online monitoring and stirring system. Before and after the workpiece transfer, a standardized deionized water rinse (3–5 consecutive rinses, 30–60 s each time) must be performed to remove residual alkaline electrolyte and reduce cross-contamination. Subsequently, the workpiece is remounted in the target tank according to a predetermined procedure and deposition is initiated under stable stirring / temperature conditions.

[0098] In Implementation B: After the main deposition is completed, the pH is adjusted from alkaline to acidic in the same tank through stepwise neutralization and slow acid adjustment. The specific steps are as follows: First, the workpiece surface is quickly rinsed with deionized water and pH neutralization buffer is added to the tank to bring the local surface pH back to 7.0±0.2 (stirring for 1–3 min). Then, diluted acid (example: 0.1–0.5 wt% H2SO4 or equimolar concentration of citric acid solution) is added stepwise using a metering pump. Under constant stirring (300–400 rpm) and temperature maintenance, the overall pH is gradually adjusted to 4.2–4.8. After the pH reaches the target, the mixture is allowed to stand for 10–30 min to restore the ion distribution and the stability of the main metal ion concentration is verified by conductivity and ion chromatography (IC).

[0099] Step 6: Perform low-temperature heat treatment on the composite-coated tool formed by deposition to stabilize the interface structure. The low-temperature heat treatment is carried out in a low-oxygen atmosphere furnace. The equipment used is a horizontal tubular atmosphere furnace with an effective furnace length of 800 mm, a temperature control accuracy of ±1°C, and high-purity quartz furnace tubes. Before heat treatment, a 30-minute atmosphere pre-conditioning is performed by introducing an argon-hydrogen mixture at a ratio of 97:3 (volume fraction) into the furnace at a flow rate controlled at 1.0 L / min. An online residual oxygen analyzer is used to confirm that the oxygen partial pressure is consistently below 1×10⁻⁻⁻⁻⁻⁶. 2 Pa. After confirmation, the heating program is initiated.

[0100] The heating process was divided into two controlled stages. In the first stage, the heating rate was controlled at 4°C / min, reaching 360°C and holding for 30 min. This allowed for the complete removal of residual electrochemical hydrogen and adsorbed moisture from the composite coating, while simultaneously promoting partial rearrangement of the metastable phase structure in the Ni–W–C interface layer, reducing internal stress by approximately 30%. In the second stage, the temperature was further increased at 5°C / min to 440°C and held constant for 15 min. The main function of this stage was to promote short-range ordering of the solid solution strengthening phases (Ni3W, Ni2Co) within the Ni–Co–WC composite layer without coarsening, thereby enhancing the atomic bonding force between the interface layer and the composite layer.

[0101] The atmosphere composition remained constant throughout the isothermal phase, and a stable flow rate was maintained using a flow controller. After heat treatment, furnace cooling was employed at a rate of approximately 2°C / min to fully release thermal stress and prevent interlayer microcracks caused by rapid cooling.

[0102] The composite coated cutting tool, after this heat treatment, exhibits a stable interface structure between the Ni–W–C phase and the Ni–Co–WC composite layer. TEM observation shows good lattice continuity at the interface with no obvious dislocation entanglement regions. XRD analysis results indicate that the Ni3W phase has sharp peaks, and the grain size stabilizes from approximately 12 nm before heat treatment to approximately 15 nm, while the WC particles show no significant growth. The residual stress measurement value decreases from 320 MPa before heat treatment to 180 MPa. Performance test results from three different batches are as follows: Processing conditions <![CDATA[Atmosphere composition (H2 / Ar, vol%)]]> First constant temperature (°C × min) Second constant temperature (°C × min) Residual stress (MPa) Interfacial bond strength (MPa) <![CDATA[Coating microhardness (HV0. 05 )]]> A (Optimal) 3 / 97 360×30 440×15 180 176 1380 B 2 / 98 350×40 420×20 210 170 1355 C 5 / 95 380×20 460×10 190 173 1370 As shown in the table, when the hydrogen content in the atmosphere is 3 vol%, and the first and second isothermal temperatures are controlled at 360°C and 440°C respectively, the resulting coating exhibits the lowest residual stress and the highest interfacial bonding strength, representing the recommended optimal parameter combination. During the heat treatment process, the furnace temperature distribution was monitored in real-time using infrared thermocouples. If the heating rate exceeds 6°C / min, micro-bulging or interlayer micro-cracks are likely to occur on the coating surface; if the oxygen partial pressure increases to 10⁻⁻⁻⁶, further damage may occur. 1 Above a certain pressure (Pa), the Ni–W phase is prone to oxidation and shift, resulting in a decrease in interfacial bonding strength of approximately 15%. Therefore, oxygen partial pressure control is one of the key factors for the reliability of this process.

[0103] In this implementation, the optimal heating rate is 4–5°C / min to avoid thermal stress buildup. The first isotherm is used for gas desorption and lattice stress relaxation, recommended at 360°C for 30 min; the second isotherm is used for short-range ordering, recommended at 440°C for 15 min. The hydrogen to argon gas integral ratio is controlled at 2–5%:95–98%, with an optimal value of 3%:97%, to achieve a slightly reducing atmosphere. Oxygen partial pressure is defined as the partial pressure of oxygen in the atmosphere, in Pa, and is detected in real-time using a residual oxygen analyzer. It should be ≤1×10⁻ 2 Pa, optimal control value 5×10⁻ 3 Pa. The recommended average cooling rate during the furnace cooling stage is 2°C / min. Excessive cooling can easily induce interfacial cracks.

[0104] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these specific embodiments are merely illustrative. Those skilled in the art can omit, substitute, and modify the details of the above methods and systems in various ways without departing from the principles and essence of the present invention. For example, combining the above method steps to perform substantially the same function and achieve substantially the same result according to substantially the same method falls within the scope of the present invention. Therefore, the scope of the present invention is defined only by the appended claims.

Claims

1. A method of electroplating a composite coating on a tungsten carbide coated tool; characterized by: The application relates to a method for preparing a cemented carbide cutting tool with a composite coating, which comprises the following steps:

1. surface activation and micro-roughening treatment of the cemented carbide cutting tool substrate to obtain a substrate surface with a target roughness and an activated energy state; 2. construction of a composite electrolyte containing multi-metal ions and a carbon source on the substrate surface, wherein the composite electrolyte comprises a first ion component for inducing deposition and a second ion component for main body deposition, the first ion component contains tungsten ions, nickel ions and a carbon complex component, and the second ion component contains nickel ions, cobalt ions and tungsten carbide particles; 3. induced deposition treatment of the substrate by adopting pulse reverse current to form a metastable self-adapting interface layer structure composed of nickel, tungsten and carbon on the substrate surface through periodic reverse potential adjustment; 4. main body metal deposition treatment on the metastable self-adapting interface layer structure by adopting constant current to form a metal composite layer containing nickel, cobalt and tungsten carbide particles on the interface layer structure through a double-potential synchronous reduction mechanism; 5. construction of a transition zone with gradient element distribution between the interface layer structure and the metal composite layer through diffusion control and deposition time adjustment; and 6. low-temperature heat treatment of the composite coating cutting tool formed through deposition to stabilize the interface structure. The surface activation and micro-roughening treatment of the step 1 comprises the following steps: 1.

1. surface activation treatment of the substrate by adopting a mixed acid solution containing 10-20 wt.% nitric acid, 10-20 wt.% hydrofluoric acid and 10-20 wt.% acetic acid to remove the surface oxide film and form a rough surface with a roughness of 0.5-1.5 microns; and 1.

2. micro-roughening treatment of the substrate by adopting a mixed acid solution containing 10-20 wt.% nitric acid, 10-20 wt.% hydrofluoric acid and 10-20 wt.% acetic acid to form a rough surface with a roughness of 0.1-0.3 microns. The construction of the composite electrolyte comprises the following steps: 2.

1. preparation of the first ion component by dissolving 0.05-0.1 wt.% tungsten powder, 0.05-0.1 wt.% nickel powder and 0.05-0.1 wt.% carbon powder in 10-20 wt.% sulfuric acid to form a tungsten ion solution, a nickel ion solution and a carbon complex solution; 2.

2. preparation of the second ion component by dissolving 0.05-0.1 wt.% nickel powder and 0.05-0.1 wt.% cobalt powder in 10-20 wt.% sulfuric acid to form a nickel-cobalt ion solution; and 2.

3. preparation of the composite electrolyte by mixing the first ion component, the second ion component and 10-20 wt.% sulfuric acid. Before the induced deposition treatment, the step 3 adopts zoning modulation of the electric field to control the local ion migration direction in the initial deposition stage, and by applying a current density ratio of 1.2:1-1.8:1 to the peripheral zone and the central zone of the cathode surface respectively, tungsten ions and carbon complex components are made to migrate along a radial migration path to form a uniform nucleation zone, the average nucleation spacing of the uniform nucleation zone is controlled within the range of 50-200 nm, and thus an induced deposition pre-state with uniform electric field distribution of the interface layer is obtained before entering the pulse reverse deposition stage. In the diffusion control stage, 0.03-0.06 wt.% polyvinylpyrrolidone is added into the electrolyte as a diffusion release agent to form a composition gradient by adjusting the metal ion migration rate; during the deposition process, the electrolyte flow rate is maintained at 0.08-0.12 m / s, the cathode and the anode are arranged in parallel in the electrolytic cell through an adjustable insulation support, the spacing is controlled by the support structure to be 40-60 mm; in the diffusion control stage, the pH of the system is maintained in the range of 4.2-4.8 through a buffer, and the diffusion layer thickness is controlled to be 80-100 microns, and thus a transition zone with a nickel element content gradient change rate of 3%-5% per micron is obtained along the thickness direction. ​ ​ 2. The electroplated composite coating method for tungsten carbide coated cutting tools according to claim 1, characterized in that: ​ A chemical activation solution containing an alkaline oxidizing agent and a complexing agent is used to chemically activate a cemented carbide tool substrate to remove a surface adsorbed carbon layer and produce a mixed layer of tungsten oxide and tungsten carbide having a thickness of ​ The activated substrate is subjected to cathodic micro-discharge treatment in a micro- electrochemical roughening bath at a current density in the range of 0.1 to 10 A / dm2 The surface roughness Ra of the substrate is adjusted by local electric field induction to a range of 0.1 to 10 μm . The tungsten oxide-carbide mixed layer and the surface rough area together form a double-layer potential structure, in which the outer layer is a high polarization area and the inner layer is an electron affinity area, for inducing a synergistic deposition reaction during the electroplating process.

3. The electroplated composite coating method for tungsten carbide coated cutting tools according to claim 1, characterized in that: ​ In A first ion solution containing tungsten ions, nickel ions and carbon complexing components was prepared under constant temperature conditions and maintained at a constant stirring rate of 300-400 rpm for 40-60 min to stabilize the conductivity at 8.5-9.5 mS / cm by ion balance adjustment; The second ion solution containing nickel ions, cobalt ions and tungsten carbide microparticles, which are dispersed by surface active agent to less than 0.1 μm, is incorporated into the first ion solution at a flow ratio of 1:1.5, and the pH of the system is controlled in the range of 8.2-8.8 by a buffer regulator. Thus, a uniform composite electrolytic system with ion concentration difference less than is obtained.

4. The electroplated composite coating method for tungsten carbide coated cutting tools according to claim 1, characterized in that: The carbon complexing component is composed of an organic complexing agent containing carboxyl and hydroxyl bidentate structure and a carbon source, and the content is 0.1-0.5% of the total solute mass The molar ratio of tungsten ions to the carbon complexing component in the composite electrolyte system is controlled to be 1:3, the molar ratio of nickel ions to cobalt ions is controlled to be 2:1, the zeta potential of the tungsten carbide particles is adjusted to-20 to-35 mV by a surface charging regulator in the composite electrolyte system, and the stable coordination structure and uniform suspension of the multi-metal ions and the carbon source in the system are maintained.

5. The electroplated composite coating method for tungsten carbide coated cutting tools according to claim 1, characterized in that: ​ 6. The electroplated composite coating method for tungsten carbide coated cutting tools according to claim 1, characterized in that: The waveform parameters of the pulse reverse current include: peak current density 0.5-0.8 A / dm 2 , reverse current density 0.15-0.25 A / dm 2 , single pulse period 40-60 ms, forward duty cycle 70-80%, and the step 3 maintains the induced deposition time for 2-4 min under the continuous pulse condition; the local electric field intensity change rate of the substrate surface is controlled to be less than 0.05 V / ms through the periodic reversal of the transient anode potential in the pulse reverse stage, and a metastable phase lattice structure with nickel, tungsten and carbon atoms arranged alternately is induced to form in the electrode interface area, wherein the nickel atom layer spacing is distributed in 0.198-0.205 nm, the average thickness of the tungsten atom enrichment area is 3-6 nm, and the carbon atoms are embedded in the interlayer vacancy area of the nickel-tungsten lattice in the form of interstitials.

7. The electroplated composite coating method for tungsten carbide coated cutting tools according to claim 1, characterized in that: The main body metal deposition process is carried out under the conditions of constant current density 1.5-2.0 A / dm 2 , tank liquid temperature 50-60 ℃, and by applying a rotating magnetic field with magnetic field strength 0.02-0.05 T in the electrolytic tank to form an axial cyclone electrolysis zone, the average particle size of tungsten carbide particles is controlled at , the dispersion concentration is 3-5 g / L; the step 4 uses a double potential control strategy under constant current conditions, wherein the first potential is used to maintain the synchronous reduction of nickel-cobalt alloy ions, and the second potential is used to induce the generation of a metal coating layer on the surface of tungsten carbide particles, forming a dense composite deposition layer with thickness 8-12 μm, nickel-cobalt phase volume fraction 60%-70%, and tungsten carbide particle volume fraction 30%-40%.

8. The electroplated composite coating method for tungsten carbide coated cutting tools according to claim 1, characterized in that: The diffusion control stage of step 5 includes five stages of current density decreasing deposition process, the first to fifth stage current density is 1.5 A / dm 2 , 1.2 A / dm 2 , 1.0 A / dm 2 , 0.8 A / dm 2 and 0.5 A / dm 2 , each stage deposition time is 90-150 s; by maintaining the electrolyte temperature at 45-55°C between each stage of deposition and adjusting the ion migration speed at a stirring speed of 150-200 rpm, the nickel-cobalt alloy ion concentration is decreased along the thickness direction by decreasing the current density, and the tungsten carbide particle distribution density is increased layer by layer, forming a gradient structure zone with a thickness of 2-6 μm.

9. The method of claim 8, wherein the tungsten carbide coated cutting tool is plated with a composite coating. ​ 10. The electroplated composite coating method for tungsten carbide coated cutting tools according to claim 1, characterized in that: The low-temperature heat treatment includes a stage temperature rising and a limited oxygen atmosphere control process, the temperature rising rate is , the first constant temperature stage temperature is , the holding time is 20-40 min, the second constant temperature stage temperature is , the holding time is 10-20 min; the heat treatment is carried out in a mixed gas atmosphere containing 2%-5% hydrogen and 95%-98% argon, the oxygen partial pressure is controlled below ; after the heat treatment, the furnace cooling mode is adopted to reduce the temperature, the temperature reducing rate is , so that the phase and the intermetallic compound in the gradient zone in the composite coating are in a thermodynamic stable state, and the interface residual stress distribution tends to be balanced.

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