Electro-fenton shear thickening polishing method suitable for wc-co alloy substrate

Abstract

The application discloses a polishing method of electro-Fenton shear thickening for a WC-Co alloy substrate, and the polishing liquid comprises FeSO4, H2O2, an inert inorganic salt electrolyte, a pH regulator, diamond abrasive grains, dispersed phase particles and deionized water; during polishing, the WC-Co alloy substrate is connected to a negative pole of an external power supply as a cathode, and a polishing tank is connected to a positive pole of the external power supply as an anode. 3+ The self-circulation mechanism of in-situ generation of H2O2 and Fe 2+ reduction and regeneration, the combination of the inert inorganic salt electrolyte, the effective extension of the activity of the polishing liquid, the preferential oxidation of the Co phase by ·OH, the double removal of the Co phase by shear thickening and the uniform reduction of the Co content of the substrate surface layer, the mild oxidation of the WC hard phase to generate a WO3 film and the peeling of the WO3 film to avoid damage to the substrate, the defects of the polishing liquid in the prior art, the easy inactivation and the difficulty in reducing the Co content, the clean, smooth, cobalt-poor and uniform surface, the high bonding force of the diamond coating, and the strong practicability. The application discloses a polishing method of electro-Fenton shear thickening for a WC-Co alloy

Description

Technical Field

[0001] This invention relates to the field of ultra-precision polishing technology, specifically to an electro-Fenton shear thickening polishing method applicable to WC-Co alloy substrates. Background Technology

[0002] WC-Co alloy cutting tools (tungsten carbide-cobalt cemented carbide tools) are widely used in high-speed cutting and precision machining. Further reducing cutting friction and extending their service life through surface coating technology has become an important development trend in advanced tool manufacturing. Among many coating materials, diamond carbon coatings, with their unique microstructure, have attracted much attention for improving tool performance.

[0003] A strong bond between the coating and the tool substrate is a key prerequisite for the excellent service performance of diamond-coated tools. Therefore, the pretreatment process for tool coating has two requirements: First, the tool surface must have good surface roughness to provide uniform nucleation sites during the coating deposition process and avoid stress concentration caused by microscopic defects on the surface, which could lead to coating peeling. Second, since diamond coatings are sensitive to the chemical composition of the substrate, the Co phase (cobalt phase) in WC-Co alloy can catalyze the graphitization reaction of carbon atoms in the coating, reducing the interfacial bonding strength between the coating and the substrate. Therefore, the tool needs to be treated with "cobalt depletion" and surface smoothing before coating deposition.

[0004] Currently, there are significant limitations in the pretreatment methods for coating WC-Co cutting tools. The main existing treatment methods include pure machining and chemical etching. Pure machining methods such as traditional sandblasting and grinding will cause scratches and other damage to the tool surface. Chemical etching methods such as acid and alkali etching will cause severe corrosion to the WC phase (tungsten carbide phase). Neither of the above two methods can effectively meet the dual requirements of "cobalt-depleted" treatment and surface smoothing.

[0005] Shear thickening polishing has promising applications in the field of tool passivation polishing (Lyu BH, He QK, Chen SH, et al. Experimental study on shear thickening polishing of cementedcarbide insert with complex shape[J]. The International Journal of Advanced Manufacturing Technology, 2019, 103(1): 585-595.). To address the limitations of the aforementioned pretreatment methods, some scholars have proposed an electrochemical-shear thickening composite polishing method. This method can promote the dissolution of the Co phase in the matrix and achieve efficient removal of the Co phase by precisely controlling the voltage and processing time. However, the electrochemical method is sensitive to process parameters and has a narrow process window (Zhou Y, Zhou X, Wang J, et al. Electrolysis combined shear thickeningpolishing method[J]. Journal of Manufacturing Processes, 2023, 107: 179-198.). In addition, although traditional Fenton effect-enhanced shear thickening polishing can achieve efficient polishing of this type of tool, the traditional Fenton system is prone to polishing fluid deactivation. The traditional Fenton reaction is violent in its initial stage. On the one hand, the reaction products are prone to precipitation; on the other hand, the violent reaction releases a large amount of heat, causing the polishing slurry temperature to rise rapidly in a short period of time, resulting in the destabilization and aggregation of the dispersed phase within the system. Both of these factors lead to the deterioration of the rheological properties of the polishing slurry and the weakening of the shear thickening effect, ultimately making it difficult for the traditional Fenton composite polishing method to achieve stable processing over a long period of time.

[0006] In summary, there is an urgent need to develop a new shear-thickening polishing method for WC-Co alloy cutting tools to ensure the activity of the polishing slurry during the polishing process, while simultaneously meeting the dual requirements of "cobalt-poor" treatment of the tool substrate and surface smoothing. This would address the shortcomings of existing pretreatment methods and provide a guarantee for the stable deposition of subsequent diamond coatings. Summary of the Invention

[0007] The purpose of this invention is to address the deficiencies and shortcomings of the prior art by providing an electro-Fenton shear thickening polishing method for WC-Co alloy matrices that can ensure the activity of the polishing slurry and effectively reduce the Co content in the WC-Co alloy matrix.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] This invention provides an electro-Fenton shear thickening polishing method applicable to WC-Co alloy matrix, using a polishing slurry. The polishing slurry comprises FeSO4, H2O2, electrolyte, pH adjuster, diamond abrasive particles, dispersed phase particles, and deionized water. The electrolyte is an inert inorganic salt, which refers to an inorganic salt that is used only as a conductive electrolyte in the system, does not participate in the Fenton redox reaction, does not undergo complexation or precipitation reactions with ions in the system, does not catalyze the ineffective decomposition of hydrogen peroxide, does not interfere with the iron ion cycle, and does not damage the stability of the shear thickening dispersion system. The inert inorganic salt is preferably any one or two of sodium sulfate and potassium sulfate.

[0010] This method includes the following polishing steps:

[0011] a) Mount the WC-Co alloy substrate on the workpiece shaft and connect the WC-Co alloy substrate to the negative terminal of the external power supply; place the carbon felt at the bottom of the polishing tank and connect the carbon felt to the positive terminal of the external power supply, with the WC-Co alloy substrate as the cathode and the carbon felt as the anode.

[0012] b) Adjust the distance between the workpiece shaft and the wall and bottom of the polishing tank to ensure that the WC-Co alloy matrix can be immersed in the polishing liquid during the polishing process, and adjust the angle between the workpiece shaft and the horizontal direction.

[0013] c) Place the polishing liquid into the polishing tank;

[0014] d) Turn on the equipment and set the workpiece axis to rotate in the opposite direction to the polishing tank rotation speed. Use the shear thickening effect of the polishing fluid to polish the WC-Co alloy matrix.

[0015] According to the above scheme, the dispersed phase particles are selected from polyhydroxy polymers.

[0016] According to the above scheme, the electrolyte is selected as Na2SO4.

[0017] According to the above scheme, the diamond abrasive grain size is #5000.

[0018] According to the above scheme, the FeSO4 content is 0.4wt% of the polishing slurry, the H2O2 content is 0.1wt% of the polishing slurry, the Na2SO4 content is 1wt% of the polishing slurry, the diamond abrasive particles are 2-9wt% of the polishing slurry, and the dispersed phase particles are 45-60wt% of the polishing slurry.

[0019] According to the above scheme, the pH adjuster is a 0.1 mol / L H2SO4 solution.

[0020] According to the above scheme, the preparation process of the polishing slurry includes the following steps:

[0021] 1) Place the dispersed phase particles, diamond abrasive grains, and deionized water in a mixing tank and initially disperse them by mechanical stirring to form a base liquid;

[0022] 2) Add the electrolyte to the base solution and stir until it is fully dissolved;

[0023] 3) Slowly add the H2SO4 solution to the solution obtained in step 2) to adjust its pH value to 3-4;

[0024] 4) The solution obtained in step 3) is subjected to ultrasonic treatment to eliminate micro-agglomerations;

[0025] 5) Add FeSO4 and H2O2 oxidant to the solution obtained in step 4), mix well to form the polishing solution.

[0026] Based on the above scheme, the chemical reaction and shear thickening synergistic removal process during polishing is as follows:

[0027] S1. In-situ generation of hydrogen peroxide: After the WC-Co alloy substrate is connected to a DC power supply, dissolved oxygen molecules in the polishing solution undergo a reduction reaction on the cathode surface, continuously generating hydrogen peroxide in situ on the WC-Co alloy substrate surface. The chemical reaction equation is as follows:

[0028] O2 + 2H + +2e − =H2O2;

[0029] S2, Fenton reaction and preferential oxidation of cobalt phase: The hydrogen peroxide generated in situ comes into contact with ferrous ions in the polishing solution, undergoing a Fenton reaction to generate ferric ions, strongly oxidizing hydroxyl radicals, and hydroxide ions; the hydroxyl radicals preferentially act on the Co phase on the surface of the WC-Co alloy matrix and oxidize it. The relevant chemical reaction equations are as follows:

[0030] Fe 2+ +H₂O₂→Fe 3+ +·OH+OH − ;

[0031] Co + 2·OH → Co(OH)2;

[0032] S3. Oxidation and Removal of the Tungsten Carbide Hard Phase: After the surface Co phase is removed, the WC hard phase is gradually exposed; the continuously generated hydroxyl radicals oxidize the exposed WC particles, generating a softer tungsten trioxide oxide film; during continuous polishing, this oxide film is mechanically abraded and removed by diamond abrasive grains, and discharged from the processing area with the polishing fluid, exposing a completely new WC-Co alloy matrix surface.

[0033] Co(OH)₂ + 2H₂+ →Co 2+ +2H2O;

[0034] S4. Oxidation and removal of the tungsten carbide hard phase: After the surface Co phase is removed, the WC hard phase is gradually exposed; the continuously generated hydroxyl radicals oxidize the exposed WC particles to generate a softer tungsten trioxide oxide film; during the continuous polishing process, the oxide film is mechanically scraped off by diamond abrasive grains and discharged from the processing area with the polishing fluid, exposing the new WC-Co alloy matrix surface;

[0035] S5, Iron ion cathode reduction and regeneration: Fe generated within the system 3+ It continuously gains electrons at the cathode, migrates to the cathode surface, gains electrons again, and is reduced and regenerated into Fe. 2+ The reduction reaction equation is: Fe 3+ +e − →Fe 2+ ;

[0036] S6. System reaction cycle maintenance: The entire process of steps S1 to S5 is continuously cycled to achieve a continuous generation of strong oxidizing hydroxyl radicals, ensuring the long-term stable operation of the electro-Fenton reaction.

[0037] The more specific mechanism is as follows: In the initial stage of polishing, within the low shear rate region, the polishing slurry maintains good fluidity. Under the action of an applied DC electric field, dissolved oxygen in the polishing slurry migrates to the WC-Co cemented carbide surface, which acts as the cathode, undergoing a two-electron reduction reaction and continuously generating hydrogen peroxide in situ. In the low shear rate environment, the generated hydrogen peroxide immediately reacts with Fe in the polishing slurry. 2+ The Fenton reaction occurs, continuously generating strong oxidizing hydroxyl radicals (·OH). Since the chemical reactivity of the Co phase is higher than that of the hard WC phase, ·OH preferentially oxidizes the surface bonding phase Co, forming a loosely textured and relatively soft Co(OH)2 layer.

[0038] When the local shear rate increases sharply, the polishing slurry undergoes a shear thickening effect, and the dispersed phase particles and diamond abrasive grains form dense particle clusters, causing the viscosity of the polishing slurry to increase instantaneously. Under high shear rate conditions, the surface Co(OH)2 layer is efficiently removed through the combined action of mechanical cutting by the diamond abrasive grains and chemical dissolution by the acidic polishing slurry, achieving effective cobalt removal from the substrate surface.

[0039] After the binder phase Co is removed, the exposed hard WC phase is gently oxidized by continuously generated ·OH to form a loosely structured WO3 oxide film with low hardness. Subsequently, under high shear rate, the particle clusters carrying diamond abrasive grains peel off the WO3 oxide film through mechanical micro-cutting, exposing a brand-new WC-Co alloy matrix surface, thus achieving surface smoothing of the matrix.

[0040] Throughout the process, oxygen reduction continuously occurs on the cathode surface to generate hydrogen peroxide, while Fe... 3+ Regenerated into Fe at the cathode 2+ This forms a self-circulating electro-Fenton system, maintaining a continuous supply of highly oxidizing free radicals (·OH). Through a step-by-step removal mechanism synergistic with "chemical oxidation-mechanical removal" and an electrochemical self-circulating system, the cobalt removal and WC surface oxidation removal processes alternate stably, effectively avoiding local over-corrosion and residual stress concentration. Ultimately, a clean, smooth, and cobalt-poor uniform pretreated surface is obtained, meeting the high adhesion requirements of subsequent diamond coatings.

[0041] According to the above scheme, step a) of the polishing step is further provided with a conductive slip ring, which is fixed on the workpiece shaft, electrically connected to the WC-Co alloy substrate, and connected to the negative terminal of an external power supply.

[0042] The beneficial effects of this invention are:

[0043] This invention effectively solves the defects of existing technologies, such as easy deactivation of polishing slurries and difficulty in reducing the Co content in WC-Co alloy matrices. It achieves this by generating H2O2 and Fe in situ at the cathode. 3+ Fe reduction and regeneration 2+ The self-circulating mechanism, combined with an inert inorganic salt electrolyte, prolongs the activity of the polishing slurry and ensures stable processing. It utilizes the preferential oxidation of the Co phase by ·OH, combined with shear thickening to achieve its dual removal, uniformly reducing the surface Co content; the WC hard phase is gently oxidized to form a WO3 film, which is then peeled off, avoiding damage to the substrate. Ultimately, a clean, smooth, and uniformly cobalt-poor surface is obtained, meeting the high adhesion requirements of diamond coatings and demonstrating strong practicality. Attached Figure Description

[0044] Figure 1 This is a simplified schematic diagram of the electro-Fenton shear thickening and polishing apparatus of Example 1;

[0045] Figure 2 This is a diagram illustrating the material removal mechanism of the WC-Co alloy substrate surface under the synergistic effect of the electro-Fenton-shear thickening polishing fluid of the present invention;

[0046] Figure 3 This is a schematic diagram showing the surface roughness and material removal rate of the WC-Co alloy substrate under different polishing methods;

[0047] Figure 4 These are schematic diagrams of the surface morphology of WC-Co alloy substrates under different polishing methods;

[0048] Figure 5 This is a schematic diagram comparing the scanning electron microscope morphology and Co element content of WC-Co alloy substrates under different polishing methods.

[0049] Figure 6 The image shows the nano-scratch test results of a diamond coating attached to a WC-Co alloy substrate with the same roughness.

[0050] Figure 1 In the middle: 1. WC-Co alloy matrix; 2. Workpiece shaft; 3. Conductive slip ring; 4. Polishing tank; 5. Carbon felt; 6. Polishing fluid; 7. Polishing tank drive shaft; 8. External power supply. Detailed Implementation

[0051] The technical solution of the present invention will be further described in detail below through specific embodiments and comparative examples.

[0052] Example 1

[0053] This embodiment describes an electro-Fenton shear thickening polishing method applicable to WC-Co alloy matrices. The diamond abrasive is #5000, and the dispersed phase particles are polyhydroxy polymers with a particle size of 5-30 micrometers. The mass percentages of each ingredient are shown in Table 1.

[0054] Table 1

[0055] Diamond abrasive grains 5wt% <![CDATA[Na2SO4]]> 1wt% <![CDATA[FeSO4]]> 0.4wt% <![CDATA[H2O2]]> 0.1wt% Dispersed phase particles 53wt% Deionized water 40wt% <![CDATA[H2SO4]]> 0.5wt%

[0056] In this case, the preparation of the polishing slurry for the electro-Fenton shear thickening polishing method suitable for WC-Co alloy substrates includes the following steps:

[0057] 1) Place the dispersed phase particles, diamond abrasive grains, and deionized water in a mixing tank and initially disperse them by mechanical stirring to form a base liquid;

[0058] 2) Add Na2SO4 electrolyte to the base solution and stir for 5-10 minutes to ensure it is fully dissolved;

[0059] 3) Slowly add the H2SO4 solution to the solution obtained in step 2) to adjust its pH value to 3-4;

[0060] 4) The solution obtained in step 3) is subjected to ultrasonic treatment to eliminate micro-agglomerations;

[0061] 5) Add FeSO4 and H2O2 oxidant to the solution obtained in step 4), mix well to form the polishing solution.

[0062] The WC-Co alloy substrate was polished using the polishing slurry prepared above. Specific polishing parameters are shown in Table 2.

[0063] Table 2

[0064] Workpiece axis tilt angle 5° Polishing tank speed 75rpm Workpiece shaft speed 5rpm Polishing time 15min Voltage 0.9V Polishing gap 1mm

[0065] A detailed schematic diagram of the polishing process for the WC-Co alloy matrix is ​​shown below. Figure 1 As shown, the WC-Co alloy matrix 1 and the shear-thickening polishing device include a workpiece shaft 2, a conductive slip ring 3, a polishing tank 4, a carbon felt 5, a polishing fluid 6, a polishing tank drive shaft 7, and an external power supply 8. The external power supply 8 is a DC power supply. During the polishing process, the workpiece shaft 2 and the polishing tank drive shaft 7 are driven independently. The polishing steps include:

[0066] a) Connect the conductive slip ring 3 to the workpiece shaft 2, and simultaneously install the WC-Co alloy substrate 1 on the workpiece shaft 2; connect the conductive slip ring 3 to the negative terminal of the external power supply 8; place the carbon felt 5 at the bottom of the polishing tank, connect the carbon felt 5 to the positive terminal of the external power supply 8, and use the workpiece 1 as the cathode of the electro-Fenton reaction and the carbon felt 5 as the anode of the electro-Fenton reaction.

[0067] b) Adjust the distance between the workpiece shaft 2 and the wall and bottom of the polishing tank 4 to ensure that the workpiece 1 can be immersed in the polishing liquid 6 during the polishing process. Adjust the angle between the workpiece shaft 2 and the horizontal direction to 5°.

[0068] c) Place the above polishing liquid into the polishing tank;

[0069] d) Turn on the equipment, set the workpiece axis and the polishing tank to rotate in opposite directions, and use the shear thickening effect of the polishing fluid to polish the WC-Co alloy matrix 1.

[0070] Comparative Example 1

[0071] This comparative example demonstrates a shear-thickening polishing method. The specific parameters of the polishing fluid are shown in Table 3. The diamond abrasive grains have a particle size of #5000, and the dispersed phase particles are selected from polyhydroxy polymers with a particle size of 5-30 micrometers.

[0072] Table 3

[0073] Diamond abrasive grains 5wt% Dispersed phase particles 55wt% Deionized water 40wt%

[0074] The preparation of the polishing slurry in this comparative example includes the following steps:

[0075] 1) Place the dispersed phase particles, diamond abrasive grains, and deionized water in a mixing tank and initially disperse them by mechanical stirring to form a base liquid;

[0076] 2) The base liquid is ultrasonically treated to eliminate micro-agglomerates, thus obtaining the polishing liquid.

[0077] This comparative example did not have an external voltage applied, and the remaining polishing parameters were the same as in Example 1. The polishing steps are as follows:

[0078] a) Mount the WC-Co alloy matrix onto the workpiece shaft;

[0079] b) Adjust the distance between the workpiece shaft and the wall and bottom of the polishing tank to ensure that workpiece 1 can be immersed in the polishing liquid during the polishing process. Adjust the angle between the workpiece shaft and the horizontal direction to 5°.

[0080] c) Place the above polishing liquid into the polishing tank;

[0081] d) Turn on the equipment and set the workpiece axis to rotate in the opposite direction to the polishing tank rotation speed. Use the shear thickening effect of the polishing fluid to polish the WC-Co alloy matrix.

[0082] Comparative Example 2

[0083] This comparative example uses the Fenton reaction shear thickening polishing method, which is free of electric field. The specific parameters of the polishing slurry in this comparative example are shown in Table 4. The diamond abrasive grain size is #5000, the dispersed phase particles are polyhydroxy polymers with a particle size of 5-30 micrometers, and the pH of the polishing slurry is adjusted to 3-4 before polishing.

[0084] Table 4

[0085] Diamond abrasive grains 5wt% <![CDATA[FeSO4]]> 0.4wt% <![CDATA[H2O2]]> 0.1wt% Dispersed phase particles 54wt% Deionized water 40wt% <![CDATA[H2SO4]]> 0.5wt%

[0086] The preparation of the polishing slurry in this comparative example includes the following steps:

[0087] 1) Place the dispersed phase particles, diamond abrasive grains, and deionized water in a mixing tank and initially disperse them by mechanical stirring to form a base liquid;

[0088] 2) Slowly add the H2SO4 solution to the base solution to adjust its pH value to 3-4;

[0089] 3) The solution obtained in step 2) is subjected to ultrasonic treatment to eliminate micro-agglomerations;

[0090] 4) Add FeSO4 and H2O2 oxidant to the solution obtained in step 3), mix well to form the polishing liquid.

[0091] The polishing parameters and polishing steps of this comparative example are the same as those of Comparative Example 1.

[0092] Comparative Example 3

[0093] This comparative example uses an electrolytic shear thickening polishing method, which involves an electric field. The specific parameters of the polishing fluid in this comparative example are shown in Table 5. The diamond abrasive grain size is #5000, and the dispersed phase particles are polyhydroxy polymers with a particle size of 5-30 micrometers.

[0094] Table 5

[0095] Diamond abrasive grains 5wt% <![CDATA[Na2SO4]]> 1wt% Dispersed phase particles 54wt% Deionized water 40wt%

[0096] The preparation of the polishing slurry in this comparative example includes the following steps:

[0097] 1) Place the dispersed phase particles, diamond abrasive grains, and deionized water in a mixing tank and initially disperse them by mechanical stirring to form a base liquid;

[0098] 2) Add Na2SO4 electrolyte to the base solution and stir for 5-10 minutes to ensure it is fully dissolved;

[0099] 3) The solution obtained in step 2) is subjected to ultrasonic treatment to eliminate micro-agglomeration, thus obtaining the polishing solution.

[0100] The polishing parameters and polishing steps in this comparative example are the same as those in Example 1.

[0101] After polishing four WC-Co alloy substrates using the four polishing methods described above, the surface roughness and material removal rate of the WC-Co alloy substrates are as follows: Figure 3 As shown.

[0102] Comparative Example 1, relying solely on mechanical action, achieved an initial material removal rate of 315.42 nm / min with shear thickening polishing. However, due to the non-uniformity of the abrasive cutting depth, its final surface roughness Sa remained as high as 23.50 ± 2.45 nm. Notably, this set of data exhibited the largest error bar among the four methods, reflecting the randomness and instability of a single mechanical grinding process, making it difficult to obtain uniform surface quality in a short time. Introducing the Fenton reaction in Comparative Example 2 or the electrolytic reaction in Comparative Example 3 significantly improved processing efficiency. In Comparative Example 3, the material removal rate under electrolytic reaction jumped to 550.15 nm / min, while the surface roughness decreased to 14.70 ± 1.65 nm. In Comparative Example 2, the material removal rate and surface roughness reduction under Fenton-assisted shear thickening polishing reached 585.73 nm / min and 12.60 ± 1.25 nm, respectively. However, although Comparative Example 3 showed a significant improvement in efficiency with the aid of electrolysis, the dispersion of its roughness data (± 1.65 nm) was still relatively large, suggesting fluctuations in the surface microstructure.

[0103] The electro-Fenton-enhanced shear-thickening polishing method in Example 1 achieved optimal efficiency and quality. Within the same 15 min, the material removal rate remained high at 668.62 nm / min, while the surface roughness was significantly reduced to 9.80 ± 0.68 nm. This set of data not only had the lowest mean but also the smallest error range, strongly demonstrating that under the synergistic effect of cathodic protection and electrocatalytic oxidation, the substrate surface was not only rapidly leveled but also achieved a high degree of microscopic uniformity, avoiding quality fluctuations caused by mechanical scratches and electrochemical pitting.

[0104] The scanning electron microscope morphology of the polished WC-Co alloy matrix surface and the Co element content are as follows: Figure 5 As shown in Table 6, the specific contents of Co and O elements are as follows.

[0105] After 15 minutes of shear thickening and polishing treatment, the surface of the WC-Co alloy matrix still retained relatively obvious original damage characteristics. Energy dispersive spectroscopy analysis showed that its oxygen content was only 1.29 wt%, while the cobalt content was as high as 6.47 wt%, and it showed significant spot-like and banded enrichment in spatial distribution.

[0106] The surface of Comparative Example 3, after electrolytic shearing thickening and polishing treatment, exhibited certain electrochemical ablation characteristics. Although the cobalt content decreased to 1.1 wt%, obvious blocky enrichment areas were still visible in the energy dispersive spectroscopy (EDS) spectrum. This again confirms the non-selective nature of the anodic dissolution mechanism, where the current preferentially attacks surface protrusions or specific grain boundaries, resulting in uneven material removal. In some areas, the metal coating layer was not completely stripped off and remained as residual clusters, making it difficult to achieve comprehensive interface purification.

[0107] In Comparative Example 2, the interface cleaning effect was significantly enhanced after the introduction of the Fenton chemical activation mechanism. Surface scratches were almost completely eliminated after treatment, and the cobalt content was significantly diluted to 0.12 wt%, with a finer distribution.

[0108] The electro-Fenton shear thickening polishing method in Example 1 demonstrated optimal interface control within 15 minutes. Energy dispersive spectroscopy (EDS) analysis showed that the oxygen content on the sample surface after electro-Fenton shear thickening polishing reached 3.57 wt%, the highest among the four methods, confirming the efficient oxidation of the surface by hydroxyl radicals driven by cathodic electrocatalysis, effectively generating an easily removable softened oxide layer on the workpiece surface. At this point, the cobalt content dropped to a minimum of 0.10 wt%, exhibiting an extremely uniform spatial distribution. The evolution of surface quality and cobalt distribution fully demonstrates that the electro-Fenton shear thickening polishing process can effectively eliminate the damaged surface layer, providing a clean and microstructure-complete interface foundation for subsequent diamond-like carbon (DLC) coating deposition.

[0109] Table 6

[0110] Example 1 0.10 3.57 Comparative Example 1 6.47 1.29 Comparative Example 2 0.12 1.35 Comparative Example 3 1.10 1.15

[0111] To investigate the actual impact of differences in surface integrity of WC-Co alloy substrates caused by different polishing methods on the adhesion performance of subsequent diamond coatings, nano-scratch tests were conducted on samples deposited on WC-Co alloy substrates with the same roughness (Sa ≈ 5 nm). Based on the characteristic evolution of the coefficient of friction (COF) with increasing normal load during the scratching process, the mechanical response and failure modes of the coating at different stages were defined. Simultaneously, scratch morphology images obtained by ultra-depth-of-field microscopy were used for auxiliary judgment. In the early stages of scratching, the indenter is highly susceptible to the influence of surface micro-protrusions, leading to violent COF oscillations. As the load increases, the indenter penetrates the coating, forming a stable plastic tillage, and the COF curve initially enters a stable state. This inflection point is defined as the steady-state load-bearing starting point L of the coating. C1 When the load continues to increase to the point where large-area interfacial spalling occurs, the COF will show a step-like and significant increase. This critical failure load is defined as L. C2 Subsequently, the coating was completely scraped off, and the COF tended to stabilize at a high level, defined as the complete failure load L. C3 . Figure 6 The friction coefficient-load evolution curves of each group of samples were recorded, where L C2 It is the core evaluation index for measuring the strength of membrane-substrate bonding.

[0112] like Figure 6 As shown in section (a), although the shear-thickening polishing method of Comparative Example 1 reduced the macroscopic roughness of the WC-Co alloy matrix to the 5 nm level, the adhesion of its diamond coating (L) was significantly reduced. C2 The shear-thickening polishing process relies primarily on the powerful mechanical cutting of diamond abrasive grains, leaving behind numerous hidden scratches and a work-hardened layer on the surface. This microscopic inhomogeneity necessitates the application of a large load (L) by the indenter. C1 = 12.23 N) is needed to forcibly overcome surface resistance and establish a steady-state tillage. And crossing L C1 Subsequently, the damaged layer of the WC-Co alloy substrate at the bottom is prone to brittle fracture under gradually increasing stress, which leads to the peeling off of the coating and manifests as an premature rise in the COF curve.

[0113] Introducing Comparative Example 2 ( Figure 6 (Part (b)) or Comparative Example 3 ( Figure 6 After the process in part (c), the bonding strength was significantly improved. Comparative Example 3 showed that the L-shaped material after electrolytic shear thickening and polishing... C2The COF curve was increased to 38.30 N, but it exhibited frequent and severe sawtooth fluctuations during the rising phase. This was attributed to the "non-selective" anodic dissolution inducing micro-pitting at the grain boundaries, resulting in localized "suspended" coatings above them. Stress concentration occurred when the indenter slid across the edge of the pits, causing premature localized cracking of the coating and generating a large amount of wear debris, leading to severe fluctuations in frictional resistance. Comparative Example 2, with its Fenton shear thickening polishing, reduced pitting defects due to the uniformity of chemical oxidation, and its L... C2 The load was further increased to 41.56 N.

[0114] WC-Co alloy matrix after electro-Fenton shear thickening and polishing treatment in Example 1 ( Figure 6 The middle (d) section exhibits the best comprehensive mechanical properties. On the one hand, thanks to the extremely excellent microscopic smoothness and uniformity of the surface, the indenter can withstand extremely low loads (L... C1 = 8.37 N) can quickly end the break-in period and transition to the steady-state load-bearing stage; on the other hand, its large-area spalling critical load L C2 Up to 50.27 N, a significant improvement of 51.3% compared to the STP group, and completely penetrating (L) C3 The occurrence of (= 61.71 N) was significantly delayed. The results show that this method can effectively avoid electrochemical pitting in the tool substrate and alleviate / eliminate mechanical damage in the substrate, providing an ideal substrate for diamond coatings.

Claims

1. An electro-Fenton shear thickening polishing method applicable to WC-Co alloy matrix, characterized in that, The polishing fluid includes FeSO4, H2O2, electrolyte, pH adjuster, diamond abrasive particles, dispersed phase particles, and deionized water, wherein the electrolyte is an inert inorganic salt. This method includes the following polishing steps: a) Mount the WC-Co alloy substrate on the workpiece shaft and connect the WC-Co alloy substrate to the negative terminal of the external power supply; place the carbon felt at the bottom of the polishing tank and connect the carbon felt to the positive terminal of the external power supply, with the WC-Co alloy substrate as the cathode and the carbon felt as the anode. b) Adjust the distance between the workpiece shaft and the wall and bottom of the polishing tank to ensure that the WC-Co alloy matrix can be immersed in the polishing liquid during the polishing process, and adjust the angle between the workpiece shaft and the horizontal direction. c) Place the polishing liquid into the polishing tank; d) Turn on the equipment and set the workpiece axis to rotate in the opposite direction to the polishing tank rotation speed. Use the shear thickening effect of the polishing fluid to polish the WC-Co alloy matrix.

2. The electro-Fenton shear thickening and polishing method for WC-Co alloy substrates according to claim 1, characterized in that, The dispersed phase particles are selected from polyhydroxy polymers.

3. The electro-Fenton shear thickening and polishing method for WC-Co alloy substrates according to claim 2, characterized in that, The electrolyte used is Na2SO4.

4. The electro-Fenton shear thickening and polishing method for WC-Co alloy substrates according to claim 1, characterized in that, The diamond abrasive grain size is #5000.

5. The electro-Fenton shear thickening and polishing method for WC-Co alloy substrates according to claim 3, characterized in that, The FeSO4 content is 0.4wt% of the polishing slurry, the H2O2 content is 0.1wt% of the polishing slurry, the Na2SO4 content is 1wt% of the polishing slurry, the diamond abrasive particles are 2-9wt% of the polishing slurry, and the dispersed phase particles are 45-60wt% of the polishing slurry.

6. The electro-Fenton shear thickening and polishing method for WC-Co alloy substrates according to claim 1, characterized in that, The pH adjuster is a 0.1 mol / L H2SO4 solution.

7. The electro-Fenton shear thickening and polishing method for WC-Co alloy substrates according to any one of claims 1-6, characterized in that, The preparation process of the polishing slurry includes the following steps: 1) Place the dispersed phase particles, diamond abrasive grains, and deionized water in a mixing tank and initially disperse them by mechanical stirring to form a base liquid; 2) Add the electrolyte to the base solution and stir until it is fully dissolved; 3) Slowly add the H2SO4 solution to the solution obtained in step 2) to adjust its pH value to 3-4; 4) The solution obtained in step 3) is subjected to ultrasonic treatment to eliminate micro-agglomerations; 5) Add FeSO4 and H2O2 oxidant to the solution obtained in step 4), mix well to form the polishing solution.

8. The electro-Fenton shear thickening and polishing method for WC-Co alloy substrates according to claim 7, characterized in that, The chemical reaction and shear thickening synergistic removal process during polishing in this method is as follows: S1. In-situ generation of hydrogen peroxide: After the WC-Co alloy substrate is connected to a DC power supply, dissolved oxygen molecules in the polishing solution undergo a reduction reaction on the cathode surface, continuously generating hydrogen peroxide in situ on the WC-Co alloy substrate surface. The chemical reaction equation is as follows: O2+2H + +2e − =H2O2; S2, Fenton reaction and preferential oxidation of cobalt phase: The hydrogen peroxide generated in situ comes into contact with ferrous ions in the polishing solution, undergoing a Fenton reaction to generate ferric ions, hydroxide ions, and strongly oxidizing hydroxyl radicals; these hydroxyl radicals preferentially act on the Co phase on the surface of the WC-Co alloy matrix and oxidize it. The relevant chemical reaction equations are as follows: Fe 2+ +H2O2→Fe 3+ +·OH+OH − ; Co + 2·OH → Co(OH)2; S3. Oxidation and Removal of the Tungsten Carbide Hard Phase: After the surface Co phase is removed, the WC hard phase is gradually exposed; the continuously generated hydroxyl radicals oxidize the exposed WC particles, generating a softer tungsten trioxide oxide film; during continuous polishing, this oxide film is mechanically abraded and removed by diamond abrasive grains, and discharged from the processing area with the polishing fluid, exposing a completely new WC-Co alloy matrix surface. Co(OH)2+2H + →What 2+ +2H2O; S4. Oxidation and removal of the tungsten carbide hard phase: After the surface Co phase is removed, the WC hard phase is gradually exposed; the continuously generated hydroxyl radicals oxidize the exposed WC particles to generate a softer tungsten trioxide oxide film; during the continuous polishing process, the oxide film is mechanically scraped off by diamond abrasive grains and discharged from the processing area with the polishing fluid, exposing the new WC-Co alloy matrix surface; S5, Iron ion cathode reduction and regeneration: Fe generated within the system 3+ It continuously gains electrons at the cathode, migrates to the cathode surface, gains electrons again, and is reduced and regenerated into Fe. 2+ The reduction reaction equation is: Fe 3+ +e − →Fe 2+ ; S6. System reaction cycle maintenance: The entire process of steps S1 to S5 is continuously cycled to achieve a continuous generation of strong oxidizing hydroxyl radicals, ensuring the long-term stable operation of the electro-Fenton reaction.

9. The electro-Fenton shear thickening and polishing method for WC-Co alloy substrates according to claim 1, characterized in that, Step a) of the polishing step also includes a conductive slip ring, which is fixed on the workpiece shaft, electrically connected to the WC-Co alloy substrate, and connected to the negative terminal of an external power source.

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