A method for removing surface electric erosion pits of CoCrWNi alloy wire

Abstract

The present application belongs to the technical field of alloy surface treatment, and discloses a method for removing surface electric erosion pits of CoCrWNi alloy wire. The electrolyte is prepared from phosphoric acid, sulfuric acid, water and glycerol; the wire is used as an anode, and electrolytic polishing is carried out at a temperature of 60 DEG C and a voltage of 11 V for 2 min 30 s; and after polishing, deacidification, neutralization and drying passivation treatment are sequentially carried out. By adding glycerol and controlling the "high-temperature fast polishing" window, the method can selectively flatten the flange of the electric erosion pit and fill the pit bottom by using the anode selective dissolution and viscous film leveling mechanism, effectively removes the electric erosion pits with a depth of microns to tens of microns, and avoids over-corrosion of the substrate, so that the surface of the wire after treatment is mirror-like and glossy, without pitting and shadow, and the fatigue life and use safety of the wire are significantly improved.

Description

Technical Field

[0001] This application relates to the field of alloy surface treatment technology, specifically to a method for removing surface electro-erosion pits from CoCrWNi alloy wire. Background Technology

[0002] CoCrWNi alloy exhibits high strength and is relatively stable within a temperature range of 2100℉. Its precipitates possess excellent wear resistance, corrosion resistance, creep resistance, thermal fatigue resistance, and oxidation resistance. It is primarily used for wear-resistant surface surfacing in turbine blade interlocking devices.

[0003] For wire EDM, especially slow wire EDM equipment, the surface of the extracted wire will have regular discharge pits and recast layers, and may also be accompanied by microcracks and heat-affected zones, which will affect the surface quality and service life of the wire.

[0004] Currently, common post-processing methods for surface defects in wire EDM include mechanical polishing, chemical polishing, and conventional electrolytic polishing.

[0005] Mechanical polishing, such as sanding, grinding, and mechanical tumbling, can remove some surface defects, but it has obvious shortcomings when used on slender filaments: first, it can easily cause the filament to deform or create new scratches; second, it is difficult to uniformly treat the circumferential surface, and the bottom of the pits is often not reached; and third, it is inefficient and not suitable for batch processing.

[0006] Chemical polishing, which relies solely on chemical etching with acidic or alkaline solutions, is simple to operate, but its isotropic corrosion characteristics result in poor selectivity for electrolytic pits. Often, while the substrate around the pit is excessively dissolved, the defects within the pit are not completely removed. Furthermore, the waste liquid from chemical polishing is difficult to treat, and for CoCrWNi alloys with high tungsten content, tungsten easily forms tungstic acid precipitates in strong acids, affecting surface uniformity.

[0007] Conventional electropolishing (primarily using a phosphoric acid-sulfuric acid system) is a common method for leveling metal surfaces, mainly targeting fine micro-scratches remaining after mechanical polishing, typically at sub-micron depths. For electro-erosion pits with depths ranging from micrometers to tens of micrometers caused by wire cutting, conventional electropolishing with short processing times may result in insufficient removal, leaving residual pits. Extending the polishing time to increase removal can easily lead to over-corrosion of the substrate, forming new pits or pitting in areas other than the original pits, thus degrading surface quality. This is because there is a significant uneven distribution of current density at the bottom and edges of the electro-erosion pits. The current density is too high at the raised edges, causing preferential dissolution, while the current density is too low at the bottom, resulting in slow dissolution. Ultimately, the pits are not removed, while the surrounding area corrodes first.

[0008] Therefore, developing an electropolishing method that can selectively and controllably remove electro-erosion pits on the surface of CoCrWNi alloy wire while avoiding excessive corrosion of the substrate and maintaining surface smoothness has significant practical value and industrial implications. Summary of the Invention

[0009] Purpose of the invention: To address the shortcomings of the prior art, this application provides a method for removing surface electro-erosion pits from CoCrWNi alloy wires.

[0010] Technical solution: The electrolytic polishing method for removing electro-erosion pits on the surface of alloy wires according to the present invention includes the following steps:

[0011] Step 1: Prepare the electrolyte

[0012] The electrolyte contains phosphoric acid, sulfuric acid, water and glycerol, and the proportions by mass are: 55-65 parts phosphoric acid, 15-25 parts sulfuric acid, 15-25 parts water and 1-5 parts glycerol.

[0013] Step 2: Electropolishing

[0014] CoCrWNi alloy wire was used as the anode and immersed in the electrolyte. Electropolishing was performed for 2 to 4 minutes at a temperature of 50°C to 70°C and a voltage of 8V to 14V.

[0015] Step 3: Passivation treatment

[0016] Deacidification: Within 30 seconds after electropolishing, remove the filament and rinse it with running pure water for 1 to 3 minutes; Neutralization: Immerse the deacidified filament in a 5% to 8% sodium carbonate aqueous solution for 3 to 5 minutes, and then rinse it with pure water; Drying: Dry the neutralized filament at 60℃ to 100℃ for 15 to 20 minutes.

[0017] Furthermore, the electrolyte, by mass parts, is composed of: 60 parts phosphoric acid, 20 parts sulfuric acid, 20 parts water, and 3 parts glycerol.

[0018] Electrolytic cracking (ECC) pits are essentially depressions left by pulsed discharge ablation. During wire EDM, high-frequency pulsed discharges occur between the electrode wire and the workpiece, with localized instantaneous temperatures exceeding 10,000°C. This melts or even vaporizes the workpiece material, forming discharge pits. These pits are characterized by their depth, steep edges, and random distribution. Structurally, the inner layer is the substrate, the middle layer is the heat-affected zone, and the outer layer is a recast layer. However, due to the uneven current density distribution at the bottom and edges of the ECC pits, it is easy to cause a situation where "the pit is not removed, but the surrounding area corrodes first."

[0019] Therefore, this invention adds glycerol as an inhibitor to conventional electropolishing solution (sulfuric acid + phosphoric acid). Glycerol can be adsorbed on the anode surface, which can inhibit the dissolution of the anode. It can also form a complex with phosphoric acid, which may form a stronger inhibitory film on the anode surface, inhibiting the dissolution of the anode, slowing down the corrosion rate, protecting the leveled surface from excessive corrosion, and obtaining a bright and fine final surface.

[0020] Furthermore, the electropolishing process is carried out at a temperature of 60°C, a voltage of 11V, and a time of 2 minutes and 30 seconds.

[0021] This invention selects a high-temperature rapid polishing window of 60℃ + 2 min 30 s, which has the following four effects: the film is stable and the selective leveling is the strongest; it only rapidly dissolves the wire-cut molten hard shell, the protruding edges of the electro-erosion pit, and the micro-crack embrittlement layer; the pit slowly flattens out in 2 minutes and 30 seconds, the surface is delicate, and there is no loss of size, no tungsten removal, and no loss of gloss; the corrosion inhibition and stabilization effect of glycerin can be fully exerted to suppress local over-corrosion.

[0022] The core mechanism of this invention follows the electrochemical principle of "anodic selective dissolution + viscous film leveling". A CM64 alloy (mainly composed of Co, Cr, W, and Ni) serves as the anode (connected to the positive terminal of the power supply), undergoing oxidation under an electric field. Metal atoms lose electrons and become ions, entering the solution.

[0023] Cobalt (Co): Co → Co 2+ +2e −

[0024] Chromium (Cr): Cr→Cr 3+ +3e −

[0025] Nickel (Ni): Ni→Ni 2+ +2e −

[0026] Tungsten (W): W + 8H₂O → WO₄ 2− +16H + +6e − (Tungsten readily forms tungstate ions in strong acids)

[0027] The cathode primarily produces gas through hydrogen ion reduction:

[0028] 2H + +2e − →H2↑

[0029] Phosphoric acid, as a key component in film formation, reacts rapidly with the anolysed Co²⁺, Cr³⁺, and Ni²⁺ to generate a viscous, dense, and poorly conductive metal phosphate complex / salt film.

[0030] Co2+ +HPO4 2− →CoHPO4↓

[0031] Cr 3+ +PO4 3− →CrPO4↓

[0032] This film unevenly covers the surface: at the edge of the erosion pit, due to its protruding surface and smaller film coverage area, the resistance is low, and the current density is high, allowing for rapid dissolution; at the bottom of the erosion pit, due to its depression and larger film coverage area, the resistance is high, the current density is low, and dissolution is very slow. This selectively smooths out protrusions and fills in pits, achieving microscopic leveling.

[0033] Sulfuric acid is a strong oxidizing agent and a dissolving catalyst.

[0034] Glycerin has three main functions: First, it increases viscosity and stabilizes the film: it further increases the viscosity of the electrolyte, slows down the diffusion of metal ions, and makes the film adhere more evenly and stably. Second, it inhibits corrosion and maintains gloss: as an organic corrosion inhibitor, it adsorbs in the depressions, inhibiting excessive dissolution; at the same time, it makes the surface dissolution smoother and improves the gloss. Third, it inhibits tungsten loss: it reduces the rapid dissolution of tungsten in strong acids and maintains the uniformity of the alloy surface composition.

[0035] In summary, the microscopic mechanism for removing electrolytic erosion pits consists of three steps: First, activation and dissolution: After applying current, the molten recast layer and embrittled layer within the pit are preferentially activated and dissolved, exposing a fresh alloy surface. Second, selective leveling (the core): At the edge of the pit, due to its protruding surface and small film coverage area, the resistance is low, and the current density is high, allowing for rapid dissolution. At the bottom of the pit, due to its depression and large film coverage area, the resistance is high, the current density is low, and dissolution is slow. The result: the pit edge is leveled, the pit wall becomes gentler, and the pit depth becomes shallower, gradually "smoothing out" the electrolytic erosion pit. Third, bright polishing: After removing the macroscopic pits, the film is further finely leveled to smooth out microscopic undulations, forming a smooth mirror surface.

[0036] After electropolishing, passivation treatment is necessary to remove residual acid, prevent rust recurrence, and maintain gloss. The first step is emergency deacidification: after polishing, the CoCrWNi alloy is removed from the electropolishing solution within 30 seconds and rapidly rinsed with running pure water for 2 minutes. The second step is alkaline neutralization: immersion in a 5%–8% sodium carbonate aqueous solution for 3–5 minutes with gentle agitation. After neutralization, rinse twice with plenty of running pure water, 1 minute each time. The third step is drying in a drying oven at 60–100℃ for 15–20 minutes to thoroughly evaporate any trace moisture and residual salt from microcracks and electrolytic pits.

[0037] Beneficial effects: Compared with the prior art, the method described in this invention can effectively remove wire cutting electrical erosion pits with depths ranging from micrometers to tens of micrometers, rather than just conventional submicrometer-level scratches.

[0038] This invention achieves selective leveling of electrolytic erosion pits by adding glycerol and controlling the "high temperature rapid polishing" window (60℃, 2 min 30 s), thus avoiding over-corrosion of the substrate and the formation of new pits.

[0039] The post-treatment passivation step of this invention effectively prevents surface rust and gloss loss, ensuring the long-term stability and appearance quality of the wire. The treated wire surface is smooth, free of electrolytic pits and microcracks, significantly improving the fatigue life and safety of the wire.

[0040] The electrolyte formulation of this invention is environmentally friendly, does not contain highly toxic substances such as chromic acid, and the waste liquid treatment is relatively simple. Attached Figure Description

[0041] Figure 1 This is an image of the wire surface after electropolishing.

[0042] Figure 2 This is a comparison image of the over-corrosion process in Figure 1.

[0043] Figure 3 This is an image with a ratio of 3 orange dots. Detailed Implementation

[0044] The technical solution of this application will be described in detail below through embodiments, but the protection scope of this application is not limited to the embodiments described.

[0045] Unless otherwise specified, the CoCrWNi alloy wire used in the following examples has a diameter of 1.2 mm, and is suitable for wires with a diameter of 1.2-1.8 mm. The cathode is a stainless steel plate, the electrode spacing is 10-45 mm, and the voltage is 11 V.

[0046] Example 1

[0047] Prepare the electrolyte: Mix 60 parts phosphoric acid, 20 parts sulfuric acid, 20 parts water, and 3 parts glycerol thoroughly. Heat the electrolyte to 60℃. Immerse the CoCrWNi alloy wire (anode) and stainless steel cathode in the electrolyte, connect the power supply (11V), and electropolish for 2 minutes and 30 seconds. After polishing, remove the CoCrWNi alloy from the electropolishing solution within 30 seconds and rinse rapidly with running pure water for 2 minutes. Then soak it in a 6% sodium carbonate aqueous solution for 4 minutes, gently agitating to neutralize it, and then rinse twice with plenty of running pure water, 1 minute each time. Finally, dry it in a drying oven at 80℃ for 18 minutes.

[0048] The surface of the treated wire was observed using a stereomicroscope, such as Figure 1 As shown, the results indicate that the original electrolytic pits were completely removed, and the surface exhibited a mirror-like finish with no over-corrosion, pitting, or shadows.

[0049] Comparative Example 1

[0050] The general steps of Comparative Example 1 are basically the same as those of Example 1, except that the electrolyte formulation is: 60 parts phosphoric acid, 20 parts sulfuric acid, and 20 parts water.

[0051] The surface of the treated wire was observed using a stereomicroscope, such as Figure 2 As shown.

[0052] Comparative Example 2

[0053] The general steps of Comparative Example 2 are basically the same as those of Example 1, except that the electrolyte is heated to 60°C and electropolished for 3 minutes.

[0054] Comparative Example 3

[0055] The general steps of Comparative Example 3 are basically the same as those of Example 1, except that the electrolyte is heated to 80°C and electropolished for 2 minutes and 30 seconds.

[0056] The surface of the treated wire was observed using a stereomicroscope, such as Figure 3 As shown.

[0057] Comparative Example 4

[0058] The general steps of Comparative Example 4 are basically the same as those of Example 1, except that no passivation treatment is performed after electropolishing.

[0059] Comparative Example 5

[0060] The general steps of Comparative Example 5 are basically the same as those of Example 1, except that chemical etching is used, no electricity is applied, and there is no electrolytic polishing treatment.

[0061] The experimental results of the examples and comparative examples are shown in the table below:

[0062]

[0063] The above experimental results show that Example 1 has the best effect.

[0064] The above description is merely a preferred embodiment of this application and is not intended to limit this application.

Claims

1. An electrolytic polishing method for removing electro-erosion pits from the surface of alloy wire, characterized in that, Includes the following steps: Step 1: Prepare the electrolyte The electrolyte contains phosphoric acid, sulfuric acid, water and glycerol, and the proportions by mass are: 55-65 parts phosphoric acid, 15-25 parts sulfuric acid, 15-25 parts water and 1-5 parts glycerol. Step 2: Electropolishing CoCrWNi alloy wire was used as the anode and immersed in the electrolyte. Electropolishing was performed for 2 to 4 minutes at a temperature of 50°C to 70°C and a voltage of 8V to 14V. Step 3: Passivation treatment Deacidification: Within 30 seconds after electropolishing, remove the wire and rinse it with running pure water for 1 to 3 minutes; Neutralization: Immerse the deacidified filaments in a 5%~8% sodium carbonate aqueous solution for 3 to 5 minutes, then rinse with pure water; Drying: Dry the neutralized filament at 60℃~100℃ for 15min~20min.

2. The electrolytic polishing method for removing electro-erosion pits on the surface of alloy wire according to claim 1, characterized in that, The alloy wire is a CoCrWNi alloy wire.

3. The electrolytic polishing method for removing electro-erosion pits on the surface of alloy wire according to claim 1, characterized in that, The diameter of the alloy wire is 1.2-1.8 mm.

4. The electropolishing method for removing electro-erosion pits on the surface of alloy wire according to claim 1, characterized in that, The electrolyte, by mass parts, is composed of: 60 parts phosphoric acid, 20 parts sulfuric acid, 20 parts water, and 3 parts glycerol.

5. The electropolishing method for removing electro-erosion pits on the surface of alloy wire according to claim 1, characterized in that, The electropolishing process was carried out at a temperature of 60°C, a voltage of 11V, and a time of 2 minutes and 30 seconds.

6. The electropolishing method for removing electro-erosion pits on the surface of alloy wire according to claim 1, characterized in that, The electropolishing process described herein has an electrode spacing of 10-45 mm.

7. The electrolytic polishing method for removing electro-erosion pits on the surface of alloy wire according to claim 1, characterized in that, The passivation treatment involves removing the wire within 30 seconds after electropolishing and rinsing it with running pure water for 2 minutes.

8. The electrolytic polishing method for removing electro-erosion pits on the surface of alloy wire according to claim 1, characterized in that, The passivation treatment involves immersing the deacidified filament in a 6% sodium carbonate aqueous solution for 4 minutes, followed by rinsing with pure water.

9. The electrolytic polishing method for removing electro-erosion pits on the surface of alloy wire according to claim 1, characterized in that, The passivation treatment involves drying the neutralized filament at 80°C for 18 minutes.

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