Chemically reinforced shear-thickening polishing slurry and polishing method applicable to WC-Co alloys

Abstract

This invention discloses a chemically enhanced shear-thickening polishing slurry and polishing method suitable for WC-Co alloys, aiming to solve the problem of Co phase loss on the surface of WC-Co alloys in traditional polishing methods. The polishing slurry contains K3[Fe(CN)6], KOH, diamond abrasive particles, dispersed phase particles, and deionized water. The WC and Co phases of the WC-Co alloy react with the [Fe(CN)6] in the polishing slurry. 3‑ and OH ‑ The reaction produces a soft WO3 oxide film on the alloy surface. 3‑x A stable Co3O4 oxide film is formed. Through the shear thickening effect, the polishing slurry forms particle clusters that encapsulate abrasive grains when the relative velocity reaches a threshold. The surface oxide film is removed by the micro-cutting action of the diamond abrasive grains, achieving efficient, high-quality polishing of WC-Co alloy surfaces without Co loss. This method also significantly inhibits the loss of the Co phase, maintaining the hardness and performance of the alloy surface, making it particularly suitable for precision machining of carbide inserts.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultra-precision polishing processing, and particularly relates to a chemical enhanced shear thickening polishing liquid suitable for WC-Co alloy and a polishing method. BACKGROUND

[0002] Surface coating treatment can effectively improve the mechanical and tribological properties of the tool and prolong the service life of the tool. Before coating, the tool substrate surface needs to be polished to obtain higher surface quality and improve the adhesion between the coating and the substrate.

[0003] WC-Co alloy (tungsten carbide-cobalt alloy) is a typical hard alloy material that is difficult to polish. In the prior art, chemical enhanced shear thickening polishing is used for efficient polishing of WC-Co alloy blades with complex shapes. For example, in the existing paper "Mechanism of material removal in tungsten carbide-cobalt alloy during chemistry enhanced shear thickening polishing", Fenton reagent with the highest corrosion potential is added to the polishing liquid to prepare a shear thickening polishing liquid with high removal efficiency. However, Fenton reagent not only reacts with WC, but also reacts with Co (and preferentially reacts with Co), which causes Co to be lost on the surface of the polished WC-Co alloy, resulting in a significant decrease in the surface hardness of the hard alloy, affecting the performance of the tool, especially micro-drills made of hard alloy. Low surface Co content makes the micro-drill more prone to breakage.

[0004] In order to overcome the problem of Co loss, Chinese patent application CN116770409A provides a high-efficiency electrolytic force rheological passivation polishing liquid and passivation polishing method for inhibiting Co loss. The method uses a Co loss inhibitor and controls the electrolysis voltage to inhibit the preferential electrolysis of Co and the chemical reaction of Co during electrolysis. However, the process of this method is relatively complex. On the one hand, the generation and removal of the oxide film of WC phase are achieved through electrolysis reaction. In addition, the polishing liquid contains a large amount of chemical reagents, making it very difficult to prepare the polishing liquid. The inhibiting effect of Co is achieved by coating the Co with insulating nano-magnetic powder. However, during the polishing process, part of the coating layer is easily removed by shear thickening polishing, exposing the Co to the electrolyte, and eventually causing Co loss on the surface of the hard alloy due to electrolysis reaction. This does not completely solve the problem of Co loss inhibition.

[0005] Therefore, there is an urgent need to develop a new shear thickening polishing liquid and polishing method for WC-Co alloy to achieve high-efficiency and high-quality surface without loss of surface Co content. SUMMARY

[0006] The present application aims at the defects and deficiencies of the prior art, and provides a chemical enhanced shear thickening polishing liquid for WC-Co alloy with Co loss inhibition effect and a polishing method.

[0007] In order to achieve the above-mentioned purpose, the present application adopts the technical scheme as follows:

[0008] The present application provides a chemical enhanced shear thickening polishing liquid for WC-Co alloy, raw materials of which include K3[Fe(CN)6], KOH, diamond abrasive particles, dispersed phase particles and deionized water. 3- and OH - react to generate soft oxide film WO 3-x and stable Co3O4 oxide film, respectively, and through shear thickening, the generated oxide film is removed to realize efficient polishing of the surface of WC-Co alloy.

[0009] According to the above scheme, the mass ratio of K3[Fe(CN)6] to KOH is 1:1; the particle size of the diamond abrasive particles is #3000-#8000; the dispersed phase particles are selected from polyhydroxy polymers, the particle size of the dispersed phase particles is 5-30 microns, the polyhydroxy polymer is a micron-level material that is degradable and can stably form shear thickening effect of non-Newtonian fluid with deionized water; the content of K3[Fe(CN)6] is 0.25-1.25 wt.%, the content of diamond abrasive particles is 2-9 wt.%, the content of dispersed phase particles is 45-60 wt.%, and the balance is deionized water.

[0010] According to the above scheme, the preparation process of the chemical enhanced shear thickening polishing liquid for WC-Co alloy includes the following steps:

[0011] 1) adding deionized water and diamond abrasive particles into a batching cylinder;

[0012] 2) adding all KOH solids into the batching cylinder and stirring for 5-10 min until all KOH solids are completely dissolved and the diamond abrasive particles are uniformly dispersed in the solution;

[0013] 3) adding the same mass of K3[Fe(CN)6] solid particles into the batching cylinder and stirring for 5-10 min until complete dissolution;

[0014] 4) adding the dispersed phase particles in small amounts and multiple times into the batching cylinder and stirring for 5-10 min until uniform mixing.

[0015] The application also provides a polishing method using the chemical reinforced shear thickening polishing liquid suitable for WC-Co alloy, and a chemical reaction equation involved in the polishing method is as follows:

[0016] WC+OH - +[Fe(CN)6] 3- →WO 3-x +CO↑+[Fe(CN)6] 4- ;

[0017] 3Co+8[Fe(CN)6] 3- +8OH - →Co3O4+8[Fe(CN)6] 4- +4H2O;

[0018] wherein x=0-1 in the above chemical reaction equation.

[0019] The specific chemical reinforced shear thickening polishing principle is as follows: in the polishing process, the WC phase and the Co phase in the WC-Co alloy respectively react with [Fe(CN)6] 3- and OH - in the polishing liquid, and soft oxide films WO 3-x (x=0-1) and Co3O4 are respectively generated on the surface of the WC-Co alloy. The C atoms in the WC lattice are oxidized into CO gas, which causes the formation of bubbles and holes on the surface of the WC-Co alloy, increases the surface area, and accelerates the corrosion process until the WC phase surface is completely covered by the WO 3-x oxide film. The Co3O4 oxide film is relatively stable under alkaline conditions and is not easy to dissolve, so that the Co phase in the WC-Co alloy is preserved on the surface under the isolation of the Co3O4 oxide film. Since the WC phase has a higher reaction rate than the Co phase, the Co concentration on the surface of the WC-Co alloy after corrosion increases. The two kinds of oxide films generated subsequently inhibit the further progress of the reaction. When the relative speed of the polishing area of the polishing liquid and the WC-Co alloy workpiece reaches a threshold value, the polishing liquid produces shear thickening phenomenon, and a large number of particle clusters wrapping diamond abrasive grains are formed. The soft oxide film WO 3-x and the stable Co3O4 oxide film and the excess Co phase on the surface of the WC-Co alloy workpiece are removed by the micro-cutting action of the diamond abrasive grains in the particle clusters. When the oxide film and the excess Co phase are removed by the abrasive grains, the new matrix is exposed and participates in the new chemical reaction. Through the continuous balance between the generation of the oxide film and the shear thickening polishing of the oxide film, the ultra-precision surface processing of the WC-Co alloy workpiece is realized.

[0020] According to the above scheme, the polishing method comprises the following steps:

[0021] 1) configure the chemical enhanced shear thickening polishing solution of the applicable WC-Co alloy and add it to the polishing tank;

[0022] 2) install the WC-Co alloy workpiece on the workpiece shaft of the shear thickening polishing device;

[0023] 3) adjust the polishing position of the WC-Co alloy workpiece so that the WC-Co alloy workpiece is immersed in the polishing solution, and the angle between the WC-Co alloy workpiece and the horizontal line is 2-6°.

[0024] 4) start the device to rotate the workpiece shaft to drive the WC-Co alloy workpiece to rotate forward, while the polishing tank rotates in the opposite direction, and the polishing solution generates relative shear with the WC-Co alloy workpiece due to inertia, realizing efficient and high-quality polishing of the surface of the WC-Co alloy workpiece.

[0025] The beneficial effects of the present application are:

[0026] The present application introduces K3[Fe(CN)6] and KOH as core reaction components for the chemical enhanced shear thickening polishing solution of the applicable WC-Co alloy. Through synergistic effect, the system can precisely control the oxidation process of WC phase and Co phase, generating in-situ oxidation film (WO 3-x and Co3O4) on the alloy surface with excellent removability. During polishing, the oxidation film (WO 3-x and Co3O4) can be efficiently and selectively removed by the shear thickening polishing solution, realizing chemical mechanical polishing of the WC-Co alloy.

[0027] Especially crucially, the Co3O4 oxidation film exhibits excellent chemical stability in an alkaline environment, effectively preventing corrosion of corrosive media. This property enables the Co phase in the WC-Co alloy to be completely retained on the surface, significantly inhibiting the loss of Co element. Through this technical solution, not only high-precision polishing is realized, but also the mechanical properties of the WC-Co alloy are fundamentally guaranteed, providing an efficient and reliable solution for the ultra-precision machining of hard alloy workpieces. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of the polishing of the workpiece by the chemical enhanced shear thickening polishing solution of the applicable WC-Co alloy of the present application;

[0029] Figure 2 is a polishing principle diagram of the chemical enhanced shear thickening polishing solution of the applicable WC-Co alloy of the present application;

[0030] Figure 3 is a pure chemical corrosion principle diagram of the WC-Co alloy of the present application;

[0031] Figure 4is the surface morphology and roughness change diagram of WC-Co alloy workpiece after polishing by the polishing liquid of example 1 and comparative example 1-2;

[0032] Figure 5 is the SEM and EDS diagram of WC-Co alloy workpiece after polishing by the polishing liquid of example 1 and comparative example 1-2.

[0033] In the figure: 1-polishing tank; 2-workpiece shaft; 3-WC-Co alloy workpiece; 4-chemically enhanced shear thickening polishing liquid; 5-main drive shaft; 6-Co3O4 oxidation film; 7-diamond abrasive particles; 8-dispersed phase particles; 9-particle clusters; 10-WO 3-x oxidation film; 31-Co phase; 32-WC phase. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be further specifically described below through specific examples and comparative examples.

[0035] Example 1 (see Figures 1-3 )

[0036] This example is a chemically enhanced shear thickening polishing liquid suitable for WC-Co alloy, the diamond abrasive particles are selected as #5000, the dispersed phase particles are selected as polyhydroxy polymer with particle size of 5-30 microns, and the mass percentage of each raw material is shown in Table 1.

[0037] Table 1

[0038] Batch parameters Values Abrasive grain concentration 3 wt.% [K3[Fe(CN)6]] 0.5 wt.% KOH 0.5 wt.% Dispersed phase particles 53 wt.% Deionized water 43 wt.%

[0039] The preparation process of the chemically enhanced shear thickening polishing liquid suitable for WC-Co alloy described in this example includes the following steps:

[0040] 1) Add deionized water and diamond abrasive particles to the batching cylinder;

[0041] 2) Add all KOH solids to the batching cylinder and stir for 5-10 min until all KOH solids are completely dissolved and the diamond abrasive particles are uniformly dispersed in the solution;

[0042] 3) Add the same mass of K3[Fe(CN)6] solid particles to the batching cylinder and stir for 5-10 min until completely dissolved;

[0043] 4) Add the dispersed phase particles in small amounts and multiple times to the batching cylinder and stir for 5-10 min until mixed uniformly, and finally obtain the polishing liquid.

[0044] The polishing liquid of this example is used for polishing processing of WC-Co alloy workpiece, and the polishing parameters are shown in Table 2.

[0045] Table 2

[0046] Polishing parameters Values Workpiece shaft tilt angle 4° Polishing bath rotation speed 80 rpm Workpiece shaft rotation speed 15 rpm Polishing time 35 min

[0047] Specific workpiece polishing process as shown in Figure 1 The workpiece is a WC-Co alloy workpiece 3 composed of WC phase 32 and Co phase 31, and the shear thickening polishing device used in the process includes a polishing tank 1, a workpiece shaft 2, and a main drive shaft 5 arranged below the polishing tank 1 to drive the polishing tank 1 to rotate, and the workpiece shaft 2 is arranged inside the polishing tank 1. The detailed polishing process steps include:

[0048] 1) Configure the chemical enhanced shear thickening polishing liquid 4 suitable for WC-Co alloy as described in Example 1, and add it to the polishing tank 1;

[0049] 2) Install the WC-Co alloy workpiece 3 on the workpiece shaft 2 of the shear thickening polishing device;

[0050] 3) Adjust the polishing position of the WC-Co alloy workpiece so that the WC-Co alloy workpiece is immersed in the polishing liquid, and the included angle between the WC-Co alloy workpiece and the horizontal line is 4°.

[0051] 4) Start the device to rotate the workpiece shaft 2 to drive the WC-Co alloy workpiece 3 to rotate, at the same time, the polishing tank 1 rotates in the opposite direction, and the polishing liquid generates relative shear with the WC-Co alloy workpiece 3 due to inertia, realizing efficient and high-quality polishing of the surface of the WC-Co alloy workpiece 3.

[0052] Comparative Example 1

[0053] This comparative example is a shear thickening polishing liquid, diamond abrasive particles are selected as #5000, and the dispersing phase particles are selected as a polyhydroxy polymer with a particle size of 5-30 microns, and the mass percentages of each raw material are shown in Table Three.

[0054] Table Three

[0055] Batch parameters Values Abrasive grain concentration 3 wt.% Dispersed phase particles 53 wt.% Deionized water 44 wt.%

[0056] The preparation steps of this comparative example are basically the same, except that there is no addition step of KOH and K3[Fe(CN)6].

[0057] The polishing parameters and polishing steps of this comparative example are the same as those of Example 1, and are not described in detail here.

[0058] Comparative Example 2

[0059] This comparative example is a shear thickening polishing liquid based on Fenton reaction, diamond abrasive particles are selected as #5000, and the dispersing phase particles are selected as a polyhydroxy polymer with a particle size of 5-30 microns, and the mass percentages of each raw material are shown in Table Three.

[0060] Table 3

[0061] Batch parameters Values Abrasive grain concentration 3 wt.% FeSO4 0.6 wt.% H2O2 0.1 wt.% Dispersed phase particles 53 wt.% Deionized water 43.3 wt.%

[0062] The preparation steps for this comparative example include:

[0063] 1) Prepare Fenton's solution based on the above mass percentages of FeSO4 and H2O2;

[0064] 2) Add the remaining deionized water to the mixing tank, add the dispersed phase particles to the mixing tank in small amounts several times, and stir for 5-10 minutes until the mixture is uniform;

[0065] 3) Add the prepared Fenton solution to the mixing tank and stir for 5-10 minutes until it is evenly mixed;

[0066] 4) Finally, add diamond abrasive grains and stir evenly to obtain the polishing liquid.

[0067] The polishing parameters and polishing steps used in this comparative example are the same as those in Example 1, and will not be described in detail here.

[0068] like Figure 4 As shown, the surface roughness of WC-Co alloy workpieces treated with three different polishing slurries (Comparative Example 1: shear-thickening polishing slurry; Comparative Example 2: shear-thickening polishing slurry based on the Fenton reaction; Example 1: the polishing slurry of the present invention) exhibited significant differences. Example 1 demonstrated excellent polishing performance, with its surface roughness Sa value significantly reduced from the initial 306.73±25 nm to 2.36±0.16 nm, resulting in a lower surface roughness than existing methods (shear-thickening polishing and shear-thickening polishing based on the Fenton reaction). More notably, Example 1 showed a significantly improved polishing efficiency, reducing the surface roughness to below Sa10 nm in just 15 minutes while completely eliminating scratches.

[0069] Figure 5 SEM and EDS images revealed the effect of polishing on the microstructure of the WC-Co alloy surface. All workpieces exhibited a typical composite structure composed of WC particles and Co binder. However, in the workpiece treated with the Fenton reaction-based shear-thickening polishing slurry (Comparative Example 2), obvious voids were observed between WC particles, indicating that the surface Co metal was selectively removed. This phenomenon was further confirmed by the Co element distribution map (yellow area): the Co element distribution on the surface of the workpiece in Comparative Example 2 was significantly reduced.

[0070] The specific content changes of each element after polishing are shown in Table 4. The data in Table 4 shows that although the polishing method based on Fenton reaction can effectively reduce the surface roughness and eliminate scratches, it is accompanied by a significant Co loss problem. In contrast, the Co content of the workpiece treated by the polishing liquid (Example 1) of the present application is stably maintained at 11 wt.%, which is comparable to the workpiece treated by the shear thickening polishing liquid (Comparative Example 1), indicating that it effectively avoids the excessive loss of Co element while achieving efficient polishing.

[0071] Table 4 Element changes on the surface of WC-Co alloy workpiece after polishing

[0072] Elements Co (wt. %) W (wt. %) C (wt. %) Comparative Example 1 11.91 81.24 6.85 Comparative Example 2 0.23 92.60 7.17 Example 1 11.06 81.56 7.38

[0073] The above analysis results show that polishing WC-Co alloy with the polishing liquid of the present application can inhibit the loss of Co content on the surface of the workpiece while ensuring the polishing efficiency and quality. The surface quality requirements of WC-Co alloy material with high efficiency, high quality and no damage are achieved.

[0074] The above description is only the preferred embodiments of the present application, and any equivalent changes or modifications made to the structure, features and principles described in the scope of the present patent application are included in the scope of the present patent application.

Claims

1. A polishing method using a chemical enhanced shear thickening polishing liquid suitable for a WC-Co alloy, characterized by, The raw materials include K3[Fe(CN)6], KOH, diamond abrasive particles, dispersed phase particles and deionized water. The chemical reaction equation involved in the polishing method is: WC + OH - +[Fe(CN)6] 3- → WO 3-x + CO↑ + [Fe(CN)6] 4- ; 3Co+8[Fe(CN)6] 3- +8OH - →Co3O4+8[Fe(CN)6] 4- +4H2O; In the above chemical reaction equation, x=0-1.

2. The polishing method according to claim 1, characterized in that, the chemical enhanced shear thickening polishing liquid using a WC-Co alloy is applied. The mass ratio of K3[Fe(CN)6] to KOH is 1:

1.

3. The polishing method according to claim 1, characterized in that, the chemical enhanced shear thickening polishing liquid using a WC-Co alloy is applied. The particle size of the diamond abrasive particles is #3000-#8000.

4. The polishing method employing a chemical reinforced shear thickening polishing liquid using a WC-Co alloy according to claim 1, characterized in that, The dispersed phase particles are selected from polyhydroxy polymers.

5. The polishing method according to claim 2, characterized in that, the chemical enhanced shear thickening polishing liquid using a WC-Co alloy is applied. The K3[Fe(CN)6] is 0.25-1.25 wt.%, the diamond abrasive particles are 2-9 wt.%, the dispersed phase particles are 45-60 wt.%, and the balance is deionized water.

6. The polishing method employing a chemical reinforced shear thickening polishing liquid using a WC-Co alloy according to claim 1, characterized in that, The preparation process of the chemical enhanced shear thickening polishing liquid suitable for WC-Co alloy includes the following steps: 1) adding deionized water and diamond abrasive particles into a batching cylinder; 2) adding all KOH solids into the batching cylinder and stirring for 5-10 min until all KOH solids are completely dissolved and the diamond abrasive particles are uniformly dispersed in the solution; 3) adding K3[Fe(CN)6] solid particles of the same mass into the batching cylinder and stirring for 5-10 min until complete dissolution; 4) adding the dispersed phase particles in small amounts and multiple times into the batching cylinder and stirring for 5-10 min until uniform mixing.

7. The polishing method employing a chemical reinforced shear thickening polishing liquid of a suitable WC-Co alloy according to claim 1, characterized by, The process includes the following steps: 1) configuring the chemical enhanced shear thickening polishing liquid suitable for WC-Co alloy and adding it into a polishing tank; 2) mounting the WC-Co alloy workpiece on the workpiece shaft of the shear thickening polishing device; 3) adjusting the polishing position of the WC-Co alloy workpiece so that the WC-Co alloy workpiece is immersed in the polishing liquid and the included angle between the WC-Co alloy workpiece and the horizontal line is 2-6°; 4) starting the equipment to rotate the workpiece shaft to drive the WC-Co alloy workpiece to rotate forward, at the same time, the polishing tank rotates in the opposite direction, the polishing liquid generates relative shear with the WC-Co alloy workpiece due to inertia, and high-efficiency and high-quality polishing of the surface of the WC-Co alloy workpiece is realized.

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