Chemical mechanical polishing solution for 316L stainless steel

Abstract

The invention discloses a chemical mechanical polishing solution for 316L stainless steel. The chemical mechanical polishing solution comprises an abrasive, an oxidant, a surface modifier, a pH regulator, a stabilizer, a corrosion inhibitor and other solvents, the grinding material adopts 5-25 wt% of Al2O3, the oxidizing agent adopts 3-15 wt% of H2O2 and 0.02-0.2 M of KIO4, the surface modifier adopts 0.5-5 wt% of a silane coupling agent (KH-550) and 0.2-3 wt% of PVA (the molecular weight is 20000), the pH regulator adopts 0.05-0.15 M of aluminum nitrate and 1-3 wt% of citric acid, the stabilizer adopts 0.1-0.5 wt% of urea, the corrosion inhibitor adopts 1-2 wt% of sodium phytate and 1-3 wt% of sodium gluconate, and the other solvents adopt absolute ethyl alcohol and deionized water. Compared with the prior art, the method has the advantages that the sodium phytate, the gluconate and other biodegradable corrosion inhibitors and waste liquid CODlt are adopted; and the strain can be directly subjected to biochemical treatment, and is excellent in environmental protection property.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment, specifically a chemical mechanical polishing fluid for 316L stainless steel. Background Technology

[0002] Due to its excellent corrosion resistance and biocompatibility, 316L stainless steel is widely used in high-end fields such as medical, aerospace, marine engineering, and semiconductor processing. However, as the application of 316L stainless steel becomes more widespread, the requirements for it in some fields are becoming more stringent, which poses a more severe challenge to stainless steel polishing technology. Mechanical polishing can easily cause micro-cracks on the stainless steel surface, while traditional chemical polishing relies on highly corrosive, even highly toxic acids, such as hydrogen fluoride (HF).

[0003] Chemical mechanical polishing (CMP), as a highly efficient surface treatment method, can solve the above-mentioned problems. In the rough polishing of precision stainless steel workpieces (such as bearings and valves), efficient removal of turning / milling marks is a key requirement. However, the current industry mainly relies on mechanical polishing with high-hardness abrasives (such as alumina and silicon carbide), thus existing technologies face two major bottlenecks: First, there is a conflict between removal rate and surface quality: increasing the abrasive concentration can improve the removal rate, but it leads to a deterioration of surface roughness, while reducing the abrasive particle size can improve surface quality, but it causes a sharp drop in removal rate; second, alumina-based rough polishing solutions have inherent defects. Although existing alumina-based polishing solutions are inexpensive, when directly used on 316L stainless steel during CMP processing, abrasive embedding causes a 30% decrease in the workpiece's corrosion resistance.

[0004] Therefore, there is an urgent need to develop a high-efficiency, non-toxic special polishing fluid that minimizes abrasive residue on stainless steel surfaces. Summary of the Invention

[0005] The technical problem to be solved by this invention is to overcome the above-mentioned technical defects.

[0006] To solve the above problems, the technical solution of the present invention is: a chemical mechanical polishing fluid for 316L stainless steel, comprising abrasive, oxidant, surface modifier, pH adjuster, stabilizer, corrosion inhibitor and other solvents;

[0007] The abrasive is made of Al2O3 5~25 wt%, the oxidant is made of H2O2 3~15 wt%, KIO4 0.02~0.2M, the surface modifier is made of silane coupling agent (KH-550) 0.5~5 wt%, PVA (molecular weight 20000) 0.2~3 wt%, the pH adjuster is made of aluminum nitrate 0.05~0.15 M, citric acid 1~3 wt%, the stabilizer is made of urea 0.1~0.5 wt%, the corrosion inhibitor is made of sodium phytate 1~2 wt%, sodium gluconate 1~3 wt%, and other solvents are made of anhydrous ethanol and deionized water.

[0008] Furthermore, the alumina abrasive is selected with a particle size of 3~5 μm (70%) and 0.5~1 μm (30%), and a concentration of 5~25wt%, preferably 10%~20%. Within this range, the efficiency and cost are comparable, and 12%~18% can be further preferred, at which point the suspension of the abrasive is optimal.

[0009] Furthermore, the concentration of the oxidant H2O2 ranges from 3 to 15 wt%. Since a concentration greater than 10 wt% would make the polishing solution too oxidizing, resulting in poor surface quality of the stainless steel, while a concentration less than 5 wt% would lead to insufficient oxidation efficiency, the preferred concentration is 5 to 10 wt%, and more preferably 7 to 9 wt%. The concentration of KIO4 ranges from 0.02 to 0.2 M, preferably 0.05 to 0.1 M, and more preferably 0.06 to 0.08 M.

[0010] Furthermore, the initial concentration range of the surface modifier KH-550 is 0.5~5 wt%. A concentration less than 1% will result in incomplete coating, while a concentration greater than 2% will easily lead to agglomeration. Therefore, 1~2 wt% is preferred, with 1.2~1.8 wt% being more preferred. The initial concentration range of PVA is 0.2~3 wt%. A concentration less than 0.5% will lead to insufficient lubrication, while a concentration greater than 2% will result in excessively high viscosity. Therefore, 0.5~2 wt% is preferred, with 0.8~1.5 wt% being more preferred.

[0011] The advantages of this invention compared to existing technologies are:

[0012] The 316L stainless steel polishing slurry provided by this invention employs an H2O2-KIO4 dual oxidant system, significantly improving the efficiency of passivation film destruction, achieving a removal rate of 6-8 μm / min, more than 50% higher than traditional processes. Through the dual modification of Al2O3 abrasive with KH-550 silane coupling agent and PVA, a scratch-free mirror finish with a surface roughness Ra of 80-120 nm is achieved while maintaining high cutting force, with abrasive residue less than 0.1 at%. The product completely eliminates highly toxic substances such as hydrofluoric acid, using biodegradable corrosion inhibitors such as sodium phytate and gluconate. The waste liquid COD is <500 mg / L, allowing for direct biochemical treatment and excellent environmental performance. Furthermore, the addition of urea stabilizer reduces the H2O2 decomposition rate to below 10%, and combined with a recyclable abrasive design (recovery rate >85%), the overall cost is reduced by 30%, making it suitable for high-end fields such as medical devices and semiconductor equipment. Detailed Implementation

[0013] The specific implementation of the present invention will be further illustrated below with reference to the embodiments.

[0014] It should be noted that the terms “front,” “back,” “left,” “right,” “up,” and “down” used in the following description refer to directions in the embodiments, while the terms “inner” and “outer” refer to directions toward or away from the geometric center of a specific component, respectively.

[0015] To make the content of this invention easier to understand, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0016] [Example 1] Preparation of polishing slurry

[0017] Step 1: Surface modification of Al2O3 abrasive:

[0018] α-Al2O3 abrasive (3~5μm 70% + 0.5~1μm 30%) was dispersed in an ethanol-water mixed solution (volume ratio 3:1) with a solid-liquid ratio of 1:10.

[0019] Add KH-550 silane coupling agent (1.5% of the abrasive mass) and stir at 60°C for 2 hours.

[0020] Centrifugation was performed, followed by washing three times with deionized water and vacuum drying at 80°C to obtain KH-550 modified Al2O3.

[0021] Step 2: PVA-coated modified abrasive

[0022] The modified abrasive was added to an aqueous solution containing 1% PVA (molecular weight 20000) at a solid-liquid ratio of 1:20.

[0023] The Al2O3 was ultrasonically dispersed at 40℃ for 1 hour, filtered, and dried at 60℃ to obtain KH-550+PVA double-modified Al2O3.

[0024] Step 3: Preparation of polishing solution

[0025] (1) Add the following ingredients sequentially to the reactor:

[0026] Deionized water (60% of total mass);

[0027] Aluminum nitrate (0.1 M) and citric acid (2 wt%) were stirred until completely dissolved.

[0028] H2O2 (8 wt%), KIO4 (0.08 M), stir for 10 minutes in the dark;

[0029] Sodium phytate (1.5 wt%), sodium gluconate (2 wt%), urea (0.3 wt%).

[0030] (2) Slowly add double-modified Al2O3 abrasive (15 wt%), stir at 200 rpm for 30 minutes at 40℃ to obtain a uniform suspension.

[0031] (3) Adjust the pH to 3.0 with citric acid, and then filter (through a 100-mesh sieve) to obtain the polishing solution.

[0032] Step 4: Polishing process parameters

[0033] Temperature: 40±2℃;

[0034] Pressure: 30 kPa;

[0035] Polishing time: 20 minutes;

[0036] Workpiece: 316L stainless steel sheet (initial Ra value 1.2 μm).

[0037] In this embodiment, after the above steps, the 316L stainless steel is polished with the prepared polishing slurry under the corresponding polishing process parameters, and the polished stainless steel disc is tested. The test results are as follows: removal rate is 7.2 μm / min, surface roughness (Ra): 95 nm.

[0038] [Example 2] Comparison of Optimized Oxidant Concentration

[0039] With other components kept constant (15 wt% of double-modified Al2O3 abrasive, 0.08 M KIO4, 0.1 M aluminum nitrate, etc.), the concentration of one of the oxidants, H2O2, was adjusted (5%, 8%, 10%, 12%), and its effect on the removal rate and the surface quality after polishing was observed.

[0040] Table 1 shows the test results:

[0041] serial number <![CDATA[H2O2(wt%)]]> <![CDATA[KIO4(M)]]> Removal rate (μm / min) Ra (nm) 1 5 0.08 4.8 130 2 8 0.08 7.2 95 3 10 0.08 7.8 110 4 12 0.08 8.1 150

[0042] Conclusion: In the H2O2 concentration comparison experiment, it was found that when the H2O2 concentration was 8~10wt%, the removal rate and surface roughness reached the optimal balance (Ra<100 nm, rate>7 μm / min).

[0043] [Comparative Example 1] Performance Comparison of Single Oxidizing Agents (H2O2 Only)

[0044] With other components kept constant (15 wt% of double-modified Al2O3 abrasive, 0.1 M aluminum nitrate, etc.), KIO4 was not used. Other components were the same as in Example 2. The concentration of one of the oxidants, H2O2, was adjusted (5%, 8%, 10%, 12%), and the effect on the removal rate and the surface quality after polishing was observed.

[0045] Table 2 shows the test results:

[0046] serial number <![CDATA[H2O2(wt%)]]> <![CDATA[KIO4(M)]]> Removal rate (μm / min) Ra (nm) 1 5 0 2.1 200 2 8 0 3.5 180 3 10 0 4.0 210 4 12 0 4.3 250

[0047] in conclusion:

[0048] (1) Low oxidation rate: When only one oxidant H2O2 is added to the polishing solution, its removal rate is reduced by 47%~56% compared with Example 2 (H2O2+KIO4), which proves the necessity of KIO4 in this polishing solution to improve the oxidation rate.

[0049] (2) Poor surface quality: Ra value generally increases by 54%~91%, due to the lack of KIO4 to directionally destroy the Cr2O3 passivation film, resulting in an increase in the proportion of abrasive scratches.

[0050] [Example 3] Comparison of abrasive modification processes

[0051] Experimental Objective: To verify the effect of dual modification with silane coupling agent and PVA on improving the performance of Al2O3 abrasive. Sample Preparation:

[0052] Unmodified Al2O3 abrasive: Direct use of raw Al2O3 abrasive (3~5 μm);

[0053] KH-550 single modification: Al2O3 abrasive was dispersed in an ethanol-water solution (3:1) containing 1.5% KH-550, reacted at 60℃ for 2 hours, and then washed and dried;

[0054] KH-550+PVA double modification: Based on KH-550 modification, the abrasive is immersed in a 1% PVA aqueous solution, ultrasonicated at 40℃ for 1 hour, and then dried.

[0055] Performance testing:

[0056] Agglomeration rate: D50 change was detected by laser particle size analyzer;

[0057] Scratch depth: Measured on the polished surface using a white light interferometer;

[0058] Al residue: EDS surface scan analysis (accelerating voltage 15 kV).

[0059] Table 3 shows the test results:

[0060] serial number Abrasive type Family reunion rate (%) Scratch depth (nm) Al residue (at%) 1 <![CDATA[Unmodified Al2O3]]> 35 220 0.52 2 KH-550 Single Modification 8 120 0.15 3 KH-550+PVA dual modification 3 <50 0.07

[0061] in conclusion:

[0062] The agglomeration rate of the dual-modified abrasive was reduced by 91%, the scratch depth was reduced by 77%, and the residual Al content was only 13% of that of the unmodified abrasive.

[0063] The optimal amount of PVA to add is 1% to 2% (too low a level will result in insufficient lubrication, while too high a level will lead to increased viscosity).

[0064] In practical applications, this invention uses silane coupling agent (KH-550) and PVA to chemically and physically coat the abrasive. Through dual modification, a balance between high removal rate and low Ra is achieved. KH-550 contains amino groups and is therefore positively charged, while PVA has negatively charged hydroxyl groups. Therefore, the electrostatic adsorption of the two can enhance the stability of the coating.

[0065] This invention employs a dual-oxidant system, utilizing a synergistic oxidation mechanism. During polishing, H₂O₂ provides the basic oxidizing power, while KIO₄ generates the active IO₃⁻ under acidic conditions, jointly destroying the Cr₂O₃ passivation film of 316L stainless steel. This solves the problem of insufficient oxidation power caused by single oxidants in traditional polishing slurries. Simultaneously, KIO₄ replaces traditional oxidants KMnO₄ or NaClO, avoiding the risk of pitting corrosion caused by Cl⁻, and the complementarity of KIO₄ and H₂O₂ extends the lifespan of the polishing slurry.

[0066] This invention employs dual pH adjusters to achieve dynamic pH control. Aluminum nitrate can rapidly create an acidic environment (pH≈2.5) to activate the surface, while citric acid can buffer and maintain pH=3~4, preventing excessive corrosion from damaging the stainless steel surface. Simultaneously, the Al3+ ions from the addition of aluminum nitrate participate in the repair of the passivation film, and the addition of citric acid, replacing inorganic acids, enables biodegradability, making it environmentally friendly.

[0067] In this invention, urea is added as a hydrogen peroxide stabilizer. Through free radical capture, it inhibits the chain reaction of H2O2 decomposition into ·OH, significantly reducing the frequency of H2O2 replenishment and minimizing ineffective H2O2 loss. The addition of urea forms a hydrogen bond network with sodium phytate, enhancing the density of the protective film without affecting the oxidation activity of other components.

[0068] This invention employs a dual corrosion inhibitor system (sodium phytate + gluconate), in which sodium phytate can chelate Fe3+ / Cr3+ to form a passivation film, while gluconate is adsorbed onto active sites to block corrosion galvanic couples, thereby achieving multi-target site protection.

[0069] During the experiment, it was also found that the surface modification of alumina abrasives by silane coupling agent (KH-550) and PVA requires a specific order; they cannot be added simultaneously during preparation. In this experiment, KH-550 was first used for pretreatment of the alumina, followed by PVA post-treatment. Improper operation order can lead to poor modification of the abrasive and affect subsequent polishing results. Furthermore, concentration control is crucial. The recommended dosage of KH-550 is 1-2 wt%. Excessive dosage will result in excessive hydrophobicity of the abrasive surface, affecting PVA adsorption. The recommended dosage of PVA is 0.5-2 wt%. Excessive concentration will lead to excessive viscosity of the slurry, affecting its fluidity.

[0070] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual structure is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A chemical mechanical polishing slurry for 316L stainless steel, characterized in that: Including abrasives, oxidants, surface modifiers, pH adjusters, stabilizers, corrosion inhibitors, and other solvents; The abrasive is made of Al2O3 5~25 wt%, the oxidant is made of H2O2 3~15 wt%, KIO4 0.02~0.2 M, the surface modifier is made of silane coupling agent (KH-550) 0.5~5 wt%, PVA (molecular weight 20000) 0.2~3 wt%, the pH adjuster is made of aluminum nitrate 0.05~0.15 M, citric acid 1~3 wt%, the stabilizer is made of urea 0.1~0.5 wt%, the corrosion inhibitor is made of sodium phytate 1~2 wt%, sodium gluconate 1~3 wt%, and other solvents are made of anhydrous ethanol and deionized water.

2. The chemical mechanical polishing slurry for 316L stainless steel according to claim 1, characterized in that: The alumina abrasive is selected with a particle size of 3~5 μm (70%) and 0.5~1 μm (30%), and a concentration of 5~25 wt%, preferably 10%~20%. Within this range, the efficiency and cost are comparable, and 12%~18% can be further preferred, at which point the suspension of the abrasive is optimal.

3. The chemical mechanical polishing slurry for 316L stainless steel according to claim 1, characterized in that: The concentration of the oxidant H2O2 ranges from 3 to 15 wt%. Since a concentration greater than 10 wt% will make the polishing solution too oxidizing, resulting in poor surface quality of stainless steel, while a concentration less than 5 wt% will lead to insufficient oxidation efficiency, the preferred concentration is 5 to 10 wt%, and more preferably 7 to 9 wt%. The concentration of KIO4 ranges from 0.02 to 0.2 M, preferably 0.05 to 0.1 M, and more preferably 0.06 to 0.08 M.

4. The chemical mechanical polishing slurry for 316L stainless steel according to claim 1, characterized in that: The original concentration range of the surface modifier KH-550 is 0.5~5wt%. A concentration less than 1% will result in incomplete coating, while a concentration greater than 2% will easily lead to agglomeration. Therefore, 1~2wt% is preferred, with 1.2~1.8wt% being the most preferred. The original concentration range of PVA is 0.2~3wt%. A concentration less than 0.5% will lead to insufficient lubrication, while a concentration greater than 2% will result in excessively high viscosity. Therefore, 0.5~2wt% is preferred, and 0.8~1.5wt% is even more preferred.