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An ultra-smooth surface is required for mechanical components to improve the lubrication performance. In this study, the combination of 5-methyl-1H-benzotriazole (5-methyl-BTA) and thiazole (TA) was used as an effective composite corrosion inhibitor for chemical mechanical polishing of GCr15 bearing steel. The results reveal that, compared with the...
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High-speed grinding technology is being applied to the precision machining of 20CrMnTi steel gears, shafts and bearings suffering from fatigue damage. The response surface methodology (RSM) was used as an optimization method of high-speed grinding parameters to reach a higher anti-fatigue performance of 20CrMnTi steel workpieces. The mathematical f...
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... 6 In recent years, our research group has extendedly applied CMP to process steels. [7][8][9][10][11][12] Jiang et al. 8 investigated the effects of pH, the complexing agents such as glycine, H 2 O 2 , and benzotriazole (BTA) on the CMP performance of AISI 52100 steel (equivalent to GCr15 steel). With the slurry containing 4.0 wt% colloidal silica, 0.1 M glycine, 1.0 wt% H 2 O 2 , 10 mM BTA and at pH 4.0, the surface roughness R a could reach 1.8 nm. ...
... With 1.0 wt% H 2 O 2 and 20 mM 5-methyl-BTA, the surface roughness R a of GCr15 steel could reach 1.5 nm. Moreover, Liu et al. 11 found that combining 5 mM 5-methyl-BTA and 5 mM thiazole could further reduce the surface roughness R a of GCr15 steel to 0.8 nm. However, the material removal rate (MRR) seems low, only about 40 nm min −1 . ...
Excellent surface quality helps improve the tribological performance of gears. This study utilized chemical mechanical polishing (CMP) to process 18CrNiMo7-6 steel, a widely-used gear material. The results reveal that under the cooperative effect of oxidation and complexation, the material removal rate (MRR) can be significantly enhanced after adding K2SO4, while the surface roughness Sa nearly remains unaltered. In particular, with 1 wt% H2O2 and citrate, the MRR increases by 251% after adding 100 mM K2SO4, while the Sa slightly varies to 0.42 nm. No distinct surface defects are generated. For the mechanism, adding SO42- can promote iron corrosion and increase the amount of α-FeOOH. Citric acid can chelate α-FeOOH, forming complex compounds. The complex compounds and oxides form a relatively dense surface film, and thus the surface quality remains unchanged. In addition, the complex compounds may weaken the surface, and thereby the MRR increases. This study provides a simple approach for achieving high-efficiency CMP of steels.
... On this basis, Liu et al. [10] used 5-methyl-1H-benzotriazole as the corrosion inhibitor for GCr15 (equivalent to AISI 52,100) bearing steel CMP. The surface roughness S a of 1.5 nm could be achieved over the scan area of 97.9 μm × 97.9 μm, which can be attributed to the triazole and hydrophobic methyl functional groups of 5-methyl-1H-benzotriazole. Furthermore, Liu et al. [11] used the combination of 5-methyl-1H-benzotriazole and thiazole as corrosion inhibitors in a slurry with complex composition. With the synergistic corrosion inhibition effect, the surface roughness S a could be further reduced to 0.8 nm over the scan area of 97.9 μm × 97.9 μm. ...
9Cr18Mo stainless bearing steel is commonly used to manufacture rolling bearings in aerospace. Excellent surface quality is required to improve the service performance of bearings. In this study, chemical mechanical polishing (CMP) was employed. The results reveal that Cr has a significant impact on the CMP performance. The higher the Cr content, the lower the material removal rate (MRR). When polishing with the slurry containing the complexing agent glycine and the oxidant H2O2, the 9Cr18Mo steel surface is uneven, probably caused by unequal removal of Fe and Cr. A super-smooth 9Cr18Mo steel surface can be achieved by excluding glycine and adding 1 wt% H2O2. The surface roughness Sa is 0.63 nm, and no surface defects can be observed. During CMP, a uniform thin surface film mainly composed of evenly distributed iron oxides and chromium oxides can be formed. On the one hand, the iron oxides and chromium oxides can be removed simultaneously with a close MRR. On the other hand, the passive oxides can inhibit corrosion and protect recessed areas. Therefore, a super-smooth surface can be achieved. The findings provide an enhanced understanding of attaining a smooth surface for the material consisting of multiple chemical elements.
... Therefore, the MRR decreases. In addition, similar to the passivation film formed by corrosion inhibitors, 27,28 the PbSO 4 precipitates can protect the PZT-4 surface from dissolution and wear during the CMP process, especially the concave area. Hence, the surface roughness decreases. ...
Excellent surface quality of lead zirconate titanate (PZT) is required to achieve high performance in micro-electro-mechanical systems. In this work, PZT-4 (Pb(Zr 0.44 Ti 0.56 )O 3 ) was processed with chemical mechanical polishing (CMP). K 2 SO 4 was used to enhance the CMP efficiency. The results reveal that at pH 4 and 6, as the K 2 SO 4 concentration increases, the material removal rate (MRR) and surface roughness S a first increase, then decrease and stabilize. Interestingly, at pH 6, after adding only 55 ppm SO 4 ²⁻ , the MRR increases by 54%. After CMP, the surface becomes smooth. No visible processing damage occurs in the substrate. For the CMP mechanism, SO 4 ²⁻ in K 2 SO 4 plays an essential role in the MRR enhancement. At pH 6, PbO can dissolve, forming oxygen vacancies. After adding a low concentration of SO 4 ²⁻ , the negatively charged SO 4 ²⁻ ions can be attracted by the positively charged oxygen vacancies. Then soluble Zr(SO 4 ) 2 can be formed, promoting the dissolution of Zr ⁴⁺ . As a result, the surface integrity can be destroyed. Therefore, the MRR is improved. However, with a high concentration of SO 4 ²⁻ , the PbSO 4 precipitates can inhibit dissolution and wear. Hence, the MRR is suppressed. This research may provide a feasible approach for high-efficiency CMP of PZT.
... Therefore, the surface film may not be stably formed in the convex area due to frequent destruction by severe mechanical abrasion, whereas it may be gradually formed in the concave area [57]. As shown in Table 4, after adding additional 10 mM 1,2,4-triazole to 50 mM EDDS, the I corr decreases from 767 to 25 μA/cm 2 , indicating that a small amount of 1,2,4-triazole can effectively protect the GCr15 steel surface, especially the concave area, from corrosion and corrosive wear even when competing with EDDS [63,64]. With the protection of 1,2,4-triazole for the concave area, ideally, the surface film in the convex area is (8) nFe 2+ + 2n TAZH = Fe(TAZ) 2 n + 2n H + (9) nFe 3+ + 3n TAZH = Fe(TAZ) 3 n + 3n H + preferentially removed, thereby yielding a nanoscale planarization and a smooth surface. ...
Excellent surface quality can improve the noise-free and long-life performance of bearings. Chemical mechanical polishing (CMP) has been used to obtain smooth surfaces. However, some chemical additives in CMP slurries are not so eco-friendly. Therefore, in this study, eco-friendly chemical additives N,N′-1,2-ethanediylbis-1-aspartic acid (EDDS) and 1,2,4-triazole were used for GCr15 bearing steel CMP to satisfy the growing environmental awareness. At pH 5 and in synergy with 0.1 wt% H2O2, with the increasing EDDS concentration, the material removal rate (MRR) is improved. In the presence of 50 mM EDDS, as the 1,2,4-triazole concentration increases, the surface roughness Sa decreases. After adding 10 mM 1,2,4-triazole, a smooth GCr15 steel surface with 1.8 nm Sa is realized, and no processing damage occurs in the substrate. For the polishing mechanism, EDDS can form soluble Fe-EDDS complexes during CMP to weaken the surface film, resulting in a high MRR. The corrosion inhibition film formed by 1,2,4-triazole can suppress the corrosion and corrosive wear, leading to a low Sa. A two-step CMP method was developed for GCr15 steel. The Sa decreases from 287 to 1.8 nm after 16 min. The findings may open new avenues for developing eco-friendly CMP for bearing steels.
Graphical Abstract
... For 18CrNiMo7-6 steel, citric acid with an extra three carbon atoms in addition to carboxylic groups in synergy with H 2 O 2 can lead to a satisfactory CMP performance without obvious corrosion. To completely avoid corrosion, corrosion inhibitors can be further added [55,56]. Hopefully, the optimized slurries working with a small bonnet tool can be used for the numerical control of sub-aperture CMP of a real gear curve surface in the near future [57]. ...
Smooth surfaces are conducive to improving the lubrication of gears in mechanical systems. In this study, chemical mechanical polishing (CMP) was used to process 18CrNiMo7-6 case hardening steel, a typical material for gears. The results reveal that compared with formic acid and oxalic acid, citric acid can be used as a suitable complexing agent without causing apparent corrosion, probably due to the fact of its relatively stable adsorption. A synergistic effect exists between citric acid and H2O2. At pH 3, with 0.067 M citric acid and 1 wt% H2O2, a satisfactory CMP performance (i.e., a 514 nm/min material removal rate (MRR) and a 0.85 nm surface roughness Sa) was achieved. After polishing, no observable defects were found on the surface, and no discernible processing damage occurred to the substrate. In terms of the CMP’s mechanism, iron is first oxidized to Fe2+ and Fe3+, which then react with citric acid to form complexes. On the one hand, most of the complexes may stay on the surface to prevent further corrosion and, thus, the surface quality is excellent. On the other hand, the complexes may reduce the surface integrity and, thus, the MRR is high. The findings open new avenues for attaining ultra-smooth steel surfaces with CMP through controlling corrosive wear.
Oxidation is critical to metal chemical mechanical polishing (CMP). In this work, the role of oxidation in the material removal of GCr15 bearing steel during CMP was thoroughly investigated. Six representative oxidizers were selected to acquire the material removal rate (MRR) data. There are three distinct MRR trends. The oxidizers can be divided into three categories based on the MRR and surface composition results. For the first, with the concentration of H2O2 or KIO3 increasing, the MRR first sharply increases, then decreases and stabilizes; For the second, as the concentration of KClO3 or NaClO increases, the MRR first increases and then levels off; For the third, with the concentration of K2S2O8 or Fe(NO3)3 increasing, the MRR almost linearly increases. According to the reaction kinetics and steady state, a fundamental MRR model considering iron oxidation and removal processes was built, and then applied to the three categories of oxidizers combined with the specific oxidation paths. The fitting results agree with the MRR data. Moreover, the key to realizing efficient removal of GCr15 steel is Fe²⁺ for H2O2, KIO3, KClO3 and NaClO, while Fe3O4 for K2S2O8 and Fe(NO3)3. The findings can deepen the understanding of oxidation in metal CMP.
Lead zirconate titanate (PZT) has been widely used in microelectromechanical systems and ferroelectric memory, and a high-quality PZT surface is important to the device performance. In this study, chemical mechanical polishing (CMP) was introduced to process PZT-4 (Pb(Zr0.44Ti0.56)O3). A complexing agent ethylenediamine dihydrochloride (EDA·2HCl) was used as a crucial chemical additive in slurries to improve the CMP performance of PZT-4 because it may chelate metal ions of PZT-4, such as Ti⁴⁺. The results show that the material removal rate (MRR) of PZT-4 decreases and the surface roughness Sa increases as pH increases. At pH 4.0, with the EDA·2HCl concentration increasing, the MRR first increases, reaches the summit of 498 nm/min at 0.75 mM, and then decreases and levels off. The Sa has a similar trend. With 50 mM EDA·2HCl, the Sa reaches the minimum value of 3.5 nm, and no processing damage occurs in the substrate. For the removal mechanism, EDA can be adsorbed on PZT-4 probably via forming complex with Ti⁴⁺. With a low content of EDA·2HCl, the adsorbates of EDA distribute discretely and can be removed easily, and thus the MRR is high. As the content of EDA·2HCl increases, a relatively continuous and uniform film is formed to suppress dissolution and abrasion, and thus the MRR decreases. A two-step CMP process was developed, and a smooth PZT surface can be rapidly achieved. This study provides mechanistic insight of the role of EDA in the CMP of PZT-4, and may open new avenues of developing CMP slurries for achieving smooth surfaces of PZT materials via screening prospective complexing agents.
