Mechanical Polishing Technique Research Articles

Green chemical mechanical polishing of copper with 2,5-dihydroxy-1,4-dithianeas as the inhibitor: Experimental and theoretical studies

It is a great challenge to develop green chemical mechanical polishing (CMP) technique owing to the limited inhibitory performance of green inhibitors. In this study, 2,5-dihydroxy-1,4-dithiane (DHD) was found and utilized as a superior inhibitor in CMP slurry, which realized nanometer-scale smoothness for copper surface. The strong inhibition effect of DHD, in both static and dynamic situations, was demonstrated by microscopic observations and electrochemical characterizations. The effectiveness of DHD was achieved mainly through its chemisorption onto copper surface, determined by Langmuir adsorption isotherm. X-ray photoelectron spectroscopy and density-functional-theory calculations proved that the chemisorption occurred between the S atom of DHD and Cu. Overall, DHD as an efficient and eco-friendly inhibitor with low-cost exhibits immense potential for applications in chip fabrication, particularly at a low technology node.

Optimization and Mechanism of SiO2-Based Slurry Components for Atomically Smooth Gallium Nitride Surface Obtained Using Chemical Mechanical Polishing Technique

With the ongoing progress of mobile communication and new energy technologies, the market interest in high-frequency and high-power semiconductor devices has risen. Gallium nitride (GaN), a wide bandgap semiconductor material, has become a popular area of research in relevant fields. A sufficiently flat material surface can significantly enhance the device’s performance. Therefore, this paper explores the effect of oxidants on the quality of GaN surface during chemical mechanical polishing (CMP). Atomic force microscopy (AFM) was employed to examine the surface morphology of GaN after each CMP experiment. The aim was to evaluate the effect of specific slurry components on GaN surface quality. The results revealed that the introduction of oxidizers, particularly the potent oxidizer potassium persulfate (K2S2O8), was advantageous in reducing the surface roughness Sq and thus, enhancing the surface quality of GaN. The surface roughness (Sq) of GaN was reduced from 7.7 nm to 0.78 nm after the CMP process with the optimal components. AFM tests were conducted on different areas of the GaN surface within a range of 1 μm2, which revealed that clear images of the GaN atomic steps can be obtained, and the Sq can reach as low as 0.26 nm.

Nanoscale Surface Refinement of CoCrMo Alloy for Artificial Knee Joints via Chemical Mechanical Polishing.

In this study, we address the challenge of surface roughness in CoCrMo alloys, typically used in artificial knee joints, which can initiate a cascade of biological responses causing inflammation, osteolysis, joint instability, and increased susceptibility to infection. We propose the application of a chemical mechanical polishing (CMP) technique, using an ecologically responsible slurry composed of 4 wt% SiO2, 0.3 wt% H2O2, 1.0 wt% glycine, and 0.05 wt% benzotriazole. Our innovative approach demonstrated significant improvements, achieving a material removal rate of 30.9 nm/min and reducing the arithmetic mean roughness from 20.76 nm to 0.25 nm, thereby enhancing the nanoscale surface quality of the artificial knee joint alloy. The smoother surface is attributed to a decrease in corrosion potential to 0.18 V and a reduction in corrosion current density from 9.55 µA/cm2 to 4.49 µA/cm2 with the addition of BTA, evidenced by electrochemical tests. Furthermore, the preservation of the phase structure of the CoCrMo alloy, as confirmed by XRD analysis and elemental mapping, ensures the structural integrity of the treated surfaces. These outcomes and our simulation results demonstrate the effectiveness of our CMP method in engineering surface treatments for artificial knee joints to optimize friction behavior and potentially extend their lifespans.

Investigating surface wear characteristics of single-crystal SiC based on metal electrochemical corrosion

Aiming at the environmental pollution of the polishing solution in chemical mechanical polishing, this study introduces a chemical mechanical polishing technique for single-crystal SiC based on metal electrochemical corrosion. The wear properties of the SiC C-surface, as influenced by different materials on grinding balls (Cu, Fe, Al, and Al2O3), and different solutions (KCl, Na2SO4, Fenton, and H2O), were examined through wear experiments to elucidate the material removal mechanisms involved. The experiments demonstrated that the most significant wear marks, with a peak cross-sectional area of 46.89 μm2, were obtained when the C-face of SiC was ground with Al-paired grinding balls in an Na2SO4 electrolyte solution. Energy dispersive spectroscopy analysis of the wear debris revealed an O elemental content of 11 %, and X-ray photoelectron spectroscopy analysis indicated the existence of SiO2 and Al2O3 oxides. Subsequently, the effects of Na2SO4 solution concentration and pH on the wear pattern of the C-surface were investigated. The largest wear cross-sectional area (approximately 50 μm2) was observed when using an Na2SO4 electrolyte solution with a concentration of 1.25 mol/L at a pH of 9 in an alkaline solution. The proposed mechanism of material removal in single-crystal SiC via metal electrochemical corrosion involves the Al metal acting as a cathode. This causes galvanic coupling corrosion, generating a corrosion current, which subsequently induces oxidation of the SiO2 oxide layer on the anode SiC surface. The oxidized layer is then mechanically removed.

EFFECT OF SURFACE GLAZE TREATMENT AND MECHANICAL POLISHING ON THE COLOR STABILITY OF TWO TYPES OF CAD/CAM CERAMICS

The effect of immersion in a coffee drink solution on the color stability of two CAD/CAM ceramic restorations was investigated in this in vitro study. To this end, zirconia-reinforced lithium silicate (ZLS) and lithium disilicate (LDS) glass-ceramic blocks were surface-treated using mechanical polishing and glazing techniques. In addition, their color was examined before and after immersion in a coffee solution using a spectrophotometer, and the color changes were evaluated. A two-way analysis of variance (ANOVA) was used to examine the color changes. The material type significantly influenced color changes (P < 0.001). After glazing and mechanical polishing, LDS exhibited considerably less color change in both groups than ZLS. In both types of ceramics, the glazed group experienced less color variation than the mechanically polished group. Color changes were clinically acceptable across all groups. The glazing surface treatment produced superior color stability than the mechanical polishing technique. LDS exhibited more color stability than ZLS in both surface treatments.

Double-layered core–shell heterostructures of mSiO2@CdS@CeO2 abrasive systems toward photochemical mechanical polishing (PCMP) applications

Photochemical mechanical polishing (PCMP) technique, involved the cooperation of light-driven surface modification and force-induced material removal, is expected to be a clean, high-quality, and high-efficiency processing method. Herein, mSiO2@CdS@CeO2 hybrids with mesoporous cores and double-layered core–shell heterostructures were constructed through a three-step strategy and utilized as novel abrasive systems towards PCMP applications. Morphological, structural, and optical characterizations were systematically performed to investigate the correlation between components and polishing performances of the proposed abrasive systems. The created CdS–CeO2 heterojunction contributed to the efficient separation of photogenerated charge carriers and the production of highly reactive oxygen species, thus promoting the formation of photochemically reacted layers. The tribochemical activity and material removal enhancements might be attributed to the enrichments of trivalent cerium and oxygen vacancy in CeO2 layer after introducing CdS intermediate layer. Moreover, the involved mesoporous SiO2 cores were responsible for the optimized abrasive–wafer interface contacts and the eliminated surface damages. As expected, the proposed abrasive system enabled the nearly scratch-free and atomically planarized surfaces with angstrom-level finish (∼0.14 nm Ra, ∼0.18 nm Rq, ∼0.21 nm Rz), and simultaneously offered a ca. 63.8% of removal efficiency enhancement in PCMP compared to conventional CMP.

Thin ceramic PZT dual- and multi-frequency pMUT arrays for photoacoustic imaging

Miniaturized ultrasonic transducer arrays with multiple frequencies are key components in endoscopic photoacoustic imaging (PAI) systems to achieve high spatial resolution and large imaging depth for biomedical applications. In this article, we report on the development of ceramic thin-film PZT-based dual- and multi-frequency piezoelectric micromachined ultrasonic transducer (pMUT) arrays and the demonstration of their PAI applications. With chips sized 3.5 mm in length or 10 mm in diameter, square and ring-shaped pMUT arrays incorporating as many as 2520 pMUT elements and multiple frequencies ranging from 1 MHz to 8 MHz were developed for endoscopic PAI applications. Thin ceramic PZT with a thickness of 9 μm was obtained by wafer bonding and chemical mechanical polishing (CMP) techniques and employed as the piezoelectric layer of the pMUT arrays, whose piezoelectric constant d31 was measured to be as high as 140 pm/V. Benefiting from this high piezoelectric constant, the fabricated pMUT arrays exhibited high electromechanical coupling coefficients and large vibration displacements. In addition to electrical, mechanical, and acoustic characterization, PAI experiments with pencil leads embedded into an agar phantom were conducted with the fabricated dual- and multi-frequency pMUT arrays. Photoacoustic signals were successfully detected by pMUT elements with different frequencies and used to reconstruct single and fused photoacoustic images, which clearly demonstrated the advantages of using dual- and multi-frequency pMUT arrays to provide comprehensive photoacoustic images with high spatial resolution and large signal-to-noise ratio simultaneously.

Optimized chemical mechanical polishing of Parylene C for high-density wiring in flexible electronics

With the rapid development of flexible electronics, an increasing number of microfabrication strategies originating from the Si-based integrated circuits field have been explored on organic materials. Parylene C, a polymer, has been widely used in the microelectromechanical systems field because of its outstanding fabrication merits, such as room-temperature processability, conformal coating, and precise thin film deposition capability with the thickness tunable from 1 nm to 100 μm. As a good dielectric material, the Parylene C is also suitable for interlayer dielectrics in flexible electronics. This study develops an optimized chemical mechanical polishing (CMP) technique of Parylene C for high-density redistribution wiring in high-performance flexible electronics. The roughness of the Parylene C surface after CMP was as low as 14.3 ± 1.5 Å. The problems of slurry pollution and mechanical failure of the Parylene film that degrade the dielectric performance of the Parylene C could be avoided by taking the optimized CMP method. The multi-material structure constructed by Parylene C, Silicon and electroplated Copper was prepared and polished using the optimized CMP process. Additionally, a flexible wiring sample has been successfully patterned by the Damascene process through the optimized CMP process. In this sample, both the distance between each wire and the wire width were as small as 5 μm. The optimized Parylene C CMP process is easy-to-realize, highly efficient, low cost, and with minor defects; it provides a promising way to achieve high-density interconnection in high-performance flexible electronic devices.

Highest Quality and Repeatability for Single Wafer 150mm SiC CMP Designed for High Volume Manufacturing

Silicon Carbide (SiC) provides excellent characteristics such as superior thermal conductivity, high carrier mobility and extreme chemical stability in comparison with those of Silicon (Si). SiC is already showing significant device performance benefits in power devices, high performance communication, and LED lighting. However, SiC presents many challenges for wafer surface treatment because of its high hardness and remarkable chemical inertness. Today, mechanical polishing techniques on industrial batch CMP tools are the predominant methods for SiC wafer surface treatment, but material removal rate (MRR), surface defects and wafer flatness control are reaching fundamental limits with increasing wafer diameter. Batch processing typically results in a higher amount of surface scratches and defects, higher wafer to wafer variability, and higher wafer breakage rates. A unique single wafer chemical mechanical polishing (CMP) technique on 150mm n-doped, 4° off-axis, single crystal, 4H-SiC wafers was developed to create a virtually defect-free surface. A polishing head has been designed to manipulate polishing pressures at various zones of the wafer. This capability can modulate the removal thickness at each region on the wafer surface, resulting in a highly uniform wafer profile. Additionally, a CMP slurry has been formulated to maximize MRR from 2μm/hr to over 8.5μm/hr. Potassium permanganate has been selected as an oxidant and aluminum oxide particles as the abrasive. The oxidant concentration and abrasive content along with slurry pH level have also been optimized for ideal chemical and mechanical activity. Scratch-free wafer surfaces are observed with atomic force microscopy (AFM) and bright field (BF) and dark field (DF) inspection techniques. Roughness on the Si face is reduced to below 0.08nm. Total length of surface scratches was reduced to 10mm or less. Industrial metrics of wafer flatness, including total thickness variation (TTV) and local thickness variation (LTV) are modulated and improved. A test run completed on 25-wafers shows an overall 31% improvement of TTV post CMP process.

Simulation and experimental investigation of the surface morphology formation mechanism of a D-shaped fiber processed using a pulsed CO2 laser

Traditional D-shaped optical fibers are manufactured using mechanical polishing or chemical corrosion techniques, which inevitably introduce sub-surface defects or impurities. In this study, a new D-shaped optical fiber manufacturing method using CO2 laser ablation technology is proposed. Laser ablation technology is a complex multi-physical coupling process involving phase changes. To fully understand the surface morphology formation mechanism during CO2 pulsed laser processing, a three-dimensional numerical model and experimental analyses were used to elucidate the relationship between the fiber surface temperature distribution, surface morphology evolution, processing quality, processing efficiency, and laser parameters. The simulation results showed that the residual temperature between laser pulses was lower than the structural transition temperature of the material, and the simulated morphology was consistent with the experimental results. Moreover, the overlapping spot energy resulted in the processed surface exhibiting a periodic ripple structure. The ablation depth was proportional to the pulse width and inversely proportional to the scanning speed. In addition, different laser pulse widths had almost no effect on the roughness and flatness of the processed surface, but the laser scanning speed had a significant impact on both indexes. These results can guide the optimization of CO2 laser processing methods.

Review on the various strategies adopted for the polishing of silicon wafer — A chemical perspective

The need for sophisticated materials with outstanding mechanical capabilities and high-quality surface finishes has risen as a result of recent innovations in the engineering sector. Lapping, grinding, and honing are some of the traditional finishing procedures that are being phased out in favour of non-traditional finishing methods. MFAAF operations (magnetic-field assisted abrasive-based finishing) are precision material removal methods that have been used on a wide range of materials ranging from brittle to ductile and magnetic to nonmagnetic. The silicon wafer is the most important component in microelectromechanical systems. The surface and subsurface quality of these wafers affects their performance. In order to address the current spike in demand for microelectronics-based devices, efficient and cost-effective procedures for producing silicon wafers with high-quality surface finishes are essential. The current review describes the chemical perspective and study of silicon wafer polishing, utilizing procedures like chemical–mechanical polishing (CMP) and abrasive-based finishing techniques. Also, the operating principles, process parameters, and present limitations of such processes are discussed in this review paper, which subsequently includes a survey of relevant literature. Additionally, the potential advancements of such procedures are also highlighted.

GaN-Based Resonant-Cavity Light-Emitting Diodes Grown on Si.

GaN-on-Si resonant-cavity light-emitting diodes (RCLEDs) have been successfully fabricated through wafer bonding and Si substrate removal. By combining the chemical mechanical polishing technique, we obtained a roughness of about 0.24 nm for a scan area of 5 μm × 5 μm. The double-sided dielectric distributed Bragg reflectors could form a high-quality optical resonant cavity, and the cavity modes exhibited a linewidth of 1 nm at the peak wavelength of around 405 nm, corresponding to a quality factor of 405. High data transmission in free space with an opening in the eye diagram was exhibited at 150 Mbps, which is limited by the detection system. These results showed that GaN-based RCLEDs grown on Si are promising as a low-cost emitter for visible light communications in future.

Development of Dual-Frequency PMUT Arrays Based on Thin Ceramic PZT for Endoscopic Photoacoustic Imaging.

This paper presents a dual-frequency piezoelectric micromachined ultrasonic transducer (pMUT) array based on thin ceramic PZT for endoscopic photoacoustic imaging (PAI) applications. With a chip size of 7 × 7 mm2, the pMUT array consists of 256 elements, half of which have a lower resonant frequency of 1.2 MHz and the other half have a higher resonant frequency of 3.4 MHz. Ceramic PZT, with outstanding piezoelectric coefficients, has been successfully thinned down to a thickness of only 4 μ by using wafer bonding and chemical mechanical polishing (CMP) techniques and employed as the piezoelectric layer of the pMUT elements. The diaphragm diameters of the lower-frequency and higher-frequency elements are 220 μm and 120 μm, respectively. The design methodology, multiphysics modeling, fabrication process, and characterization of the pMUTs are presented in detail. The fabricated pMUT array has been fully characterized via electrical, mechanical, and acoustic measurements. The measured maximum responsivities of the lower- and higher- frequency elements reach 110 nm/V and 30 nm/V at their respective resonances. The measured cross-couplings of the lower-frequency elements and higher-frequency elements are about 9% and 5%, respectively. Furthermore, PAI experiments with pencil leads embedded into an agar phantom have been conducted, which clearly shows the advantages of using dual-frequency pMUT arrays to provide comprehensive photoacoustic images with high spatial resolution and large signal-to-noise ratio simultaneously.

Effects of Electrochemical Mechanical Polishing on the Polishing Efficiency and Quality of Co with H2O2 and BTA under Alkaline Conditions

With the development of technology nodes below 5 nm, cobalt has attracted extensive attention as an interconnection metal to replace Cu in the next generation of interconnection technology. Here, the appropriate concentrations of colloidal silica, H2O2, and BTA in the polishing solution were determined by static electrochemical measurement and electrochemical mechanical polishing technique. The results showed that the dynamic material removal rate of cobalt could be greatly improved after the addition of the selected solution. X-ray photoelectron spectroscopy was used to explore the reaction process and material generation in the polishing process. Co(Ⅱ)-BTA complex was found to be generated in the reaction process and adsorbed on the surface of cobalt, and it could be removed under a small mechanical force. Finally, the surface roughness of Co under different polishing time was measured by atomic force microscopy. The roughness of cobalt surface was Ra 1.35 nm polished for 10 min, and Ra was 0.418 nm after polishing for 120 min.

A study on the mechanical polishing technique by using shear thickening fluids

This paper reported the new polishing technique by using a shear thickening fluid (STF). In experiments, the steel workpiece was immersed into the STF under the static condition. When the workpiece started rotating at a certain speed, the surrounding STF became solidified due to the shear thickening effect. Consequently, the solidified STF held the abrasive particles and polished the surfaces of the workpiece. The surface roughness of the treated surfaces was clearly dependent on the size of the abrasive particles. Owing to the reversible phase transition between liquid and solid status for the STF, the polishing process can be conducted without the use of polishing pads. Moreover, the new polishing technique using the STF can polish some complex structures having the surfaces with different heights and/or orientations, which cannot be achieved by the traditional one-step polishing method.

Novel photoelectrochemically combined mechanical polishing technology for scratch-free 4H-SiC surface by using CeO2-TiO2 composite photocatalysts and PS/CeO2 core/shell abrasives

4H-SiC is a promising next-generation semiconductor. To obtain a scratch-free SiC surface with less/no residual oxide layer at an ideal material removal rate (MRR), a novel photoelectrochemically combined mechanical polishing (PECMP) technique was proposed. Polystyrene (PS)/CeO2 core/shell abrasives and CeO2-TiO2 composite photocatalysts immobilized on a titanium mesh were synthesized and characterized. The results of hydroxyl radical trapping tests present that the strongest photocatalytic activity is achieved by CeO2-TiO2 when UV-light and anodic bias are applied simultaneously (the optimal conditions). SiC-PECMP comparison tests were conducted in water containing 6.5 wt% PS/CeO2 on a home-made polisher, and after polishing, surface morphologies, surface roughness values (Ra) and MRRs were compared. The best polishing results (Ra: 0.738 nm, MRR: 1.109 μm/h) are realized under the optimal conditions. This was further demonstrated by another verification test, and a scratch-free surface (Ra: 0.113 nm) with less residual oxide layer was obtained. The scratch-free surface is attributed to the elastic core/shell abrasives and to the mild photocatalytic reaction. The ideal MRR is ascribed to the enhanced photocatalytic activity of the composite photocatalysts. Therefore, the feasibility of the proposed method is demonstrated, and this technique may be utilized to manufacture other semiconductors.

Single-Wafer Chemical Mechanical Planarization (CMP) on 150mm Silicon Carbide Substrate with Superior Surface Finish and Removal Efficiency

Silicon carbide (SiC) has excellent performances such as superior thermal conductivity, good carrier mobility and high chemical stability in comparison with those of silicon (Si). SiC has a great potential in the area of the next generation power controlling devices, high performance communication, and LED lighting. Chemical mechanical polishing (CMP) techniques combine mechanical polishing with a chemical etching action and can achieve truly defect-free surface with wafer flatness control capability, which is important for obtaining good epitaxial layer. However, Silicon carbide (SiC) presents many challenges for wafer surface treatment because of its high hardness and remarkable chemical inertness. Currently, low material removal rate (MRR) of CMP technique is a fundamental limit, it extends the CMP process time and effects the yield in mass production of substrate.In this study, we proposed an ultra-high MRR CMP process on 150mm n-doped, 4° off-axis, single crystal, 4H-SiC wafers. The process was developed at Applied Materials Mirra Durum® CMP configured with the membrane polishing head using an acidic slurry with strong potassium permanganate oxidant and thermoplastic polyurethane (TPU) pad. The effect of polishing process parameters (speed of the head and platen rotating, head sweeping distance and applied pressure) on MRR are analyzed in JMP® (SAS institute) while a design of experiments (DOE) is employed. The chemical composition of slurry, which is also critical to MRR, has also been evaluated via DOE. Potassium permanganate with certain concentration has been selected as oxidant and aluminum oxide micron particle has been used as abrasive. We have also conduct studies on the SiC wafer flatness control, which is proven to depend on structural design of polishing head. The head has been optimized to offer a flexible zone pressure control, therefore the impact on wafer flatness during the CMP process has also been minimized. In addition, accepted industry measurements of surface roughness, surface defect and wafer deformation are also taken into consideration.The successful development of CMP process provided an optimized MRR result, the reported MRR is 22.5 um/hr from C face and 6.4um/hr from Si face. The MRR have achieved highest level within literature and industry. The MRR results are analyzed by least–square modelling, which reveals that Prob >|t| is less than 0.05 for platen rotation speed and membrane pressure. Prediction profile demonstrates that MRR typically follows Preston’s law, which is a linear function of the platen speed and the pneumatic pressure applied to substrate. MRR is highly stable throughout a 2000-wafer repeat run with wafer-to-wafer uniformity of 2.4-3.7%. Scratch-free wafer surfaces are observed for the ultra-smooth wafers via atomic force microscopy (AFM) and defect inspection (Candela) tool. Roughness on Si face has been reduced from 2.0-2.5nm to less than 0.15nm with acceptable repeatability. Surface defects including scratches, pits have been greatly reduced. Total scratch length of 10mm has been achieved. Total thickness variation (TTV) is measured to characterize wafer flatness by Tropel tool, which indicates that the total amount of removed thickness on faces has a profound influence on TTV. With focused process control, post-CMP TTV can be improved by 0.6 ~2.1 um from pre-CMP TTV.

Real time detection of milk’s spoilage using Au/GO bend SMF sensor based on localized surface plasmon resonance effect

Potential of hybrid gold nanoparticles/Graphene Oxide (Au/GO) coated single mode fiber (SMF) sensor by exploiting localized surface plasmon resonance (LSPR) effect for detection of spoiled milk is studied. Various diameters of SMF’s cladding are prepared ranging from its original size, d=0.1250mm to d=0.1215mm. A mechanical polishing technique using sandpaper is applied to etch the cladding area in which results the SMF with diameter less than 0.1250mm. Hybrid layers of Au/GO are deposited onto the SMF via drop-casting technique by varies the number of layers of GO between one to five layers, meanwhile Au nanoparticles are kept constant at one layer. To generate LSPR, light with excitation wavelength of 1310nm and 1550nm are transmitted at the first end of Au/GO coated SMF resulting in strong scattering and extinction spectra. The fiber is bend about 8cm in diameter to produce evanescent waves around it. To investigate the sensitivity of sensor in detecting milk’s spoilage condition, the Au/GO bend SMF sensor is immersed into the milk’s solution which has been exposed to the environment for 24 hours, 48 hours and 72 hours. The maximum optical power response, ΔP%=6.85% is obtained when the one layer of Au/GO coated bend SMF had been immersed into the milk solution with exposure time of 24 hours. The values of ΔP% decrease about 3.50% and 2.00% respectively with the increment of exposure time at 48 hours and 72 hours. These results indicate the sensing ability of our proposed sensor to detect different levels of spoiled milk as the exposure time increased. The output of this study validates the main role of LSPR effect in enhancing the sensitivity of Au/GO bend SMF sensor for real time detection of milk’s spoilage.

Dry mechanical-electrochemical polishing of selective laser melted 316L stainless steel

This paper aims to improve the surface quality of 316L stainless steel parts manufactured by selective laser melting (SLM) using dry mechanical-electrochemical polishing (DMECP). DMECP is an advanced surface finishing method combining the advantages of both mechanical and electrochemical polishing techniques in a more environmentally friendly manner. In this paper, the SLM process-related defects causing poor surface quality are analysed first. The material removal mechanism of DMECP is investigated to continuously remove the oxide layers formed during polishing. Surface morphology and roughness evolution under different polishing conditions are characterised. The top surface roughness can be reduced by over 91% from 8.72 μm to 0.75 μm compared to side surface by over 93% from 12.10 to 0.80 μm. The material removal on the top surface is more efficient than that on the side surface under the same polishing condition. The secondary defects formed during polishing can be removed using mechanical polishing mode. The chemical element composition of the polished surface exhibits almost identical content to the initial 316L powders. Compared with the initial dark and rough surfaces, the results validate the capability of DMECP as an effective tool to improve the SLM surface quality and achieve a mirror finish.

Efficient Chemical Mechanical Polishing of AISI 52100 Bearing Steel with TiSol-NH4 Dispersion-Based Slurries

In this paper, chemical mechanical polishing technique was used to prepare an ultra-smooth surface of AISI 52100 steel. It was found that an unexpectedly high MRR of 500 nm/min and a satisfactory surface roughness Ra of 4.0 nm are achieved simultaneously by the synergistic effect of TiSol-NH4 dispersion and H2O2 at near neutral pH 6.0. During the polishing process, the organic base in TiSol-NH4 dispersion and H2O2 can be smoothly transported to the contact area along with uniformly dispersed titanium dioxide as nanocapsules, and then the chemicals for oxidation and complexation are provided to form a reaction film on the AISI 52100 steel surface, while abrasive nanoparticles provide sufficient mechanical force to abrade such a reaction film successively. With the addition of a small amount of H2O2, a porous composite layer composed of iron oxides and iron complex compounds with relatively low mechanical strength can be rapidly formed on the top surface. Therefore, the MRR first dramatically increases. When the H2O2 concentration crosses 0.1 wt% at the MRR summit and further increases, the layer gradually grows compact with high mechanical strength. Therefore, the MRR then gradually decreases. The findings can provide an efficient approach for processing bearing steels with excellent surface integrity.