Alumina Abrasives Research Articles

High-efficiency green machining of single crystal 4H–SiC based on tribo-oxidation

High efficiency, high quality and green machining of single crystal silicon carbide (SiC) is an important issue in the third-generation semiconductor industry. In this paper, a novel machining method for single crystal SiC based on tribo-oxidation is proposed. The formula and preparation process of polysaccharide bonded soft abrasive tool were designed. Dry machining of C-face of 4H–SiC substrate was carried out with the prepared environmentally friendly abrasive tool sample. The material removal mechanism of the proposed machining method was preliminarily analyzed, and the material removal rate, surface roughness and subsurface residual stress were studied. The experimental results show that the maximum material removal rate of 4H–SiC can reach 1.03 μm/min with a corresponding average surface roughness of Sa 0.816 nm. The machined surface has no brittle flaw, and subsurface residual compressive stress exists with a maximum value of 58.9 MPa. The material removal mainly attributed to the active oxidation of SiC surface induced by the friction between alumina abrasives and SiC substrate. The proposed machining method has potential application value in thinning of SiC wafers.

A novel approach of jet polishing for interior surface of small-grooved components using three developed setups

It is a challenge to polish the interior surface of an additively manufactured component with complex structures and groove sizes less than 1 mm. Traditional polishing methods are disabled to polish the component, meanwhile keeping the structure intact. To overcome this challenge, small-grooved components made of aluminum alloy with sizes less than 1 mm were fabricated by a custom-made printer. A novel approach to multi-phase jet (MPJ) polishing is proposed, utilizing a self-developed polisher that incorporates solid, liquid, and gas phases. In contrast, abrasive air jet (AAJ) polishing is recommended, employing a customized polisher that combines solid and gas phases. After jet polishing, surface roughness (Sa) on the interior surface of grooves decreases from pristine 8.596 μm to 0.701 μm and 0.336 μm via AAJ polishing and MPJ polishing, respectively, and Sa reduces 92% and 96%, correspondingly. Furthermore, a formula defining the relationship between linear energy density and unit defect volume has been developed. The optimized parameters in additive manufacturing are that linear energy density varies from 0.135 J mm−1 to 0.22 J mm−1. The unit area defect volume achieved via the optimized parameters decreases to 1/12 of that achieved via non-optimized ones. Computational fluid dynamics simulation results reveal that material is removed by shear stress, and the alumina abrasives experience multiple collisions with the defects on the heat pipe groove, resulting in uniform material removal. This is in good agreement with the experimental results. The novel proposed setups, approach, and findings provide new insights into manufacturing complex-structured components, polishing the small-grooved structure, and keeping it unbroken.

Insight into Polishing Slurry and Material Removal Mechanism of Photoassisted Chemical Mechanical Polishing of YAG Crystals.

Yttrium aluminum garnet (YAG) crystals are an important gain medium in thin-sheet solid-state lasers, and their processing quality directly affects the performance of solid-state lasers. But it is difficult to achieve high efficiency and high quality of YAG crystals by traditional chemical mechanical polishing (CMP). In this study, we developed a new polishing slurry for photoassisted chemical mechanical polishing (PCMP) of YAG crystals. The polishing slurry is composed of peroxymonosulfate (PMS), manganese ferrite (MnFe2O4), alumina (Al2O3) abrasives, and deionized water. PCMP is conducted in an ultraviolet (UV) light environment. When employing this polishing slurry for PCMP processing of YAG crystals, the material removal rate (MRR) achieved 250 nm/min and the surface roughness achieved 0.35 nm Sa. The experiments verified that both UV light and MnFe2O4 can effectively activate PMS to produce active free radicals and further enhance the chemical action of the polishing slurry. X-ray photoelectron spectroscopy (XPS) analysis results indicated that active radicals reacted with the surface structure of the crystal and removed the aluminum-oxygen octahedron in large quantities from it. The structural defects reduced the surface hardness of the crystal, which means that active free radicals can modify the crystal surface materials.

Abrasive water flow polishing of superalloy microholes drilled by electrical discharge machining

Superalloy microholes resulting from electrical discharge drilling (EDD) can have recast layers and microcracks on the machined surfaces. In this study, the abrasive water flow polishing (AWFP) of superalloy microholes machined by EDD was investigated. The recast layer and surface roughness resulting from the EDD process were evaluated through orthogonal experiments. The machining mechanism of AWFP was analyzed. The effects of AWFP parameters were investigated experimentally. The results show that the material removal rate and surface roughness at the hole exit were better than those at the entrance for one-directional fluid flow during the process. Garnet abrasives achieved better polished roughness and a lower material removal rate than alumina abrasives. The taper angle of the target holes changed slightly from positive to negative after AWFP. The corner edge was slightly rounded on the fluid inlet side. Using a bidirectional fluid resulted in better dimensional uniformity and surface roughness at the entrance and exit. This study verified that AWFP can remove the recast layer and microcracks on the hole wall caused by EDD and reduce the surface roughness from an initial Ra of 5.7 μm to an Ra of 0.6 μm.

Influence of abrasive characteristics on the wear micro-mechanisms of NbC and WC cermets during three-body abrasion

The present study has developed new insights into the wear transition mode of cermets and provides a better understanding of the role of abrasive characteristics in three-body abrasive wear. Two sintered and fully densified cermets, NbC–Ni (NbC–12Ni–10Mo2C) and WC-Co (WC-9.5Co) with similar micro-hardness (HV30 ≈ 13.5 GPa) were selected in this study. The abrasion response of cermets against different abrasive characteristics namely size (67–245 μm), hardness (silica, alumina and SiC), and shape (round and angular) was experimentally investigated according to the ASTM G65 standard. The test results showed that the specific wear rate (SWR) of the cermets increased significantly with increasing abrasive size and hardness. The size effect shows that the dominant wear micro-mechanisms shift from binder removal (rolling) to mixed binder-carbide extrusion (sliding) as the abrasives particle size changes from smaller (67 μm) to larger (245 μm). The hardness ratio between the abrasives and cermets (Ha/Hs) highlights that silica and alumina abrasives provide mild wear (Ha/Hs < 1.5), while SiC abrasives cause severe wear (Ha/Hs > 1.5). Both cermets exhibited similar SWR during mild wear, but NbC–Ni showed 7 times higher SWR than WC-Co during severe wear. The abrasives shape effect does not show a significant difference on the wear rate of the cermets.

Relevant Aspects of Titanium Topography for Osteoblastic Adhesion and Inhibition of Bacterial Colonization.

The influence of the surface topography of dental implants has been studied to optimize titanium surfaces in order to improve osseointegration. Different techniques can be used to obtain rough titanium, however, their effect on wettability, surface energy, as well as bacterial and cell adhesion and differentiation has not been studied deeply. Two-hundred disks made of grade 4 titanium were subjected to different treatments: machined titanium (MACH), acid-attacked titanium (AE), titanium sprayed with abrasive alumina particles under pressure (GBLAST), and titanium that has been treated with GBLAST and then subjected to AE (GBLAST + AE). The roughness of the different treatments was determined by confocal microscopy, and the wettability was determined by the sessile drop technique; then, the surface energy of each treatment was calculated. Osteoblast-like cells (SaOs-2) were cultured, and alkaline phosphatase was determined using a colorimetric test. Likewise, bacterial strains S. gordonii, S. oralis, A. viscosus, and E. faecalis were cultured, and proliferation on the different surfaces was determined. It could be observed that the roughness of the GBLAST and GBLAS + AE was higher, at 1.99 and 2.13 μm of Ra, with respect to the AE and MACH samples, which were 0.35 and 0.20 μm, respectively. The abrasive treated surfaces showed lower hydrophilicity but lower surface energy. Significant differences could be seen at 21 days between SaOS-2 osteoblastic cell adhesion for the blasted ones and higher osteocalcin levels. However, no significant differences in terms of bacterial proliferation were observed between the four surfaces studied, demonstrating the insensitivity of bacteria to topography. These results may help in the search for the best topographies for osteoblast behavior and for the inhibition of bacterial colonization.

Influence of Surface Roughness of Aluminum Alloy Substrate on Tensile Adhesive Strength of Plasma-Sprayed Yttria-Stabilized Zirconia Coatings

The adhesive mechanism of thermal sprayed ceramic coating is not clear because of the complicated profile of the blasted surface and the microstructure of the coating. In particular, little research has been carried out on the adhesive mechanism on light metal substrates. The objective of this study was to investigate the effect of surface roughness on the adhesive strength of yttria-stabilized zirconia coatings applied by atmospheric plasma spraying on an aluminum alloy (JIS A5052) substrate. Tensile adhesive and interfacial indentation tests were performed to evaluate their bonding properties. The substrates were blasted at three different pressures and seven different blast angles using fused alumina abrasives of three different particle sizes. Our measurements revealed that the tensile adhesive strength decreased with increasing substrate roughness (root mean square slope, RΔq). After the tensile strength tests, the fracture surfaces were observed using an FE-EPMA analyzer and analyzed using an X-ray fluorescence analyzer. It was found from elemental analysis that the fractured part shifted to the substrate with increasing RΔq. It was concluded that the tensile adhesive strength decreased with increasing surface roughness owing to the low strength of the substrate.

The Performance of Mechanically Refined Fused Alumina Abrasive Grits Compared to Diamond

The Performance of Mechanically Refined Fused Alumina Abrasive Grits Compared to Diamond

Modeling and Simulation Study of Dry Ultrasonic Vibration-Assisted Grinding of Tool Steel With Single Alumina Abrasive Grit

Abstract In the precision fabrication industries, ultrasonic vibration-assisted grinding is widely utilized for the finishing of “difficult-to-cut” materials due to its intermittent cutting mechanism and brittle-to-ductile mode machining. In this study, a two-dimensional finite element model (FEM) of single grit ultrasonic vibration-assisted dry grinding (UVADG) and conventional dry grinding (CDG) of AISI D2 steel has been developed, which taken into account the influence of longitudinal ultrasonic vibration on the workpiece with variable downfeed. The effects of ultrasonic vibration and downfeed on the chip formation mechanism, temperature field, grinding force, and equivalent stress and strain were evaluated by analytical and simulation methods. The results show that the formation of the grinding chips under UVADG is much shorter and straighter than CDG mode at all respective downfeed. The validation experiment compared the simulated and experimental grinding force in both grinding modes to verify the reliability of the FEM results. The validation results demonstrate that the FEM model can accurately describe the single grit UVADG and CDG grinding. At each downfeed, the CDG mode has generated a larger equivalent plastic strain than the UVADG mode, resulting in a higher thermomechanical load on the workpiece. According to the findings, UVADG mode has the least plastic damage on the ground surface, which may improve the surface integrity of the ground component.

Preparation of Al2O3 magnetic abrasives by combining plasma molten metal powder with sprayed abrasive powder

Magnetic abrasives play a significant role in finishing processes; however, existing magnetic abrasive particles have limited their application in industry due to poor grinding performance and low service life. In this paper, high-performance iron-based spherical Al2O3 magnetic abrasives were prepared via combining plasma molten metal powder with sprayed abrasive power. Firstly, the effects of the co-gas flow rate and current on the overall melting state of the iron matrix powder were studied to obtain the suitable process parameters; then, the magnetic abrasives were prepared by increasing the hydrogen flow rate by 25% under this process parameter, and the microscopic morphology, phase composition, bonding mode, magnetic permeability and particle size distribution of the magnetic abrasives were analyzed; finally, the grinding experiments were conducted on 316 L stainless steel. The results show that the overall fusion state of the iron matrix powder is good under the parameters of current 700 A, argon flow rate 1000 L/h and hydrogen flow rate 80 L/h. The magnetic abrasives have a very high sphericity, and the alumina abrasives with sharp cutting edges are uniformly and compactly embedded into the iron matrix and form a tight mechanical bond with it; the particle size distribution of the magnetic abrasives accounts for 85% of the iron matrix; the magnetic abrasives have excellent grinding performance. The magnetic abrasives preparation approach described in this paper has the characteristics of economy and high performance, and is expected to be used for industrial mass production.

Tribological effects of loose alumina abrasive assisted sapphire lapping by a fixed agglomerated diamond abrasive pad (FADAP)

The tribological effects between a fixed abrasive pad (FAP) and a workpiece can effectively maintain the self-conditioning process of the FAP in real time. However, the FAP is easy to be glazed along with the long-term lapping processes of hard-to-process ceramic materials. This paper proposed a novel method of loose abrasive assisted fixed agglomerated diamond abrasive lapping (LA-FADAL) to achieve efficient and stable lapping processes of sapphire. LA-FADAL tests with a fixed agglomerated diamond abrasive pad (FADAP) were carried out by changing the particle size and volume fraction of loose alumina abrasives in lapping slurries. The influences of the different alumina abrasives on the processing performance of the FADAP were discussed. Material removal mechanisms in the LA-FADAL processes were proposed based on the tribological effects of loose alumina abrasive assisted sapphire lapping by the FADAP. The loose alumina abrasives with the similar size as the diamond grains embed in the surface of the fixed AD abrasive could not remove sapphire materials directly and effectively by mechanical actions, mainly played a role of dressing the FADAP to enhanced the self-sharpening ability of AD abrasives, and further improved the self-conditioning ability of FADAPs.

Influence of holding time on the interfacial solid solution and mechanical properties of agglomerated white fused alumina abrasives

In this paper, the aging relationship between holding time and the interfacial solid solution was utilized to prepare high-performance agglomerated white fused alumina (AWA) abrasives. The influence of holding time on the interfacial solid solution and mechanical properties of AWA abrasives were systematically investigated, and the grinding performance was thoroughly analyzed. The results showed that increasing the holding time caused the Al2O3 to violently infiltrate the interface between the white fused alumina (WA) particles and the vitrified bond, which led to the precipitation of a large amount of β-spodumene and monoclinic celsian in the vitrified bond and transformed the simple mechanical bonds between the WA particles and the vitrified bond into stronger chemical bonds. Thus, it was possible to control the mechanical properties of the AWA abrasives by adjusting the holding time. Specifically, after sintering at 760 °C for 4h, the single particle compressive strength and impact toughness reached the maximum values of 26 N and 63%, respectively. In comparison with the WA grinding wheel, the grinding ratio of the AWA grinding wheel was increased by 17.9% and the workpiece surface roughness was reduced by 21.1%.

Design of a CBN composite abrasive to improve the performance of HSG rail maintenance grinding wheel

A heavy-load resin grinding wheel with zirconia alumina abrasives plays a vital role in rail high-speed grinding (HSG) maintenance. However, the grinding wheel has the defect of short service life. Abrasives are the central performers in the cutting behavior of grinding wheels. A cubic boron nitride (CBN) composite abrasive was developed to enhance the performance of grinding wheels. The results showed composite abrasives bonded more tightly with the resin matrix, strengthening the structure of the wheel. The grinding efficiency and ratio of the composite grinding wheel were improved by 99.8% and 102% respectively, and the rail morphology was optimized.

Electrostatic Self-Assembled Composite Abrasives for Chemical Mechanical Polishing of A-Plane Sapphire

Sapphire substrates with different orientations have wide applications due to their excellent physical, chemical and optical properties. However, the chemical mechanical polishing of sapphire is challenging due to its chemical inertness, extreme hardness and brittleness. Herein, chemical mechanical polishing of A- and C-plane sapphire was systematically studied using α-Al2O3 and silica abrasives and polishing mechanism was analyzed by X-ray photoemission spectroscopy (XPS) and nanoindentation meter. The high MRR selectivity for C-plane sapphire in α-Al2O3 slurry is the synergy of selective hydration of C-plane and stronger crystal structure of A-plane. The low MRR selectivity for C-plane sapphire in silica slurry can be attributed to the formation of Al2SiO5 on both planes which reduced the impact of strong mechanical effect of α-Al2O3 abrasives. To improve the MRR of A-plane sapphire, a new nanocomposite particle with alumina as the core and silica as the soft shell was prepared by an electrostatic self-assembly method. The new composite abrasives combined the mechanical effect of α-Al2O3 abrasives and chemical effect of silica abrasives and demonstrated substantially higher MRR for A-plane sapphire than pure alumina abrasives, pure silica abrasives and physical mixture of alumina+silica abrasives.

Particle Size Effects on Abrasion, Surface Polishing and Stain Removal Efficacy in a Tooth Model System

Four calcined alumina abrasive particles [ultrafine (0.05 μm), 3 μm, 9 μm and 20 μm] with defined sizes were investigated for their effects on toothbrush abrasion, surface polishing and stain removal in vitro. The existence of a critical particle size (CPS) was shown for the first time in a tooth model system and in the present study a CPS of ~2.3 μm for d10, 4.3 μm for d50 or 7.8 μm for d90 for the calcined alumina abrasives was apparent. The d10, d50 and d90 values indicate that 10%, 50% and 90% of the particles measured were less than or equal to the size stated. This dimension enabled maximum abrasive action on the tested specimens resulting in the largest wear depth, greatest surface polishing and best stain removal. The enamel wear depth decreased when brushed with abrasives above the critical particle size and became almost independent of further particle size increases, which is useful for minimising wear effects in the development of dentifrice. The findings provide new information on abrasive particle size for modification and control of toothpaste abrasivity and cleaning.

Optical and strong blue emission properties of alumina abrasive grains mediated grinding induced SiO2 glass surfaces for navigation grade sensors

We report, fused silica samples have been processed with various grit sizes (3, 5, 12 and 25 μm) of Aluminium oxide (Al2O3) abrasives. Aluminium oxide has a significant effect on the vibrational and optical properties of the silica glass. The prepared samples were characterized through UV–Vis spectroscopy, Photoluminescence spectroscopy and Raman spectroscopic technique to understand the effect of aluminium oxide powders with different grit size on the silica glass. The transmittance spectra of all the fused silica samples excellent transmission at far infrared and visible region up to approximately 2750 nm. The steady-state photoluminescence (PL) measurement of all the samples was performed under excitation wavelength of 300 nm at room temperature which shows the maximum emission peak at 430 nm. The typical Raman spectra for all the samples were recorded at 532 nm excitation at room temperature to study the Alumina abrasive induced vibrational properties.

Synthesis and characterization of the rheological behavior of MR fluid for polishing silicon wafer using double-disc chemical-assisted magneto-rheological finishing process

Double-disc chemical-assisted magneto-rheological finishing (DDCAMRF) process is a successfully developed precision material removal process that has been applied to the polishing of brittle materials viz. monocrystalline silicon wafer. The mechanism of silicon polishing using the DDCAMRF process depends mainly on the magneto-rheological (MR) fluid, which behaves as a multi-point finishing tool. The MR fluid synthesized in the present work comprised of carbonyl iron powder, alumina abrasives, deionized water, and glycerol as the base fluid. The application of a magnetic field in the prepared MR fluid samples significantly affects its rheological properties, which in turn affects the quality of finished wafer surface. Therefore, the rheological, as well as magnetic properties of prepared MR fluid samples need to be studied in detail. The flow behavior of MR fluid is affected by the applied magnetic field, which therefore exhibits transition from Bingham-fluid like structure to gel-like structure. To characterize MR fluid's magnetic behavior, the M−B curve of the prepared MR fluid samples was plotted to determine the saturation magnetization using the data obtained from vibrating sample magnetometer (VSM). Rheological properties like viscosity and yield stress of the prepared MR fluid were measured by using the parallel-plate rheometer. The obtained rheological data from the rheometer was fitted using the defined constitutive equations of respective fluid models, viz. Bingham-Plastic (BP), Herschel-Bulkley (HB), and Casson’s (CS), respectively. The experimental results were analyzed, and the effect of increase in temperature on viscosity and yield stress was also discussed.

Mechanical and sandblasting erosion resistance characterization of chemical strengthened float glass

The purpose of this work is to study the influence of the immersion temperature and the treatment time of the ion exchange of soda-lime glass in molten KNO3 bath on its mechanical properties, and in particular the erosion resistance using Sahara sand and alumina abrasives. EDS analysis showed that the depth of penetration of K+ into glass increases as temperature and treatment time increase. The effect of ion exchange temperature and time on mechanical reinforcement was studied by micro-indentation, scratch test, wear and erosion test. All of these mechanical properties are improved after ion exchange treatments; erosion and wear resistance behave the same, either by using natural abrasives such as Sahara sand or by using an aggressive abrasive as alumina grits.The increase in the ion exchange time induces an increase in Vickers hardness of about 15–40% compared to annealed glass. Samples processed at 520°C for a short period of 2h show better mechanical properties compared to samples processed at 480°C for longer times. In this case, the sample has a higher surface density which made the glass in compression not only because the potassium ions occupy the ionic substitution spaces but also the free spaces.

A multiscale simulation approach to grinding ferrous surfaces for process optimization

A fundamental optimization of a grinding process usually involves expensive equipment and experimental matrices covering a large parameter space. To aid this often cumbersome procedure, here we present three simulation approaches that are intrinsically related and even use the same software, but consider the grinding process at different levels of detail, thus spanning several length scales. Using a molecular dynamics (MD) model, we subject a nanocrystalline carbon steel work piece to grinding by hard alumina abrasives and study material removal and surface topography. A second, much larger MD model allows us to additionally study the microstructural and stress response of a polycrystalline ferritic work piece with a grain size that qualitatively reproduces macroscopic material behavior. Finally, the material point method is introduced as a way of modeling a machining process at the mesoscale in a mesh-free fashion, which is highly advantageous because it intrinsically treats the large deformations during chip formation correctly without the need for repeated remeshing. We discuss which aspects of the grinding process or the work piece quality may be optimized using the adopted approaches, and we show that although our simulations span almost four orders of magnitude in length, the obtained material removal rates agree well. Thus, the presented mesh-free multiscale approach opens new avenues for simulation-aided optimization of grinding processes.

Characterization of High-Speed Alumina Abrasive Grinding Wheel

The high-speed grinding wheel can be defined as a self-sharpening composite structural tool composed from abrasive grains held in a specific binder. The main properties of grinding wheels depend on the type of abrasive elements, grit size, grade, binder and the resulting structure, which is influenced by several crucial technological processing steps. Preparation of an initial mixture of abrasive particles together with permanent binder’s mixture and temporary binder followed by pressing and high-temperature sintering is the essential technological step in the manufacturing of high-quality grinding wheels. High demands placed on functionality and quality together with constantly increasing effort to improve existing properties of grinding tools require detailed characterization of all input raw materials. For further research and development is crucial know, how each technological step can influence the final quality of the product. This contribution is focused on the characterization of four alumina abrasives with different grit size and two in chemical composition different binder mixtures which were used for the production of two different high-speed grinding wheels. Initial abrasive grains, binders and metallographic samples of high-speed grinding wheels were evaluated by means of scanning electron microscopy. The porosity of grinding wheels with different binding agents was also determined ustilizing digital image analysis technique.