Abstract: Wide-band-gap semiconductors such as silicon carbide, gallium nitride, and diamond are known as hard-to-process materials. In this study, two types of chemical mechanical polishing (CMP)-related processing equipment were designed to create novel high-efficiency and high-quality processing technology for these crystal substrates. Applying these apparatuses, the processing mechanisms are discussed and the processing characteristics of the hard-to-process substrates investigated. The two types of prototype processing equipment were the closed chamber-type processing environment control CMP equipment and the plasma fusion CMP equipment. In the former, high-efficiency processing was attempted by introducing a photocatalytic reaction while adding ultraviolet (UV) irradiation to a high-pressure oxygen atmosphere. In the latter, we expected a synergistic effect that could bring out the features of atmospheric pressure plasma chemical vaporization machining (P-CVM) and CMP, especially with a diamond substrate that is very hard and chemically stable. When the processing mechanisms of these equipment were examined, the processing was promoted while forming reaction products such as hydrated and oxide films on the extreme surface. Therefore, the chamber-type CMP equipment by UV irradiation was particularly effective in a high-pressure oxygen environment. In the plasma fusion CMP equipment, high-efficiency processing of the diamond substrate was possible when P-CVM and CMP were simultaneously operated in an oxygen atmosphere. Furthermore, based on the studied processing mechanism, a "cyclic processing method" consisting of two steps, a pseudo radical field / reaction product formation step and a new surface contact magnetorheological finishing step, was proposed as a highly efficient processing process.
Abstract: Based on the Purchasing Managers' Index, the relevant data of the superhard material industry, the import and the export data of superhard commodities of China Customs, and the import data of United States and Japan Customs, 6 tables and 8 charts are summarized in this study to analyze the economic operation of the superhard industry in the first half of 2022. The data shows that the growth rate of industrial added value of superhard industry is 27.4%, which is 23.0 percentage points higher than that of enterprises above the national size. The profit growth rate is 65.0%, which is 64.0 percentage points higher than that of enterprises above the national scale (74.4 percentage points higher than the 10.4% decline in manufacturing). The growth rate of export delivery value is 10.2% (the export value of superhard goods according to the statistics of the General Administration of Custom increases by 20.6% year on year, which is 7.4 percentage points higher than the national exports value). China dominates the imported market of superhard goods in United States and Japan. In the dilemma of national macroeconomic development, the main economic indicators of the superhard material industry are far higher than the corresponding national indicators, which shows the trend of vigorous development of the superhard industry.
Abstract: The diamond retention of traditional impregnated diamond matrix comes from the mechanical holding force. The residual compressive stress on the diamond surface is an important index used to evaluate the mechanical holding force. The existing calculation methods for the compressive stress were compared and evaluated. The results showed that the calculation results of the empirical formula and the representation formula of the elastic equation were quite different from the actual value, revealing that the forms of the formulas were not reasonable enough. The mechanic calculation formula based on the theory of elastic-plastic mechanics, and the finite element numerical simulation method had very good validity. The analysis of the cooling process of WC-based diamond composites after sintering showed that there occurred plastic deformation inside the matrix during the cooling process, and that around the diamond particles there formed a plastic deformation zone. The plastic deformation could absorb a part of the strain energy, relieve the thermal mismatch stress between the diamond and the matrix, and release part of the static pressure stress on the diamond surface. After cooling, the residual compressive stress would occur on the diamond surface and was the source of the mechanical holding force of the matrix to diamonds.
Abstract: Diamond bit is an important tool for drilling. In recent years, with the application of new composite materials and the continuous progress in precision machining technology, combined with the continuous innovation of drilling equipment, diamond bits have achieved rapid development. This paper briefly introduces some new progress of efficient rock breaking technology with diamond bit, and puts forward the possible development directions in the future.
Abstract: The Cu–B alloy with boron mass fraction of 0.5% was used as the metal matrix, and the diamond with an average particle size of 500 μm was used as reinforcement, the diamond/Cu–B alloy composites were prepared by gas pressure infiltration method. The effects of gas pressure parameters on the microstructures and the thermophysical properties of the composites were studied. The results show that the interfacial bonding effect and the thermal conductivity between diamond and Cu–B alloy are enhanced and the thermal expansion coefficient is reduced with the increase of gas pressure. When the gas pressure is 10 MPa, the interfacial bonding effect is the best. The carbide layer formed at the interface completely covers the diamond, the thermal conductivity of the sample at 100 ℃ is 680.3 W/(m·K), and the thermal expansion coefficient is 5.038×10−6 K−1, which meets the thermal expansion coefficient requirements of electronic packaging materials.
Abstract: To improve the binding properties of diamond coating on carbide tools, three micrometer crystal diamond coatings were successfully deposited on YG8 carbide substrate via hot-filament chemical vapor deposition, whose boron gradient ranged from high (HGBMCD) to low (LGBMCD) and zero (MCD). The effect of the gradient size of the decreasing concentration of boron doping method on the nucleation and growth properties of diamond coatings during deposition was investigated. The results showed that the nucleation density of diamond increased with the doping of boron and that the diamond grains became smaller and more uniform after six-hour growth. Among them, the grain size of LGBMCD was mostly in the range of 2 to 3 μm. In addition, the graphite phase in the gradient boron-doped diamond coating was inhibited throughout the growth process, and IDia/IG was up to 14.65 in HGBMCD. The concentrations of the boron and cobalt compounds (i.e., Co2B and CoB) increased as the boron doping gradient decreased. Meanwhile, the residual stress in the diamond coatings gradually changed from compressive stress to tensile stress due to the doping of gradient boron, and the calculated residual stress decreased first and then increased, with the minimum residual stress of –0.255 GPa. Rockwell indentation showed that the gradient doping of boron improved the binding properties of diamond coatings, and that the optimal binding properties were observed at the LGBMCD, which was up to HF2 level at 1 470 N. Therefore, a proper boron doping gradient was demonstrated to improve the quality and binding performance of diamond coatings.
Abstract: Cr/Al/B/diamond powder was used as raw material, and a small amount of Cr2O3 or B2O3 was added to induce thermal explosion reaction. The results show that under the protection of high-purity Ar, the sample after thermal explosion reaction is seriously powdered, and it is easy to separate the binder from the diamond particles. After the thermal explosion reaction of the raw material system added with Cr2O3, the main phase in the binder is Cr2AlB2, and the composite coating containing Cr3C2 and Al will be formed on the diamond surface. The grain size of the composite coating is 0.5～7.0 µm. When the mass fractions of diamond are 10% and 20%, the surface of diamond particles in the samples are well coated, and the initial and the final oxidation temperatures of coated diamond are significantly higher than that of uncoated diamond. However, when the mass fraction of diamond is high, the coating effect on the diamond surface is slightly poor. After the thermal explosion reaction of the raw material system added with B2O3, the coating effect on the diamond surface is poor, and only half or less of the diamond particles are coated.
Abstract: The PCBN material was prepared by high temperature and high pressure method at 1 500℃ and different holding times with CBN-TiN-Ti-Al2O3 as the initial raw material. The phase compositions, microstructures, mechanical properties and cutting performance of PCBN under different sintering holding times were discussed. The results show that the holding time has no obvious effect on the phase compositions of PCBN, but it is helpful to improve its crystallinity and to realize its sintering uniformity and densification. When the holding time is 9.00 min, the PCBN material with the best comprehensive performance can be obtained with the relative density of 99.1%, the bending strength of 910.9 MPa, the wear ratio of 7120 and the microhardness of 33.5 GPa. The tool made of this PCBN can process up to 365 die steel parts.
Abstract: In the process of free abrasive lapping, the driving mode and process parameters directly affect the flatness and surface roughness of the workpiece. To explore the effect of free abrasive lapping process parameters based on rotary swing drive on the planarization of MPCVD polycrystalline diamond film, a kinematic model of single abrasive grain in rotary swing drive plane lapping process was established in this study. According to the actual lapping process, this paper adopts the multi-abrasive random distribution model for computer simulation and introduces the uniformity dispersion coefficient of multi-abrasive trajectory to analyze the diamond surface abrasive trajectory. The results suggest that when the speed ratio equals 0.5, the dispersion coefficient of abrasive trajectory is the largest; when the speed ratio is less than or equals 0.5, the dispersion coefficient of abrasive trajectory is positively correlated with the speed ratio; and when the length of the swing arc chord of the lapping workpiece disc is larger than the diameter of the diamond film, the motion trajectory of the abrasive particles relative to the whole diamond film surface is evenly distributed. The optimal lapping parameters are obtained by computer simulation. Through the 2 inch polycrystalline diamond lapping test, the final surface PV value of diamond is 2.4 μm, the surface roughness Ra is 139 nm and the material removal rate dMRR is 10.1 μm/h.
Abstract: In view of the difficulties in processing SiCp/Al materials by traditional grinding methods, the rapid wear of grinding tools, and the difficulties in obtaining high surface quality after processing, the ultrasonic vibration grinding method can significantly improve the processing effect. By analyzing the ultrasonic vibration trajectory of a single abrasive particle, it is concluded that its movement trajectory is a space ellipse shape, which can realize intermittent contact processing between the abrasive particle and the workpiece. The ultrasonic vibration grinding test is carried out on the SiCp/Al material with a volume fraction of 40% by using a resin-bonded diamond grinding head. Under different spindle speeds n, feed rates v, grinding depths ap and abrasive particle sizes d, the single-factor test method is used to detecte surface roughness of the workpiece. How each process parameter influences the Sa value of the workpiece surface roughness is obtained. And it is verified that ultrasonic vibration grinding of SiCp/Al can effectively improve the surface quality. The surface roughness of workpiece after ultrasonic vibration grinding decreases to 45 nm compared with 79 nm after ordinary grinding. The surface roughness of the workpiece first decreases and then increases with the increase of n, and it is the smallest when the speed is 1 800 r/min. The surface roughness of the workpiece increases with the increase of v and ap, and decreases with the decrease of d. And the optimal parameter combination in the test parameters is obtained: n=1 800 r/min, v=5 mm/min, ap=1 μm,d=4.5 μm.
Abstract: Gallium oxide crystal is one of the most representative fourth generation semiconductor materials with the advantages of high band gap, high voltage resistance and short absorption cutoff edge. It has broad application prospects. Micro-cracks, scratches and other surface defects are prone to appear in the polishing process of Gallium oxide crystal, which is difficult to achieve high-quality surface processing and cannot meet the requirements of corresponding devices. Moreover, the existing polishing process of gallium oxide crystal is complex and inefficient. Fixed abrasive polishing technology has the advantages of controllable abrasive distribution and depth of cut, and high utilization rate of abrasive. In this study, fixed abrasive polishing of gallium oxide crystal was adopted, and the effect of matrix hardness, abrasive concentration of polishing pad, the additives of polishing slurry on material removal rate and surface quality were investigated. The results show that when the hardness of the polishing pad is moderate II, the abrasive concentration is 100%, and the slurry additive is oxalic acid, the material removal rate is 68 nm/min and the surface roughness Sa value is 3.17 nm in fixed abrasive polishing of gallium oxide crystal. Fixed abrasive polishing technology can achieve high-efficient and high-quality polishing of gallium oxide crystal.
Abstract: The abrasive wear characteristics of large length to diameter ratio CBN single-pass honing tools during ultrasonic dressing process were studied by single abrasive test with 4Cr13 stainless steel as dressing material. The test results show that the average cutting force during ultrasonic cutting is reduced by 60%～80% compared to that during ordinary cutting. However, the abrasives break in a short time and the grinding ratio is seriously reduced. The abrasive-workpiece contact ratio during ultrasonic cutting is mainly between 0.6 and 0.8, and the abrasives are mainly in the intermittent cutting process. Moreover, the maximum cutting width during ultrasonic cutting increase by 2.7 times compared with that during ordinary cutting, leading to an increase in the maximum cutting force on the abrasives. According to the point cloud information, the abrasive was modeled inversely, and a single abrasive cutting simulation model was established to quantitatively analyze the maximum cutting force. The simulation results show that, compared with that during ordinary cutting, the maximum cutting force during ultrasonic cutting is more than 20% higher, and the fluctuation of cutting force is more than 80%.
Abstract: In order to study the effect of abrasive arrangement pattern on grinding the surface of structured grooves, grinding wheels with three different abrasive orderly arrangements, namely phyllotactic pattern, staggered pattern and array pattern, were used to grind a flat surface. Firstly, the mathematical models of the three abrasive arrangements were established. Secondly, the parameters of grinding wheels were designed according to characters of drag reduction on structured groove surface. And the MATLAB was used to simulate the grinding process, the results of which were compared with the theoretically calculated values. Finally, the reliability of the model and simulation was proved by grinding experiment. The results show that all the three orderly abraive arrangements can be used to grind the micro-groove surface at a grinding depth of 0.050 0 mm, while the axial distances of adjacent abrasive rows are 0.04 mm (phyllotaxis pattern), 0.40 mm (staggered pattern) and 0.80 mm (array pattern), respectively. The groove surfaces ground by the grinding wheels with array abrasive or staggered abrasive are more stable, but the groove parameter ratios cannot meet the requirement of 0.2～1.0. By using the grinding wheel with phyllotactic arranged abrasive, the machined grooves meet the requirements on feature parameters of drag-reduction surface.
Abstract: To improve the polishing efficiency and precision, the optimum processing parameters of Si in the chemical mechanical polishing (CMP) process were analysed by CMP experiments and response surface methodology. The results show that polishing pressure has the largest influence on the material removal rate and surface roughness of Si polishing. The second largest influential factor is polishing rotational speed and the third is polishing fluid flow rate. The prediction models of material removal rate and surface roughness are established. The optimum processing parameters are obtained when the polishing pressure is 48.3 kPa, polishing rotational speed is 70 r/min and polishing fluid flow rate is 65 mL/min with the prediction models and by experiments. With these processing parameters, the material removal rate and surface roughness are 1 058.2 nm/min and 0.771 nm, respectively.
Abstract: To improve the chemical mechanical polishing (CMP) performance of 316L stainless steel, the effect and its mechanism of complexing agent types on the CMP process of 316L stainless steel were studied. The influence of complexing agent types, including glycine, oxalic acid and citric acid, and their concentrations on polishing performance of 316L stainless steel were investigated with material removal rate (MRR) and surface roughness Ra as indexes. Electrochemical workstation, contact angle measuring instrument and X-ray photoelectron spectroscopy (XPS) were performed to analyze the affecting mechanism of complexing agents on 316L stainless steel CMP processing. The results indicated that only when the mass fraction of glycine was 0.2%, both higher MRR of 210 nm/min and lower Ra of 1.613 nm could be obtained. The inhibition effect of complexing agent with high concentration on 316L stainless steel MRR was because the complexing agent enhanced the corrosion resistance and reduced the oxidation rate of 316L stainless steel surface. The XPS results showed that part of glycine complex would be attached on the surface of 316L stainless steel to produce corrosion inhibition.
Abstract: In order to improve the thermal stability of PCD during practical application, the mixed solution of sulfuric acid and hydrogen peroxide was selected to remove cobalt from PCD. The effect of decobaltization on microstructure and mechanical property of PCD as well as its mechanism were studied. According to the SEM results, several deep corrosion pits were observed on the surface of PCD after the 48 h decobaltization process under room temperature, indicating that the cobalt phase was almost removed. Besides, the depths of decobaltization on the upper and lower surfaces were 176 μm and 162 μm, respectively. Based on the EDS results, the remaining mass fraction of cobalt in the decobaltized layer was determined to be 0.93%, while that in the non-decobaltized layer was 7.64%. This suggested that 87.83% of cobalt was dissolved and removed in the mixed solution of sulfuric acid and hydrogen peroxide. The residual stress of PCD samples was also measured. The residual stress before and after decobaltization was 483.91 MPa and 330.35 MPa, respectively. The reduction of 31.73% indicated that decobaltization could effectively reduce the residual thermal stress in PCD.
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