[OBJECTIVES] To perform mirror polishing on the inner surface of medical TA1 pure titanium capillary tubes to reduce the residual of test samples and improve the precision of capillary pipetting, thereby enhancing the detection accuracy and reliability of in vitro diagnostic equipment. A novel chemical-assisted magnetic compound fluid polishing method is proposed to address the issues of poor quality and difficulty in polishing the inner surface of pure titanium capillaries. This method combines chemical oxidation with mechanical removal to achieve efficient and precise polishing of the inner surface of medical TA1 pure titanium capillaries.

[METHODS] By combining chemical oxidation with mechanical removal principles, a chemical-assisted magnetic compound fluid polishing method was developed to achieve efficient and precise polishing of the inner surface of medical TA1 pure titanium capillaries. Initially, single-variable experiments explored the effects of iron powder mass, hydrogen peroxide mass fraction, and malic acid mass fraction in the polishing fluid on the material removal rate and roughness of the TA1 capillary inner surface. The surface changes of TA1 material in an acidic oxidative environment were observed, and the polishing principle was analyzed comprehensively. Subsequently, energy spectrum analysis of the inner surface elements of the TA1 capillary before and after polishing was conducted to assess the impact of the polishing process on the changes in element types and content. Finally, the surface morphology of the TA1 capillary inner surface before and after polishing was characterized using a scanning electron microscope and a contact profilometer, analyzing the patterns and reasons for changes in inner surface roughness.

[RESULTS]  Single-factor polishing experiments on TA1 capillaries showed that the mass of iron powder, the mass fraction of hydrogen peroxide, and the mass fraction of malic acid in the polishing fluid significantly affected the post-polishing surface roughness and material removal rate. As the mass of iron powder increased, the surface roughness decreased then increased, and the material removal rate increased then decreased. With the increase in hydrogen peroxide mass fraction, the surface roughness slightly decreased, and the material removal rate slightly increased. As the malic acid mass fraction increased, the surface roughness continued to decrease, and the material removal rate continued to rise. Etching experiments indicated that a porous oxide layer formed on the TA1 surface in an acidic oxidative environment, demonstrating the CAMCF's principle of simultaneous oxidation and mechanical removal. Compared to the original inner surface of the TA1 capillary, the polished inner surface showed no change in element types, with a slight increase in oxygen content. Characterization of the TA1 capillary inner surface before and after polishing with a scanning electron microscope and contact profilometer revealed that the original surface had deep and wide drawing cracks and varied cracks and pits on the split titanium blocks. The original roughness was Ra 675nm. After polishing, minor cracks and subtle defects were essentially eliminated, deep and wide drawing cracks significantly reduced, and uniform abrasive scratches appeared in the flat areas, reducing the surface roughness to Ra 19.5nm.

[CONCLUSION] The chemical-assisted magnetic compound fluid polishing technique demonstrated its feasibility for efficient and precise polishing of the inner surface of medical TA1 pure titanium capillaries. Within the experimental parameter range, the optimal polishing fluid composition was 2mg of iron powder, 7.2% hydrogen peroxide mass fraction, and 6% malic acid mass fraction. The polishing process did not alter the element types on the inner surface of the TA1 capillary, only slightly increasing the oxygen content. After polishing with the optimal parameters, the cracks on the inner surface of the TA1 pure titanium capillary were essentially eliminated, the maximum material removal depth in the polished area was 28μm, and the surface roughness reduced from Ra 675nm to Ra 75nm, with the crack-free area reaching a roughness of Ra 19.5nm, achieving mirror polishing of the inner surface of the pure titanium capillary.

The development of China’s superhard industry in the first half of 2023 is analyzed according to statistical data, as well as the import and the export data of customs and the national macroeconomic indicators. It is found that the industry falls short of development expectations due to the structural adjustment of the manufacturing industry. The main indicators, including the total industrial output value, the sales revenue, the total profit and the export delivery, are all in a negative growth, especially the total profit which decreases 39.5% year-on-year. Against the backdrop of relatively weak global markets, the export destinations are increasingly concentrated due to the rapid development of emerging economies. For example, the markets in the Middle East and Russia have shown higher vitality. It is suggested that the companies take active decisions and explore emerging markets for breakthroughs in products and vitality in development.

To investigate the microscopic influence of ultrasonic vibration on the surface flaws of particle-reinforced titanium matrix composites TiC_p/TC4 during cutting with ultrasonic vibration of PCD tools. A two-dimensional cutting microscopic non-homogeneous model for TiC_p/TC4 was established using ABAQUS/Explicit finite element software, and different volume fractions of the multi-particle cutting simulation were performed to analyze the changing rule of cutting speed on cutting temperature using a combination of simulation and experimental methods, to elaborate the particle force crushing process of PTMCs during the cutting process, and to discuss the defect manifestation. The results show that ultrasonic vibration cutting, the cutting temperature is always lower, the surface defects are mostly particle cut off and particle protrusion, and ultrasonic vibration can effectively block the stress between the particle and the substrate continues to transfer, so that the stress is prioritized in the transmission between the particles, reducing substrate deformation, prompting the particles to break first, and improving the surface. The experimental results were validated to be consistent with the simulation results.

[OBJECTIVES] Grinding is one of the ultraprecision machining methods for efficiently thinning and flattening hard and brittle materials such as sapphire. However, traditional grinding processes cannot meet the requirements for high material removal rates and high surface quality simultaneously. Exploring the use of aggregated diamond abrasives and their corresponding processing methods is beneficial for achieving efficient and stable high-quality grinding of hard and brittle materials.

[METHODS] A novel process was proposed, using ceramic binders and fine diamond abrasives (grain size 3 μm) sintered to form aggregated diamond abrasives (average grain size 30 μm) for grinding purposes. Comparative grinding experiments were conducted on sapphire substrates using the prepared aggregated diamond abrasives and single-crystal diamond abrasives with grain sizes of 3 μm and 30 μm. The grinding performance of the aggregated diamond abrasives was systematically investigated, and a material removal model was established to further reveal the material removal mechanism during processing with these abrasives.

[RESULTS] (1) Aggregated diamond abrasives exhibited a higher material removal rate. Under the same conditions, grinding with aggregated diamond abrasives for 15 minutes achieved a material removal rate of 1.127 μm/min, an 89.1% increase compared to using 3 μm single-crystal diamond abrasives. (2) Aggregated diamond abrasives demonstrated superior processing stability. Over a 120-minute processing cycle, their material removal rate showed the least reduction, with a rate of 0.483 μm/min after 120 minutes, marking a 57.14% decrease from the rate at 15 minutes. In comparison, the material removal rates of 3 μm and 30 μm single-crystal diamond abrasives decreased by 78.02% and 71.2%, respectively.  (3) Aggregated diamond abrasives resulted in better surface quality. The lowest surface roughness Ra after grinding with aggregated diamond abrasives and 3 μm single-crystal diamond abrasives were 9.45 nm and 8.75 nm, respectively, while using 30 μm single-crystal diamond abrasives yielded a lowest Ra of 246 nm. (4) The wear and removal patterns of aggregated abrasives during processing differed from those of single-crystal diamond abrasives. The latter’s wear was through abrasion dulling, characterized by chipping, flattening, and abrasive wear of the cutting edges. In contrast, the aggregated diamond abrasives underwent micro-fracturing, characterized by the shedding of micro-fine single-crystals from the abrasive surface and the binder network disintegration. Statistical analysis of the particle size distribution of the grinding fluid during the grinding process revealed  that after 30 minutes of grinding, the particle size distribution curve of aggregated diamond abrasives shifted to the left, with a 51.5% decrease in peak volume fraction. The change in the abrasive particle size distribution curve was relatively small. At the same time, a trapezoidal peak composed of abrasion debris and detached micro-fine single-crystal abrasives formed on the left side of the curve. In contrast, a significant leftward shift was observed in the curve for 30 μm single-crystal diamond abrasives, with the peak volume fraction decreasing by 82.8%. The change in the abrasive particle size distribution curve was relatively large, forming a low peak wave on the left side of the curve. Aggregated diamond abrasives employed a multi-edge cutting method, primarily relying on multiple micro-fine single-crystal diamond grains on the surface to remove material from the workpiece. In contrast, single-crystal diamond abrasives engaged in single-edge cutting, mainly relying on the edges and corners of the abrasive for material removal.

[CONCLUSION] During the grinding process, aggregated diamond abrasives remove material from the workpiece surface through the combined action of multiple micro-fine single-crystal diamond grains on the surface layer. This ensures consistency in cutting depth and enhances surface quality. Under the impact and compression between the workpiece and the grinding disc, the aggregated diamond grains undergo abrasive wear and micro-fracturing, exposing the micro-fine diamond grains encapsulated within the binder and achievi ng cutting edge renewal and self-sharpening. This leads to higher efficiency and more stable processing capability. Therefore, the multi-edge cutting and micro-fracturing characteristics of aggregated diamond abrasives enable the efficient, stable, and high-quality grinding of sapphire substrates.

In order to solve the problem that it is difficult to grow diamond films with high binding force on the surface of high cobalt cemented carbide, the Cr/CrSiN film was used as the transition layer, and the nanocrystalline diamond films (NCD), the submicrocrystalline diamond films (SMCD) and the microcrystalline diamond films (MCD) were deposited on the cemented carbide by hot filament chemical vapor deposition method, and their binding forces were studied. The results show that the Cr/CrSiN transition layer can be used to deposit diamond films with excellent bonding strength on the surface of high cobalt cemented carbide. NCD has the best binding force, followed by SMCD, and MCD has the worst binding force. When the grain size of the diamond film increases, the bonding forces of the diamond film weaken due to the poor toughness of the diamond films and severe carbonization of the transition layer. When the crystal size of the diamond film increases, the binding force of the diamond film becomes weak due to the poor toughness of the diamond film and serious carbonization of the transition layer.

[OBJECTIVES] Brittle materials, characterized by low fracture toughness, are susceptible to subsurface damages such as microcracks during grinding processes. This damage can adversely affect the performance and lifespan of the components. Precise measurement of the depth of subsurface microcracks is crucial for selecting appropriate machining allowance in subsequent processes. While current methods for measuring subsurface microcracks have limitation, machine learning models show significant potential in predicting machining quality of brittle materials. However, these models often require extensive labeled data, which is difficult to obtain in practice, thus limiting their learning capabilities. To address the challenge of limited effective samples for analyzing subsurface microcrack depths in brittle materials ground with fixed abrasives, this study proposes a collaborative training approach for a Support Vector Regression (SVR) model，tailored for small datasets, capable of accurately predicting microcrack depth caused by grinding different brittle materials.

[METHODS] This study employed the SVR model as the foundational learner, with inputs including Mohs hardness, elastic modulus, fracture toughness of the brittle materials, diamond abrasive grain size and grinding pressure. The output was the depth of subsurface microcracks resulting from grinding. Integrating semi-supervised and supervised learning concepts, the study developed both a collaborative training SVR model and a PSO-SVR model. The model’s predictive performances were assessed using mean square error (MSE) and mean absolute percentage error (MAPE). Further, the impact of various labeled training set partitioning strategies on the MSE of the test set was examined using the collaborative training SVR model. The study also compared the predictive performances of the collaborative training SVR model and the PSO-SVR model under separate dataset partitioning strategies. Finally, the study validated the models through grinding and angle polishing experiments to measure subsurface microcrack depths in materials not included in the training set, evaluating the collaborative training SVR model's predictive accuracy against experimental results. 

[RESULTS] When using separate dataset partitioning strategies, the initial MSE values of the two learners in the collaborative SVR model were 5.79 and 0.98, ultimately converging to 1.15 and 0.35, respectively. For mixed dataset partitioning strategy, the initial MSE values were 4.02 and 1.13, converging to 2.0 and 0.70, respectively. When predicting small dataset, the collaborative training SVR model demonstrated a reduction in MSE and MAPE by 9% and 17%, respectively, outperforming the PSO-SVR model. The collaborative model provided more reliable and stable predictions for both individual test samples and entire test sets. The measured subsurface microcrack depths in glass-ceramics and calcium fluoride under different processing conditions were 4.13, 5.03, 5.67, and 5.89 μm, with prediction errors ranging from 1.2% to 13.8%, averaging at 7.7%, which was significantly lower than the test set’s average prediction error of 12.5%.

[CONCLUSION] Dividing the labeled dataset using both separate and mixed partitioning methods can reduce the MSE of the collaborative training SVR model on the test set, with the separate method achieving smaller MSEs and superior outcomes. Compared to the supervised learning PSO-SVR model, the collaborative training SVR model demonstrates smaller MSE and MAPE values, with more stable prediction errors. The close agreement between the experimentally measured subsurface microcrack depths and the model's predictions underscores its robust generalization capability, confirming the model's ability to provide accurate and stable predictions of subsurface microcrack depths in various brittle materials after grinding.

[OBJECTIVES] Diamond is the hardest known naturally occurring single crystal mineral in nature, and due to its high hardness and brittleness, it has become a typical difficult-to-process material. With the development of ultrasonic composite processing technology and the updating of diamond grinding technology, ultrasonic vibration-assisted grinding shows advantages such as high surface integrity and low damage for hard brittle materials. In order to improve the surface quality of natural diamonds, ultrasonic vibration was introduced to conduct composite grinding on natural diamonds.

[METHODS] Utilizing the composite action of abrasives on the surface of diamonds during ultrasonic-assisted grinding, as well as the characteristics of natural diamonds, a non-elastic collision theory model was established to calculate the amplitude of ultrasonic vibration. Due to the anisotropy of natural diamonds, two-dimensional planar unidirectional cutting was used to avoid its influence. Mathematical limit approach was employed to simulate and analyze circular motion as linear motion. Using surface roughness as an indicator, an orthogonal experiment was established to study the effects of ultrasonic amplitude, grinding speed, and abrasive particle size on the removal of natural diamond (100) crystal surface material, and to seek the optimal process parameters. To improve grinding efficiency, diamond micro-powder with a basic particle size greater than 1.0 μm was typically selected. Coarse-grained diamond grinding powder can improve grinding efficiency. Therefore, diamond micro-powder with particle size designations of M1/2 (basic particle size of 1.0~2.5 μm), M2/4 (basic particle size of 1.5~3.5 μm), and M3/6 (basic particle size of 2.5~5.0 μm) was selected. An L34 (9) orthogonal experiment was conducted on the easy grinding direction of the natural diamond (100) crystal surface at ultrasonic amplitudes of 3.0, 6.0, and 9.0 μm.

[RESULTS] The primary and secondary relationships affecting diamond surface roughness were ultrasonic amplitude (B) > abrasive particle size designation (D) > grinding disc speed (C). The optimal process parameter combination for achieving the lowest diamond surface roughness was identified as B2C2D3, with an ultrasonic amplitude of 6.0 μm, a grinding disc speed of 2,800 r/min, and an abrasive particle size designation of M3/6. Under the optimal process parameter combination, good surface quality could be achieved after 30 minutes of grinding: the surface roughness Ra of diamond after traditional grinding was 44.81 nm, whereas after ultrasonic-assisted grinding, the surface roughness Ra was 16.21 nm, representing a decrease of 63.83%. SEM inspection of the natural diamond surface revealed cracks and scratches after traditional mechanical grinding, whereas the surface quality of diamonds ground using the optimal process parameters was good, without defects such as cracks or fractures. It can be concluded that using the optimal grinding process parameters can significantly reduce the surface roughness of natural diamonds and improve their surface quality.

[CONCLUSION] Theoretical calculations revealed that the range of ultrasonic amplitude values for the easy grinding direction of natural diamond (110) crystal surfaces was 3.1~8.7 μm, and for the easy grinding direction of (100) crystal surfaces was 2.9~9.1 μm. Simulation and analysis of cutting on (100) crystal surfaces showed that the stress experienced by the workpiece and abrasive particles increased with increasing amplitude, while the temperature decreased, indicating that ultrasonic processing could effectively reduce cutting temperature and chip accumulation. Ultrasonic vibration grinding experiments showed that the overall surface quality of materials was superior to that of traditional mechanical grinding. Among the three elements of grinding, the degree of influence was in the order of ultrasonic amplitude > abrasive particle size designation > grinding disc speed. The optimal process parameter combination obtained through orthogonal experiments was an ultrasonic amplitude of 6.0 μm, a grinding disc speed of 2,800 r/min, and an abrasive particle size designation of M3/6. Under these optimal conditions, the surface roughness of ground diamonds was as low as 16.21 nm, representing a decrease of 63.83% compared to traditional mechanical grinding.