In order to solve the problems of low hardness in the grinding phase material of magnetic abrasive particles prepared by the existing sintering method, the grinding effects on high-hardness and poor magnetic conductivity materials, such as titanium alloys, were found to be poor. Additionally, the hardest diamond material could not be used as the grinding phase to prepare magnetic abrasive particles by the sintering method. In this study, the cBN-Fe magnetic abrasive particles were prepared by sintering with Fe powder as the matrix and cBN powder as the grinding phase. The study focused on using Ti-6A1-4V (TC4) plates as the grinding objects, and the effects of sintering time, heating rate and raw material ratio on the grinding performances of cBN-Fe magnetic abrasive particles were explored using a control variable method. The aim was to determine the optimal preparation process parameters of cBN-Fe magnetic abrasive particles. Taking 45^# steel and 202 stainless steel as grinding workpieces, the performance of cBN-Fe magnetic abrasive particles were compared with that of Al₂O₃-Fe and SiC-Fe magnetic abrasive particles, both prepared by the sintering method. The surface roughness and morphology of the workpieces before and after grinding with three kinds of magnetic abrasive particles were compared. Moreover, the grinding performance and service life of different magnetic abrasive particles were investigated. The results show that the best grinding performances for cBN-Fe magnetic abrasive particles was achieved when using a mass ratio of Fe powder to cBN powder of 3∶1, a sintering temperature of 1150 ℃, a sintering time of 6 h, a holding time of 2 h and a heating rate of 3.19 ℃/min. Furthermore, it is found that the grinding performance of cBN-Fe magnetic abrasive particles is better than that of Al₂O₃-Fe and SiC-Fe magnetic abrasive particles prepared by sintering. The service life of cBN-Fe magnetic abrasive particles is 1.6 times and 1.3 times longer than that of Al₂O₃-Fe and SiC-Fe magnetic abrasive particles, respectively.

[Objectives]  Polycrystalline diamond (PCDs) compacts are extensively used in industries such as oil drilling, geological exploration, and high-speed machining tools. To further enhance the density of PCDs and thus improve their performance, this research investigates the powder density, particle size distribution, and changes in their microstructure under different pressures for diamond micro-powders with varying particle sizes and proportions. The objective is to understand the fragmentation behavior and obtain diamond formulations with higher density.

[Methods] A set amount of diamond micro-powders was placed in a fixed-size niobium cup, shaken and compacted before sealing. The cup was then positioned in a synthetic pyrophyllite block, layered with metal plugs, molybdenum, carbon, zirconia, magnesia, and sodium chloride, replicating the structure used in synthesizing PCD tools. A cold isostatic press and a cubic press were employed to apply different pressure gradients. At 220 MPa, the sealed niobium cups underwent liquid pressurization in the cold isostatic press, while the cubic press facilitated pressures  of 20, 30, and 40 MPa. After compression, the samples’ mass and volume were measured to calculate their density. Scanning electron microscopy (SEM) was used to observe the morphology of the internal powders, and a laser particle size analyzer was used to observe particle size distribution. The crushing conditions and patterns of diamond micro-powders were then summarized.

[Results]  In summary, the density of diamond micro-powders increased with pressure. After compaction, density distribution ranges from 1.5 to 2.1 g/cm3. For samples of the same volume, coarser particles exhibited higher densities than finer ones, with mixed powder samples showing intermediate densities. This indicated that in the compacted state, there was a larger void ratio between fine particles, and in mixed powders, fine particles were not effectively dispersed among large particles. After cold isostatic pressing at 0.22 GPa, there was a significant increase in sample density, with the density of mixed powders increasing by nearly half, indicating a compact particle arrangement without crushing. Under pressure, particles re-arranged, reducing voids and allowing fine particles to fill the gaps between larger ones. High-pressure treatment in cubic pressing at 20, 30, and 40 MPa resulted in internal pressures of approximately 3.5, 5.0, and 7.0 GPa respectively. Diamond micro-powders underwent fragmentation under high external pressure, and sample densities continued to change, increasing with pressure. Particle size analysis of the crushed powders revealed significant changes in particle size distribution of large particles under high pressure, indicating severe crushing. The density of the mixed powder samples also increased. However, the addition of small diamond micro-powders significantly reduced the crushing of larger particles, with less changes in particle size distribution, which helped maintain the original formulation. SEM observation showed clear crushing of larger particles and validated the stacking model of different particle sizes in the mixed powders. Small particles were evenly distributed among the larger particles, acting as a buffer to increase contact points and reduce stress concentration, thus significantly reducing the occurrence of crushing and rapidly increasing density.

[Conclusions]  During the cold pressing stage of synthesis process for PCD compacts, diamond micro-powders of all types undergo varying degrees of crushing, with single-component large particles being most notably affected, while the inclusion of small diamond micro-powders significantly reduces this effect. Mixing large and small diamond particles effectively alleviates the crushing of diamond micro-powders and allows for higher density under the same pressure, resulting in PCDs with higher density and improved performance.

The ceramic CBN grinding wheels are widely used in the fields of forming and precision machining, and the research on them is of great significance in improving the machining quality and efficiency of workpieces. The research progress of ceramic CBN grinding wheels in recent years is summarized from various aspects, including CBN abrasive grains, modifier addition, preparation and grinding performances. Additionally, the future development prospects are also discussed. Regarding CBN abrasive grains, the synthesis of CBN single crystal is explored, and the surface treatment of CBN abrasive grains, as well as the treatment methods when adding a strong magnetic field, are introduced. Concerning modifier, the influences of adding pore forming agents, oxides, metal materials and nano-materials on the performances of ceramic CBN grinding wheels are discussed. In the preparation of ceramic CBN grinding wheels, the methods of forming and sintering are described. Moreover, the grinding applications of ceramic CBN grinding wheels on difficult-to-machine materials such as steel, nickel base alloy and titanium alloy are introduced, and the factors affecting the grinding performances of CBN grinding wheels are proposed.

To investigate the strengthening effect of calcium sulfate whiskers as a reinforcing filler for resin grinding tablets, experimental splines and resin grinding tablets were prepared by the hot pressing method. The effects of different whisker lengths and mass fraction on the hardness, bending strength and microstructures of the splines were examined, and the grinding performances of the grinding tablets on artificial granite were studied. The results show that when the mass fraction of the whisker is constant, the bending strength of the spline decreases with the increase of the whisker length, while the hardness remains relatively unchanged. One the other hand, when the whisker length keeps constant, the bending strength of the spline shows a trend of increasing and then decreasing with the increase of the whisker mass fraction. Using the grinding tablet to grind artificial granite, the best abrasion resistance of 1.973 min/% and good sharpness of 76.8 cm³/min are achieved when the length of calcium sulfate whisker ranges  from 10 to 60 μm and the mass fraction is 10%.

Using the layered design concept of fine-grained diamond in the upper layer and the coarse-fine diamond in contact with the cemented carbide layer in the lower layer, the polycrystalline diamond compact (PDC) with multiple diamond layers for drilling was prepared. The differences in microstructure and performance between the single-layer diamond PDC and the multi-layer diamond PDC with different particle sizes were compared. The internal defects and surface morphology of the PDC were characterized using ultrasonic scanning and scanning electron microscopy (SEM), and the heat resistance, impact resistance and wear resistance of the PDC were tested, respectively. The results show that the comprehensive performance of the multi-layer diamond PDC is good. The surface layer is wear-resistant, while the lower layer is more impact-resistant. The PDC exhibits a more balanced combination of heat resistance, impact resistance and wear resistance. Specifically, the fine-grained diamond layer PDC demonstrates higher wear resistance but lower heat and impact resistance; while the coarse-grained diamond layer PDC exhibits better heat and impact resistance, but poor wear resistance.

As the core component of magnetorheological polishing equipment, the key factor determining the success of magnetorheological polishing is whether the excitation device can generate a stable and uniform high gradient magnetic field. The sector permanent magnet was used to design the excitation device of the magnetorheological polishing wheel. The ANSYS Electronics Desktop and other softwares were used to simulate and analyze the excitation device various aspects, including the number of permanent magnets, magnetization modes, arrangement modes, and air gap widths. The magnetic induction lines and magnetic induction intensity distribution under different working conditions were obtained. The results show that when the air gap width is 4 mm, the magnetic induction intensity produced by axial magnetization of a single permanent magnet is the largest, reaching 358.4 mT. Theoretically, a polishing ribbon with a width of 26 mm and a height of 6.0 mm can be formed on the surface of the polishing wheel.

The surface of 10 to 30 μm fine-grained diamond was plated with Cr, and the Cr- plated diamond was mixed with Ni-Cr-B-Si powder and placed on the surface of carbon steel. The wear-resistant coating was prepared by using a laser heat source to melt the preset powder on the surface of carbon steel. The results show that the thickened Cr coating on the diamond surface can effectively protect the diamond in the laser high-temperature thermal field, avoids oxidation and graphitization of the diamond at high temperatures, and achieves metallurgical bonding between the diamond and the metal matrix. The metallography, phase and morphology of the coating are analyzed, and it is found that the diamond can significantly improve the cooling rate of the coating, refine the condensing structure, increase the hardness, and enhance the wear resistance of the coating. The wear resistance of the cladding coating with a mass fraction of 20% Cr-plated diamond is 4.6 times higher than that of without diamond, and the corresponding friction coefficient is nearly 50% lower.

Cubic press is the primary equipment for diamond production in China. Its key component, the hinge beam, bears continuous alternating loads in the working environment and is prone to failure and breakage. In this paper, a method combining response surface method (RSM) and multi-objective genetic algorithms (MOGA) is proposed to optimize the hinge beam of the new hexagon top press. Firstly, the parametric model of the hinge beam is established, with the dimensions of key parts as design parameters, the maximum stress and displacement as objective functions, and the maximum mass is constrained. Then, the optimal space-filling design (OSF) is used as the design of experiments (DOE) to obtain the design experimental points. The proxy model is obtained by the response surface method. Afterward, the global optimum solution is searched using the MOGA method, and the optimal result of the hinge beam is evaluated. The results show that the stiffness and strength of the optimized hinge beam are effectively improved with a slight increase in weight, and the stress concentration is also significantly reduced, providing a useful reference for the design and development of the press.