With the development of electronics and optical industry, the high-efficiency ultra-precision polishing technologies of flat and curved surfaces are in high demand. The traditional magnetorheological polishing technology, using flexible polishing head, has the disadvantages of low polishing efficiency and small processing area. In this study, a novel tray-type magnetorheological polishing process using low-frequency alternating magnetic field excitation was developed to improve the efficiency of magnetorheological polishing for large surfaces and to make polishing magnetorheological cluster generate a cyclical fluctuation up and down, and then improve the cross-cutting effects of abrasives. With the developed excitation system, a large bowl-shaped varying magnetic field was generated in the working area, and the effects of current frequency, working gap, trough rotation speed, and workpiece rotation speed on the improvement rate of surface roughness and material removal rate were systematically investigated. A series of experiments were conducted on K9 glass specimens to verify the polishing performance. Experimental results show that the surface roughness of K9 glass was improved from 567.08 to 9.63 nm in 120 min.

High-quality and high-efficiency processing of gallium nitride (GaN) crystals is urgently required for optoelectronic communications and other major industries. This study proposes a novel high-efficiency non-damage magnetorheological chemical polishing (MCP) process to overcome the existing problems of low efficiency and lattice distortion during processing. The effects of the MCP fluid composition and key processing parameters on the surface roughness and material removal rate (MRR) of GaN crystals were studied experimentally. The results showed that a compounded abrasive containing silica fluid exhibited better polishing effects than a single abrasive. The polishing efficiency could be improved by adding NaOH solid particles, and the MRR reached 13.19 nm min⁻¹ when the pH of the MCP fluid was 10. The MRR increased gradually with an increase in the pole rotation speed and worktable speed and a decrease in the polishing gap. The surface roughness of the GaN crystals was improved from Ra 115 nm to Ra 0.375 nm after polishing for 4 h. The surface and sub-surface damage of the polished GaN crystals was analyzed using scanning electron microscope and transmission electron microscope. The results confirmed that the MCP process can realize the non-damage polishing of GaN crystals. Moreover, a prediction model for the surface roughness of GaN crystals in the MCP process was constructed. The overall difference between the actual and predicted surface roughness values for the model was 11.6%.

The preparation process of FeNiCrCoAl high-entropy alloy at the atomic scale was simulated using molecular dynamics, and its microstructure was analyzed to study its micro-mechanical properties during nanoscale scratching. The simulation results showed that FeNiCrCoAl primarily experienced main frictional forces from the [010] direction and radial frictional forces from the [001] direction during the nanoscale scratching process. All three frictional forces exhibited certain fluctuations, which were partly attributed to the formation of face-centered cubic and hexagonal close-packed atomic structures during frictional wear. In addition, plastic flow was observed continuously within the high-entropy alloy matrix. Furthermore, the effects of temperature and Fe atomic content on the nanoscale scratch characteristics of FeNiCrCoAl high-entropy alloy were investigated. The results indicated that an increase in temperature resulted in a nonlinear decrease in frictional forces and a reduction in the quantity of the two types of phase-transition atomic structures formed. Increasing the Fe atomic content induced lattice distortion effects in the high-entropy alloy, leading to an increase in the potential energy of the matrix and the formation of more phase-transition atomic structures, thus hindering the frictional wear process of FeNiCrCoAl high-entropy alloy.