The material removal mechanism of aluminate magnesium spinel was investigated by nanoindentation and microscratch test. The hardness increases with the increase of load. The influence of scratch speed and scratch load on the removal mechanism of spinel was analyzed based on the penetration depth, tangential force and acoustic emission (AE) signal. It was found that with the increase of scratch speed, the area of elastic-plastic removal and brittle plastic transition increased. The AE signal appears at the beginning of a brittle plastic transition for the first time. Moreover, the tangential force growth rate of spinel in the elastic-plastic stage is lower than that in the brittle removal stage. The results indicated that improving scratch speed and reducing the scratch load is beneficial to reduce the range of brittle removal of spinel, thus increasing the range of plastic removal and brittle plastic transition.
Single-crystal silicon is a typical infrared optical material, commonly machined by single-point diamond turning (SPDT) with micro-level figure accuracy and nano-level roughness. However, the tool marks, surface damage and middle-frequency error left by the diamond turning process may greatly affect the imaging quality. Magnetorheological finishing (MRF) is a deterministic, sub-aperture polishing technology that is very helpful in improving both surface nano-roughness and surface figure and can be used to polish silicon materials. Although the feasibility of MRF for single-crystal silicon has been proved, there are still some problems such as low material removal rate and uncontrollable surface integrity. In this study, the MRF mechanism for single-crystal silicon was explored, and the preparation method of MR fluid was optimised. An experiment was performed to machine a large-aperture single-crystal silicon aspheric surface on an MRF machine developed by China Academy of Engineering Physics. After polishing for several times, the figure accuracy PV improved from 5.9 μm to 0.56 μm, and roughness Rq reduced to 1.2 nm, verifying the excellent performance of MRF in infrared material processing.
Potassium dihydrogen phosphate (KDP) is the irreplaceable nonlinear single crystal as optical frequency conversion and electro-optical switch in inertial confinement fusion (ICF) laser system. Based on the water solubility characteristics of KDP crystal, we propose an abrasive-free jet polishing (AFJP) method for KDP crystal with the purpose of improving surface quality without the embedding of particles. According to the AFJP experimental results, the jet spot generated by AFJP is of an approximately Gaussian shape. The feasibility of this approach has been studied through spot experiments. And the material removal mechanisms can be divided into contact removal and slipping removal.
To achieve the super-smooth surface of the fused silica via using the magnetorheological finishing (MRF) technique, the synergistic effect of the rotational speed, viscosity, and working gap is well investigated. According to the pressure field simulation based on the two-dimensional Reynold equation, the working gap is of remarkable importance to the surface roughness among three parameters. Furthermore, such result is also revealed by the MRF experiment. Accordingly, the optimized process parameters are identified, and the final surface roughness is achieved as low as 0.22 nm.
KEYWORDS: Clocks, Pulsed laser operation, Beam controllers, Signal generators, Laser optics, Picosecond phenomena, Seaborgium, Multiplexers, Temperature metrology, Control systems
The timing sequence, between different pulses in SG-III laser facility, is controlled with three arbitrary waveform generators. The external clock and trigger are used to inhibit the timing jitter, which is provided by the synchronization system. Close-loop monitoring is used to make sure that the temporal phase can be recovered after reboot of the arbitrary waveform generator. The verification experiment shows that the three arbitrary waveform generators can work synchronously , which ensures the synchronization error control of the SG-III laser facility.
A polymer coating was designed and prepared to modify the surface of CIP to match the hardness of KDP, and deliquescence removal was explored by addition proper water online. The above techniques not only weaken the mechanical scratches and increase removal rate, but also are beneficial for subsequently cleaning. Removal function exhibits particular transitional zone on the edge of finishing spot which clearly demonstrates the existence of different processing mechanisms simultaneously. The figure accuracy and PSD1 of a large-aperture KDP are apparently converged after MRF.
The CeO2 nanoparticles with modified surface and mean sizes distribution during 107.0 nm - 127.7 nm are used as abrasive in magnetorheological finishing (MRF) fluid. The slow rotation dispersion without shearing thinning is better
than fast emulsification dispersion. Steady D-shaped finishing spots and high quality precise processing surface with
PV=0.1λ, GRMS=0.002λ/cm, Rq=0.83 nm are obtained on a 435 mm x 435 mm BK7 glass under self-developed MRF
apparatus.
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