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Reaction-bonded silicon carbide (RB-SiC) is an important optical material used widely in the aerospace industry. The machining accuracy of RB-SiC optical elements must satisfy the requirements of high-performance system development. However, RB-SiC is typically hard and brittle, making precise machining difficult. Thus, the material removal and synergistic deformation mechanisms of SiC and silicon (Si) must be investigated for ultraprecision machining. In-situ laser-assisted diamond cutting is an effective method for the ultraprecision cutting of hard and brittle materials. In this research, we investigated the influence of temperature on the material deformation process in detail. Firstly, the physical properties of RB-SiC, including its hardness and depth of plastic deformation, were investigated through high-temperature nano-indentation experiments. Furthermore, grooving experiments were carried out to investigate the brittle-to-ductile transition under ordinary and in-situ laser-assisted diamond cutting, respectively. Finally, the deformation of the machined surface/subsurface was revealed via scanning electron microscopy and transmission electron microscopy observations. [ABSTRACT FROM AUTHOR]

• In-situ laser assisted diamond cutting was utilized for fused silica. • Temperature dependence of thermal parameters identified by algorithm. • The validity of temperature simulations was corroborated experimentally. • A Sa of 12.9 nm could be obtained under the optimized process parameters. Fused silica is typically a difficult material to machine using conventional methods due to its high brittleness and hardness, despite its significance in optical systems such as high-power lasers and astronomical telescopes. Laser assisted diamond cutting has emerged as a promising and cost-effective alternative for machining fused silica. This study investigated the machinability and thermal response of fused silica during in-situ laser assisted diamond cutting through finite element analysis and cutting experiments. The temperature dependence of thermal parameters, identified by Beetle Antennae Search, was taken into consideration in the thermal model. To minimize surface roughness and determine the optimal machining parameters, various methods were employed, including analysis of variance, signal-to-noise ratio, and Particle Swarm Optimization coupled with Artificial Neural Network. The results indicated that various factors involved in in-situ laser assisted diamond cutting had a significant impact on the thermal response of fused silica, resulting in different surface roughness. Among these factors, spindle speed, feed speed, cutting depth, and laser power contributed to surface roughness by 17.34 %, 12.28 %, 12.03 %, and 48.31 %, respectively. By utilizing the optimal combination of parameters, which comprised a spindle speed of 2700 rpm, feed speed of 1.7 mm/min, cutting depth of 2.7 μm, and laser power of 12.5 W, a smooth surface finish of Sa 12.9 nm could be obtained. [ABSTRACT FROM AUTHOR]

• Raman spectroscopy identified the bright and dark SiC in the SEM image as 3C-SiC and 6H-SiC. • Large-grained SiC maintained ductile cutting while brittle fractures occurred at interfaces. • Cross slips and high-density stacking faults significantly enhance plastic deformation. • The intersection of the 3C-SiC/6H-SiC interfaces becomes the initiation of the lateral crack. • The lateral crack propagates along the [111]//[0001] direction of the FCC-HCP interface. Reaction-bonded silicon carbide (RB-SiC) is considered as an excellent optical material in aerospace engineering. However, the multiple complex interfaces and high hardness make it difficult to be precisely machined. In this research, the in-situ laser-assisted diamond cutting was applied to precisely machining RB-SiC. Firstly, Raman spectroscopy was adopted to identify 3C-SiC and 6H-SiC components in RB-SiC. As following, the in-situ laser-assisted diamond cutting was experimentally carried out to analyze the subsurface deformation and fracture in detail. It was clarified that the cross slips and high-density stacking faults significantly enhance the plastic deformation of RB-SiC. Moreover, the dislocations rapidly plugged at the intersection of 3C-SiC/6H-SiC interfaces resulting in the lateral crack which propagates along the [111]//[0001] direction. [ABSTRACT FROM AUTHOR]

Single crystal silicon is an important optical material used widely in the infrared systems. The surface quality and subsurface damage of silicon seriously affect the service performance. In this study, an in-situ laser-vibration hybrid assisted diamond cutting technology is proposed. The properties of cutting device were tested as experimental parameters. A series of grooving experiments were carried out with different cutting methods and the microlenses on silicon were successfully fabricated based on better manufacturing parameters. The surface morphology and subsurface damage was investigated from sin-wave structure manufacturing. Experimental results show that in-situ laser-vibration hybrid assisted diamond cutting effectively improves surface quality and inhibits subsurface lattice distortion. Compared with conventional diamond cutting, the depth of brittle transition increases by about 10 times with 1075 nm. Under the same cutting parameters, the formation of surface cracks of microlenses and sin-wave structure are significantly inhibited by applying in-situ laser-vibration hybrid assisted diamond cutting. This new technology is an effective and promising method for ultra-precision machining silicon. [Display omitted] • In-situ laser-vibration hybrid assisted diamond cutting technology is proposed and used in machining single crystal silicon novelly. • Compared with conventional diamond cutting, the depth of brittle transition increases by about 10 times with 1075 nm. • Surface and subsurface quality is improved compared with single force- or heat-field assisted cutting. [ABSTRACT FROM AUTHOR]

The transition of material removal mode of polycrystalline 3C-SiC cutting with temperature, i.e., from brittle mode cutting that is dominated by inter-granular fracture and grain pulling-out at low temperature to ductile mode cutting that is governed by intra-granular cracking and dislocation slip. [Display omitted] • Temperature-dependent mechanical properties of both grains and GBs in polycrystalline 3C-SiC at elevated temperatures are derived. • Temperature-dependent properties of 3C-SiC GBs are bridged between MD simulation and FE simulation with cohesive zone model. • There is transition from brittle mode by inter-granular fracture toductile mode by intra-granular cracking with temperature. While the deformation behavior of grain boundaries has a strong impact on the mechanical response of polycrystalline materials, investigating the coupled thermal–mechanical properties of grain boundaries in their real formats is crucial for enhancing the ductile machinability of hard brittle polycrystalline ceramic materials. In the present work, we report the thermal softening-suppressed inter-granular fracture, accompanied with enhanced stacking fault formation, increased healing ability of grain boundaries and promoted ductile material removal, in diamond cutting of polycrystalline 3C-SiC at elevated temperatures by multi-scale simulations. Molecular dynamics simulations and experiments of high temperature nanoindentations are performed to derive the temperature-dependent mechanical properties of bulk polycrystalline 3C-SiC. Furthermore, molecular dynamics simulations of Mode I (tension) and Mode II (shearing) loading of a Σ9<1 1 0>{1 2 2} symmetric tilt grain boundary at elevated temperatures are performed to extract the temperature-dependent mechanical properties of grain boundaries in polycrystalline 3C-SiC. A novel finite element model of heat treatment-assisted diamond cutting of polycrystalline 3C-SiC with the comprehensive consideration of thermal properties of both grains and grain boundaries at elevated temperatures is established to reveal the transition of material removal mode, grain boundary failure behavior, cutting force characteristics and chip profile with temperature. [ABSTRACT FROM AUTHOR]