Abstract
Surface and subsurface damages appear inevitably in the grinding process, which will influence the performance and lifetime of the machined components. In this paper, ultra-precision grinding experiments were performed on reaction-bonded silicon carbide (RB-SiC) ceramics to investigate surface and subsurface damages characteristics and formation mechanisms in atomic scale. The surface and subsurface damages were measured by a combination of scanning electron microscopy (SEM), atomic force microscopy (AFM), raman spectroscopy, and transmission electron microscope (TEM) techniques. Ductile-regime removal mode is achieved below critical cutting depth, exhibiting with obvious plow stripes and pile-up. The brittle fracture behavior is noticeably influenced by the microstructures of RB-SiC such as impurities, phase boundary, and grain boundary. It was found that subsurface damages in plastic zone mainly consist of stacking faults (SFs), twins, and limited dislocations. No amorphous structure can be observed in both 6H-SiC and Si particles in RB-SiC ceramics. Additionally, with the aid of high-resolution TEM analysis, SFs and twins were found within the 6H-SiC closed packed plane, i.e., (0001). At last, based on the SiC structure characteristic, the formation mechanisms of SFs and twins were discussed, and a schematic model was proposed to clarify the relationship between plastic deformation-induced defects and brittle fractures.
Highlights
In the family of SiC, reactionbonded silicon carbide (RB-SiC) material has received ever increasing attention as a promising mirror material for space optical applications due to its high strength, high chemical inertness, enhanced radiation stability, thermal shock resistance and high specific stiffness (E/ρ) [1, 2]
Some undesirable surface and subsurface damage such as micro cracks, pulverization layer induced by brittle fracture, and plastic deformation defects are easy to generate in the grinding process, which will impact the surface integrity and reduce the lifetime of the machined components [6]
The results showed that pulverization and scattered cracks are the main grinding damage in the subsurface of SiC, and the damage depth is related to the brittleness property of the work material
Summary
In the family of SiC, RB-SiC material has received ever increasing attention as a promising mirror material for space optical applications due to its high strength, high chemical inertness, enhanced radiation stability, thermal shock resistance and high specific stiffness (E/ρ) [1, 2]. Specific to silicon carbide ceramics, Agarwal et al [18] conducted a high machining rate grinding experiments to study the surface/ subsurface damage formation and material removal mechanism. Mishra et al [26] used molecular dynamics simulations (MD) to investigate polycrystalline SiC wear in the nanoscale range with a nanoscale cutting tool They attributed atomic scale deformation mechanisms of SiC to grain-boundary sliding, which is accommodated by heterogeneous nucleation of partial dislocations, formation of voids at the triple junctions due to dislocation restrained and grain pull-out. Xiao et al [28] revealed that intensive dislocation activities, including Frank partial dislocations and basal plane edge dislocations play a major role in the ductile deformation These MD simulation studies provide a fundamental understanding of material removal and subsurface defects formation mechanisms. At last, based on the stress distribution around the abrasives and RB-SiC composite microstructures, the correlation of the plastic deformation defects with the crack nucleation and propagation is analyzed
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