Material removal mode and friction behaviour of RB-SiC ceramics during scratching at elevated temperatures

Thermal assistance is considered a potentially effective approach to improve the machinability of hard and brittle materials. Understanding the material removal and friction behaviour influenced by deliberately introduced heat is crucial to obtain a high-quality machined surface. This paper aims to reveal the material removal and friction behaviours of RB-SiC ceramics scratched by a Vickers indenter at elevated temperatures. The material-removal mode, scratching hardness, critical depth of the ductile–brittle transition, scratching force, and friction are discussed under different penetration depths. The size effect of scratching hardness is used to assess the plastic deformation at elevated temperatures. A modified model is established to predict the critical depth at elevated temperatures by considering the changes in mechanical properties. The results reveal that the material deformation and adhesive behaviour enhanced the ductile-regime material removal and the coefficient of friction at elevated temperatures

A new grinding force model for micro grinding RB-SiC ceramic with grinding wheel topography as an input

The ability to predict grinding force for hard and brittle materials is important to optimize and control the grinding process. However, it is a difficult task to establish a comprehensive grinding force model that takes into account of brittle fracture, grinding conditions and random distribution of grinding wheel topography. Therefore, this study developed a new grinding force model for micro-grinding of RB-SiC ceramics. First, the grinding force components and grinding trajectory were analyzed based on the critical depth of rubbing, ploughing and brittle fracture. Afterwards, the corresponding individual grain force were established and the total grinding force was derived through incorporating the single grain force with dynamic cutting grains. Finally, a series of calibration and validation experiments were conducted to obtain the empirical coefficient and verify the accuracy of the model. It was found that ploughing and fracture were the dominate removal modes, which illustrate the force components decomposed is correct. Furthermore, the values predicted according to proposed model are consistent with the experimental data, with the average deviation of 6.793% and 8.926% for the normal and tangential force, respectively. This suggests that the proposed model is acceptable and can be used to simulate the grinding force for RB-SiC ceramics in practical

Fundamental understanding of the deformation mechanism and corresponding behavior of RB-SiC ceramics subjected to nano-scratch in ambient temperature

To get insight into nano-scale deformation behavior and material removal mechanism of RB-SiC ceramic, nanoscratch experiments were performed using a Berkovich indenter. Structure changes in chips and subsurface deformation were characterized by means of Raman spectroscopy. The result shows that the SiC phase underwent amorphization in ductile chips, while no amorphous feature can be observed in brittle chips and substrate within scratch groove. The following estimated stress surround the indenter reveals that amorphous deformation in ductile chips is governed by tangential stress (above 95 GPa), whereas the dislocations-based substrate deformation mechanism was dominated by normal stress. In the end, the effects of normal load and scratching velocity on the scratch behavior including scratch residual depth, elastic recovery and friction coefficient that related to RB-SiC ceramic deformation mechanism were also analyzed. With the increase of normal load, the deformation mechanism transfers from ductile to brittle fracture mode and cause the decrease of elastic recovery and the increase of residual depth and friction coefficient. Furthermore, the increased high density of dislocations as a result of the increased scratching velocity give rise to the increase of scratch hardness, which finally result in the increase of elastic recovery and decrease of residual depth and friction coefficients. This study contributes a new understanding of the brittle material deformation mechanism during a nano-scale scratching process