A molecular dynamics investigation into nanoscale scratching mechanism of polycrystalline silicon carbide

In this study, 3D molecular dynamics simulations were conducted to investigate the nanoscale scratching mechanism of polycrystalline SiC constructed by Voronoi site-rotation and cut method. The scratching process, SiC crystal structure evaluation, scratching force, stress, and temperature, surface morphology, and subsurface damage (SSD) were discussed after simulation. The results indicate that the ductile scratching process of polycrystalline SiC could be achieved in the nanoscale depth of cut through the amorphous crystal structure phase transition, which is the primary material removal mechanism in nanoscale SiC scratching. The silicon atom can penetrate into the diamond grit which may cause the wear of diamond tool. The disorder grain boundary (GB) atoms can transit to hexagonal diamond structure and generate dislocation during the scratching. Furthermore, the higher scratching speed results in smaller scratching force, smaller normal stress, and higher temperature due to the larger impaction breaking more Si-C bonds, which makes the SiC material more ductile and easier to remove. The tangential stress shows great dependence on the grain and GB geometry and position due to the stress concentration in the GB. It is also found that the higher scratching speed encourages the pileup atoms in the front of grit to flowing to the grit side to form the groove protrusion, which can get a shallower SSD thickness and a wider SSD layer. SSD results also indicate that at least three types of the material removal mechanism-amorphous transition, intergranular fracture, and transgranular fracture - exists in the polycrystalline SiC scratching process. (C) 2018 Elsevier B.V. All rights reserved.