Damage characteristics and material removal mechanisms of CVD-SiC in nanotests: A comparative with sintered SiC

Abstract

High sensitivity to crack and damage of chemical vapor-deposited silicon carbide (CVD- SiC) restricts the high-efficiency and low-damage manufacturing of CVD-SiC components. This paper aims to reveal the damage and material removal mechanisms of CVD-SiC after being scratched by diamond abrasives. The mechanical properties, scratching force, depth of ductile-brittle transition, residual depth and material removal damages of the CVD-SiC were discussed by the indentation, nano-scratching experiments, and compared with sintered silicon carbide (SSiC) ceramics. The results demonstrated that the mechanical properties of CVD-SiC are better than SSiC. In terms of hardness and fracture toughness, CVD-SiC demonstrates a 10– 20% and 20– 30% higher level of performance than SSiC, respectively. SSiC exhibits a brittleness level approximately 30% higher than that of CVD-SiC. SSiC ceramics are prone to crack deflection, intergranular fracture and transgranular fracture during indentation, indicating a higher propensity for brittle fracture in SSiC. The crack propagation in CVD-SiC is relatively regular. Both materials undergo the ductile, ductile-brittle transition and brittle stage, and the fluctuation variability of CVD-SiC material is notably lower than that of SSiC during the brittle stage. Compared with SSiC, the residual depth, groove width and transverse force of CVD-SiC are smaller under the same normal load. The critical depth of ductile-brittle transition of CVD-SiC is about 2 times that of SSiC in experimental and theoretical, indicating that CVD-SiC easily achieves ductile grinding. The mechanical properties, crack system and crystal structure of the CVD-SiC and SSiC materials cause the divergences in brittle removal. The radial-median crack system dominates the material removal of CVD-SiC. The disparity of deformations on the inside and outside of the crystal in the brittle stage leads to significant fluctuation variability of force and depth of SSiC during the scratching.