Strain rate effect on the ductile brittle transition in grinding hot pressed SiC ceramics

Abstract

Surface and subsurface damage are still persistent technical challenges for the abrasive machining hot pressed-silicon carbide (HP-SiC) ceramics. Therefore, an investigation of the material behavior and critical depth of ductile to brittle transition (DBT) is essential for improving high precision and quality grinding HP-SiC ceramics. In this paper, single-grit grinding experiments with different scratch speed were conducted to study strain rate effect on the critical depth of DBT. The nanoindentations were performed to test the hardness and Young's modulus changes of DBT position under different scratch speeds. The material removal mechanism and phase changes underneath the scratch groove were investigated using Raman tests. Based on the specific energies consumed in ductile and brittle modes of machining, a theoretical model of the critical depth of DBT was developed. The experimental results suggest that high scratch speeds generate high nanohardness, high Young's modulus and high critical depth of DBT of HP-SiC ceramics. The measured critical depth of DBT shows a good agreement with the predicted value calculated by the developed model. The subsurface damage depth reduced with high strain rate. Furthermore, the Raman results revealed that dislocations and amorphous transformation dominated the ductile removal mechanism of HP-SiC grinding. The fracture chips and subsurface damage depth was determined by the lateral crack and median crack, respectively. This paper's results provide a fundamental understanding of the effect of grinding speed on the material removal mode of HP-SiC ceramics.