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.
Highlights
Due to high specific stiffness, high chemical inertness, high thermal conductivity and enhanced radiation stability, silicon carbide (SiC) is emerging as a prime candidate for several engineering applications, which are common in combustion environments, military-grade vehicle control sensing and space exploration [1,2,3,4]
As a typical hard and brittleness material, hot pressed (HP)-SiC is difficult to machine as it always generating surface defects and considerable subsurface damage during processing, which affects the lifetime of components
High quality products of ceramics free of cracks can be achieved by ductile regime machining
Summary
Due to high specific stiffness, high chemical inertness, high thermal conductivity and enhanced radiation stability, silicon carbide (SiC) is emerging as a prime candidate for several engineering applications, which are common in combustion environments, military-grade vehicle control sensing and space exploration [1,2,3,4]. The grinding process involves a complex behavior of interaction between mass random grains that are distributed on the wheel and workpiece surface Such cases that lead to the exploration of machining deformation and removal mechanisms are difficult. Cao et al [7] found the cutting ability of the tool was significantly improved by the assistance of ultrasonic when comparing the results of scratch tests with and ultrasonic assistance They put forward that the critical depth of cut for the ductile to brittle transition is increased by 56.25% with ultrasonic assistance. A comprehensive scanning electron microscope (SEM) observation for scratch topography and Raman analysis of the removal mechanism were completed to explain the strain rate effect on the DBT of HP-SiC ceramics. The results will provide a more practical investigation for the ductile machining of HP-SiC, which helps to minimize and avoid the induced damages in machining processes
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