科研之友
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摘要
Recent developments in SiC based ceramic materials have shown a possibility of graphene dispersion at grain boundaries (GBs) significantly modifying bulk thermomechanical properties. Graphene and SiC have been known to have significant electronic affinity for each other. This work presents an electronic density of states-mechanical strength correlation based understanding of the effect of graphene layer defects on the tensile strength of selected 3C-SiC GBs that incorporate graphene layers. The tensile deformation simulations are performed using Car-Parrinello molecular dynamics (CPMD) method. Three different SiC GBs are examined (unit GB, Sigma 3 tilt SiC GB, and Sigma 9 tilt SiC GB). For each examined GB type, graphene layers with four different defect types are examined. Analyses establish quantitative correlation between the tensile strength of the examined GBs and graphene defect type in GBs. Of the defects examined, double vacancy defect most significantly deteriorates GB strength. GB failure strain is mainly determined by graphene cleavage fracture strain. Graphene cleavage is accompanied by monoatomic carbon chain formation, pentagon ring formation, and heptagonal ring formation. The specific mechanism closely depends upon the graphene-SiC interaction strength defined based on total electron density of states. The interaction strength variation is found to be closely correlated to the tensile strength variation in GBs. Examination of electron density variation points to specific sites of graphene cleavage fracture that correlates to earlier failure mechanism observations. Observations are used to predict strength of SiC GBs as a function of GB misorientation angle. The developed relation predicts other reported values in literature quite closely.
- 出版日期2014-9
