Graphite interface mediated grain-boundary sliding leads to enhanced mechanical properties of nanocrystalline silicon carbide

Mechanical properties and microstructural deformation characterization of nanocrystalline silicon carbide (n-SiC) have been studied at room-temperature by using nanoindentation and uniaxial microcompression tests abetted with Raman spectroscopy and transmission electron microscopy (TEM). The enhanced mechanical properties of n-SiC observed from indentation and uniaxial micropillars compression tests is mainly attributed to nano-size effect and soft interface phase at the grain boundaries. TEM reveals that the n-SiC upon deformation undergoes grain boundary sliding with the assistance of graphitic interface phase thereby enhancing the strength, fracture toughness and plasticity. The critical crack length values estimated for n-SiC are two to three orders of magnitude smaller than that usually found for brittle ceramics, which implies that plasticity can be achieved before crack initiation and failure. Our density functional theory molecular dynamics simulations agree with the experimental results and provide an atomistic insight in which the graphite along the grain boundary facilitates the grain boundaries sliding in n-SiC.