Defect-shape effect on strength and toughness in SiC nanowires

Abstract

Silicon carbide (SiC) nanowires (NWs) are important candidates for revolutionizing a number of power electronics and high-temperature thermal and structural application areas. Despite rigorous theoretical studies available on effective elastic modulus of nanostructured materials (such as nanotubes or nanowires), the methodologies applicable for determining extreme mechanical properties (such as strength and toughness) remain inadequate. The difficulty arises from the challenge in measuring the structural parameters of nanowires and determining their complex stress patterns that directly affect nucleation and propagation of cracks. Furthermore, brittle nanowires always contain defects of different shapes. This makes it even more challenging to examine the mechanical properties of nanowires. A few papers discussing the diameter dependence of mechanical properties and crack behaviors of defect-free nanowires have been published recently. But research on defect-shape effect is still rare. ☐ In this thesis, SiC nanowires containing defects of different shapes are investigated using atomistic simulations. The results show both strength and toughness of nanowires to be strongly dependent on the shape of the defect as well as the various structural parameters (such as aspect ratio, length, cross-sectional area, and etc.) describing the defect. An atomic scale analysis of stress distribution and bond strain is used to describe the shape-dependent properties. Furthermore, using the variation in stress distribution, we elucidate the relation between the structural characteristics with crack nucleation and propagation path in the nanowire for different defect shapes.