Mechanical properties, stress distributions and nanoscale deformation mechanisms in single crystal 6H-SiC by nanoindentation

Abstract

© 2017The nanoscale elastic-plastic deformation behavior of single crystal 6H-SiC was systematically investigated by using nanoindentation with a Berkovich indenter. The effect of loading rates on the critical pop-in load, pop-in displacement and maximum shear stress was observed which indicates that phase transformation in 6H-SiC is highly unlikely. Results further indicated that the elastic-plastic transition was evidenced by stable pop-in events under conditions of an indentation load of 0.54 mN with a loading rate of 20 µN/s. In the load-independent region, hardness was determined as 33 ± 2 GPa and elastic modulus had a stabilized value of 393 ± 8 GPa. The significant indentation size effect and depth independent hardness in 6H-SiC was analyzed by Nix-Gao and proportional specimen resistance models. By coupling the Hertzian contact theory and Johnson's cavity model, elastic-plastic transitions were determined in detail. Johnson's cavity model was used to figure out the plastic zone size. The stress distribution was also calculated based on the critical load responsible for the elastic plastic transition. Theoretically, the calculated maximum tensile strength (13.5 GPa) and cleavage strength (31 GPa) revealed that the pop-in was not initiated by the cleavage fracture. The deformation behavior was further elaborated to confirm the slippage on the basal plane determined by the critical resolved shear stress and Schmidt factor analysis.