Predict the fatigue unloading elastic-plastic reduction mechanism of single crystal 3C-SiC Newton layer by reconstructed multi-dimensional dynamic static combination indenter

Abstract

To explore the elasto-plastic reduction mechanism of single crystal 3C-SiC Newton layer under fatigue unloading. Reconstructed multi-dimensional single crystal 3C-SiC Newton layer unloading dynamic - static combined head. The evolution law of dislocation loop, the trend of load displacement and the direction of strain concentration expansion during fatigue unloading are analyzed. According to the stress characteristics of nanoindentation process and the requirements of real indentation environment, the NVE ensemble matrix and boundary condition parameters are integrated and optimized. The influence of indenter shape on the evolution process of dislocation ring emergence, fracture and connection and the evolution mechanism are analyzed. Through diamond identification method and stress-strain analysis method, the multi-dimensional force analysis of plastic unloading of nano-indentation is realized. It is found that the yield limit of semi-circular indenter first reaches the yield limit from the elastoplastic loading stage to the plastic loading stage than the normal four-cone. Combined with the load displacement curve, the real stress characteristics of the nano-indentation single crystal 3C-SiC Newton layer are analyzed. The results show that elastoplastic reduction existed in fatigue unloading, and the generation and development of micro-dislocation rings in elastoplastic deformation reduction under fatigue unloading of different dimensions indenter are different. The ultimate yield stress of semi-circular indenter is 3.82GPa and the ultimate strain is 1 %，the ultimate yield stress of positive quad conical indenter is 6.60GPa and the ultimate strain is 1.5 %. The elasto-plastic reduction mechanism of fatigue unloading is directly driven by the plastic evolution mechanism of dislocation ring.