Insights into Indentation Cracking of 6H-SiC at Elevated Temperatures Using 3D-FIB Tomography and Crystal Plasticity Coupled with Cohesive Zone Modeling.

High-temperature fracture behavior of the 6H-SiC was investigated using a combination of high-temperature nanoindentation, 3D-FIB tomography, and crystal plasticity finite element modeling coupled with cohesive zone modeling (CPFEM-CZM). At temperatures above 400°C, a clear transition of the indentation-induced crack morphology was observed, including the shift from three-fold ⟨ 11 2 ¯ 0 ⟩ to six-fold ⟨ 10 1 ¯ 0 ⟩ corner cracks, and the formation of sub-surface lateral cracks. This thermally-activated transition of crack morphology was clearly captured by incorporating the orientation-dependent slip laws and cohesive surface energies into the CPFEM-CZM modeling, after calibration with the experimental load-displacement data. Successful validation of the CPFEM-CZM model allows detailed extraction of the plastic work and cohesive surface energy from individual crack surfaces, and provides a physical- and indentation-based method for measuring fracture toughness from materials with anisotropic plasticity and fracture. The complicated interplay between plasticity and fracture at the nanoscale can be understood mechanistically using such techniques, which aligns well with the theme of this special edition on bridging the length scale effects in mechanical testing. We dedicate this manuscript to Professor Gerberich's pioneering work in small-scale fracture mechanics, and hope to continue his legacy.