Random and correlated damage initiation in impact-loaded SiC ceramics

Samples of SiC ceramics differing in porosity in the range 1–9 % were damaged by a falling weight, and the acoustic emission (AE) and fractoluminescence (FL) activity lasting up to 1.3 μs was detected. The recorded time series of AE and FL pulses were used for constructing the energy release distributions in individual damage events occurring at the microscopic and nanostructural scale levels, respectively. A critical pore concentration was found, at the transition over which the random energy release in primary defect nucleation changes for the scaling one at the nanostructural level. These changes in the mechanical behavior were explained by the growth of the area of the oxidized film on the pore surface in more porous sintered samples. At the microstructural scale level, any qualitative changes in the scaling mechanical behavior of ceramics were not observed.