Fully amorphous ceramics in the system silicon-carbon-nitrogen were produced with the polymer precursor route using the commercially available polysilazane CerasetTM. Besides their high temperature thermal stability, these ceramics show excellent high temperature creep resistance. Not many investigations have been dedicated to the fracture mechanics of these materials. This paper provides data on toughness measurements utilizing bulk and indentation techniques. The double cantilever beam method (DCB) was used to study crack propagation. To determine the intrinsic toughness, the crack opening displacements (COD) of indentation cracks were determined.

Precursor‐derived Si‐C‐N ceramics after creep testing in air were characterized using X‐ray diffractometry (XRD) and transmission electron microscopy (TEM). XRD analysis showed that the crept Si‐C‐N ceramics were covered by an α‐cristobalite layer. TEM observations revealed that the precipitated nanocrystallites in the crept Si‐C‐N ceramics were β‐SiC. Between α‐cristobalite and crept Si‐C‐N ceramic, there was an intermediate zone in which Si2N2O nanocrystallites were distributed homogeneously. Moreover, Si2N2O nanocrystallites were often found covering the surface of nanosized gas channels in the crept Si‐C‐N ceramics, where no α‐cristobalite phase was detected. Based on these observations, a two‐step oxidation mechanism of Si‐C‐N ceramics during creep testing in air was proposed.

This work focuses on the high-temperature deformation of amorphous Si–(B)–C–N ceramics fabricated from polymers. Compression creep tests were performed at temperatures of 1350–1500 °C with stresses ranging from 5 to 300 MPa. A continuous decrease in the deformation rate with time is found. Overall, the total deformation rate can be decomposed into free shrinkage, anelastic deformation and viscous deformation. Although the viscosity depends on the annealing treatment, it is independent of the loading history. The linear rise in the viscosity and the decrease in the shrinkage rate are thought to be related to defect annihilation during annealing.

The toughness of amorphous precursor‐derived ceramics in the Si‐C‐N system is investigated. Crack‐growth data are obtained from DCB specimens, whereas the crack‐tip toughness is determined from the crack‐tip profile of indentation cracks. For amorphous Si‐C‐N ceramics that have been fabricated via the powder route, an R‐curve effect is observed. The initial values of the rising R‐curve are consistent with the estimated crack‐tip toughness.