A fractal analysis of the crack extension paths in a Si3N4 ceramic tool composite

Abstract

A Si3N4/TiC0.7N0.3 ceramic tool composite with high flexural strength and fracture toughness was fabricated by hot-pressing sintering technology. The microstructure of the composite was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The crack extension paths were analyzed by the fractal geometry method, which were obtained by Vickers indentation, microstructure detection and thermal shock tests. The analysis results showed that the crack paths in the Si3N4 composite had a very obvious fractal characteristic. The fractal dimensions of the crack paths and fracture surfaces were calculated based on the box counting. The crack propagation of the composite, including crack deflect, bridging, internal propagation and a mixed fracture type, was characterized by a more tortuous path which increased the propagating resistance. Especially, the crack deflection and the mixed fracture type played a more effective role in the crack resistance. Moreover, the cracks showed higher deflection angles and more complex structure of the fracture surface, while the composites presented higher fractal dimension. Thus, the fractal method can provide an effective means to quantitatively describe the resistance to cracks and fracture.