Fracture Properties for Advanced Pore-Free SiC Dispersing of Si Particles

Advanced pore-free SiC (APF-SiC) with uniformly dispersing metal Si particle was developed by new process of manufacture. This ceramic material was investigated for mechanical properties and fracture behavior by evaluating tests such as 4-point bending, static fatigue and indentation at room temperature. It was found that bending strength of APF-SiC indicates about two times of strength for usual reaction-sintering SiC (RS-SiC). In addition, their mechanical properties (such as Poisson's ratio and Fracture toughness) are nearly equal. However, as for Weibull modulus and Young's modulus APF-SiC became smaller than RS-SiC. It is considered to be due to difference of their fracture mechanics. APF-SiC has the dispersing metal silicon particles of about 100 nm instead of the potential defects. As the load given to a specimen increases, a lot of cracks continues to occur in the boundary between metal silicon and silicon carbide and so the strain energy in and around them is released. Some clusters are formed by uniting some cracks. When maximum stress intensity factor around the cluster reached to a critical value, macroscopic fracture occurred with fracturing from some places at same time. The scatter as well as the fracture strength depends on the size of a cluster. In the static fatigue test of APF-SiC, the time dependence was not recognized in fracture strength. In addition, all experimental values obtained were more than the average of bending strength. This fracture strength property can be explained by a conceptual model that the cracks due to a constant bending load had stopped initiating and started uniting on releasing the energy around the cluster of many cracks.