Estimation of thermal shock fracture toughness of Si3N4

An infrared radiation heating method was proposed previously as anew technique for estimating thermal shock strength and thermal shock fracture toughness of ceramics using a thin-circular disk with or without an edge crack, heated by infrared rays at the center with a constant heat flux. In this paper, thermal shock fracture toughness was measured by the above method in four kinds of silicon nitride. Temperature distributions, thermal stresses and stress intensity factors for the specimens were also analyzed considering the temperature dependent thermal conductivity, thermal diffusivity and thermal expansion of the materials. The experimental results show that the highest value of thermal shock fracture toughness was observed in the material having the higher thermal conductivity, which was developed by growing the grains and decreasing the amount of the grain boundary phase.