Numerical modelling of the effect of microstructure on thermal conductivity of highly anisotropic silicon nitride at elevated temperatures

Silicon Nitrides (Si3N4) are potential candidates for the structural components and wear parts in engines. However, the thermal conductivity of Si3N4 ceramics is variable. Understanding on the control mechanisms of thermal conduction is important to fabricate Si3N4 ceramics with desired thermal conductivity. Experiments were usually used to study the thermal conductivity of ceramics. However, they usually give a combined result and are not conducive to figure out the contribution of each factor. In the present work, a microscopic model, which is two-dimensional and doesn’t describe an isotropic case but a fibre-like configuration, is proposed to quantitatively characterize the effects of microstructures on the thermal conductivity of Si3N4 ceramics at elevated temperatures numerically. Microstructures are controlled conveniently by combining Voronoi diagram and grain boundary scaling. The heat transfer analysis is conducted using finite element method. The influences of temperature, grain boundary phase thickness and constituent, grain size, and grain size distribution on the thermal conductivity of Si3N4 ceramics are investigated. The control mechanism of thermal conductivity is discussed in view of microstructures.