Multiscale modeling of the thermal conductivity of polycrystalline silicon carbide

Abstract

A multiscale modeling, involving molecular dynamics and finite element calculations, of the degradation of the thermal conductivity of polycrystalline silicon carbide due to the thermal (Kapitza) resistances of grain boundaries is presented. Molecular dynamics simulations focus on the ⟨111⟩ family of tilt grain boundaries in cubic SiC. For large tilt angles a simple symmetry and shift procedure is used to generate the grain boundaries while for small angles the boundary structure is obtained by inserting arrays of edge dislocations. The energy and thermal resistances of the grain boundaries are presented. The latter are fed into a finite element homogenization procedure, which enables to calculate the effective thermal conductivity of the SiC polycrystal as a function of its average grain size. The decrease in the thermal conductivity of a polycrystal as a function of its grain size is qualitatively reproduced. However, available experimental values of the thermal conductivity of polycrystalline SiC tend to indicate that the present Kapitza resistances cannot be directly used for prediction of the thermal conductivity of polycrystalline silicon carbide. We suggest possible explanations for this discrepancy, which seems rather common to Kapitza resistances calculated with molecular dynamics simulations.