Internal Friction Analysis of CaO-Doped Silicon Carbides

Abstract

Internal friction originated from sliding and diffusional flow along grain boundaries was monitored (as a function of both temperature and damping frequency) in model SiC polycrystals with an intergranular SiO 2 glassy film. Emphasis was placed on the change of the internal friction characteristics upon additional Ca cation. It is expected that Ca cation segregates to the intergranular glass phase and modifies its network structure. The presence of a relaxation peak of internal friction due to grain-boundary sliding enabled quantitative evaluation of the activation energy for viscous flow of the intergranular glass and the related viscosity magnitude. A peak-analysis procedure, according to the peak-shift method (i.e., monitoring peak shift upon damping frequency change), is proposed, which quantitatively revealed the activation energy for viscous flow in various impurity-doped intergranular glasses. The presence of chemical gradients at grain boundaries, namely the presence of families of boundaries within the SiC polycrystal with different chemical characteristics, has also been analyzed by taking into account the dependence of peak morphology on damping frequency.