Grain‐Boundary Viscosity of BaO‐Doped SiC

Internal friction characterization of the viscosity of a residual SiO 2 /BaO glass, segregated to grain boundaries of polycrystalline SiC, is presented. The anelastic relaxation peak of internal friction, arising from viscous slip along grain boundaries wetted by a glass phase, is analyzed. Two SiC polycrystals, containing SiO 2 /BaO glasses with different compositions, are studied and compared with a SiC polycrystal containing only pure SiO 2 . The internal friction peak is first analyzed with respect to its shift upon frequency change. This analysis allows quantitative assessment of both the intrinsic viscosity and the activation energy for viscous flow of the grain‐boundary phase. Both parameters markedly decrease with increasing amounts of BaO dopant, which is consistent with data reported in the literature on SiO 2 and SiO 2 /BaO bulk glasses with the same nominal composition. Analysis of the peak morphology is also attempted, considering the evolution of peak width while varying the grain‐boundary glass composition. Moreover, the role of microstructural parameters, such as the distributions of grain size and grain‐boundary angles, on the broadening of the internal friction peak is addressed, and a procedure is proposed that allows quantitative evaluation of the activation energy for viscous flow of intergranular glass merely from the width of the internal friction peak.