Internal friction of polycrystalline ceramic oxides

Low-frequency internal friction behavior was investigated in high-purity Al2O3 and MgO polycrystals, with emphasis placed on the anelastic peak component arising from grain-boundary relaxation. Internal friction measurements were performed at temperatures up to approximate to 2000 K, with varying both the oscillation frequency and the grain size of the polycrystal by about one order of magnitude. A fitting procedure is shown which enables us to separate the anelastic peak component from the overall internal friction response. An analysis of the peak shift at frequency change was considered as a method of experimentally deriving both the activation energy for the elementary transport phenomenon occurring with viscous slip at the grain boundary, and the magnitude of the intrinsic grain-boundary viscosity. A classification of the viscous response of grain boundaries according to their degree of coherency and an estimate of their thicknesses, namely the region over which atomic diffusion is enhanced, was also attempted. For this purpose, a peak deconvolution analysis was performed with the evolution of the peak morphology monitored as a function of grain growth in the respective polycrystals when subjected to repeated annealing cycles. [S0163-1829(99)01830-4].