Internal friction of alumina polycrystals with engineered grain boundaries was measured in the low frequency range of the torsional forced-vibration. The maximum shear stress amplitude was 50MPa. Owing to the very high temperature reached during these experiments (1900K), internal friction spectra could be detected which revealed new important features of the intrinsic rheological behavior of alumina grain boundaries. The monotonically rising internal friction background and the torsional creep behavior, both of a diffusive origin, were systematically characterized upon modifying the grain-boundary structure of alumina with the addition of selected cation dopants (e.g., Ti and Lu). The combined characterizations of internal friction spectrum and torsional creep rate permitted the precise assessment of the role played by various cation dopants in locking or promoting the diffusive grain-boundary flow, which governed polycrystal deformation.

Internal Friction Behavior of Alumina Polycrystals with Engineered Grain Boundaries. K.Nakagawa, G.Pezzotti, K.Ota, Y.Ikuhara, H.Yoshida, T.Sakuma: Materials Transactions, 2002, 43[7], 1557-60