High Temperature Behaviour of Al2O3-SiC Nano Composites

Internal friction experiments were performed on Al2O3 materials reinforced with SiC nanoparticles with the aim to further investigate and validate a previously proposed high temperature deformation mechanism involving combined recoverable viscoelastic and plastic phenomena. For internal friction assessment, sinusoidal loading/unloading cycles were applied to bending samples both at various loads and temperatures using two different frequencies. During the tests, stress and strain variation were continuously recorded as a function of time. At the lower test temperature, i.e. 1200 C, the presence of a viscoelastic effect of the K-V type is supported by the shape of the curves issued from experimental data and those predicted from an analytical expression. At 1300 C, an additional plastic strain undoubtedly takes place, as a slight and continuous shift of the elliptical loops towards larger strains is emphasised, independently of the frequency used. On the basis of previous creep experiments, this permanent strain can be attributed either to non-recoverable GBS limited to SiC free grain boundaries or to dislocation motion (above a threshold stress value), as confirmed by TEM observation. 6 refs.