High temperature deformation of spinel-zirconia composites Effect of zirconia content

摘要

Creep experiments have been performed on a spinel matrix and two composites, containing 20 and 30 wt. percent of zirconia particles, respectively, in stress and temperature ranges 8-200 MPa and 1350-1410 deg C. The creep rates may be described as the result of two sequential processes that occur at low and high stress, respectively. In addition, a threshold stress was observed that strongly complicated the determination of the stress and grain size exponents and of the activation energy at low stress. The plastic flow of composites may be deduced from that of the spinel matrix by an inclusion model that considers the zirconia grains as soft inclusions. This description reinforces the role of spinel-spinel boundaries in the deformation of the composites, in agreement with measurements of grain boundary sliding capacity for the two kinds of boundaries present in the composites. A model developed by Artz et al. [E. Artz, M.F. Ashby, R.A. Verrall, Interface controlled diffusional creep, Acta Metall. 31 (1983) 1977-1989] may account for the creep rates of the matrix at low stress with a good accuracy. This model supposes that the boundary dislocation density is the factor that limits the creep rates in this low stress range. The grain boundary sliding is probably accommodated by grain boundary diffusion in the whole stress range.