Heterogeneous Ceramics Research Articles

Effect of temperature on the densification/creep viscosity during sintering

The densification and creep rates of polycrystalline zinc oxide and of alumina powder compacts have been measured simultaneously in a loading dilatometer, under constant heating rate and constant temperature conditions. The data show that the ratio of the densification to the creep rate is remarkably constant within a wide temperature range for densification, from the earliest stages of densification to at least the onset of the final stage. As a consequence, the ratio of the densification to the creep viscosity is nearly independent of temperature or sintered density. The analysis leads to a simple method for determining the simultaneous densification over the creep rate ratio. The implications of the result for the processing of heterogeneous ceramics and composites are discussed.

Subcritical growth of long cracks in heterogeneous ceramics

This paper models the subcritical growth of long cracks in ceramic structures containing heterogeneities. In such cases, the microstructure is believed to promote deflection of the crack. Due to this, the following effects are observed: (i) there is scatter in the KI-V data; (ii) N, the subcritical crack growth susceptibility coefficient, as obtained from specimens with long cracks, erroneously shows large values as compared to specimens with small flaws; and (iii) the lifetimes predicted from long-crack experiments (especially in the double torsion load relaxation mode) are more than the predictions from short cracks. All of the effects mentioned above are explained by the present model.

Subcritical growth of long cracks in heterogeneous ceramics

Subcritical growth of long cracks in heterogeneous ceramics