PLASTIC-DEFORMATION OF CUBIC ZIRCONIA SINGLE-CRYSTALS AT 1400 DEGREES-C

Cubic zirconia single crystals stabilized with 11 mol% yttria were def ormed in air at 1400 degrees C and around 1200 degrees C at different strain rates along [1 (1) over bar 2] and [100] compression directions . The strain rate sensitivity of the flow stress was determined by str ain rate cycling and stress relaxation tests. The microstructure of th e deformed specimens was investigated by transmission high-voltage ele ctrum microscopy, including contrast extinction analysis for determini ng the Burgers vectors as well as stereo pairs and wide-angle tilting experiments to find the active slip planes. At deformation along [1 (1 ) over bar 2], the primary and secondary slip planes are of {100} type . Previous experiments had shown that the dislocations move easily on these planes in an athermal way. During deformation along [100], mainl y dislocations on {110} planes are activated, which move in a viscous way by the aid of thermal activation. The discussion of the different deformation behaviours during deformation along [1 (1) over bar 2] and [100] is based on the different dynamic properties of dislocations an d the fact that recovery is an essential feature of the deformation of cubic zirconia at 1400 degrees C. The results on the shape of the def ormation curve and the strain rate sensitivity of the flow stress are partly at variance with those of previous authors.