MICROTENSILE SUPERPLASTICITY IN CERAMIC FIBERS

Superplastic experiments were carried out in tension on small specimens having a cross section of approx. 50 x 1.1-mu-m, and a gage length of 4 mm. The specimens, in the form of fibers, were prepared by lithography from thin films that were obtained by physical vapor deposition. Experiments with ZrO2-2.6 mol% Y2O3 exhibited a threshold stress for superplastic flow. While the measurements of the average flow stress were in agreement with data from bulk materials, the stress-strain curves obtained from the microspecimens were serrated, which we attribute to discrete grain sliding events. The serrations are believed to occur because the gage section contained relatively few grains. A new approach for conceptualizing superplastic flow in ultrafine grained ceramics is proposed.