Influence of Flat Cavity Formation on Stress vs. Strain and Strain-Rate Relations of Superplastic Deformation in 3Y-TZP

Abstract

During superplastic deformation (SPD) of tetragonal zirconia polycrystals containing 3 mol% yttria (3Y-TZP) at high strain-rates, a number of crack-like flat cavities having very narrow gaps lying along grain boundaries mostly normal to the tensile axis are produced in addition to conventional cavities. In order to see when (from which strain point) the flat cavities get started to form, the tensile deformation of the 3Y-TZP was interrupted at different strain points including a yield point, and then a small angle neutron scattering (SANS) technique was applied to examine the existence of the flat cavities. It was found that no flat cavities were produced at the yield point but they got started to form soon after the yielding, i.e., after a superplastic flow began. The formation of the flat cavities can decrease the cross-sectional area of the specimen, resulting in a decrease in the flow stress apparently. It is therefore recommended that the formation of the flat cavities should be taken into consideration for an accurate evaluation of the flow stress in SPD at high strain-rate deformations. [doi:10.2320/matertrans.M2009381]