Characterization of Cavities in Superplastically Deformed Tetragonal Zirconia Polycrystals by Means of Small Angle Neutron Scattering
Abstract
Small angle neutron scattering (SANS) method was applied to investigate morphology of cavities in superplastically deformed 3 mol% yttria stabilized tetragonal zirconia polycrystals (3Y-TZP). The 3Y-TZP specimens were deformed in tension at 1723 K with an initial strain rate of 3.3×10−4 s−1 in the air to pre-determined nominal strains ranging from 0.0 to 200%. Three kinds of SANS instruments having individually different scattering vector ranges were used. Results obtained from a pinhole SANS instrument revealed that initially fine and equi-axed cavities evolved, with the progress of the deformation, into the anisotropic ones with their longest diameters parallel to the tensile direction. Results obtained from a double bent-crystal and a Bonse-Hart SANS instruments showed that the average radius of all cavities existing in the specimens decreased initially with increasing nominal strain, but subsequently this trend was reversed when the nominal strain exceeded about 100%. Specific surface of cavities began to increase at a nominal strain of approximately 20%. Size distributions obtained from the SANS data showed that highest peaks appeared at a cavity radius of around 200 nm for each of the specimens deformed to different strains, which indicated that the cavities with radius of around 200 nm accounted for the largest in number among all the cavities existed.