AN EXAMINATION OF THE IMPLICATIONS OF VOID GROWTH IN SUBMICROMETER AND NANOCRYSTALLINE STRUCTURES

Tensile experiments were conducted on fully dense tetragonal zirconia stabilized with approximately 3 mol% yttria and with a submicrometer grain size. Examination of the specimens after superplastic-like flow revealed the development of internal cavitation and the extent of the cavitation increased with increasing strain rate. Nanocrystalline materials have an apparent potential for superplastic forming operations but this potential may be limited because of the presence of residual porosity from the fabrication process or because of the nucleation and growth of cavities during superplastic flow. It is shown by calculation that diffusion will play a dominant role in the growth of internal voids in nanocrystalline structures because each grain boundary impinging on a void provides a path for rapid diffusion.