SANS investigations of porosity in superplastically deformed ceramics

V. Ryukhtin^1,2, J. Šaroun¹, S. Harjo³, Y. Motohashi³

1-Nuclear Physics Institute, 25068 Řež near Prague, Czech Republic.

2-Charles University, Faculty of Mathematics and Physics, Ke Karlovu 3, 121 16 Praha 2, Czech Republic.

3-Ibaraki University, Faculty of Engineering, The Research Center for Superplasticity, Hitachi, Ibaraki, 316-8511 Japan.

Superplastic deformation of ceramics leads to the creation of cavities, which have a significant influence on the mechanical and thermal properties of the final product. Small-angle neutron scattering (SANS) is a unique tool for non-destructive measurement of these cavities, which provides information averaged over the macroscopic volume of deformed material [1]. Superplastically deformed samples of 3Y-TZP (3 mol% yttria stabilized tetragonal zirconia polycrystals) and 3Y-TZP and 20wt% of Al₂O₃ samples were studied by SANS. The specimens were pulled in tension up to nominal strains ranging from 0.0 to 150% at two different strain rates. Measured scattering curves obey the Porod law and therefore do not provide information about the size of the cavities. However, analysis of the 2-dimentional SANS data permits to evaluate the specific surface and anisotropy. Observed scattering curves can be interpreted by a model consisting of two types of pores - prolate cavities with longer axis oriented parallel to the strain and flat cracks or coalesced cavities oriented perpendicular to the strain axis. The latter were not observed in the material containing Al₂O₃ and their amount increased with increasing applied strain and strain-rate. Significantly lower scattering intensity for the samples containing alumina indicates that the volume of cavities generated in the course of deformation is much lower compared to the pure 3Y-TZP.

[1] S. Harjo, N.Kojima, Y.Motohashi, J.Saroun, V.Ryukhtin, P.Strunz, M.Baron, R.Loidl, Mater. Trans. 43 (2002) 2480-2486.