Crystallography and Interlamellar Stresses in NiO-ZrO₂(cubic) Directionally Solidified Eutectics. C.R. Hubbard^#, E.C. Dickey^* and V.P. Dravid^{*; #}High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, TN 37831 and ^*Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208.

The preferred growth directions of [-110]_NiO//[100]_ZrO2 result in strong crystallographic texture and formation of directionally solidified eutectics (DSEs). The DSE specimens are composed of grains of the order of 0.1-0.2 mm. Within a grain, the NiO and ZrO₂ lamellae have specific crystallographic orientation relationships and each grain is essentially two interpenetrating single crystals. The interfaces between the two phases are chemically and structurally abrupt with no voids, impurities or reaction phases. Interlamellar residual stresses due to thermal expansion mismatch have been measured. The triaxial strain tensors for both phases were measured using single-crystal x-ray diffraction techniques on isolated grains of the DSE. From the strain tensors, the stress tensors were calculated taking into account the full elastic anisotropy of the phases. The resulting stress tensors indicate that large compressive stresses accumulate in ZrO₂ while large tensile stresses build up in NiO parallel to the lamellae during the solidification process. The large magnitudes of the stresses indicate that the interfaces between the lamellae are very well bonded and do not facilitate stress-relieving processes during fracture.

Supported by NSF no. DMR-95284888 and U.S. DOE contract DE-AC05-96OR22464, as part of the ORNL HTML Fellowship Program.