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Stress analysis at Twin lamellae in monoclinic Zirconia by HRTEM

At the end of twin lamellae in monoclinic Zirconia the stresses are very high: Every second twin lamellae has a compressive stress, the other tensile stresses. The tensile stress region can withstand the high stress until a certain stress level by bending the lattice planes. The bending was measured experimentally and the strain and stress was calculated. Above the stress level, which is very high (35 GPa), cracks are formed. The crack length is proportional to the width of the twin lamellae over a wide range.
At the compressive regions of the twin lamellae triangular shaped regions (precipitates) of a high pressure phase of Zirconia with orthorhombic structure has been observed. The lattice constants (a=1.01, b=0.5 c=0.5 or 0.25) were measured from HRTEM micrographs. The system is a suitable model system to estimate the material parameter critical tensile stress for microcrack formation.
This system is also an example of fractral microstructure: The phase transformation from the tetragonal to the monoclinic phase is performed in differnet steps by forming the orthorhomic phase in some regions as an intermediate step. Four generations of twins were observed.

M. Ruhle, L.T. Ma, W. Wunderlich, A.G. Evans,
TEM-Studies of Phases and Phase Stabilities in Zirconia Ceramics,
Physica B 150 (1988) 86-98

W. Wunderlich, M. Ruhle,
Critical tensile Stresses for Microcracking in Monoclinic Zirconia,
High Tech Ceramics CIMTEC 6, (ed. by P. Vincenzini), Milan, Italy, 1987, pp. 1219-1224

W. Wunderlich, M. Ruhle,
Critical Tensile Stresses for Microcracking in Monoclinic Zirconia,
Advances in Ceramics, Science and Technology of Zirconia, 3rd Conf., Tokyo, Japan,
Sep. 1986, pp. 509-515

W. Wunderlich,
Fractal Aspects of the Martensitic Transformation in Zirconia,
in: The Martensitic Transformation in Sc. and Tech., ed. E. Hornbogen, N. Jost,
1989 DGM Info-Ges. (Proc. Conf., 09-10.03.1989, Bochum), pp. 513-518

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