Hydrostatic and triaxial compression experiments on unpoled PZT 95/5--2Nb ceramic: The effects of shear stress on the [ital F][sub [ital R]1][r arrow]A[sub 0] polymorphic phase transformation
- Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
We conducted a series of hydrostatic and constant shear stress experiments at room temperature on three different sintering runs of unpoled, niobium-doped lead-zirconate-titanate ceramic (PZT 95/5--2Nb) in order to quantify the influence of shear stress on the displacive (possibly martensitic), first-order, rhombohedral[r arrow]orthorhombic phase transformation. Inter- and intra-batch variations were detected, but some generalizations can be made. In hydrostatic compression at room temperature, the transformation began at approximately 260 MPa, and was usually incompletely reversed upon return to ambient conditions. Strains associated with the transformation were isotropic, both on the first and subsequent hydrostatic cycles. Results for the constant shear stress tests were very different. First, the confining pressure and mean stress at which the transition begins decreased systematically with increasing shear stress. Second, we observed that the rate of transformation [ital decreased] with increasing shear stress and the associated elastic shear strain. This result contrasts with the typical observation that shear stresses increase reaction and transformation kinetics. Third, strain was not isotropic during the transformation: axial strains were greater and lateral strains smaller than for the hydrostatic case, though volumetric strain behavior was comparable for the two types of tests. However, this effect does not appear to be an example of transformational plasticity: no [ital additional] unexpected strains accumulated during subsequent cycles through the transition under deviatoric loading. If subsequent [ital hydrostatic] cycles were performed on samples previously subjected to shear stress, strain anisotropy was again observed, indicating that the earlier superimposed shear stress produced a permanent mechanical anisotropy in the material.
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 6948541
- Journal Information:
- Journal of Materials Research; (United States), Vol. 7:12; ISSN 0884-2914
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
NIOBIUM
COMPRESSION
CRYSTAL-PHASE TRANSFORMATIONS
PZT
ANISOTROPY
CERAMICS
DOPED MATERIALS
ORTHORHOMBIC LATTICES
STRAINS
TEMPERATURE RANGE 0273-0400 K
TRIGONAL LATTICES
VERY HIGH PRESSURE
CRYSTAL LATTICES
CRYSTAL STRUCTURE
ELEMENTS
LEAD COMPOUNDS
MATERIALS
METALS
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
TEMPERATURE RANGE
TITANATES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
ZIRCONATES
ZIRCONIUM COMPOUNDS
360603* - Materials- Properties