Ferroelasticity of the displacive tetragonal phase in Y 2 O 3 partially stabilized ZrO 2 (Y-PSZ) single crystals
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Ferroelasticity of the displacive tetragonal phase in Y2 O3 partially stabilized ZrO2 (Y-PSZ) single crystals J. Mart´ınez-Fern´andez, M. Jim´enez-Melendo, and A. Dom´ınguez-Rodr´ıguez Departmento de F´ısica de la Materia Condensada-Instituto de Ciencia de Materiales, Universidad de Sevilla-CSIC, Apdo. 1065, 41080 Sevilla, Spain (Received 1 August 1994; accepted 19 February 1996)
Ferroelasticity of the tetragonal displacive (t 0 ) phase was studied on 4.7 mol % Y2 O3 partially stabilized zirconia single crystals. Samples were deformed at 1400 ±C at constant strain rate to induce the ferroelastic behavior. Domain reorientation due to the applied stress has been studied as a function of the compression axis and aging time at 1600 ±C. Domain switching was found in the as-received and 2-h-aged crystals deformed along the k100l direction, in which an exceptional high flow stress was reached (.700 MPa). Transmission electron microscopy observations were performed on deformed and undeformed crystals to study the microstructural changes associated with the domain switching. Incremental strain steps on the stress-strain curves and surface texture on the lateral faces of the deformed samples were correlated with the microstructural evidence.
I. INTRODUCTION
Y2 O3 -stabilized ZrO2 crystals have received increasing attention in the past years because of their high strength and toughness at low temperatures, related to the stress-induced martensitic transformation of coherent tetragonal ZrO2 (t-ZrO2 ) precipitates to monoclinic symmetry.1 This alloy also shows excellent mechanical properties at high temperatures, with structural superplasticity in fine-grained tetragonal (Y-TZP)2 and partially stabilized (Y-PSZ)3 polycrystals, and potent solid-solution and precipitation hardening in Y-PSZ single crystals.4–7 Y-PSZ ceramics are a mixture of tetragonal and cubic phases. Two different tetragonal phases are present as follows8–12 : a metastable, Y2 O3 -rich phase nontransformable to monoclinic symmetry (the so-called pseudocubic or t 0 -ZrO2 phase), and a low Y2 O3 -content precipitate phase (t-ZrO2 ), capable of undergoing the martensitic transformation. The former phase is the major component in alloys rapidly cooled from the hightemperature single cubic c-ZrO2 field. It is formed via a diffusionless and displacive transformation, and is characterized by the formation of three variants mutually (nearly) orthogonal to each other and the presence of antiphase domain boundaries (APB’s). It is now well established that the tetragonal t 0 -ZrO2 phase is ferroelastic,13–16 exhibiting hysteresis between the stress s and the strain e. In this kind of material, orientation of a particular domain from one direction to another equivalent is possible by the application of an external force. The stress-induced domain reorientation (switching) has been suggested as the mechanism responsible for the high fracture toughness and strength found at low temperatures in ceria- and yttria-doped 1972
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