Mechanisms Governing the Enhanced Plasticity of Ceramics by a Modest Electric Field

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NON-TECHNICAL DESCRIPTION: Ceramics are an important class of technological materials being used in insulators, fuel cells, gas turbines and various other electronic and structural components. However, the processing of ceramics is usually performed at high temperatures and slow rates. It was discovered that the application of a modest electric field enhances the processing rate, thereby reducing the required processing time or temperature. This offers the potential of significantly reducing the required energy and related cost. Thus, the use of an electric field provides a novel approach to the processing of materials. The objective of the proposed research is to determine the atomic mechanisms responsible for the beneficial effect of an electric field with the aim of optimizing the conditions. A major factor is the electronic space charge which exists in ceramic materials. A post-doctoral scholar and undergraduate students from underrepresented groups will be trained during the course of this project. TECHNICAL DETAILS: It was discovered in prior work that the application of an electric field during the plastic deformation of the polycrystalline oxides MgO, Al2O3 and ZrO2(3Y-TZP) gave a significant reduction in flow stress. In the case of 3Y-TZP the reduction consisted of three components: one due to Joule heating, a rapid reversible component due to the direct effect of the field on the plastic deformation kinetics and an irreversible, cumulative component due to the effect of the field on the microstructure. These effects are attributed to ionic conduction, a reduction in the energy to form vacancies and a retardation of dynamic grain growth. In contrast to 3Y-TZP, MgO and Al2O3 did not exhibit the same three components. Theoretical considerations indicate that the three components are related to the space charge at the grain boundaries. Therefore, the objective of the research is to determine the physical mechanisms responsible for the reduction in flow stress in oxides which occurs with application of an electric field, with focus on the role of the valence of solute additions on: (a) the space charge at the grain boundaries and (b) the related grain boundary structure employing advanced high-resolution electron microscopy techniques. To obtain information on the time constants relating to the mechanisms, the influence of the electric field frequency is being investigated.