Influence of an applied dc electric field on the plastic deformation kinetics of oxide ceramics

Abstract

A modest dc electric field markedly reduced the tensile flow stress at high temperatures in three polycrystalline oxides, i.e. MgO, Al₂O₃ and yttria-stabilized tetragonal ZrO₂ (Y-TZP). The reduction in flow stress Δσ_E in Y-TZP consisted of three components: (i) Δσ_T due to Joule heating, (ii) a rapid, reversible component obtained in on-off and electric field step tests and (iii) the cumulative effect of the field on microstructure. Only Δσ_T and occurred in MgO and Al₂O₃. It is concluded that results from a reduction in the electrochemical potential for the formation of vacancies corresponding to the diffusion of the rate-controlling ion in the space-charge at the grain boundary. The calculated magnitude of the space-charge zone width and its temperature and solute composition dependence are in accord with theory and experiment; is attributed mainly to the retardation of grain growth by the field. The retardation could be due to one or more of the following effects of the field on the space-charge zone: (i) an increase in the segregated solute ions, (ii) a decrease in grain boundary energy and (iii) a decrease in solute ion mobility.

Keywords:

• oxide ceramics
• flow stress
• electric field
• grain size
• space-charge
• Debye length

Acknowledgements

The data upon which this paper is based were obtained during support by the US Army Research Office under Grant Nos. DAAH04-946-0311 and DAA19-02-1-0315 with Drs W. Simmons and W. Mullins, project managers, and by the US Department of Energy, Office of Freedom Car and Transportation Technology, Dr P. Becher, project manager. The authors also wish to acknowledge stimulating discussions with Drs Paul Becher and Rishi Raj.