Influence of an electric field on the plastic deformation of fine-grained MgO at high homologous temperatures

The effect of a de electric field up to 385 V/cm on the stress-strain behav ior in tension of fine-grained MgO (d(o) = 5.3 mum) was determined at 1500- 1600 degreesC. The field produced a decrease in the flow stress and an incr ease in the elongation. The reduction in how stress was reversible and prop ortional to the field strength, amounting to similar to 50% of the flow str ess for E = 220 V/cm. The field had only little, if any, influence on the s tress exponent n = partial derivative ln (epsilon) over dot/partial derivat ive ln sigma, which had a value of similar to 1.0, indicating that it did n ot change the rate-controlling mechanism. The decrease in flow stress produ ced by the held is given by Delta sigma (E)* = ZeEx(sc)/Omega where Z = + 2 is the charge on the rate-controlling Mg2+ ions, e is the ele ctron charge, E is the field strength, x(sc) is the width of the space char ge region and Omega is the atomic volume. The present results are the first of their kind which provide experimental support for the use of an electro chemical potential in diffusion flux equations pertaining to the plastic de formation of ceramic materials. (C) 2000 Acta Metallurgica Inc. Published b y Elsevier Science Ltd. All rights reserved.