Dynamic recrystallization during creep of proton-conducting barium cerate perovskites

Abstract

Uniaxial compression tests were conducted on perovskite-structured barium cerate polycrystals doped with 5-at.% yttrium and 5-at.% ytterbium and submicrometric grain sizes, at temperatures between 1423 and 1573 K (0.70–0.78Tm) and different initial strain rates. In contrast to conventional superplastic ceramics, the stress–strain curves show a pronounced and smooth stress drop before the steady state is attained. The stress level and the associated strain at the peak of the curves increase with increasing the deformation rate or decreasing the temperature. This behavior is characteristic of metallic materials with dynamic recrystallization during deformation under warm and hot conditions. Microstructural observations have shown that preexisting twin boundaries, developed during cooling from the sintering temperature because of various crystal phase transformations, are critical in refining the grain structure through interactions with dislocations. The dependences of the peak, steady state, and critical stresses with strain rate and temperature in the present ceramics are adequately described by the constitutive equations used in metallic materials based on the Zener–Hollomon parameter and the work hardening rate.