Softening of the Elastic Modulus of Zirconia Held in a Steady State of Flash

Abstract

Once triggered by the application of electric field and furnace heating, a polycrystal can be held in a constant state of flash with the furnace switched off. The specimen temperature can now be controlled by the current flowing through it. We report on the measurement of the elastic modulus of 3 mol% yttria stabilized zirconia in such a state of flash. Significant softening of the elastic modulus is measured. The decline in the modulus steepens with temperature. In contrast the nominal modulus tends to stabilize at higher temperatures. The mechanical damping increases under flash. The experiments were done by activating the flash along a partial length of a cantilever beam. Modal finite element analysis simulations were used to determine the modulus in the flashed section. The temperature was estimated from a black body radiation model and also measured with a pyrometer. This work was driven by recent theoretical results that show that Frenkel pairs can be nucleated by the proliferation of phonons near the edge of the Brillouin zone. We discuss a possible "phonon resonance" mechanism for the nucleation of Frenkel pairs.