The effect of oxygen partial pressure on dislocation creep in polycrystalline uranium dioxide

Abstract We report a set of compression test experiments carried out on sintered uranium dioxide at 1500°C, at constant strain rates and under controlled oxygen partial pressures. The macroscopic data indicate an initial strain hardening stage followed by a quasi steady–state period during which changes in the stress level are sluggish. The data are further interpreted in a continuum mechanics, finite strain framework, in both one and two–dimensional geometries, whence stress and oxygen partial pressure exponents of the creep law are estimated. The stress exponent is indicative of power–law creep. The oxygen partial pressure exponent is consistent with a strain–rate limited by vacancy mediated self–diffusion of the slowest moving ion, suggesting a climb–controlled recovery process. Some samples are further characterized using SEM/EBSD which reveals signs of plastic deformation typical of recovery creep. The effect of oxygen pressure upon microstructure is discussed.