Plastic deformation in nonstoichiometric UO2 + x single crystals—II. Deformation at high temperatures

Abstract

Single crystals of UO 2 + x (5 × 10 −6 ⩽ x ⩽ 10 −1) have been deformed in equilibrium CO CO 2 mixtures at 1073, 1273 and 1673 K in compression. The primary glide plane is dependent on orientation, temperature and extent of non-stoichiometry, such that {001}〈1̄10〉 glide is most common at low O U ratios and high temperatures, while {111}〈1̄10〉 glide is prevalent at high O U ratios and low temperatures. The critical resolved shear stress (CRSS) for {001} glide is nearly independent of x, while the CRSS for {111} glide decreases with increasing x. At low values of x, slip is controlled by interactions between dislocations and extrinsic defects; the dislocation and defect mobilities are nearly equal (for the strain rates examined) at temperatures between 1350 and 1650 K. At high values of x, the interactions between dislocations and extrinsic defects still play a major role in controlling dislocation motion; however, it appears that the presence of oxygen interstitial defect clusters serves to diminish the hardening effects of impurities for {111} glide. When deformed specimens with high values of x are reduced to low values of x, dislocations apparently act as sinks for “exsolved” oxygen, resulting in increase in strength on further deformation.