DISLOCATION SUBSTRUCTURES IN DEFORMED URANIUM DIOXIDE SINGLE CRYSTALS

Single crystals of uranium dioxide were deformed in compression to nominal strains of 1 and i %. The crystals were oriented to promote slip on only one slip system of the family {100} 〈110〉. The strain rate and temperature ranges studied were 10-3 to 10-1 min and 750 to 1400°C, respectively. The dislocation density of the as-grown crystals was 2 × 106/cm2. Sections of the deformed specimens were examined by transmission electron microscopy, indicating that the dislocation substructures at a strain of 1% consist of numerous dipoles and dipole loops, the edge components of the dipoles lying along 〈110〉 directions. At 5% strain, extensive dislocation tangles are present in addition to the dipole configurations. Particular features are noted in the dislocation arrangements which can be related to several of the theories of dipole formation. The critical resolved shear stress on the {100} 〈110〉 slip system is reported as a function of temperature, as is the variation in the appearance of the loaddeflection curve with temperature level. Of particular interest is the markedly serrated load-deflection behavior observed at 1150 °C, and the minimum in the shear stress curve at 950 °C. The dislocation density as a function of strain has been evaluated, and dislocation velocities are estimated. © 1969.