X-ray diffraction study of low temperature aging in U-5.8Â wt.%Nb

In order to study the effect of low temperature on microstructure of U-Nb alloy α″ phase, and interpret the low temperature aging mechanism, the U-5.8 wt.%Nb alloy was investigated during aging at 200 °C using X-ray diffraction (XRD), in situ tensile test and transmission electron microscopy (TEM). The phase transformation of α″ → γ° is found by XRD after aging 4 h at 200 °C. The γ° transforms to α″ during tensile test by stress-induced. The experimental results disclose that the phase transformation of γ° → α″ occurs at the stage of twinning (de-twinning) deformation. Therefore, the phase γ° formed during aging can hamper the deformation of twinning (de-twinning), and strengthens the alloy remarkably. The phase transformation between α″ and γ° is reversible nanoscale martensitic transitions. The microstructure of dark/bright striations was found in TEM image, which present in both as-quenched and aged samples. The striations, made up of dislocation, are different from the structure of spinodal decomposition. The crystallography relationship of low temperature aging mechanism was also discussed in this paper.