High-Temperature Nitriding Kinetics of Zr-U-Based Alloys

The kinetic laws of nitride formation are revealed. The sequence of structural transformations characterizing high-temperature (at 1900 degrees C) nitriding of Zr-U alloys with 2 and 5 wt % U in the range 3.560 min is presented. For each composition, high-temperature nitrogen saturation results in the decomposition of a (Zr,U) solid solution to form ZrN-(ZrN1 - n/UxEy/U)-ZrN composite structures (where E = O, N; n, x, y are stoichiometric coefficients). The decomposition of the solid solution gives rise to zirconium nitride and metallic uranium. The latter accumulates impurities, which are present in the initial solid solution, in the central part of the sample. The kinetic curves for a temperature of 1900 degrees C are approximated by an exponential law and correspond to zirconium nitriding. The nitriding rate of the (Zr,U) solid solution increases with the uranium content. To complete the formation of a compact solid solution nitride (Zr,U)N of a stoichiometric composition, the reaction temperature and time should be increased.