Formation of nitrides at the surface of U–Zr alloys

The phase behavior of ternary system U–Zr–N was investigated by surface analysis of U–Zr alloys reacted with nitrogen gas by Auger electron spectroscopy (AES) and electron-probe microanalysis (EPMA). U–18, –50 and –67 at.% Zr alloys were reacted with nitrogen at 0.19 kPa and 1273 K, and the reaction layers were analyzed. The reaction layers formed at the alloy surfaces were (U,Zr)N/ZrN/αZr/alloy matrix. The compositions of the (U,Zr)N mononitride phases changed from those of the matrix alloys to ZrN continuously. The thicknesses of the (U,Zr)N layers were below about 0.2 μm and were larger for U-rich alloy.