Abstract

The microstructure of Zr alloys has been a subject of study during the last decades due to its influence on the manufacturing of fuel elements sheaths for power reactors. In particular, Zircaloy - 4 is widely used as a fuel cladding material.


It is known that during the initial oxidation of zirconium alloys thin coherent oxide films of ZrO2 form over the whole surface, including the intermetallic particles lying on the surface. The precipitates are accommodated in the oxide film in a non- oxidized state, and then the zirconium present inside the precipitates is gradually oxidized to either cubic or tetragonal ZrO2. The precipitates into the oxide layer are subjected to delayed oxidation as compared to the matrix, accompanied by the rejection of a significant proportion of their iron content. Previous works showed that precipitates undergo chemical composition changes after open furnace oxidation and it was suggested that a progressive Fe rejection towards the oxidized precipitate / oxidized matrix frontier takes place.