Characterization of precipitates present in Zry-4 and in the oxide layers grown on the alloy

Full text: Structural analysis of the oxides in zirconium alloys has received much attention in the last two decades, since they play an important role in the fabrication process of fuel elements sheaths for nuclear power reactor, as well as in the corrosion processes during service. There is considerable much information in the literature about growth and characterization of oxide layers, evolution of precipitates after oxidation or irradiation, and on the influence of these precipitates on the corrosion and irradiation processes, but there is still some lack of information about distribution and characterization of precipitates within oxides, information wich is necessary in order to complete the alloy specifications. In the present work we report the results of the characterization study of the prescipitates present in the Zry-4 alloy before and after oxidation in an open furnace. Different thermal treatments were given to the alloy in order to obtain different size distribution of the precipitates. Specimens were then oxidised in an open furnace at 650 C degree. Size distributions of the precipitates were obtained by Scannig Electron Microscopy (SEM). According to the particular heat treament, precipitates between 1 and 5 μm mean size were observed. Energy Dispersive (EDS) and Wavelength Dispersive (EPMA) Spectroscopy techniques, revealed the composition changes of the precipitates before and after oxidation. Those located inside the alloy showed the usual Zr/Cr/Fe composition ratio, being %at Fe / %at Cr ∼ 1,4. However, precipitates in the oxide grown layer were composed only by Zr and Cr, with no Fe detected