Changes in chemical structure of oxidation reaction layers of Zircaloy-4 and Ti by micro X-ray diffractometry

A micro X-ray diffractometer with a micrometer sized beam concentrator was developed to investigate the changes in the chemical structures of oxide layers for Zr-based alloys (Zircaloy-4) and Ti metal from the center of the cross section to the surface. Zircaloy-4 and Ti metal were chosen because of their use as a fuel cladding and a heat exchange tubing in a nuclear reactor, respectively. The diffraction patterns were obtained from the cross sectional specimens of the oxidized Zircaloy-4 and Ti metal at 50 μm intervals. For the cross section of Zircaloy-4, Zr metal (hexagonal) was identified in the center, ZrO2−x (hexagonal, about 200 μm in thickness) inside the edge and ZrO2 (monoclinic, about 400 μm in thickness) at the edge. In the case of Ti metal, Ti metal (hexagonal) was identified in the center, TiO (cubic, about 200 μm in thickness) inside the edge and rutile-TiO2 (tetragonal, about 230 μm in thickness) at the edge. From this study, it was concluded that the intermediate phase formed between the fuel and the cladding can be identified by the micro-XRD system.