THE OXIDATION AND CORROSION OF ZIRCONIUM AND ITS ALLOYS. XIII. SOME OBSERVATIONS OF HYDRIDE IN ZIRCONIUM AND ZIRCALOY-2 AND ITS SUBSEQUENT EFFECT ON CORROSION

An examination of hydride platelets in Zr and Zircaloy-2 by autoradiography and electron-microscopy showed that normal metallographic techniques provide a satisfactory method for identifying hydride in these materials. The standard methods do not give a good estimate of the size (particularly the thickness) of hydride platelets. Studies showed that the hydride platelets are very thin (500-1000A) and that the greater apparent thickness of them, when observed metallographically, results from etching out of the hydride together with some of the surrounding metal. No positive correlation was established between the presence of hydride at the oxide/metal interface and breakdown of the oxide film during the oxidation of either Zr or Zircaloy-2. The cracking of the oxide which is associated with the sites of hydride particles is apparently mechanical in nature. (auth)