REDISTRIBUTION OF THE ALLOYING ELEMENTS DURING ZIRCALOY-2 OXIDATION

摘要

The redistribution of the alloying elements from the intermetallic particles into the oxide matrix has been examined for oxides formed on Zircaloy-2 in steam at 400, 500 and 600 degrees C. The outer area of the oxide where the alloying elements are fully oxidised was emphasised. At 400 degrees C little migration of Fe, Cr or Ni for any distance greater than the particle radius away from the original particle boundary was found, Within one radius of this boundary only iron migrates out of the precipitate and forms local agglomerations of almost pure iron oxide around the particle periphery. After 500 degrees C oxidation the iron has diffused to greater distances from the original particle boundary and segregates in individual ZrO2 crystallites that are high in iron. Si is found segregated in the boundaries of such crystallites but not elsewhere. Chromium remains largely within the boundaries of the intermetallic but forms infrequent small 'growths' on the periphery. Small Zr-2(Fe/Ni) particles show both iron and nickel diffusing out and segregating but this segregation happens within the particle boundary for Zr-2(Fe/Ni) particles larger than 1 mu m. At 600 degrees C most of the alloying elements diffuse out of the particle volume into the oxide matrix, and little or no segregation outside the particle boundaries was found. These effects can be interpreted in terms of the local oxygen partial pressure within the oxide and the effect this may have on the diffusion of the alloying elements. (C) 1997 Elsevier Science B.V. [References: 29]