EFFECTS OF CHEMICAL-COMPOSITION AND PRECIPITATION ON CORROSION-RESISTANCE OF ZIRCALOY

Seven kinds of Zr-Sn-Fe-X (X: Ni, Fe) alloys and three kinds of Zr-Sn-Fe-Ni-Cr alloys were used to make clear the effect of chemical composition on corrosion resistance of Zircaloy. Chemical composition, crystal structure and morphology of precipitates in each alloy were characterized by SEM, TEM and quantitative EDX analysis. As the compositional ratio of Fe/Ni of alloy increases, the crystal structure of precipitates changed from tetragonal Zr2(Ni, Fe) to cubic Zr(Fe, Ni)2. This change was accompanied by an increase of corrosion resistance, an increase of concentration of solute Fe in the matrix and a refinement of particle size of precipitates. A good correlation between corrosion resistance and concentration of solute Fe was obtained for Zr-Sn-Fe-Ni alloy, and the concentration of solute Fe in high corrosion resistant alloys were higher than 0.02 w/0. The fact that an addition of Cr to Zr-Sn-Fe-Ni alloy decreased corrosion resistance suggests that concentration of solute Fe was decreased by the precipitation of hexagonal Zr(Cr, Fe)2. By an addition of Ni to Zircaloy, corrosion resistance remarkably increased and extremely fine precipitation of hexagonal Sn2Ni3 was confirmed. Therefore, existence of Sn2Ni3 is considered to be effective to increase the corrosion resistance of Zircaloy. © 1990, Atomic Energy Society of Japan. All rights reserved.