IRON-BEARING PRECIPITATES IN ZIRCALOYS - A MOSSBAUER-SPECTROSCOPY STUDY

Mossbauer spectroscopy of Fe-57 was used to study the chemical form an d distribution of iron in Zircaloy-2 and Zircaloy-4. The spectra of Zi rcaloy-4 consist of two overlapping quadrupole-split doublets, which c an be ascribed to precipitates of the pseudobinary Laves-phase interme tallic compound Zr(Cr,Fe)(2), which has a hexagonal MgZn2 (C14) type s tructure and cubic MgCu2 (C15) type structure. In Zircaloy-2, a large fraction of iron was also found in the form of Zr-2(Fe,Ni) precipitate s, having a tetragonal Al2Cu (C16) type structure. Characteristic room -temperature values of Mossbauer spectral parameters were determined f or the three types of intermetallic precipitates. At liquid helium tem perature, both alloys exhibit a poorly resolved magnetic hyperfine spl itting, attributed to the low-temperature ferromagnetism of cubic Zr(C r,Fe)(2) Laves-phase particles. This effect is more pronounced in Zirc aloy-4 than in Zircaloy-2. The possibility of determining volume fract ions of different phases from their relative spectral areas is discuss ed.