Thermodynamic analysis of irradiation-induced amorphization of intermetallic particles in Zircaloy

The intermetallic precipitate particles Zr2(Ni,Fe) in Zircaloy-2 and Zr(Cr,Fe)2 in Zircaloy-4, dissolve and amorphize under irradiation. Pursuing a previous analysis, we have studied those effects on the basis of the metastable free-energy diagram of the reference system Zr-Fe (calculated using Miedema's model) and considering some aspects of the modification of this free-energy diagram by irradiation. We then can explain why both phases Zr2(Ni,Fe) and Zr(Cr,Fe)2 can be amorphized at low temperatures (below 350 K) without composition changes if sufficient energy can be accumulated by irradiation-produced defects and chemical disorder, and also that at intermediate temperatures (about 580 K) a driving force exists for particle amorphization at the matrix-particle interface for Zr(Cr,Fe)2 but not for Zr(Ni,Fe)2. (author)