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A variety of forms of irradiation have been observed to induce an amorphous phase: heavy ion, proton, and electron. More recently neutron irradiation has been observed to induce an amorphous transformation in Laves precipitates found in Zircaloy and austenitic steel. Up to this point, only conjectures have been made about the irradiation conditions necessary to achieve the amorphous transformation and about the characteristics of a material susceptible to the amorphous transformation. From these conjectures, a theory to explain the amorphous transformation is developed, and its application illustrated by simulation with a computer model. The amorphous transformation of the Zr(Fe, Cr)2 phase in Zircaloy induced by neutron irradiation is used as the example in the model. The theory proposes that during irradiation the free energy of the crystalline state increases beyond that of the amorphous state, and thus in efforts to minimize the free energy of the system the amorphous transformation occurs. The factors that contribute to this increase in free energy include the defect formation energies and the energies of mixing that arise as the lattice is disordered. The later contribution is found to be significant. It is this factor that makes the amorphous transformation possible at defect concentrations lower than required for transformation when defect generation alone is considered.
amorphous transformation, laves phase, free energy, neutron irradiation
Graduate student/engineer, University of California-Berkeley/General Electric Company, Berkeley, CA
Lead engineer, Knolls Atomic Power Laboratory, Schenectady, NY