Irradiation-induced phase transformations in zirconium alloys

Abstract

Abstract Ion and electron irradiations were used to follow the irradiation-induced crystalline-to-amorphous transformation in Zr3Fe, ZrFe2, Zr(Cr,Fe)2 and ZrCr2, as well as in Zr(Cr,Fe)2 and Zr2(Ni,Fe) precipitates in Zircaloy-4. 40Ar and 209Bi ion irradiations of Zr3Fe were performed at 35–725 K using ions of energy 15–1500 keV. The effect of the deposited-energy density θ v in the collision cascade on the nature of the damaged regions in individual cascades was investigated. The amorphization kinetics of Zr3Fe during in situ electron irradiation were also determined. The electron fluence required for amorphization increased exponentially with temperature, and the critical temperature for amorphization was about 220 K, compared with 575–625 K for ion irradiation. The difference between the heavy ion and electron irradiation results is attributed to the fact that ion irradiation produces displacement cascades, while electron irradiation produces isolated Frenkel pairs. The dependence of the damage production of the incident electron energy was determined for Zr3Fe and the results could be analysed in terms of a composite displacement cross-section dominated at high energies by displacements of Zr and Fe atoms; by displacements of Fe atoms at intermediate energies; and by secondary displacements of lattice atoms by recoil impurities at low energies. An investigation was initiated on ZrFe2, Zr(Cr,Fe)2 and ZrCr2 to study the effect of variation of the stoichiometry and the presence of lattice defects on irradiation-induced amorphization. The irradiation-induced amorphization of the intermetallic precipitates Zr(Cr,Fe)2 and Zr2(Ni,Fe) in Zircaloy-4 was also studied during in situ bombardment by 40Ar ions of energy 350 keV. The amorphization morphology was shown to be homogeneous. These results are discussed in the context of previous experimental results of neutron and electron irradiations, and likely amorphization mechanisms are proposed.