Effect of Oversized Alloying Elements on Damage Rates and Recovery in Zirconium
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Effect of Oversized Alloying Elements on Damage Rates and Recovery in Zirconium Valeriy Borysenko, Yuri Petrusenko and Dmitro Barankov CYCLOTRON Science & Research Establishment, National Science Center - Kharkov Institute of Physics & Technology, Kharkov, Ukraine ABSTRACT Studies were made into the influence of oversized rare-earth atoms on the processes of radiation defect accumulation and annealing in two-component zirconium alloys. Zr and Zr-X alloys (where X = Sc, Dy, Y, Gd and La) have been irradiated with 2 MeV electrons at 82 K. The radiation-induced resistivity has been measured in situ as a function of dose. As compared to unalloyed zirconium, the alloys have exhibited a decrease in the resistivity gain, this decrease being proportional to both the concentration and the size of dopant atoms. A possible explanation for the effect is offered. The difference between the recovery processes in zirconium and in its alloys has been studied. To this end, the irradiated specimens were subjected to isochronal annealing at temperatures between 82 and 350 K. It is shown that Dy, Y, Gd and La atoms trap interstitial atoms at stage I of the recovery. The dissociation of interstitial-impurity complexes takes place at stage II. In zirconium alloys with Dy, Y and Gd, splitting of recovery stage III into two substages has been revealed. The Zr-La alloy has not shown this splitting. Isothermal annealing data were used to determine the activation energies of recovery stages, and also to calculate the activation energy spectra for zirconium and its alloys. The oversized atoms of rareearth metals are shown to interact effectively with both the interstitials and the vacancies in the zirconium matrix. This effect must be taken into account when developing new radiationresistant Zr-base alloys or modifying the ones already existing. INTRODUCTION Currently the central problems in the radiation physics of metals and alloys are the following questions: investigations of properties of point defects and their interaction with alloying additions; radiation-stimulated segregation and phase transformations on irradiation in alloys; vacancy swelling and the behavior of transmutation gas impurities. By the present time much work has been done to investigated both theoretically and experimentally the point defect properties in a wide variety of metals. However, the processes of point defect interaction with impurity atoms, particularly in bcc and hcp lattices, are still not clearly understood. Of special interest is the investigation into the interaction of radiation-induced point defects with substitutional atoms in the hcp lattice of zirconium. This paper reports the results from studies into the influence of oversized atoms of rare-earth metals on the kinetics of radiationdefect accumulation and annealing in the zirconium matrix. EXPERIMENTAL DETAILS Zirconium alloys with rare-earths (Sc, Dy, Y, Gd and La) have been prepared for the experiments. The alloys were melt in a laboratory arc furnace in a purified helium atmosphere.
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