Diffuse X-ray scattering studies of defect reactions in electron-irradiated dilute nickel alloys. I. Ni-Si

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Abstract
Huang diffuse scattering was employed to study defect properties in dilute Ni-Si alloys. Ni alloys containing 1 at.% and 0.05 at.% Si were irradiated with electrons at 4.2K and were subsequently isochronally annealed. It was found that, prior to annealing, the Frenkel-pair resistivities and self-interstitial atom configurations were the same in the alloys as in pure Ni. The independence of the Frenkel-pair resistivity to Si concentration indicates that the resistivities arising from Frenkel pairs and Si solute are linearly additive in Ni. After annealing through stage I to 85 K, the defect cluster size grew to 1.5, 2.3 and 3.0 interstitial atoms for the 1 at.% Si, 0.05 at.% Si and pure Ni specimens, respectively. These results demonstrate that self-interstitial atoms are not immobilised by single Si atoms in Ni, but rather complexes involving several Si atoms and/or two interstitial atoms are the stable defects at the end of annealing stage I. It was also observed that Si solute in Ni strongly suppresses the growth of interstitial clusters in stage II. In the 1 at.% Si alloys di-interstitials were immobilised up to temperatures between 200 and 300K. There was no indication that Si solute reduced vacancy mobility in annealing stage III. The consequences of these results for the understanding of high-temperature radiation effects in alloys are discussed.