Interstitial-impurity interactions in copper-silver and aluminum-magnesium alloys

Our purpose has been to determine the configurations and dynamical properties of complexes formed between interstltials and oversized impurities in electron-irradiated aluminum and copper. Measurements were taken of the ultrasonic attenuation (at 10 and 30 MHz) and resonant frequency (at 10 MHz) in single crystal sample s of Cu-Ag and AI-Mg. A variety of peaks appeared in both materials in plots of the logarithmic decrement versus temperature. The simultaneous presence of multiple defects was established by the different annealing behavior shown by each peak. It was found that interstitial trapping in our oversized systems was generally weaker than in previously studied undersized systems. The principal features in Cu-Ag that must be accounted for by a model include the following: 1) Three low-temperature peaks (including the main one at 16 K, peak 1) were seen having trigonal symmetry. 2) Peak annealed away at 110 K uncorrelated with any resistivity recovery. 3) Peak 1 grew at 60 K, correlated with a resistivity decrease. For AI-Mg, the principal features associated with the main peak (peak 6) include: 1) Peak 6 was seen at a high temperature (>135 K) having trigonal symmetry. 2) It annealed away at 121 K and seemed to correlate with a resistivity decrease. 3) The remaining peaks (1-5) grew while peak 6 annealed away. The implications of an existing model were developed. This model was based on the predominant influence of size effects in determining impurity-interstitial interactions. Predictions were compared with the experimental results. No evidence was found for the deeply-trapped -orthorhombic defect predicted by the existing model. Therefore, two alternative models were developed. Model A uses a "canted dumbbell" at the next-nearest neighbor position to explain the results. Model B uses a point interstitial at an octahedral position. A distinction between the two which is subject to experimental check is that model A predicts that interstitial migration between different impurity atoms occurs near 121 K in Cu-Ag while model B predicts a migration temperature near 60 K.U of I OnlyThesi