Interstitial-impurity trapping in Al--Fe and Al--Zn. [Electron irradiation

Abstract

Ultrasonic attenuation and velocity measurements were made as a function of polarization, temperature, frequency and annealing before and after electron irradiation near 65/sup 0/K of Al--Fe and Al--Zn dilute alloys. Multiple relaxation processes were observed in both alloys. In the case of Al--Zn, the simultaneous annealing near 130/sup 0/K of resistivity, diaelastic modulus changes, and a paraelastic relaxation peak in C' allows for a characterization of the individual defects. The results provide strong evidence that below 130/sup 0/K, the -mixed dumbbell is the predominant interstitial trapping configuration. The temperature dependence of the relaxation peak near 4.9/sup 0/K is not that expected for a thermally activated process, but provides evidence for defect tunneling. A second trapping configuration present in low concentration anneals out near 100/sup 0/K, and probably arises from -mixed defects. In Al--Fe, the observation of the diaelastic effect and a peak in the C' mode not previously seen in earlier internal friction measurements, together with an identification of this peak with the major defect species resolves the apparent contradiction between the internal friction and channeling symmetry evidence. This allows for an interpretation in terms of a -mixed dumbbell which is consistent with previous theory and channeling and Moessbauer measurements.more » The results for Al--Fe differ greatly from those obtained earlier for Al--Mn, suggesting that current theories based only on size differences require extension.« less