Ultrasonic response of dilute<i>Al</i>Fe alloys irradiated with 2.5-MeV electrons

Ultrasonic attenuation and velocity measurements were made as a function of polarization, temperature, frequency, and annealing before and after 2.5-MeV electron irradiation of dilute AlFe alloys. In addition to the relaxation peaks observed in earlier low-frequency internal-friction measurements, two new relaxation peaks were found. One of these has all the properties predicted by a size-effect model. The peak structure observed is very different from that found for AlMn, suggesting that theories based only on impurity size require extension.