Ultrasonic studies of radiation damage in an aluminum-manganese alloy

A technique has been developed for ultrasonic studies of the properties of crystals containing defects produced by electron radiation of dilute alloys. The method permits measurements of both relaxation and resonance effects for multiple defects for all three independent elastic modes in cubic crystals at low enough defect concentrations to avoid defect interaction effects. A multiple-peak structure was found in an aluminum-manganese alloy. This together with annealing data indicates that more than one defect configuration was present, despite optimum conditions for avoiding complications due to multiple-interstitial and multiple-solute-atom complexes. The major defect is a strongly trapped 〈100〉-symmetry mixed dumbbell which rotates between equivalent positions near 130 K at 10 MHz. Existing theories predict some but not all of the effects found. In particular, the fact that the mixed dumbbell rotates between equivalent positions at high and not low temperature, and that this defect configuration does not increase in concentration with annealing, remains as challenges to theory. Also the fact that the multiple peaks found differ greatly from those found in Al-Fe suggests that other aspects besides size effects should be taken into account. The results show that the technique should also be valuable for studies of other alloys.