The Effect of Lattice Defects on Internal Friction of Niobium.

Irradiation, cold-worked and quenching effects in arc melted commercial niobium have been studied using the low frequency (1 c/s) internal friction technique. A relaxation peak at about 110°K has been found after irradiation and cold-work, which is thought to involve the relaxation of dislocation loops or the relaxation of point defects constituting weak dislocation pinning points. The peak is absent in the fully annealed material and after quenching. After cold-work the peak anneals out in two stages occurring at temperatures ranging from 80°C to 160°C and 240°C to 340°C. Relaxation peaks have also been found in the temperature range from 185°K to 240°K after irradiation and after annealing cold-worked and quenched specimens at 70°C. A room temperature strain of 0.3% partially supresses the peak in cold- worked and irradiated specimens. After irradiation the peaks increase on annealing up to a temperature of about 200°C, then anneal out in the temperature range from 200°C to 380°C. After cold-work, the peaks increase on annealing up to a temperature of about 90 C and anneal out in the temperature range from 240°C to 340°C. After quenching, the peaks increase on annealing up to a temperature of about 140°C and anneal out in the temperature range from 220°C to 300°C. These peaks are believed to be due to the relaxation of some type of point defect configuration. The activation energies of these peaks as calculated from their "half-widths" have been found to be of the order of magnitude of 1.0 to 1.2 eV with frequency factors of about 10 26 sec[-1]. The results are discussed in terms of current relaxation theories