Mechanical studies of irradiation-induced defects in Cu and W

Measurements of internal friction and Young's elastic modulus in the kilohertz range are reported on single-crystal and polycrystalline Cu and W samples after irradiation by 10- to 14-MeV protons and deuterons, primarily at temperatures near 4 K. Stress-induced ordering studies in Cu identify stage ${\mathrm{I}}_B$ as responsible for the 10-K anelastic process; a shape factor $\Delta \lambda =0.20\pm 0.02$ was found for this defect. W shows anelastic peaks near 10, 14, 30, 42, and 53 K. The 10- and 30-K peaks are removed by a 40-K anneal, the 14-K peak is created by this same anneal. Attempt frequencies and activation energies for reorientation are reported for these defects. Dielastic effects seem unaffected by cold work, but the 10-K peaks are totally suppressed in both Cu and W by a plastic compression of 10 to 20%. Dielastic effects anneal out in stage I in Cu, while only about 1/3 of the effect anneals out in W by an anneal to 50 K. Cold work has a large effect upon the amount and rate of pinning, especially in Cu. Cold work also seems to reduce the role of thermally activated defect motion in the pinning process.