ULTRASONIC STUDY OF ALPHA-COMPLEX PEAKS IN SINGLE-CRYSTALS AND POLYCRYSTALS OF PURE MOLYBDENUM AT MEGAHERTZ FREQUENCIES

Measurements of the temperature dependence of the ultrasonic attenuati on at 5, 10 and 28 MHz in molybdenum single crystals of 99.995% purity , oriented along 111!, 110! and 100!, have provided a detailed stud y of the alpha complex of dislocation relaxation peaks following compr essive stressing at room temperature. At 5 MHz the peaks were at 148, 167 and 206 K, independent of the orientation of the crystal. As expec ted, each of the peaks moved to higher temperatures as the frequency o f measurement was increased and from these data the activation enthalp ies and attempt frequencies were 0.18 eV and 6.6 x 10(11) Hz, respecti vely, for alpha1, 0.22 eV and 1.84 x 10(13) Hz, respectively, for alph a2, and 0.20 eV and 4.95 x 10(11) Hz, respectively, for alpha3. Simila r measurements at 10 MHz on polycrystals of the same purity showed the effects of increasing the applied stress from 0.2 to 29 MPa and of ir radiation with doses D(gamma) of gamma-rays up to 8.6 x 10(8) gammavt and doses D(n) of neutrons up to 10.8 x 10(9) nvt. It was found that t he peaks' strength Q(max)-1 varied as D(-m), where m is a parameter fo r each irradiated peak.