Acoustic quality factor of molybdenum and tungsten at low temperatures

The amplitude-independent acoustical mechanical quality factors Q of 99.95% pure polycrystalline molybdenum and tungsten have been measured as a function of temperature and heat treatment from 50 mK to 300 K. Data were obtained from 1 kHz torsional modes of resonators designed to minimize extraneous loss effects. Thermal annealing at temperatures above the recrystallization temperatures yielded strongly enhanced Q. Maximum Q values of 4.38×107 in Mo and 1.23×107 in W were observed in annealed material at the lowest measurement temperatures. Internal friction peaks and backgrounds are discussed. The temperature dependence of the resonator frequency is reported. Mo and W are compared with Al-5056 as suitable materials for fabrication of cryogenic resonant-bar gravity-wave antennas.