The bordoni peak in silver single crystals at megahertz frequencies

Abstract

The dislocation relaxation maximum has been investigated at frequencies of 5, 10 and 30 MHz. The three (very high-purity) silver crystals of crystallographic orientation (111), (110) and (100) which are given a resolved shear stress of 20 MPa were found to produce dislocation relaxation maximum at 107 K in all the three samples. The ma.xhnum shifts to 117K when measurement is carried out at 10 MHz and to 127 K at 30 MHz. The results reveal that the maximum is orientation independent. The activation energy and the attempt frequency were calculated and found to be equal to 0.105 eV and 2.109 Hz, respectively. Meanwhile the larger magnitude of the maximum was found on the (111) crystal and the least was on the (100) crystal. Finally, it was clearly shown that the dislocation relaxation strength decreases as the frequency increases. PACS 62.20 -Mechanics and rheology of solids. PACS 61.70.Le -Slip, creep, internal friction, and other indirect evidence of dislocations. PACS 43.35.Bg -Ultrasonic velocity, dispersion, scattering diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsion. PACS 62.40 -Anelasticity, internal friction, and mechanical resonances.

Low-temperature ultrasonic attenuation measurement in very pure gold polycrystals at megahertz frequencies

“…the Niblett-Wilks peak, was absent). Similar results were observed when studying the dislocation relaxation peak in silver [24] (since both gold and silver have high stacking fault energy). The peak occurs in the temperature ranges of 178-168 K at 5 MHz frequency, 186-182 K at 10 MHz frequency, and 237-232 K at 30 MHz frequency.…”