ULTRASONIC ATTENUATION MEASUREMENTS OF DISLOCATION DAMPING IN COPPER SINGLE CRYSTALS BETWEEN RT AND 15 K UNDER (COMPRESSION/TENSION) BIAS STRESS

Abstract
Measurements of ultrasonic attenuation under slowly varying cyclic compression/tension loading of the samples ("cyclic bias stress"=CBS) provide information on the interaction between dislocations and pinning points. The present paper describes an apparatus for CBS measurements at cryogenic temperatures, some mandatory experimental techniques and presents several results. Attention is focused on the following requirements and techniques : (i) continuous loading of the samples under variable rate at stresses bellow yield ans steady transition from pur tension to pure compression through σ=0 by a computer controlled preloaded disk spring arrangement and a double membrane centering of the loading bar at its cryogenic end ; (ii) stress free mounting and temperature changes of very soft samples provided by Ga soldering of the precision lapped samples to precision lapped joining pieces ; (iii) elimination of mismatch stresses due to different thermal expansion of sample and attached ultrasonic transducer by application of novel PVDF (=polyvinylidene-flouride) foil transducers.