The ultrasonic Bordoni peak in copper crystals and the kink picture

Abstract

The ultrasonic logarithmic decrement and modulus defect in high purity copper crystals was measured at 10, 30 and 50 MHz in the temperature interval 5-373 K. The samples were deformed at room temperature in the 3-20% range along the 111 crystallographic direction. The experimental data were fitted over the whole interval of temperatures, assuming the contribution of two kink mechanisms: (i) relaxation by kink pair formation with diffusion in the dislocation line and (ii) overdamped resonance of the kink chain with a temperature dependent number of kinks in the dislocation lines. With this procedure both primary and secondary properties of the high frequency Bordoni peak could be satisfactorily explained. Numerical data are reported for peak parameters and for the kink diffusion coefficient.

Ultrasonic investigation of the interaction of hydrogen-dislocations in copper crystals

“…In this equation a is the interatomic distance in the dislocation line direction, N o is the number of geometrical kinks in the dislocation line, H k = enthalpy of creation of one kink, k B is the Boltzmann's constant, and A is a constant [2]. For high purity copper it holds that B(T)  T [2] and, as we shown from experimental results,…”

“…For comparison, the inset shows the ultrasonic attenuation for a high purity copper measured in an hydrogen free [2] and 3 days aged [6] hydrogenated samples, where the respective dislocation background were subtracted from the experimental data.…”

“…Both  o and v o were measured in a <111> non-deformed copper sample, irradiated with -rays until total pinning of dislocations [8]. We assume that the temperature dependence of the dislocations free attenuation and velocity on a deformed sample is the same as that in undeformed samples [2]. Also corrections due to pulse path length variation with temperature were introduced [7].…”

“…zero applied stress [2]. In this equation a is the interatomic distance in the dislocation line direction, N o is the number of geometrical kinks in the dislocation line, H k = enthalpy of creation of one kink, k B is the Boltzmann's constant, and A is a constant [2].…”

“…The kink picture has proven to be the best approach to explain the internal friction and ultrasonic attenuation of cold-worked samples of high purity FCC metals [1]. At 10 MHz to 50 MHz frequencies the two attenuation peaks known as Niblet-Wilks and Bordoni peaks (hereafter denominated NWP and BP, respectively) are present in cold-worked high purity copper crystals, superposed to a dislocation related background, which were well described in terms of the kink picture [2]. While the NWR and BR relaxations are considered to be produced by the mechanism of kink pair formation with kink diffusion in the phonon field (KPF), the dislocation background is attributed to the resonance of the oscillating kink-chain with a kink density  T [2].…”