Papers by Author: U. Straube

Abstract: The ultrasound pulse echo overlap method has been used to determine the elastic stiffness coefficients and the corresponding ultrasonic attenuation for a single crystal of the Ni40Ti50Cu10 alloy as a function of temperature. The elastic stiffness coefficients exhibit anomalies near the martensitic phase transition. In the shear stiffness coefficient, corresponding to C44 propagation mode in austenite, a large jump occurs from 36 GPa, above the transition, down to 15 GPa, below the transition. This jump is accompanied by a strong increase in the ultrasonic attenuation. The stiffness coefficients corresponding to C11 and C' = (C11 – C12)/2 modes in austenite show an anomaly at the phase transition, however, these are small effects compared to the one associated with C44 mode. The elastic behavior of this crystal has been characterised down to a temperature of 100 K.

Abstract: The chemical diffusion coefficient (Dc) of hydrogen in the Ni30Ti50Cu20 shape memory alloy has been determined in the temperature range 700 - 1150 K by investigating the kinetics of H2 absorption. The mobility of H has also been deduced between 250 K and 280 K from a Snoek-type internal friction peak. The values of the Einstein diffusion coefficient (DE) derived from the relaxation time of this peak were in keeping with those of Dc obtained at low H contents (nH = H/Me < 0.01 ). The combined Arrhenius plot of DE and Dc gave the following values for the diffusion parameters: W = 0.52 ± 0.02 eV, D0 = (5±2)x10-4 cm2/s.