J. Phys. IV France 11 (2001) Pr8-87-Pr8-87
Effect of hydrogen on the damping properties of NiTi alloysB. Coluzzi, A. Biscarini, R. Campanella, G. Mazzolai and F.M. Mazzolai
Department of Physics, Istituto Nazionale di Fisica per la Materia Condensata, University of Perugia, Italy
The effect of hydrogen dopings on the internal friction and the Young's modulus has been investigated in the alloys Ni50.8Ti49.2, Ni49Ti51 and Ni40Ti50Cu10 as a function of the hydrogen content nH (nH=H/Me atomic) and frequency. It has been found that hydrogen strongly affects the anelastic spectrum of these alloys in the temperature domain. The IF peak occurring at the austenite-martensite (A-M) transition in the solubilized Ni50.8Ti49.2 alloy is enhanced by hydrogen at low contents (nH<l.3) and reduced at high hydrogen contents ( nH > 1.3). An additional IF peak is introduced in the same alloy by H for nH>1.3. This second peak, which appears at temperatures higher than the martensite start temperature Ms, is likely due to hydrogen re-distributions over subsets of interstitial sites within a hydride, under the applied alternating stress fields associated with the sample vibrations. The relaxation parameters of this peak, which is thermally activated, are in keeping with the expectations from H diffusion high temperature data. In the aged alloy Ni49Ti51 H suppresses the low temperature IF background and introduces a thermally activated relaxation, which is associated with H dragging processes by twin boundaries. A relaxation effect, again ascribable to H dragging processes by twin boundaries, has also been evidenced with the Ni40Ti50Cu10 alloy. The most remarkable result of these investigations is the fact that hydrogen appears to be a very sensitive tool to probe twin boundary dynamics.
© EDP Sciences 2001