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MM: Fachverband Metall- und Materialphysik

MM 31: Postersitzung II

MM 31.44: Poster

Mittwoch, 16. März 2011, 17:15–18:45, P5

Low-temperature relaxation in NiTi-based shape memory alloys — •Joan Torrens-Serra, Daniel Salas, Eduard Cesari, and Sergey Kustov — Departament de Física, Universitat de les Illes Balears, cra. de Valldemossa km 7.5, E-07122, Palma de Mallorca, Spain

We have studied the structural changes occurring in different Ni-Ti and Ni-Ti-Fe alloys over the temperature range from 13 to 300 K by means of mechanical spectroscopy, calorimetry (DSC) and electrical resistivity measurements. Several binary and ternary alloys were used with different thermal and mechanical history, which demonstrate distinct transformation paths: B2-B19', B2-R and B2-R-B19'. Temperature dependence of the internal friction (IF) was studied over the range 90-137 kHz for different strain amplitudes from 3*10E-7 to 5*10E-5. In addition to the martensitic and intermartensitic transformations, the IF curves showed a peak at about 90 K in annealed and water-quenched samples independently of their composition which can not be detected by DSC or electrical resistivity measurements. The thermally activated nature of the relaxation has been confirmed using different measurement frequencies. Since the IF peak is observed for ultrasonic frequencies at temperatures of around 90 K, it corresponds to a new relaxation phenomenon, not reported so far in Ni-Ti family of alloys, with the activation energy of the order of only 0.01 eV. On the other hand, no relaxation is found in deformed alloys not subjected to annealing heat treatments. The origin of this relaxation may be attributed to the presence of interstitial hydrogen atoms.