Stress-assisted atomic diffusion in NiTiHf shape memory alloys.

Stress-assisted atomic diffusion behavior in NiTiHf shape memory alloys was investigated by measuring the internal friction at temperature range of 300–1070 K. A thermally activated internal friction peak was recorded in the B2-ordered phase in the temperature range of about 850–950 K (at 1 Hz, depending on alloy composition), with activation energy of 1.79 ± 0.05 and 2.00 ± 0.10 eV and relaxation time of 2.7 − 2 + 1 ∙ 10 − 12 and 1.7 − 5 + 1 ∙ 10 − 13 s for Ni 50 Ti 35 Hf 15 and Ni 50 Ti 30 Hf 20 alloys, respectively. It was proposed that the short-range diffusion of Ni-atoms under the stress is the main relaxation mechanism in the studied alloys. The diffusion coefficients of Ni in the B2-ordered phase were estimated to be 3.72·10−8 and 5.90·10−7 m2s−1 for Ni 50 Ti 35 Hf 15 and Ni 50 Ti 30 Hf 20 alloys, correspondingly. [Display omitted] • A thermally activated IF peak was found in the B2-ordered phase of NiTiHf alloys. • The activation energy and relaxation time of relaxation process was estimated. • The main relaxation mechanism is short-range diffusion of Ni-atoms under the stress. • The diffusion coefficients of Ni in B2-ordered phase for NiTiHf alloys were estimated. [ABSTRACT FROM AUTHOR]