Z. Yan, L. Cui, Y. Zheng, T. Liu, X. Jiang, China University of Petroleum, Beijing, China
The effect of hydrogen on the transformation characteristic and microstructure of NiTiNb shape memory alloy was investigated. Samples were charged with hydrogen by electrolysis for different time. DSC results showed that new reversible transformation peaks around 110°C appeared, and the transformation enthalpies of the thermal peaks increased with the increasing charging time. They had a narrow hysteresis (almost 5°C) which was quite a novel characteristic for large hysteresis NiTiNb alloy. X ray diffraction (XRD) results illustrated that the {110} diffraction peak of the b-Nb phase shifted to lower angles with a corresponding lattice parameter increased from 2.3356 Å to 2.4427 Å (corresponding to nearly 14% of volume increase), while the lattice parameter of the {110}B2 diffraction peak of NiTi alloy increased from 2.1361 Å to 2.1453 Å (corresponding to just 1.3% of volume increase).
Summary: This study investigated the effects of hydrogen on the transformation characteristic and microstructure of NiTiNb shape memory alloy. X ray diffraction (XRD) results illustrated that the {110} diffraction peak of the -Nb phase shifted to lower angles with a corresponding lattice parameter increased from 2.3356 Å to 2.4427 Å (corresponding to nearly 14% of volume increase) due to hydrogen-induced structural changes. Moreover, new peaks around 110℃ appeared in DSC curves after hydrogen-charging which may attribute to hydrogen-induced martensitic transformation.
