Spontaneous bending of Ni-Ti alloy plates caused by preferential hydrogen absorption

Abstract

When the polished Ni-Ti alloy plates were hydrogen charged cathodically, it was newly found that the plates were bent spontaneously as the hydrogen charging time increased. The degree of the spontaneous bending was closely related to the structural change on the surface of the plates. When only one side of the specimen surfaces was polished by an emery paper or buffed, the spontaneous deformation was clearly identified after hydrogen charging. In contrast, when both sides of the specimen surfaces were polished in the same level, such deformation was not observed. Thermal hydrogen desorption analysis showed that the degree of the spontaneous bending was clearly related to the difference of the hydrogen concentration, probably in the thickness direction. It was also found that when hydrogen was released from the specimen by heating, the spontaneous bending was disappeared. Based on the X-ray diffraction analysis of the polished specimen surfaces before and after hydrogen charging, it was revealed that the amount of hydrogen entered into the specimen was promoted by the polishing because of the crystal lattice distortion and the strain-induced martensite transformation. © 2008 The Japan Institute of Metals.