Behavior of hydrogen in an Ni3Al compound investigated by means of hydrogen microprint technique

Hydrogen microprint technique, which can visualize microscopic location in the surface where hydrogen atom has been evolved, was applied to an isothermally forged Si-23.4 mol%Al alloy sheet to investigate the behavior of hydrogen in Ni3Al compounds. Considering that Ni3Al shows marked embrittlement in hydrogen gas atmosphere, the surface location on one side where hydrogen atoms had been evolved was observed by SEM, with the other side exposed to hydrogen gas of 0.1 MPa. The influence of tensile deformation by 3% on the behavior of hydrogen was also investigated. When the specimen was not deformed, largest number of hydrogen atoms penetrated into the specimen, although their distribution was not uniform. It was found that hydrogen evolution quantity was decreased by the deformation. When the specimen was not exposed to the hydrogen gas, a small amount of hydrogen was evolved at slip steps by the deformation, while no hydrogen was detected in the specimen which was not deformed. From the results obtained, it was concluded that hydrogen molecules in the environment were decomposed into atoms at Ni3Al surface and penetrated into the interior. It was deduced that hydrogen atoms were trapped by dislocations and moved with gliding dislocations in Ni3Al, in a way similar to other metallic materials.