Visualization of Hydrogen in Metals by Hydrogen Microprint Technique
Shigeru Kuramoto, Motohiro Kanno
It is very important from a practical viewpoint to study hydrogen behavior in metals because hydrogen embrittlement has been related with concentration of hydrogen at the crack initiation sites. In order to reveal the mechanism of the embrittlement, experimental methods to characterize hydrogen concentration to localized area should be established. Hydrogen microprint technique (HMT) is a simple and powerful method to visualize hydrogen behavior in high resolution. When polished surface of a specimen is covered with nuclear emulsion containing numerous submicron particles of silver bromide, hydrogen in the specimen reduce the silver bromide. Thereby silver particles left on the surface after fixing represent the sites of hydrogen emission. In this article, details in experimental procedure of HMT are described with emphasis on functions of nuclear emulsion and fixing solution, and the results on hydrogen behavior in metals using HMT are reviewed. The effects of plastic deformation and stress gradient on hydrogen transport in metals are also presented in relation to the mechanisms of hydrogen embrittlement that have been proposed so far.