Hydrogen diffusion in a thin film of Pd, Ni and Cu deposited on iron

Abstract

Much effort has been made to provide resistance to the environment by surface modification or coating of different kinds of metals. As to hydrogen embrittlement, particularly, permeation and diffusion of hydrogen in multi-layered heterogeneous metals have been investigated. In those, hydrogen diffusion is usually analyzed provided that hydrogen diffuses according to Fick`s law in each layer and a concentration ratio of hydrogen on the interface between heterogeneous metals is a constant k. However, it has also been reported that hydrogen diffusion is disturbed at interfaces. The assumption that hydrogen concentration is continuous at interfaces, i.e. K = 1, has also been applied. The effect of interfaces on hydrogen diffusion has not yet been clarified. Moreover, as a thin film, the diffusion coefficient of hydrogen decreases in comparison with one in the bulk. The process of hydrogen diffusion in multi-layered metals is not simple, because it depends on not only the boundary condition at interfaces, but also the property of thin films. Furthermore, it is considered that the characteristics of interfaces and thin films is affected by how they are made and the combination of metals. In this paper, nickel, copper and palladium, in which diffusion coefficients and solubilities of hydrogenmore » are different from those in iron, are coated on iron. Hydrogen diffusion in thin films is compared between coating methods, electro-deposition (ED), vapor deposition (VD) and ionized cluster beam (ICB) methods.« less