0033-1732/01/3701- $25.00 © 2001 MAIK “Nauka /Interperiodica” 0053 Protection of Metals, Vol. 37, No. 1, 2001, pp. 53–60. Translated from Zashchita Metallov, Vol. 37, No. 1, 2001, pp. 60–68. Original Russian Text Copyright © 2001 by Votyakov, Vasyutkin, Senyavin, Tovbin. 1 INTRODUCTION Hydrogen corrosion of palladium membranes is pri- marily predetermined by the change in the phase state of the metal. An increase in the concentration of dis- solved hydrogen at a temperature below 565 K causes the appearance of local β-phase regions with an increased hydrogen content within α-phase with a low hydrogen content. The crystal lattice constant of β- phase exceeds that of α-phase by approximately 10% [1–3]. This results in the appearance of internal stresses in the metal. One of the main ways for the relaxation of internal stresses is the development of a system of non- equilibrium defects, namely, pores and dislocations. At the macrolevel, this manifests itself in the bending, cracking, and destruction of the membrane. A similar situation is observed during the desorption of hydrogen from a strongly hydrogenated membrane. As a simplest example, we can quote the data of [4], by which a 20-μ m foil of individual palladium is damaged by through cracks after the first phase transition, while a 100-μ m foil looses its tightness after ten or dozen cycles of hydrogenation and evacuation. Hydrogen cor- rosion does not essentially depend on whether hydro- gen affects the metal under catalytic or electrochemical conditions. The processes of destruction and plastic deforma- tion are tightly related to each other. The plastic defor- mation is mainly predetermined by the nucleation of dislocations and their motion along the crystal [5]. The problem of the mutual effect of included atoms on the evolution of the system of dislocations is very complex 1 The work was financially supported by the Russian Foundation for Basic Research, project no. 97-03-33197. and poorly studied. Such situations can be analyzed numerically (as was done in [6, 7] for low concentra- tions of admixtures). A more widely used approach takes into account only the effect of dislocations on the character of nonuniform distribution of included atoms around the core of a dislocation within the so-called Cottrell’s atmosphere [8, 9] (see, e.g., [10] on the effect of dislocations on the kinetics of metal degassing). This approach is limited by the suppositions about the low concentration of hydrogen and the constancy of the metal properties. However, experimental studies [11] reveal the necessity of a more detailed investigation of the mutual effect of the dissolved atoms and the metal. The modern state of the problem is given in [12], in which the con- tinuum dynamic model of a metal–hydrogen system is discussed as well as its consequences that enable one to analyze a number of elastic hydrogen effects. A micro- scopic model of a metal–hydrogen system was con- structed in [13]. It is based on a closed system of equa- tions and describes all the processes proceeding in a membrane during the hydrogen transfer in the same manner. These are the migration of included atoms and the change in the phase state of the membrane with the account of the changing mechanical stresses and prop- erties of micrononuniform matrices during the phase reconstruction. The obtained system of equations can be solved only numerically. In this work, in terms of the model of [13], we dis- cuss the effect of included hydrogen on the characteris- tics predetermining the motion of edge dislocations in the widest possible range of the concentration of included hydrogen (from zero to one per a metal atom). These problems were not earlier considered at the The Effect of Included Hydrogen on the Motion Parameters of Edge Dislocations in Palladium Membranes 1 E. V. Votyakov, N. F. Vasyutkin, M. M. Senyavin, and Yu. K. Tovbin Karpov Institute of Physical Chemistry, Vorontsovo pole 10, Moscow, 103064 Russia Received December 15, 1999 Abstract—The effect of included hydrogen on the mechanical and transport properties of palladium mem- branes is discussed. The dissolution of hydrogen in palladium changes the properties of the metal and can result in its hydrogen embrittlement and cracking, which depends on the motion parameters of dislocations. During the slipping motion of edge dislocations, hydrogen atoms affect the Peierls activation barrier. During the creep- ing motion, the included hydrogen affect the diffusivities of interstitial metal atoms. On the basis of the atomic model, the concentration dependence of the shear modulus, as well as the self-diffusivities and mass transfer coefficients of the included hydrogen and palladium atoms, is analyzed. The rates of elementary jumps of included atoms between interstitial sites are calculated according to the transition state model for imperfect reaction systems. An increase in the concentration of included hydrogen at the change in the phase state of the membrane under nonequilibrium conditions is shown to reduce the mobility of edge dislocations and promote the accumulation of internal stress.