The Portevin-Le Chatelier Effect in hydrogenated nickel

Abstract

The macroscopic activation energy for the initiation of the serrations which are characteristic of the Portevin-Le Chatelier Effect in hydrogenated nickel, was found to be 0.59 ev at 0.21 at. pct H. This differs markedly from the 0.33 ev previously reported by earlier workers.1 Also, it differs from activation energy for hydrogen diffusion in nickel,Q D , which is reported to be 0.42 ev.13 The difference between the macroscopic activation energy for the disappearance (Q U ) and initiation of the serrations (Q L ) was found to be approximately equal to the binding energy of hydride to dislocations (ΔE), of 0.14 ev. The concentration dependence for the initiation and disappearance of serrations was found to approach a saturation level at approximately 0.08 at. pct H. The dominant dislocation locking mechanism responsible for the serrated yielding is thought to be one involving the drift flow of hydrogen to dislocations under an electrical driving force and the ultimate precipitation of the hydride. Electron microscopy has confirmed that an enhanced dislocation multiplication accompanies serrated yielding in hydrogenated nickel.