Trap theory of Hydrogen embrittlement

Abstract

A theory has been developed that relates many particularities of hydrogen embrittlement to the behavior of the trap population of the material during its exposure to hydrogen. In particular, it is shown that reversible traps may act as innocuous sinks or as detrimental hydrogen sources, depending on test conditions. Two conditions will determine what role will prevail. One is related to the initial state of the material prior to the test, i.e. whether it has been precharged or not. The other concerns the transport mode of hydrogen in the lattice: as dislocation atmospheres, by interstitial jumps in the lattice, or along short circuit paths. Thus, each particular situation that is equivalent to a commonly used test technique is examined and the conclusions regarding hydrogen penetration or release and hydrogen embrittlement, are drawn. Because of the good agreement between theory and literature data, it is concluded that many apparent enigma of hydrogen embrittlement, such as the difference usually made between internal and external hydrogen embrittlement, can readily be interpreted as long as the trap characteristics of the material and the test conditions are precisely known.