Hydrogen Assisted Crack Growth in High Purity Low Pressure Hydrogen Gas

Abstract

At low partial pressures of hydrogen (less than 0.1 MPa), hydrogen interacts with the metal and lowers the cohesive strength of the lattice (Oriani and Josephic, 1977). The decohesion theory postulates that regions exist near the crack tip with hydrogen concentrations, which are several orders of magnitude larger than the lattice concentration of hydrogen. The microstructure strongly influences the embrittlement process and the crack growth kinetics. (Kumnick and Johnson, 1980). Thus it can be expected, that the experimental study of the mechanism of gaseous hydrogen embrittlement is facilitated by studying the process at the crack tip in its simplest form under the most simple boundary conditions. For these reasons FeSi-single crystals are used, since the micro-processes for ductile and brittle fracture are well known in this alloy (Vehoff and Neumann, 1979, 1980). Tests are carried out at different temperatures, hydrogen pressures and plastic crack tip opening rates in order to investigate the influence of the hydrogen concentration at the crack tip on the brittleness of the fracture process (Wei and co-workers, 1980).