Simulation of hydride-induced steady-state crack growth in metals ? Part I: growth near hydrogen chemical equilibrium

Abstract

Hydride-induced sub-critical crack growth in metals is simulated, by taking into account the coupling of hydrogen diffusion, hydride precipitation and material deformation. The terminal solid solubility of hydrogen in a stressed metal is derived analytically for hydrides of any shape with different elastic properties than those of the solid solution. The general relation considers full anisotropy of both hydride and metallic phases. It is shown that a hydrostatic stress plateau develops in the area of hydride precipitation near the crack tip, when crack propagates under conditions approaching hydrogen chemical equilibrium, near the threshold stress intensity factor. The plateau hydrostatic stress depends strongly on remote hydrogen concentration and temperature. However, it is nearly independent of the yield stress and the hardening of the metal. The same hydrostatic stress develops also behind the crack tip in the presence of hydrides. The characteristics of the near-tip field are used for estimating a critical remote hydrogen concentration, below which no hydride precipitation occurs, and the threshold stress intensity factor. The theoretical estimates compare favorably with experimental measurements.