Hydrogen-assisted cracking of iron-based amorphous alloys: Experimental and finite element observations

This chapter proposes a coupled fracture mechanics/diffusion approach to model the failure of metallic glasses due to hydrogen embrittlement in the absence of external loads. The model can be employed to predict time to failure of amorphous Fe80B11S19 ribbons in which high-pressure bubble formation and interconnecting crack propagation occur during electrochemical hydrogen charging. The crack propagation process clearly depends on a variety of parameters, including mutual interaction between bubbles, the geometry, and dimensions of the specimen, and the length of the crack relative to bubble size. In the absence of mutual interaction between stress fields around adjacent bubbles, gas accumulation in bubbles is more rapid. The intersection point between the p-V curves for the fracture mechanics-based elastic solution and for the equation-of-state of real hydrogen gas can be used, in conjunction with the value of the critical pressure, as a failure criterion. Crack propagation is characterized by the existence of an incubation period in which the hydrogen fills the bubbles and cracks until a critical pressure is reached. The model can be extended to other failure mechanisms, and may be useful for materials selection. For example, a similar approach can be utilized to predict the synergistic effects of helium and hydrogen in isotropic and anisotropic crystalline metals.