Interpreting hydrogen-induced fracture surfaces in terms of deformation processes: A new approach

Interpreting topological features on fracture surfaces in terms of the underlying deformation processes has traditionally been based on assumed knowledge of the processes and mechanisms with no direct correlation being established. By using a combination of high-resolution scanning electron microscopy (SEM), atomic force microscopy and focused-ion beam machining to enable investigation by transmission electron microscopy of the microstructure immediately beneath the surface, correlation of developed structure with the topology of the fracture surface becomes possible. Using this methodology, features on hydrogen-induced fracture surfaces that appear flat at low resolution under SEM are revealed to be decorated with fine-scale undulations that are associated with an underlying dense arrangement of dislocations. The formation of this microstructure and the fracture surface are discussed in terms of hydrogen embrittlement models, with the conclusion reached that the surface formation can be understood within the framework of the enhanced plasticity model of hydrogen embrittlement establishing the conditions that favor the formation of the observed surface features.