On the Implication of Hydrogen on Inter-granular Fracture

Abstract

The intergranular fracture promoted by hydrogen ingress in the material depends on densities and organizations of defects near grain boundaries. Particularly, we illustrate first the relation between the grain boundary character and the different defects and trapping sites stored, and their consequences on hydrogen transport and segregation. High-angle Random boundaries (R) are considered as a disorganized phase where the hydrogen diffusion is accelerated, while the Special boundaries (Coincident Site Lattice, CSL) constitute a potential zone for hydrogen trapping due to the high density of trapping sites as dislocations and vacancies. The predominance of one phenomenon depends on several parameters, such as the grain size, the probability of grain boundaries connectivity, the grain boundaries energy and the excess of free volume. Additionally, our experiments confirm that hydrogen promotes vacancies formation, probably in grain boundaries. In a second part, we have explored the role of the Random grain boundaries on damage assisted by hydrogen. Tensile strengthening is reduced under hydrogen flux when the fraction of random grain boundaries increases. These results support the idea that hydrogen flux promotes intergranular fracture more than the hydrogen concentration.