Hydrogen enhanced decohesion at grain boundaries - insights from ab-initio calculations
- Date: May 27, 2021
- Time: 02:00 PM - 03:00 PM (Local Time Germany)
- Speaker: PD Dr. habil. Rebecca Janisch
- Research Group Leader: Mechanical Properties of Interfaces Department of Micromechanical and Macroscopic Modelling ICAMS, Ruhr-Universität Bochum
- Location: Online
- Room: Virtual Lecture
- Host: Dr. Maria Jazmin Duarte-Correa
Grain boundaries in ferritic microstructures play a dual role in the
context of hydrogen embrittlement: on the one hand, they act as H traps
and thus reduce the amount of mobile H in the system. On the other hand,
exactly this trapping is expected to promote hydrogen enhanced
decohesion at the grain boundaries. In order to understand and
ultimately influence the segregation process, as well as the cohesive
properties of interfaces in ferrite, a detailed understanding is
required, between the local composition and residual strain on the one
hand and the solubility of hydrogen and its impact on the cohesive
strength on the other. This talk summarises some recent results of
ab-initio studies of H segregation at Fe single crystal cleavage planes,
as well as at special symmetrical tilt grain boundaries. The solution
energy of hydrogen was investigated in the presence of different
alloying elements [1,2] as well as a function of tractions normal to the
interface [3]. The qualitative findings are, that in relaxed as well as
strained microstructures, H tends to accumulate at the grain
boundaries, and the influence of alloying elements on this process is
comparatively weak. For low to medium H concentrations, H clearly
reduces the surface energies, and hence the work of separation, but it
has only a mild effect on the transgranular or intergranular fracture
stress. The quantitative results, however, depend significantly on the
loading and relaxation scheme. Whether this is only a technical issue,
or also has some physical background, will be discussed in the
presentation. Finally, an outlook on ongoing work on the effect of
increasing the H concentration will be given.