Prof. Motomichi Koyama
from Tohoku University, Japan will be visiting WW1 on Feb. 19, 2020.
He will give a talk on Wednesday, Feb 19 at 14:00 in Room 3.31, Martensstraße 5. He will talk about "Effects of dislocation planarity and compositional complexity
on hydrogen embrittlement of austenitic steels".
Stable austenitic steels have been recognized as hydrogen-resistant materials.
However they also show hydrogen-assisted failure when exposed to a severe hydrogen
atmosphere, e.g. 100-MPa hydrogen gas. In this talk, we present two examples of
hydrogen embrittlement of stable austenitic steels: Fe25Cr1N steel and equiatomic
high-entropy alloy. The former shows extremely enhanced dislocation planarity
because of the Cr-N coupling. The strong dislocation planar motion causes stress
concentration on grain boundaries, which results in intergranular fracture when
hydrogen is introduced. In addition, the dislocation planar array can act as
quasi-cleavage fracture path. Therefore, the hydrogen-assisted failure in the
high-nitrogen steel occurs via dislocation-planarity-driven microstructural cracking.
The high-entropy alloy shows hydrogen-assisted intergranular fracture.
The brittleness can be reduced by grain refinement or reducing Mn content.
In the presentation, details of these phenomena are given with
electron channeling contrast images.