Regensburg 2025 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 7: Materials for the Storage and Conversion of Energy
MM 7.1: Talk
Monday, March 17, 2025, 15:45–16:00, H22
Effect of stress induced nanohydride formation on dislocation nucleation and pinning in FeCr alloys — •Ali Tehranchi1, Jing Rao2, Lekshmi Sreekala2, Jazmin Duarte2, Gerhard Dehm2, Jörg Neugebauer2, and Tilmann Hickel1 — 1BAM Federal Institute for Materials Research and Testing, ali.tehranchi@bam.de, Germany — 2Max Planck Institute for Sustainable Materials
The detrimental effects of hydrogen (H) on the mechanical properties of metals are universally acknowledged. However, the mechanisms behind these effects remain unclear. In situ nano-indentation experiments are powerful tools for probing the effect of H on the hardness and plasticity of metals. In this work, ab initio calculations and stress dependent phase diagrams in chemical potential space are used to clarify the effect of nanohydrides on the pop-in load of in situ nanoindentation of FeCr alloys. It is shown that the anisotropic stress field of the indenter with a radius of 170 nm facilitates the formation of nanohydrides with significantly lower elastic constants and containing high eigen shear strain. The shear stress associated with these inhomogeneous inclusions is responsible for the experimentally observed reduction in critical shear for dislocation nucleation and the pop-in loads in these indentation experiments. On the other hand, for indenters with a larger radius, the pop-in load is increased due to the pinning of the pre-existing dislocations by the same nanohydrides which are not capable to form underneath the indenter because of the lower magnitude of its induced stress field. The formation of nanohydrides under loading has significant implications for H-embrittlement and H-storage.
Keywords: nanoindentation; homogeneous dislocation nucleation; nanohydride; inhomogeneous inclusion; dislocation pinning