• Siegl, Wolfgang

Abstract

The aim of this research was to analyze the behavior of hydrogen in iron and iron-based materials and how it is influenced by different microstructural components. Dislocations, grain boundaries, and precipitates can act as hydrogen traps, accumulating hydrogen and hindering hydrogen diffusion in the material.A series of pure iron and iron-based alloys was analyzed, each containing different types and densities of hydrogen traps. Electrochemical permeation experiments were done to determine hydrogen diffusivity, thermal desorption spectroscopy was used to gain detailed information on the number and types of traps present in the material as well as their trapping energy for hydrogen.The results show that hydrogen traps can be created by mechanical material deformation. More severe deformation increases the number of generated traps. Appropriate heat treatment allows lattice recovery and reduces the trap density. Trap activation energies of dislocations, grain boundaries, and martensite lath boundaries range from 27 to 37 kJ mol^(-1), vacancies in iron are stronger traps with an activation energy of around 51 kJ mol^(-1). A significant trapping effect of grain boundaries was only observed in materials with grain sizes in the nanometer region but not in materials of larger grain sizes. Carbide precipitates are effective hydrogen traps with activation energies of up to 61 kJ mol^(-1) for Ti-carbide. It is assumed that strong traps have a positive effect on a material’s resistance against hydrogen embrittlement while weak traps have the opposite effect. In addition, increased diffusivity for hydrogen may reduce the susceptibility to hydrogen embrittlement.

Topics

• density
• impedance spectroscopy
• grain
• grain size
• experiment
• carbide
• Hydrogen
• dislocation
• precipitate
• iron
• activation
• susceptibility
• diffusivity