Investigation of hydrogen embrittlement in a high manganese twinning induced plasticity steel : a correlative electron microscopy and atom probe tomography study

Khanchandani, Heena; Raabe, Dierk (Thesis advisor); Münstermann, Sebastian (Thesis advisor); Gault, Baptiste (Thesis advisor)

Aachen : RWTH Aachen University (2022)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2022

Abstract

Many countries are currently working towards developing a hydrogen-based energy supply and consumption chain in order to minimize carbon emissions while meeting the needs of modern industrialized societies. For instance, the United States and many European countries aim to achieve net-zero carbon emissions by 2050 [1]. It is hence important to develop the materials which can be utilized for hydrogen-energy-related generation, storage and transport which is a challenging task because most of the high strength metallic materials are prone to hydrogen embrittlement.Hydrogen embrittlement can cause a dramatic deterioration of the mechanical properties of high-strength metallic materials. The degradation of the mechanical properties of metallic systems associated to the ingress of hydrogen leads to the premature catastrophic failures of many structural components [2-5]. It is hence crucially important to understand the impact of hydrogen on individual materials systems. Despite decades of experimental and modelling studies, the exact underlying mechanisms behind hydrogen embrittlement remain elusive. Twinning induced plasticity steels (TWIP) are promising structural materials which can potentially be used for hydrogen storage and transport [6]. TWIP steels belong to a class of high manganese steels with manganese content higher than 20 wt.% [7]. They are austenitic with face centered cubic crystal structure. However, TWIP steels are prone to hydrogen embrittlement [8]. Numerous mechanisms have been proposed in the literature to explain the hydrogen embrittlement susceptibility of TWIP steels such as the influence of hydrogen on the material’s stacking fault energy, phase stability and diffusivity [4]. In this thesis, the hydrogen embrittlement mechanism in a TWIP steel of composition Fe 28Mn 0.3C (wt.%) has been investigated by using a multiscale approach. The tensile specimens were charged with hydrogen by cathodic charging and tensile tests were performed on the hydrogen-charged and the uncharged samples. The microstructural changes due to the tensile deformation with and without hydrogen were examined by correlative electron backscatter diffraction and electron channeling contrast imaging. It was inferred from this study that hydrogen interacts with the structural defects and modifies the dislocation structure. In order to examine this interaction of hydrogen with specific microstructural features by atom probe tomography (APT) and hence determine their role in hydrogen embrittlement, various cryogenic workflows were developed. The successful workflows were employed to study the segregation of tritium at a coherent Σ3 twin boundary and the segregation of deuterium at a random high angle grain boundary in the studied TWIP steel by APT. The current study hence suggests that the coherent Σ3 twin boundaries are hydrogen trapping sites in TWIP steels.

Institutions

• Division of Materials Science and Engineering [520000]
• Chair of Materials Physics and Institute for Physical Metallurgy and Materials Physics [523110]