Hydrogen embrittlement controlled by reaction of dislocation with grain boundary in alpha-iron

Abstract

Hydrogen atoms absorbed by metals in hydrogen-containing environments can lead to the premature fracture of the metal components used in load-bearing conditions. Since metals used in practice are mostly polycrystalline, grain boundaries (GBs) can play an important role in hydrogen embrittlement of metals. Here we show that the reaction of GBs with lattice dislocations is a key component in hydrogen embrittlement mechanism for polycrystalline metals. We use atomistic modeling methods to investigate the mechanical response of GBs in alpha-iron with various hydrogen concentrations.Analysis indicates that dislocations impingement and emission on the GB can provoke it to locally transform into an activated state with a more disordered atomistic structure, and introduce a local stress concentration. The activation of the GB segregated with hydrogen atoms can greatly facilitate decohesion of the GB. We propose a hydrogen embrittlement model that can give better explanation of many experimental observations.

Hydrogen Trapping in bcc Iron

“…Grain Boundary and Free Surface Intergranular cleavage failure has been experimentally observed in various materials exposed to H-rich environments [91][92][93]. Therefore, GBs are often seen as one of the central microstructural elements in investigations of HE.…”

Application of Molecular Dynamics Calculations to Elucidation of the Mechanism of Hydrogen-Induced Crack Initiation in Fracture Toughness Tests Using Tempered Martensitic Steels

“…Because direct in-situ observation of the behavior of lattice defects such as dislocations, grain boundaries and atomic vacancies in steel under applied stress is extremely difficult, the role of lattice defects in microcrack initiation was investigated by molecular dynamics (MD) calculation, [13][14][15] which makes it possible to analyze the activity of lattice defects under stress in the presence of hydrogen by simplifying and modeling the lattice defects. For example, in a previous study by Wan et al 16) using the MD calculation approach, tensile simulations of twist grain boundaries (TGBs) in the presence of hydrogen were conducted. That study clarified the fact that the elementary processes of dislocation emission and absorption on the grain boundary, void formation and growth on the grain boundary, and fracture along the grain boundary occurred in order.…”

“…This is the same level of hydrogen as that at which the effect of hydrogen appeared remarkably in the previous study using MD calculation. 16) On the other hand, for example, the amount of hydrogen permeated into the sample held in 40 MPa high pressure hydrogen gas without loading is approximately 0.3 wt ppm. However, when stress is applied, it is predicted that the amount of hydrogen penetration near the crack tip under stress will increase extremely due to the increased size of the interstitial sites and the large local stress concentration in the vicinity of lattice defects such as dislocations and grain boundaries.…”

Energetic and atomic structural analyses of the screw dislocation absorption at tilt grain boundaries in BCC-Fe

“…Impurities in iron, such as sulfur and phosphorus, cause GB embrittlement 2 , 3 . In addition, hydrogen embrittlement is a significant problem in industrial applications in delayed fracture 4 – 6 . Because the suppression of brittle fracturing is an industrial issue, the factors influencing embrittlement, especially impurity concentrations and the decohesion mechanism, have been discussed 7 – 9 ; in particular, the study of changes in interatomic bonds at the GBs based on the first-principles method has been reported 2 .…”