Study Hydrogen Embrittlement Research Articles

Phase field modeling of hydrogen embrittlement

A numerical framework is developed in this paper to study hydrogen embrittlement. A hydrogen diffusion equation is derived, and a trapping density function is proposed in the framework of the phase field model. Effect of hydrogen enhanced localized plasticity (HELP) and hydrogen enhanced decohesion (HEDE) are modeled by reducing the yield stress and decreasing the critical energy release rate respectively. Simulation results of a compact tension specimen and a double notched tension specimen show that hydrogen accumulates at the crack/notch tip region driven by positive hydrostatic stress as well as more traps produced by plastic deformation in this area. Both HELP and HEDE reduce the load carrying capacity of the specimen, and their effects depend on the model parameters. The proposed model provides a numerical tool that can be used to comprehensively simulate hydrogen embrittlement and predict the ductile to brittle transition of the material due to the presence of hydrogen.

Hydrogen embrittlement in metallic nanowires

Although hydrogen embrittlement has been observed and extensively studied in a wide variety of metals and alloys, there still exist controversies over the underlying mechanisms and a fundamental understanding of hydrogen embrittlement in nanostructures is almost non-existent. Here we use metallic nanowires (NWs) as a platform to study hydrogen embrittlement in nanostructures where deformation and failure are dominated by dislocation nucleation. Based on quantitative in-situ transmission electron microscopy nanomechanical testing and molecular dynamics simulations, we report enhanced yield strength and a transition in failure mechanism from distributed plasticity to localized necking in penta-twinned Ag NWs due to the presence of surface-adsorbed hydrogen. In-situ stress relaxation experiments and simulations reveal that the observed embrittlement in metallic nanowires is governed by the hydrogen-induced suppression of dislocation nucleation at the free surface of NWs.

Study hydrogen embrittlement and determination of E110 fuel cladding mechanical properties by ring compression testing

.Zirconium based alloys are commonly used as material for fuel claddings in the light water reactors. Claddings act as first metallic barriers against loss of fission products during the nuclear power plant operation, intermittent storage or final dry storage. The integrity of claddings is always critical issue during reactor operation and during storage of spent fuel. In this work, ring compression testing method developed was applied to study hydrogen embrittlement, to evaluate the stress-strain behaviour and hoop fracture properties of E110 (Zr-based) fuel claddings. The results show that the collapse load and the tensile strength values depend strongly on hydrogen concentration. In particular, tensile strength experiment data shows significant change in its trend after reaching the maximum hydrogen solubility limit.

In situ small-scale hydrogen embrittlement testing made easy: An electrolyte for preserving surface integrity at nano-scale during hydrogen charging

An electrolyte for electrochemical hydrogen charging of corrosion-susceptible alloys is developed, which preserves the surface integrity at nano-scale by minimizing the surface roughness alternation. To assure the formation and adsorption of the hydrogen from the electrolyte, permeation tests were performed on Fe 3 wt%Si ferritic steel. X-ray photoelectron spectroscopy method was used to check the effect of the glycerol-based solution on the chemical composition of the sample surface. The surface analysis revealed minimal chemical and topography alteration on the surface after different electrochemical treatments. Various types of in situ small-scale mechanical tests such as nano-indentation, micro-pillar compression, and micro-cantilever bending tests were performed inside this electrolyte while the samples being charged with hydrogen under cathodic potential. These small-scale mechanical tests showed that the solution facilitates studying hydrogen embrittlement in nano- or micro-scale.

A Numerical Model to Study the Hydrogen Embrittlement Effect

Hydrogen embrittlement is a complex phenomenon which can affect steel structures used for different applications, as pipelines, storage vessels and fuel cells. In literature, many works have been proposed to study hydrogen embrittlement, but a unified solution to fully understand the phenomenon is still not defined.Aim of this work is to develop a reliable numerical tool to estimate the influence of hydrogen on the fracture toughness of steel. A 2D finite element model of a C(T) specimen is developed using a zero-thickness layer of cohesive elements to simulate crack propagation. Starting from an initial model without hydrogen, the embrittlement effect is simulated by modifying the traction- separation law (TSL) of cohesive elements, according to relationships taking into account hydrogen diffusion at the crack tip and plastic strain. Parameters of TSL are calibrated in order to reproduce the experimental toughness data. The model can be very useful to understand, from the viewpoint of fracture mechanics, the hydrogen embrittlement phenomenon in the studied steel, but also it can be extended in the future to estimate the influence on fracture toughness of different parameters, as hydrogen concentration or change in mechanical properties.

Rising Displacement Stress Corrosion Cracking Testing

Fracture-mechanics-based test and evaluation techniques provide insight into the phenomenon of stress corrosion cracking (SCC) and help to develop guidance for avoiding or controlling SCC. In addition to constant load and constant deflection tests, techniques that are based on rising load or rising displacement procedures are applied increasingly in fracture mechanics SCC testing. Rising displacement tests on precracked specimens were used for studying hydrogen embrittlement (HE) and to serve as a basis for modeling material degradation caused by the uptake of atomic hydrogen from the environment. The measurements of the crack-tip opening angle and of the crack-tip opening displacement combined with crack growth velocity data served to rationalize the experimental findings by comparison with the results of simulations of HE using various models.

Effects of grain-boundary segregation and precipitation on the hydrogen susceptibility of nickel

The straining electrode tensile test was employed to study hydrogen embrittlement in three grades of nickel. Aging at intermediate temperatures (400 to 800 °C) after solution annealing caused sulfur segregation to grain boundaries in the materials. This sulfur segregation was found to influence intergranular hydrogen embrittlement, and the effect was most prominent when the surface supply of hydrogen was low and when the grain boundaries were free of graphite precipitates. Aging also induced graphite precipitation at the grain boundaries of one grade of nickel (Nickel 200). The presence of these grain-boundary particles reduced susceptibility to hydrogen embrittlement, but at the same time caused a form of aging embrittlement. The effect of the second-phase precipitate, when present, masked the effect of sulfur segregation on hydrogen susceptibility.

Use of linear mechanics of fracture in studying hydrogen embrittlement of titanium alloys

Use of linear mechanics of fracture in studying hydrogen embrittlement of titanium alloys