Cathodic hydrogen embrittlement in alloy 718

Le Journal de Physique IV, 2000

This paper presents a simulation method that is aimed at investigating the elementary mechanisms governing the process of Stress Corrosion Cracking under cathodic hydrogen discharge. Key issues concerning the experimental evidences of localised corrosiondeformation interactions and the relevant modelling are briefly recalled. The simulation method is introduced and the first results on elementary configurations outline the basic mechanisms of hydrogenplasticity interactions at a Stress Corrosion crack tip. The effect of hydrogen on the density of a dislocation pileup is examined. The particular situation at the tip of a loaded crack is examined via the introduction of image forces on diffusing interstitial hydrogen. Conclusions are drawn concerning the basic ingredients of the model, as well as future developments of the simulation technique.

Corrosion Science, 2006

The present paper focuses on the observed corrosion-induced embrittlement of alloy 2024 and tries to answer the key question on whether the observed embrittlement is attributed to hydrogen uptake and trapping in the material. Hydrogen is produced during the corrosion process and is being trapped in distinct energy states, which correspond to different microstructural sites. The formation of a hydrogen-affected zone beneath the corrosion layer is supported by fractographic analysis. Removal of the corrosion layer leads to complete restoration of yield strength but only partial restoration of ductility. Additional heat treatment to release the trapped hydrogen leads only to complete restoration of ductility.

Acta Materialia, 2010

This paper summarizes recent work at the University of Illinois on the fundamental mechanisms of hydrogen embrittlement. Our approach combines experimental and theoretical methods. We describe the theoretical work on hydride formation and its application to hydrogen embrittlement of Ti alloys through the stress-induced hydride formation and cleavage mechanism, the localization of shear due to solute hydrogen, and finally, we present experimental evidence that favors the decohesion mechanism of hydrogen embrittlement in a β-Ti alloy.

Journal of Materials Engineering and Performance, 2017

The hydrogen embrittlement susceptibility of near-peak-aged UNS N07718 (Alloy 718) was evaluated by performing slow strain rate tests at room temperature in air and substitute ocean water. Tests in substitute ocean water were accomplished in an environmental cell that enabled in situ cathodic charging under an applied potential of 21.1 V versus SCE. Some specimens were cathodically precharged for 4 or 16 weeks at the same potential in a 3.5 wt.% NaCl-distilled water solution at 50°C. Unprecharged specimens tested in substitute ocean water exhibited only moderate embrittlement with plastic strain to failure decreasing by about 20% compared to unprecharged specimens tested in air. However, precharged specimens exhibited significant embrittlement with plastic strain to failure decreasing by about 70%. Test environment (air or substitute ocean water with in situ charging) and precharge time (4 or 16 weeks) had little effect on the results of the precharged specimens. Fracture surfaces of precharged specimens were typical of hydrogen embrittlement and consisted of an outer brittle ring related to the region in which hydrogen infused during precharging, a finely dimpled transition zone probably related to the region where hydrogen was drawn in by dislocation transport, and a central highly dimpled ductile region. Fracture surfaces of unprecharged specimens tested in substitute ocean water consisted of a finely dimpled outer ring and heavily dimpled central region typical of ductile fracture.

ABSTRACT The effects of dissolved hydrogen on dislocation motion in stainless steel have been studied in an attempt to understand how hydrogen impacts deformation, which is important for understanding hydrogen embrittlement in these alloys. Indentation tests of stainless steels before and immediately after exposure to high hydrogen gas pressures have been conducted to examine the effects of dissolved hydrogen on indentation induced slip steps.

International Journal of Hydrogen Energy, 2017

In situ electrochemical nanoindentation has been used to study the effect of hydrogen on the nanomechanical response of Alloy 718. Observations show that hardness increase as a result of hydrogen charging. Also, the hydrogen charging gives a reduced pop-in load and pop-in width. This is related to a reduction in the energy needed for dislocation nucleation and the mobility of the dislocations in the presence of hydrogen. Two grains with different orientations has been tested here. The pop-in load and width obtained in the (101) orientation was more affected by the presence of hydrogen than those achieved in the (111) oriented grain.

Hydrogen embrittlement is a type of deterioration that can be linked to stress corrosion cracking. Aluminum alloys are known to be susceptible to hydrogen embrittlement. Still, a lot of confusion exists on the transport of hydrogen and its possible role in stress corrosion cracking in aluminum alloys. The aim of this work is to provide evidence of corrosion induced hydrogen embrittlement in 6063 aluminum alloy. A constant area of the standard fatigue samples was charged with hydrogen for a constant period of 3 hours. The effect of aging time, temperature and hydrogen content on the fatigue resistance properties of 6063 alloy was investigated. Experimental results have revealed that the number of cycles required to fail the alloy are significantly affected by diffusion of hydrogen, aging time, and aging temperature in the aluminum alloy. Scanning electronic microscope (SEM) was used to study the fracture surfaces produced by different processes. The SEM results show brittle fracture surfaces with inter-granular cracks and fatigue striations in the alloy.

Corrosion, 2016

Hydrogen embrittlement is a common, dangerous, and poorly understood cause of failure in many metal alloys. In practice, it is observed that different types of damage to industrial components have been tied to the presence and localization of hydrogen in metals. Many efforts have been made at understanding the effects of hydrogen on materials, resulting in an abundance of theoretical models and papers. However, a fully developed and practically-applicable predictive physical model still does not exist industrially for predicting and preventing hydrogen embrittlement. The connection of microstructure-based behaviors of materials and effects on the macroscopic measurable characteristics (stress levels, hardness, strength, and impact toughness) is of the utmost importance to achieve a unified model for hydrogen embrittlement. This paper gives an overview of the application of a model for structural integrity analysis of boiler tubes made of plain carbon steel exposed during operation to a local corrosion process and multiple hydrogen assisted degradation processes: hydrogen embrittlement and high-temperature hydrogen attack. The model is based on the correlation of mechanical properties to scanning electron microscopy fractography analysis of fracture surfaces in the presence of simultaneously active hydrogen embrittlement micromechanisms. The proposed model is practical for use as a predictive maintenance in power plants, as it is based on the use of standard macro-mechanical tests.

2002

Fatigue <html_ent glyph="@amp;" ascii="&amp;"/> Fracture of Engineering Materials and Structures, 2005

The present work aims to provide evidence of corrosion-induced hydrogen embrittlement of the aircraft aluminium alloy 2024. An extensive experimental investigation involving metallographic and fractographic analyses as well as mechanical testing was performed. The corrosion exposure led to a moderate reduction in yield and ultimate tensile stress and a dramatic reduction in tensile ductility. Metallographic investigation of the specimens revealed a hydrogen-rich embrittled zone just below the corrosion layer. Furthermore, fractographic analyses showed an intergranular fracture at the specimen surface followed by a zone of quasi-cleavage fracture and further below an entirely ductile fracture. Mechanical removal of the corroded layers restored the yield and ultimate stress almost to their initial values but not the tensile ductility. The tensile ductility was restored to the level of the uncorroded material only after heat treatment at 495 • C. Measurement of hydrogen evolution with temperature showed that by heating the corroded alloy at 495 • C, the trapped hydrogen is released. c 2005 Blackwell Publishing Ltd. Fatigue Fract Engng Mater Struct 28, 565-574 565