Original citation: Barrera, O., Bombac, D., Chen, Y., Daff, T. D., Galindo-Nava, E., Gong, P., Haley, D., Horton, R., Katzarov, I., Kermode, James R., Liverani, C., Stopher, M. and Sweeney, F.. (2018) Understanding and mitigating hydrogen embrittlement of steels : a review of experimental, modelling and design progress from atomistic to continuum. Journal of Materials Science . Permanent WRAP URL: http://wrap.warwick.ac.uk/98590 Copyright and reuse: The Warwick Research Archive Portal (WRAP) makes this work of researchers of the University of Warwick available open access under the following conditions. This article is made available under the Creative Commons Attribution 4.0 International license (CC BY 4.0) and may be reused according to the conditions of the license. For more details see: http://creativecommons.org/licenses/by/4.0/ A note on versions: The version presented in WRAP is the published version, or, version of record, and may be cited as it appears here. For more information, please contact the WRAP Team at: [email protected] warwick.ac.uk/lib-publications J Mater Sci ReviewREVIEW Understanding and mitigating hydrogen embrittlement of steels: a review of experimental, modelling and design progress from atomistic to continuum O. Barrera1,2,* , D. Bombac3 , Y. Chen4 , T. D. Daff5 , E. Galindo-Nava3 , P. Gong6 , D. Haley4 , R. Horton7 , I. Katzarov8 , J. R. Kermode9 , C. Liverani7 , M. Stopher3 , and F. Sweeney6 1 Oxford Brookes University, Wheatley Campus, Wheatley, Oxford OX33 1HX, UK 2 Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK 3 Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, UK 4 Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK 5 Engineering Laboratory, University of Cambridge, Trumpington Street, Cambridge CB2 1PZ, UK 6 Department of Materials Science and Engineering, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK 7 Department of Physics, Imperial College London, Prince Consort Road, London SW7 2BB, UK 8 Department of Physics, King’s College London, Strand, London WC2R 2LS, UK 9 Warwick Centre for Predictive Modelling, School of Engineering, University of Warwick, Coventry CV4 7AL, UK Received: 11 October 2017 ABSTRACT Accepted: 28 December 2017 Hydrogen embrittlement is a complex phenomenon, involving several length- and timescales, that affects a large class of metals. It can significantly reduce the Ó The Author(s) 2018. This ductility and load-bearing capacity and cause cracking and catastrophic brittle article is an open access failures at stresses below the yield stress of susceptible materials. Despite a large publication research effort in attempting to understand the mechanisms of failure and in developing potential mitigating solutions, hydrogen embrittlement mechanisms are still not completely understood. There are controversial opinions in the liter- ature regarding the underlying mechanisms and related experimental evidence supporting each of these theories. The aim of this paper is to provide a detailed review up to the current state of the art on the effect of hydrogen on the degra- dation of metals, with a particular focus on steels. Here, we describe the effect of hydrogen in steels from the atomistic to the continuum scale by reporting theo- retical evidence supported by quantum calculation and modern experimental characterisation methods, macroscopic effects that influence the mechanical properties of steels and established damaging mechanisms for the embrittlement of steels. Furthermore, we give an insight into current approaches and new mit- igation strategies used to design new steels resistant to hydrogen embrittlement. Address correspondence to E-mail: [email protected] https://doi.org/10.1007/s10853-017-1978-5 J Mater Sci List of symbols Kmin Stress intensity factor at minimum loading TDA Thermal desorption analysis Kmax Stress intensity factor at maximum loading K APT Atom probe tomography RK min Kmax Kt Stress intensity factor DK Kmax À Kmin IG Intergranular fracture n0 Total number of chemical bonds HID Hydrogen-induced decohesion nH Distribution of hydrogen by chemical HELP Hydrogen-enhanced local plasticity bonds HIPT Hydrogen-induced phase transformation K0 Stress intensity factor increment HESIV Hydrogen-enhanced strain-induced rY Flow stress vacancy formation H r0 Yield strength in the presence of hydrogen AIDE Adsorption-induced dislocation emission rh Hydrostatic stress SANS Small-angle neutron scattering re Effective stress TEM Transmission electron microscopy CZM Cohesive zone modelling CMD Centroid molecular dynamics Introduction SFE Stacking fault energy PIF Path-integral formulation Hydrogen has remarkable properties and has for RPMD Ring-polymer molecular dynamics quite some time been promoted as a fuel for a zero DFT Density functional theory carbon future. It is the lightest element, making it a kMC Kinetic Monte Carlo cornerstone of quantum mechanics as a rare example MC Monte Carlo of an exactly solvable two body problem. Hydrogen EAM Embedded atom model can dissolve in most metals and alloys [62], and its SSRT Slow strain rate test interactions with crystal lattice features are a reason TRIP Transformation-induced plasticity for concern in iron, steel, nickel, titanium, vanadium, hl Hydrogen occupancy in the lattice zirconium, silicon and other metals used in engi- ht Hydrogen occupancy in trapping sites neering [3]. Problems connected to hydrogen in Nt Trap density materials are manifested in numerous ways, e.g. Nl Lattice density stress corrosion cracking, hydrogen-induced crack- Cl Hydrogen concentration in the lattice ing, hydride cracking and other deleterious effects, Cl0 Reference hydrogen concentration often leading to catastrophic fracture. Since catas- Ct Hydrogen concentration in trapping sites trophic failure is unacceptable in engineering, DS Devanathan Stachurski hydrogen’s detrimental effects need to be reduced as DL Lattice diffusivity much as possible. Hydrogen-induced degradation Deff Effective diffusivity and all phenomena associated with its deleterious tlattice Lag time in an ideal lattice effects are known as hydrogen embrittlement (HE), ttrap Lag time in traps implying a hydrogen-induced transition from ductile SKP Scanning Kelvin probe to brittle behaviour. Research into the effects of SKPFM Scanning Kelvin probe force microscopy hydrogen on mechanical properties was launched at BCC Body-centred cubic the end of the nineteenth century by studying effects FCC Face-centred cubic on iron and steels by Johnson [86] and later con- FCT Tetragonally distorted FCC firmed by Reynolds [174]. Since then, the effect of BCT Body-centred tetragonal H-assisted degradation has been widely researched HCP Hexagonal close packed and explained [11, 35, 213, 241]. However, the a BCC phase underlying mechanisms are still being discussed with c FCC phase numerous theories suggested and extensively cHydride FCC hydride phase reviewed [30, 123, 138, 169, 178, 227]. Due to com- HCP phase plexity of the HE phenomena, it is required to have martensite FCC c transformed in HCP phase knowledge of the hydrogen interactions on the metal p Plastic strain surface, how it enters the metal, its transport through J Mater Sci the crystal lattice, its interaction with crystal defects from atomistic simulations to continuum modelling (vacancies, dislocations, grain boundaries, solutes) and by adopting recently developed advanced char- and precipitates, inclusions, interfaces, etc., and most acterisation and testing procedures. One of the most importantly, its effect on the modification of material important aims of the HEmS programme grant is the properties. Experimental studies on HE have shown design of a new family of high-strength steels resis- that the presence of H atoms in a solid has a large tant to hydrogen embrittlement. influence on both crack nucleation and propagation The objective of this paper is to give a reader [227]. It is established that HE is connected to the fast insight into the changes caused by hydrogen residing diffusion of H atoms through the solid materials in materials, a process that can have catastrophic lattice, often by quantum mechanical tunnelling even effects. We mainly focus on iron and steels; other at room temperature followed by interaction with metal systems are briefly introduced to explain crystal defects. These interactions are often dominant additional effects that the presence of hydrogen can in determining the influence of H on metals. More- cause. Following catastrophic fractures related to over, interactions of hydrogen with crystal defects hydrogen we will then discuss where hydrogen is and its influence are fundamentally less understood likely to reside and how hydrogen moves inside the than diffusion of hydrogen in the perfect crystal material. The detection of hydrogen inside the lattice. material is extremely challenging. We believe that It is common to refer to H atoms in the lattice as combining experimental, numerical and theoretical diffusible hydrogen,1 which moves through the nor- techniques is the way forward to make a break- mal interstitial sites in the crystal lattice, and trapped through in understanding hydrogen embrittlement in hydrogen, which is non diffusible and resides around metals. We discuss relevant experimental methods various crystal imperfections. These imperfections available in the literature, such as thermal desorption serve as traps for H