About HEmS

HEmS (Hydrogen in metals - from fundamentals to the design of new steels) is a major initiative to investigate the process of embrittlement of metals from hydrogen. The research is funded by the Engineering and Physical Sciences Research Council (EPSRC) and is a joint collaboration between the Universities of Oxford, Cambridge, Sheffield and Imperial and King's Colleges London.

It has been known for over a hundred years that hydrogen causes catastrophic failure in high strength steels. The overall aim of HEmS is to provide a comprehensive understanding of the process of hydrogen embrittlement in steels, through an integration of advanced characterisation, testing and modelling techniques. This new understanding will be used to develop new ultra-high strength steels that are resistant to embrittlement in the presence of hydrogen.

Potential applications of this research are envisaged across a wide range of key UK industries, including the automotive and energy sectors, and it is anticipated that this research will impact directly on the fuel efficiency of the next generation of cars, and the service lifetimes of wind turbines and energy pipelines.

Attendees at the Royal Society Discussion meeting ‘The challenges of hydrogen and metals’, Jan 2017
Attendees at the Royal Society Discussion meeting
‘The challenges of hydrogen and metals’, Jan 2017

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University of Oxford

Professor Alan Cocks

Alan Cocks Professor of Materials Engineering
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Dr Paul Bagot

Paul Bagot Departmental Lecturer in 3D Atom Probe
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Dr Michael Moody

Michael Moody Lecturer in Materials and Fellow of Trinity College
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Dr Olga Barrera

Olga Barrera Postdoctoral Research Assistant, Solid Mechanics Group
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Dr Daniel Haley

Daniel Haley Postdoctoral Researcher, Atom Probe Group, Dept. of Materials
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Yi-Sheng Chen

Yi-Sheng Chen Ph.D. Student, Atom Probe Group, Dept. of Materials
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University of Cambridge

Dr Pedro Rivera

Pedro Rivera Assistant Director of Research, SKF University Technology Centre
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Dr Gábor Csányi

Gábor Csányi Reader in Engineering
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Dr David Bombač

David Bombač Postdoctoral Research Associate
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Dr Thomas Daff

Thomas Daff Research Associate, Department of Engineering
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Dr Enrique Galindo-Nava

Enrique Galindo-Nava Royal Academy of Engineering Fellow
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Dr Siamak Soleymani Shishvan

Siamak Soleymani Shishvan Research Associate, Department of Engineering
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Dr Isaac Toda-Caraballo

Dr Isaac Toda-Caraballo Research Associate, Department of Materials Science and Metallurgy
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Beriham Basha

Beriham Basha Ph.D. Student, Department of Materials Science and Metallurgy
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Miles Stopher

Miles Stopher Ph.D. Student, Department of Materials Science and Metallurgy
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Andrej Turk

Andrej Turk Ph.D. Student, Department of Materials Science and Metallurgy
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Imperial College London

Professor Michael Finnis

Michael Finnis Chair in Materials Theory and Simulation
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Dr Erlend Davidson

Erlend Davidson Research Associate, Department of Materials
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King's College London

Professor Tony Paxton

Tony Paxton Theory & Simulation of Condensed Matter
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Professor Alessandro De Vita

Alessandro De Vita Theory & Simulation of Condensed Matter
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Dr Ivaylo Katzarov

Ivaylo Katzarov Postdoctoral Research Associate, Department of Physics
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Dr Henry Lambert

Dr Henry Lambert Postdoctoral Research Associate, Department of Physics
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Dr Sebastian Echeverri Restrepo

Dr Sebastian Echeverri Restrepo Visiting Research Fellow from SKF Group
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University of Sheffield

Professor W Mark Rainforth

W Mark Rainforth Head of Department and Professor of Materials Science and Engineering
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Dr Peng Gong

Peng Gong Postdoctoral Research Associate, Department of Materials Science and Engineering

Dr. Francis Sweeney

Francis Sweeney Postdoctoral Research Associate, Department of Materials Science and Engineering
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Dr Robert Horton

Postdoctoral Research Associate, Department of Materials, Imperial College London
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Dr. James Kermode

Assistant Professor, School of Engineering, University of Warwick
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Dr Wojciech Szlachta

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The research activities under HEmS are divided into four major themes, or work packages (WPs). These are summarised in this figure, together with the flow of information between the different activities. WP1 focuses on the design of microstructures that are resistant to hydrogen embrittlement and will synthesise information from all the other research activities. Pioneering new characterisation techniques are being employed in WP2 together with mechanical testing across a range of scales to provide new insights into the embrittling process. We are generating significant modelling and experimental data in each of our research projects. The generation, storage and flow of data between the different research activities is being managed in WP3. A range of integrated modelling activities across all scales relevant to the embrittling process are being followed in WP4. The activities within these work packages are described in further detail below.

Diagram showing the inter-relationships between the different work packages

WP1 Microstructural Design against Hydrogen Embrittlement (leader Pedro Rivera)

Work package 1 focuses on the application of thermodynamic and kinetic principles in designing alloys resistant to hydrogen embrittlement. Initially, the work will be of a computational nature, but once desired microstructural scenarios are devised, prototype alloys will be cast and heat treated. Advanced characterisation methods will be employed to ensure processing leads to the desired microstructures. The final aim is to achieve alloys that, whilst exposed to hydrogen, preserve their mechanical properties. Modelling the deformation behaviour of the newly designed alloys, under the presence of hydrogen, will be performed. Mechanical testing will be employed to test and refine the deformation models, and will feed back into microstructural design and alloy optimisation activities.

Work package 1 strongly interacts with work package 2. Partly in finding industrially sound processing routes to achieve the desired microstructures and partly in advanced characterisation work to demonstrate the desired microstructures created, all the while displaying the structural properties sought after.

As these optimal microstructures are discovered, the focus will be on how these can be realised in practice. This will require: Phase thermodynamics, where the conditions (temperature and composition) for the formation of desired phases will be examined with the use of thermodynamic databases in combination with genetic optimisation algorithms; Phase kinetics, to ensure that the critical scales of the various phases is achieved; Plasticity and Fracture Modelling, where computational schemes based on the models of work package 4 will be adopted to ensure ultra-high strength, together with a quantitative understanding of hydrogen effects.

WP2 Production, Characterisation & Testing (leader Mark Rainforth)

The effect of hydrogen embrittlement in limiting the use of ultra-high strength steels is well known. However, hydrogen can degrade the properties of steels with a wide variety of different microstructures; from martensitic steels for bearing applications through to multiphase steels, such as TRIP steels, for automotive applications.

The main objectives of work package 2 will be to:

  1. Pioneer new methods of characterising hydrogen in steels to improve our understanding of the origin of hydrogen embrittlement and elucidate the mechanisms of hydrogen trapping. To use these techniques to validate the findings in WP4. To use this combined knowledge as an input into WP1 for Microstructural Design.
  2. To manufacture a range of bespoke steels with enhanced resistance to hydrogen embrittlement using the combined outputs from all the programme’s work packages.
  3. To validate the performance of the bespoke steels through an appropriate wide range of mechanical property testing.

Work package 2 has three main sub-packages in its research plan which will help achieve the research aims of the programme:

WP2.1 Advanced characterisation (leader Mike Moody)

This sub-work package will implement an array of microscopy techniques, to provide atomic scale physical and chemical analysis, including local bonding information. Novel imaging techniques will be developed to make direct observations of hydrogen at cracks and feed new insights into the modelling activities of WP1 and WP4. Of particular note, atom probe tomography (APT) studies of deuterium charged samples will enable 3D atomistic visualisation of hydrogen trapping sites. New Bayesian enhanced imaging techniques developed in combination with WP3 will enable direct identification of microstructural features that act as traps.

WP2.2 Bespoke material production (leader Mark Rainforth)

The pinnacle of this project will be the manufacturing and testing of alloys to evaluate the success of our material design through all the WPs. We possess outstanding metals processing facilities, with access to the latest technologies, including melting, near net shape casting and thermomechanical processing. A range of bespoke steels will be manufactured through the melting facility at Sheffield University and with our programme partners at SKF, Tata Steel and ThyssenKrupp Steel Europe.

WP2.3 Mechanical properties (leader Mark Rainforth)

We also have unique facilities for mechanical testing, particularly for hydrogen limited performance applications. The feed through from WP4 on the elucidation of mechanisms and WP3 on data generation to WP1 on microstructural design will significantly accelerate the targeting of key microstructures. Investigative techniques such as focused ion beam microscopy will provide mechanistic understanding on how the microstructural design has altered the hydrogen behaviour in the material for a particular application. The experimental programme also provides further input into WP3 on data generation and curation.

WP3 Data-intensive Modelling (leader Gábor Csányi)

The hydrogen in metals programme encompasses materials modelling at a wide range of length and time scales covering aspects from the most fundamental level of quantum mechanical electronic structure calculations (also known as "first principles" modelling) to thermodynamic and kinetic modelling of phase transformations, of the industrially relevant alloys and processes.

These activities are not carried out in isolation, but rely on a significant flow of information from the lower towards the higher length scale models. Work package 3 is partly about consistently handling the generation, archiving and distributing of the data, and partly about novel algorithms that process lower length scale data to determine parameters of higher length scale models. This includes, amongst others, deriving the interaction laws between atoms from their electronic interactions, the calculation of thermodynamic phase diagrams of alloys and the response of defects such as cracks and interfaces to both chemical and elastic boundary conditions relevant to hydrogen embrittlement.

Another activity of this work package will look to enhance the analysis of experimental data coming from atom probe tomography, which builds 3D maps of atomic structures, using Bayesian probabilistic modelling aided by first principles calculations.

Computational data will be made available to our partners on the programme’s website, via a database that allows the easy depositing, search and retrieval of atomistic structures and the associated quantities. Experimental data will be stored using the software package of a programme partner company, Granta Design. One of the goals of the project is to integrate the handling of atomistic calculated data within Granta's products.

WP4 Elucidation of Mechanisms (leader Tony Paxton)

Work package 4 focuses on discovering exactly how hydrogen embrittlement occurs at the atomic scale. Until we understand the fundamental processes that lie behind the phenomena we cannot act to ameliorate hydrogen embrittlement through alloy design. There have been a number of mechanisms put forward in the last decades to explain how hydrogen embrittlement occurs, including hydrogen enhanced decohesion (HEDE), hydrogen enhanced local plasticity (HELP) and hydrogen enhanced stress induced vacancy formation (HESIV). One of our tasks is to find under what conditions of microstructure, temperature, stress and strain rate the various mechanisms are dominant.

Work package 4 is a programme of materials theory and simulation, but because of the extended scope of research within the large HEmS project consortium, this programme will be linked intricately with the largely experimental research of work packages 1 and 2.

Work package 4 divides into four sub-packages of research:

WP4.1 Atomistic (leader Alessandro De Vita)

We aim to exploit the latest simulation technology in machine learning, in particular a method we call "learn on the fly". This combines the efficiency of classical and Gaussian approximation interatomic potentials with the chemical accuracy of density functional theory. By following explicitly, in real time molecular dynamics, the growth of fracture under load, we hope to discover the chemomechanical principles that lie behind hydrogen embrittlement.

WP4.2 Thermostatistics (leader Mike Finnis)

This work area will focus on how we can calculate the chemical potential of hydrogen in steel. The problem is how to exploit modern methods of free energy calculation in atomistic simulation. We hope to calculate phonon and configurational contributions to free energies using a range of techniques, including the quasi-harmonic approximation and Monte Carlo methods. We will also employ path integral theory in order to address the important quantum effects experienced due to the light mass of the hydrogen nucleus. This means that we will be studying the phenomenon of tunnelling.

WP4.3 Mesoscopic processes (leader Tony Paxton)

This package undertakes to do modelling at the length scale of atoms and beyond. We will use atomistic input data into models using kinetic Monte Carlo and cohesive zone theory that allow us to follow processes in plasticity and fracture, using realistic regimes of temperature and strain rate. We will be following the propagation of a crack under conditions of given hydrogen chemical potential, and at a length scale in which the simulation is able to explore microscopic processes that arise in the competition between crack advance and crack blunting, by dislocation emission and absorption. The effect of hydrogen on the outcome of this competition is what we are looking to discover.

WP4.4 Continuum modelling (leader Alan Cocks)

At this length and time scale we can use input from the other sub-packages on the HEmS programme to make explicit models that encompass actual microstructure and a complete process zone at the crack tip. We can study the formation and linkage of micro cracks, decohesion at interfaces and grain boundaries, with rate dependent crystal plasticity finite element models. Initially, we will be able to simulate the mechanical response of simple model microstructures and then extend the methodology to study the response of microstructures designed in work package 1, and tested in work package 2.




International Institute for Carbon-Neutral Energy Research (I2CNER)

Thomas Young Centre


If you are interested in learning more about the HEmS research activities, or would like to contribute to our activities in any way, please contact:

Charles Harper
Department of Engineering Science
University of Oxford
Parks Road
T: +44 (0)1865 613946
E: hems@eng.ox.ac.uk
Twitter: @HEmSgrant