Interfacial strengthening of metallic and ceramic alloys: a modelling framework for bridging length scales

Lead Research Organisation: King's College London
Department Name: Physics

Abstract

There is a highly successful tradition of the applied mechanics community providing underpinning modelling for new fields of Materials Science/Engineering. A UK team has been identified to develop new modelling approaches to bridge length scales between atomistics and the meso-level (on the order of microns), and between the meso and macroscopic levels. The importance of size effects in Materials Engineering is increasing due to the development of new fine-structure metallic alloys (e.g. nanostructured metallic alloys) and ceramic coatings on length scales in the range 1 Onm to 1 Omicrons. Conventional continuum descriptions fail to predict the dependence of strength upon microstructural size, and the associated evolution of microstructure with deformation. A variety of phenomenological nonlocal plasticity theories such as the Fleck and Hutchinson strain gradient theory have been proposed to predict size dependence in rate independent plasticity. It is now timely to develop multiscale physically-based modelling techniques in order to underpin and improve upon the phenomenological models, for both plasticity and creep.Modelling strategies are now reasonably well established for undertaking first-principle density functional theory calculations, molecular dynamics simulations, discrete dislocation dynamics simulations and continuum finite element calculations over limited domains of length and time scales. But gaps exist in the modelling space map, reflecting gaps in materials understanding, such as the strengthening mechanisms of grain boundaries leading to the Hall-Petch and inverse Hall-Petch effects. The main scientific objective of this project is to develop a hierarchy of methods involving information transfer from one level to the next. As a secondary objective, current modelling strategies will be extended to a wider range of length and time-scales.We plan to inject the physics through four levels of modelling with each level interconnected to the one above/below. The four levels of modelling are Level 1: Molecular dynamics calculations to connect atomistics to discrete dislocation. These calculations will allow for diffusion effects to be included in the discrete dislocation calculations and clarify the interaction between dislocations and interfaces. Level 2: Discrete dislocation and diffusion calculations to predict strength, creep resistance and fracture toughness dependence on grain size using the diffusion and interface reaction models developed in level 1. Level 3: Homogenisation techniques will be developed and applied to the underlying discrete dislocation model in order to identify a set of macroscopic equations for the relevant internal variables. Level 4: Development of robust macroscopic constitutive laws using the homogenisation calculations will be used to discriminate between the competing phenomenological theories. Finally, a limited set of experiments including room and high temperature torsion and bending experiments will be conducted in order to guide and validate the modellingThis project will lay the foundations for the sustainability of the UK's international reputation in micromechanical modelling. Strong collaborations will be extended with world-leading groups such as Harvard and Brown in the US and MPI Stuggart in Europe. Two 3-day workshops will be held in Cambridge mid-term and towards the end of the project. The purpose of these workshops will be to train the next generation of UK researchers and to help them develop links with the leading international groups. This, coupled with the direct training in a range of modelling strategies given to the researchers working on this proposal, will ensure that there is a strong base for the future development of materials modelling in the UK.

Publications

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Description The grant enabled the full development of an atomistic modelling technique called "Learn On The Fly" LOTF, based on fundamental quantum mechanical (QM) theory, which proved particularly effective for investigating materials' mechanical properties which are affected by chemical reactions.

Brittle materials were targeted, and output notably included (i) the first ever QM dynamical simulation of a complete stress-corrosion process, which rationalised how hydrogen atoms can be used to cut silicon wafers in the semiconductor industry (SmartCut; technology); (ii) the first QM study of dynamical instabilities incurred during the catastrophic brittle fracture of silicon crystals.
Exploitation Route The method developed during the project can be used by increasingly less-specialised operators, including industrial R&D personnel, and can be applied to increasingly large classes of materials. Delivering a simulation protocol which is generally applicable to all structural materials including metals, made it possible to participation in a UK program grant investigating hydrogen embrittlement, in close collaboration with major steel industrial groups (Tata Steel, Rolls-Royce, SKF, and ThissenKrupp Steel among others).
Sectors Aerospace, Defence and Marine,Chemicals,Energy,Environment

 
Description The project spawned (1) a EC-funded network which studied the development of advanced glass devices (in collaboration with Schott AG, based in Mainz); (2) a 4-year collaboration with the international mining company Rio Tinto Plc., which studied brittle fracture processes, in view of applications to rock crushing and grinding; (3) a collaboration with ANL and USAFLR which investigate advanced oxide interfaces and Ni superalloys for jet engine technologies.
Sector Manufacturing, including Industrial Biotechology
 
Description Brown University 
Organisation Brown University
Country United States 
Sector Academic/University 
Start Year 2006
 
Description Corus UK 
Organisation Tata Steel Europe
Country United Kingdom 
Sector Private 
Start Year 2006
 
Description Harvard University 
Organisation Harvard University
Country United States 
Sector Academic/University 
Start Year 2006
 
Description Max Planck Institute for Metal Research 
Organisation Max Planck Society
Department Max Planck Institute for Metals Research
Country Germany 
Sector Public 
Start Year 2006
 
Description Polytechnic School INRIA 
Organisation Polytechnic School INRIA
Country France 
Sector Academic/University 
Start Year 2006
 
Description Princeton University 
Organisation Princeton University
Country United States 
Sector Academic/University 
Start Year 2006
 
Description University of California, Santa Barbara 
Organisation University of California, Santa Barbara
Country United States 
Sector Academic/University 
Start Year 2006