Deformation of Nanostructures and Small Volumes
Lead Research Organisation:
University of Cambridge
Department Name: Materials Science & Metallurgy
Abstract
Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.
Organisations
People |
ORCID iD |
| William Clegg (Principal Investigator) |
Publications
Howie P
(2011)
Fracture modes in micropillar compression of brittle crystals
in Journal of Materials Research
Korte S
(2009)
Micropillar compression of ceramics at elevated temperatures
in Scripta Materialia
Korte S
(2010)
Onset of plasticity in InxGa1-xAs multilayers
in Acta Materialia
Korte S
(2011)
Discussion of the dependence of the effect of size on the yield stress in hard materials studied by microcompression of MgO
in Philosophical Magazine
Korte S
(2011)
Deformation of silicon - Insights from microcompression testing at 25-500°C
in International Journal of Plasticity
Korte S
(2008)
Elastic and plastic properties of In x Ga 1- x As
in Journal of Physics D: Applied Physics
Korte S
(2008)
Discontinuous yield in InGaAs thin films
in Surface and Coatings Technology
Östlund F
(2011)
Ductile-brittle transition in micropillar compression of GaAs at room temperature
in Philosophical Magazine
| Description | The initial aim of the work at Cambridge was to understand the deformation of the coherently strained InxGa1-xAs multilayers, which had given rise elsewhere to the ideas on a minimum volume being required for deformation. While there must inevitably be a scale at which this happens, for instance as the sample size approaches the activation volume, the sample sizes here tended to be larger than this. An assumption of the initial analysis was that the yield stress did not vary with the In concentration in the layers. To investigate this, films of InGaAs were made with varying In concentrations. Using spherical indentation to determine the onset of yield, it was shown that both the elastic modulus and yield stress were influenced by the In concentration and that this assumption was incorrect. The deformation of the multilayers was studied using spherical indentation. Similar results were obtained to those at QMUL. An essential point of the initial analysis was that the onset of deformation should occur in a volume extending further than a single layer thickness. However this proved impossible to see by examining the sample in the electron microscope after it had been deformed. Micropillar compression and nanoindentation experiments in the transmission electron microscope were therefore carried out at the National Centre for Electron Microscopy at L.B.N.L. in Berkeley, California. These showed that deformation was more prevalent in the weaker layer. Based on these results, a straightforward analysis to be developed, using the information gathered on the effect of In on the yield stress, where the yield pressure of the multilayer is related to the onset of flow in the weaker layer determined by both its intrinsic yield pressure and coherency strains. This gave good agreement both with our observations and with the previous experimental observations obtained elsewhere, as well as being consistent with the observations of the effects of internal stresses in films in the literature. The observation that the micropillars could be plastically deformed without cracking led to the micropillar compression being investigated as a technique for studying plasticity in brittle materials without the requirement for high confining pressures. Work, in collaboration with the group of J. Michler at EMPA, CH, showed that such behaviour occurred below a critical pillar size and that this could be quantitatively explained by a decrease in the crack driving force in small pillars, consistent with observations in a range of systems. It was also shown, for the first time, that in single crystals individual slip systems could be interrogated, whereas in indentation multiple slip systems are required, that tests could be carried out over a range of temperatures, again for the first time, and that size effects in hard materials are much more limited at the length scales investigated than they are in soft metals. |
| Exploitation Route | The techniques developed here enable the study of plastic flow in brittle materials. Normally such materials would break rather than plastically deform. However, the plastic flow behaviour can be of great importance both at low and high temperatures in structural applications, in hard coatings for cutting tools and even in electronic materials. This work is now being developed in a range of other projects, some with industrial funding and others with academics in the UK, Europe and the US. The development of small-scale test techniques has, more recently, been used to study deformation in diamond, in collaboration with Element 6, whose main research centre moved from South Africa to Harwell in 2013. There has also been work studying the deformation of hard coatings in collaboration with the Singapore Institute for Manufacturing Technology (SIMTech). This has led to coatings being made, where recent work has shown that plastic flow requires dislocations to be nucleated within each 10 nm grain, giving rise to great improvements in wear resistance. |
| Sectors | Aerospace, Defence and Marine,Energy |
| Description | The observation that the micropillars could be plastically deformed without cracking led to the micropillar compression being investigated as a technique for studying plasticity in brittle materials without the requirement for high confining pressures. Work, in collaboration with the group of J. Michler at EMPA, CH, showed that such behaviour occurred below a critical pillar size and that this could be quantitatively explained by a decrease in the crack driving force in small pillars, consistent with observations in a range of systems. It was also shown, for the first time, that in single crystals individual slip systems could be interrogated, whereas in indentation multiple slip systems are required, that tests could be carried out over a range of temperatures, again for the first time, and that size effects in hard materials are much more limited at the length scales investigated than they are in soft metals. |
| Sector | Aerospace, Defence and Marine |
| Impact Types | Economic |
| Description | Accelerated Metallurgy (ACCMET) |
| Amount | € 700,000 (EUR) |
| Funding ID | 263206 |
| Organisation | European Commission |
| Department | Seventh Framework Programme (FP7) |
| Sector | Public |
| Country | European Union (EU) |
| Start | 03/2011 |
| End | 02/2016 |
| Description | Building New Capability in Structural Ceramics |
| Amount | £77,009 (GBP) |
| Funding ID | EP/F033605/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 07/2008 |
| End | 06/2013 |
| Description | Doctoral Training Partnership(DTP) in Structural Metallic Systems for Gas Turbine Applications-Universities of Cambridge,Swansea and Birmingham |
| Amount | £9,469,808 (GBP) |
| Funding ID | EP/H022309/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 10/2009 |
| End | 09/2014 |
| Description | HiTempProp |
| Amount | £109,605 (GBP) |
| Funding ID | 252520 |
| Organisation | European Commission |
| Department | Seventh Framework Programme (FP7) |
| Sector | Public |
| Country | European Union (EU) |
| Start | 10/2011 |
| End | 03/2013 |
| Description | Structural Metallic Systems For Advanced Gas Turbine Applications |
| Amount | £2,740,824 (GBP) |
| Funding ID | EP/H500375/1 |
| Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
| Sector | Public |
| Country | United Kingdom |
| Start | 10/2009 |
| End | 09/2014 |