Processing of Advanced Materials Group

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Advanced metallics

Processing of oxide dispersion strengthened alloys for fission and fusion power
Z. Hong, M. Gorley, Dr. H. Zhang, Professor S.G. Roberts, Professor P.S. Grant

Oxide dispersion strengthened alloys comprise a metallic alloy with a dispersion of sub-micron oxide particles. The fine scale dispersion of the ceramic particles gives rise to strain fields around the particles, which can confer strength and other properties by interaction with dislocations in a manner similar to that of fine scale precipitates produced by ageing heat treatments in conventional metallurgical alloys. The particles also have the potential to stabilize microstructural features such as grain size at intermediate temperature. A further potential benefit of these particles in steels for nuclear applications is that they or the interface between the particles and the matrix may act as a 'sink' for vacancies and He induced by a neutron flux environment, partially mitigating otherwise severely damaging effects such as embrittlement. The size, volume fraction, chemistry, etc. of particles influences the final properties. However, there are few systematic studies that relate the detail of the oxide particle mixing/dissolution and re-precipitation behaviour to the processing parameters of practical interest. We are invesigating the dynamics of the critical metallic-ceramic mixing process. We are developing ideas for identifying and assuring the quality of milled powders so that downstream properties are evolved optimally. Alternative processes to mechanical mixing are also being explored. Funded by EPSRC.

Powder and liquid based processing of novel dispersion strengthened copper alloys for fusion applications
A. Morrison, Professor P.S. Grant

Nanostructured oxide dispersion strengthened (ODS) copper alloys with a high density of nano-sized dispersoids exhibit high thermal conductivity, excellent irradiation resistance, high temperature microstructural stability, which makes them promising candidates as heat sink materials in nuclear power generation. Processing plays an important role in determining performance because the stabilising, fine-scale nano-clusters of ceramic particles are developed during the early stages of processing and cannot be subsequently manipulated.

The objectives of our work are to develop an in-house manufacturing capability for Cu ODS alloys, in which powder metallurgy and spray forming will be two key processing techniques. These primary processing approaches are being developed as an alternative to the commercial in-situ oxidation route during casting and heat treatment. The primary processing will be complemented by spark plasma sintering consolidation processing to ensure full density. At each stage the nano/micro-structure will be investigated using a range of microstructural techniques, both in Oxford and at the new Materials Research Facility at CCFE. This information will be used to rationalise the mechanical response of alloys assessed by a combination of conventional and micro-mechanical testing, with the aim identifying the process-material combinations that provide optimum mechanical properties and microstructural stability. Funded by CCFE.

Spray forming of Ni superalloys for high temperature applications
Dr A. Sato, Professor P.S. Grant

Spray forming produces cast microstructures with comparatively low macro- and micro-structural chemical segregation and is thus well-suited for the manufacture of complex chemistry, multi-component alloys that otherwise show strong elemental segregation. Although spray formed Ni superalloys have shown properties equivalent or superior to their conventionally cast/wrought counterparts, they have not been adopted commercially because of the difficulties in ensuring a high process yield and the complexity and associated cost of large-scale Ni superalloy melting. As an alternative, we are developing a hybrid arc spray forming (HASF) process in which costly, large-scale alloy melting as pre-cursor to spray forming is avoided by the use of a consumable wire feedstock. To achieve thermal conditions of melt spray forming - essential to produce a refined, polygonal grain structure - a customised secondary atomisation system and other proces modifications have been implemented. been developed. Mechanical properties are suggesting that this route may offer an attractive combination of convenience and low cost for advanced alloy fabricatoin. Funded by Mitsubishi Heavy Industry, Japan.

Modelling and experiments concerning dendrite fragementation
Dr. Z. Guo*, Dr. E. Liotti and Professor P.S. Grant

This project concerns the control of nucleation and subsequent microstructural evolution during solidification by intrinsic grain multiplication using external physical means such as acoustic/shock waves and pulsed magnetic fields. Fragments from broken dendrites are well-known to multiply the number of final grains in a casting, and so provide grain refinement and attendant improvements in quality and performance. The central idea of this project is to enhance dramatically this effect by disrupting continuously the thermal conditions in the melt and at growing solid/liquid interface, without any melt contamination. While various external field approaches have been developed, there remains some uncertainty in the mechanism of dendrite fragmentation, and this project will study both the underlying physics of grain multiplication as well as a new approach for its enhancement. Critical to the work is the use of phase field modelling and fluid flow modelling to explore the conditions that promote grain multiplication. (* Royal Society Newton Fellow, Tsinghua University, China).

Development of high performance products comprising dissimilar metals by spray forming
R. Senbing, S. Zhao, Professor P.S. Grant

Spray forming is being researched in order to produce clad tubes and cylinders with different interior and external properties. Critical to these materials is control of the interface between the materials in terms of its strength and toughness, inter-diffusion, phase formation, and response to downstream processing. Successful development of this approach will facilitate a range of unusual products optimised for niche, high value applications in a number of industries. In collaboration with Dr. J. Mi, University of Hull. Funded by Baosteel, China.

Processing and properties of tungsten coatings for fusion reactors
Dr D. Armstrong, Professor P.S. Grant

Tungsten is the key plasma facing material for use in any future nuclear fusion device due to its high melting point, good sputter resistance and low activity. However its refractory nature leads to inherent difficulties in its processing and many traditional production routes are not available. Vacuum plasma spraying is one of the most attractive methods of producing tungsten coatings for this application, but thermal mis-match between the tungsten and substrates such as steel or copper lead to the development of complex residual stresses which degrade the performance of the coating. Other challenges include microstructural control, and characterising the properties of tungsten in the coating arrangement.

This project will use recently upgraded vacuum plasma spraying equipment to produce both pure and alloyed tungsten coatings on novel substrates. In-situ process data will be recorded including temperatures, deflections, etc. Coatings will be characterised using state of the art microscopy and micro-mechanical testing facilities, as well as thermal loading, and finite element analysis used to understand the evolution of the stress state. By consideration of the process conditions in manufacture, the microstructure and the properties of the coatings, optimisation will be performed to produce practical tungsten coatings for further testing and application.

Energy storage and related

Novel high energy density high reliability capacitors
A. Mahadevegowda, Dr. C. Johnston, Dr. H.E. Assender, Professor P.S. Grant

Current capacitor technology significantly limits the temperature capability and electrical performance of power electronics relative to the "More Electric Airframe" systems requirements, which are emerging rapidly as a key priority for both aeroengine and airframe manufacturers. Novel capacitor materials combining high dielectric ceramics and high performance polymers are being developed for aero-engine applications, particularly within the more electric aircraft concept. Investigations include characterisation of the fundamental material properties using advanced analytical instruments, clean room characterisation of the electrical properties, development of fabrication routes, and modelling of behaviour for lifetime prediction. (Funded by Technology Strategy Board, Labinal Power, ICW Ltd)

Energy storage for low carbon grids
Dr C. Fu, Professor P.S. Grant

We are developing novel approaches for the fabrication of electrochemical energy storage devices that are relevant to grid-scale energy storage applications as part of the EPSRC Grand Challenge Project: Energy Storage for Low Carbon Grids that is a large scale, multi-partner project led by Imperial College London. We aim to address the many aspects of integrating energy storage into future energy networks. Our current focus is on spray processed electrodes in new materials for grid applications, and we will later apply some of our process developments to battery, fuel cell and device manufacture. Funded by EPSRC.

Development of flexible energy storage and generation systems based on nano-hybrid materials
C.A. Huang, Professor J-M Kim, Professor P.S. Grant

The focus of the research is the development of sub-components and devices for energy storage and environmental energy harvesting based on functional nanostructures and novel fabrication approaches. The core of the research is the exploitation of layer-by-layer approaches for the fine scale arrangement and control of nanomaterials over large areas. This ambitious research builds on key know-how developed in Oxford on LbL processing of suspensions and is directed to both energy storage (primarily supercapacitors) and energy harvesting (piezo-based), and the exploration of processing strategies for their combination in flexible devices. Funded by KETEP, S. Korea.

Nanostructures for energy applications
L. O'Neill, Professor P.S. Grant

Nano-structured materials are attractive for some energy related applications because they can provide very high surface areas per unit mass, leading to high energy densities in various storage applications. A supercapacitor (electrochemical capacitor) stores electrical energy either in the form of ions at an electrode/electrolyte interface (electrical double-layer capacitor, EDLC) or by faradic redox reactions at the electrode (pseudo-capacitors). Both types offer high power density (rapid discharge), excellent reversibility, and long cycle life. We are fabricating comparatively large amounts of both multi-walled CNTs (by chemical vapour deposition) or single wall CNTs (by arc discharge) in-house, purifying them, functionalizing their surface to improve their ion storage capability, and then processing them into large area films or buckypaper - on a variety of flexible or stiff substrates. In some cases, other process steps can add nanoparticles to provide superimposed pseudo-capacitance. Our goal is to demonstrate the potential benefits of this approach over existing materials at the laboratory scale, and also to ensure that we develop processing technologies that at all stages offer the potential for cost-effective scaling to the near-industrial, and then full industrial use. The ability to process and characterize fully these materials in-house is key to this strategy. Funded by EPSRC Grant: Supergen Energy Storage.

Structure-property relationships in graded nanocomposites for microwave applications
Q. Lei, Professor C. Grovenor, Professor P.S. Grant

There has been a great deal of international interest in the exciting electro-magnetic properties that can be achieved in metamaterials but very little work has been undertaken on how to process them in the large volume, techniques required for engineering applications. This project will focus on using a range of microstructural analysis techniques to investigate how the morphology and chemistry of conducting phases in dielectric matrices develop during scalable synthesis techniques, and how these microstructures control the properties. Funded by a China Government Scholarship and by EPSRC grant EP/I034548. In collaboration with partners in Queen Mary London and Exeter Universities.

The Quest for Ultimate Electromagnetics using Spatial Transformations (QUEST)
Dr F. Castles, Dr D. Isakov, Professor C.R.M. Grovenor, Professor P.S. Grant

The overall project is aimed at bridging the gap between theory, modelling, manufacture and testing relating to spatial transformations, which is a technique in which material properties are spatially varied in order to achieve designed and novel manipulations of electromagnetic waves, such as cloaking and invisibility. With nearer-term potential applications also in communications, wireless energy transfer, sensors and security, there is intense global competition to manufacture engineering-scale materials that demonstrate innovative EM manipulations leading to important technological advances. QUEST focuses particularly on the microwave domain and involves Queen Mary University of London, the University of Exeter, as well as the University of Oxford.

The work at Oxford is focused on developing new approaches for the manufacture of materials with spatially varying properties, particularly dielectric permittivity and permeability, using a range of processes based on spray deposition of nano-suspensions, extrusion and bonding of composites, casting of loaded epoxies and 3D printing. Manufacturing tasks are supported by microstructural examination using a wide range of excellent spectroscopy, microscopy and other facilities. The EM performance of our new materials is assessed initially in-house, with more sophisticated measurements available at partners for the most promising approaches.

Processing and properties of nanocomposite materials for electromagnetic applications
Y. Wang, Professor P.S. Grant

We are using novel processing of polymers to create materials with anisotropic electrical and magnetic properties, and arranging these according to designs that allow unusual and previously unattainable manipulations of microwaves. A mixture of processing for coatings, strip and bulk are being used, and these methods are being combined in order to achieve the required designs. Funded by DSTL.

The 350m2 Advanced Processing Laboratory that is the hub of the group's processing research and houses many of our specialist facilities.

Contact

Professor Patrick Grant
Department of Materials, Oxford University
Parks Road, Oxford OX1 3PH, UK
T: 44-1865-283763 or 283324
F: 44-1865-848785
patrick.grant@materials.ox.ac.uk

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