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Details of Grant 

EPSRC Reference: EP/K011413/1
Title: Disruptive Solidification Microstructures via Thermoelectric Control
Principal Investigator: Pericleous, Professor A
Other Investigators:
Researcher Co-Investigators:
Project Partners:
Department: Mathematical Sciences, FACH
Organisation: University of Greenwich
Scheme: Standard Research
Starts: 01 February 2013 Ends: 31 July 2016 Value (£): 278,790
EPSRC Research Topic Classifications:
Materials Characterisation Materials Processing
EPSRC Industrial Sector Classifications:
Aerospace, Defence and Marine
Related Grants:
EP/K006649/1 EP/K007734/1
Panel History:
Panel DatePanel NameOutcome
09 Nov 2012 Engineering Prioritisation Meeting - 9 Nov 2012 Announced
Summary on Grant Application Form
Modern society has been transformed by the development of alloys that are lighter and stronger. We have invented a new method to potentially further enhance mechanical properties, reducing weight and increasing recyclability, whilst reducing the energy consumed during manufacturing. Many prior improvements were due to an understanding of how to control alloy microstructure during solidification. However, there are only two commonly utilised methods for control: cooling rate and composition (including things like grain refinement). We propose a novel additional tool to manipulate alloy microstructures as they grow. To have a third method of control could be transformative to the metals industry in the UK, enabling all new products/properties to be developed.

Alloys are a combination of many elements that commonly solidify as crystalline structures known as dendrites. The shape of these dendrites and their growth into linked grains produces the microstructure that ultimately determines overall material performance. Techniques for controlling the microstructure are therefore of paramount importance and via computational simulations performed by the proposers as part of an EPSRC funded PhD study, we have theoretically demonstrated that a new mechanism by which magnetic fields can be used to alter, or disrupt this microstructure is possible.

The new mechanism we propose utilises thermoelectricity, a relatively unexplored phenomenon in solidification. The fundamental principle relies on the fact that current is caused to circulate around the interface of two materials with different Seebeck coefficients, provided a thermal gradient exists along that interface. This effect has many practical applications in other fields: thermoelectric coolers in microelectronics; thermoelectric materials used to produce electricity from temperature differences within car engines. Both examples use semiconductor materials as these generally have larger Seebeck coefficients. Surprisingly this effect is also significant on the microscopic scale along the solid-liquid front of a solidifying alloy. It is in fact an inherent part of the system.

As a dendrite solidifies, latent heat is released creating temperature variations, and simultaneously some elements are partitioned more into either the liquid or solid phase. This compositional variation causes a discontinuity in the Seebeck coefficient, creating a potential across the interface resulting in thermoelectric currents between hot and cold regions. When solidification is subjected to an external magnetic field, these currents interact with it to create fluid motion. This phenomenon -named by the first researchers to observe it as Thermoelectric Magneto-hydrodynamics (TEMHD) - causes microscopic flow between dendrite arms and circulations around the dendrite. This flow can alter the dendrite shape, leading to further thermoelectric currents, and so on. Experimental evidence shows that external magnetic fields can lead to significant changes in microstructure, but so far a detailed analysis of how this occurs has not been conducted. Numerical simulations by the proposers have given some insight into the complex nature of the problem.

To harness this technique in real castings, systematic experimental and numerical studies are proposed. Real-time 3D observation of growing microstructure under various magnetic fields at Diamond light source will unequivocally prove our as yet only theoretical hypothesis. Numerical simulations are essential to design these experiments, optimising alloy and magnetic fields, maximising the impact on microstructure and hence properties. Key parameters (Seebeck coefficient, magnetic field and thermal gradient) will be examined through the use of a fully coupled 3D numerical model and experiments for a range of alloys.

Key Findings
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Organisation Website: http://www.gre.ac.uk