Mullis, AM, Castle, EG and Cochrane, RF (2016) The origins of spontaneous grain refinement in deeply undercooled metallic melts. In: IOP Conference Series: Materials Science and Engineering. 4th International Conference on Advanced Solidification Processes (ICASP-4), 08-11 Jul 2014, Beaumont Estate, Old Windsor, UK. IOP Publishing
Abstract
Spontaneous grain refinement in undercooled metallic melts has been a topic of enduring interest within the solidification community since its discovery more than 50 years ago. Here we present a comparative study of the solidification microstructures and velocity-undercooling behaviour in two dilute Cu-Ni alloys (3.98 & 8.90 wt.% Ni), which have been undercooled by a melt encasement (fluxing) method. Cu-3.98 wt.% Ni shows grain refinement at both low and high undercooling, with a dendritic growth regime separating the two grain refined regions. Within the grain refined region dendritic fragments are clearly evident in the centres of the refined grains and on the surface of the undercooled droplet, suggesting a dendritic fragmentation mechanism. Cu-8.90 wt.% Ni displays also grain refinement at both high and low undercoolings. In the low undercooling grain refined region the samples display curved grain boundaries with a dendritic substructure that extends across grains, indicative of a recovery and recrystallisation mechanism. Conversely, prior to the onset of the high undercooling grain refinement transition extensive regions of dendritic seaweed are observed, suggesting that it is remelting of a dendritic seaweed that gives rise to this structure. Consequently, in two closely related Cu-based systems we have strong microstructural evidence for the operation of all three mechanisms currently considered to give rise to grain refinement. This may help to resolve the grain refinement controversy, although it remains to be determined what factors determine which mechanism operates in any given system.
Metadata
Item Type: | Proceedings Paper |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | (c) 2016, IOP. Reproduced in accordance with the publisher's self-archiving policy. |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Engineering & Physical Sciences (Leeds) > School of Chemical & Process Engineering (Leeds) > Institute for Materials Research (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 07 Oct 2016 15:44 |
Last Modified: | 07 Oct 2016 15:44 |
Published Version: | http://dx.doi.org/10.1088/1757-899X/117/1/012054 |
Status: | Published |
Publisher: | IOP Publishing |
Identification Number: | 10.1088/1757-899X/117/1/012054 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:101238 |