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Instruments / Technical Area	Publication Details	Published
I12-JEEP: Joint Engineering, Environmental and Processing	Revealing the mechanisms by which magneto-hydrodynamics disrupts solidification microstructures B. Cai , A. Kao , E. Boller , O. V. Magdysyuk , R. C. Atwood , N. T. Vo , K. Pericleous , P. D. Lee Acta Materialia DOI: 10.1016/j.actamat.2020.06.041 Diamond Proposal Number(s): [12631, 13764, 19216] Show Abstract ▼ Abstract: A key technique for controlling solidification microstructures is magneto-hydrodynamics (MHD), resulting from imposing a magnetic field to solidifying metals and alloys. Applications range from bulk stirring to flow control and turbulence damping via the induced Lorentz force. Over the past two decades the Lorentz force caused by the interaction of thermoelectric currents and the magnetic field, a MHD phenomenon known as Thermoelectric Magnetohydrodynamics (TEMHD), was also shown to drive inter-dendritic flow altering microstructural evolution. In this contribution, high-speed synchrotron X-ray tomography and computational simulation are coupled to reveal the evolution, dynamics and mechanisms of solidification within a magnetic field, resolving the complex interplay and competing flow effects arising from Lorentz forces of different origins. The study enabled us to reveal the mechanisms disrupting the traditional columnar dendritic solidification microstructure, ranging from an Archimedes screw-like structure, to one with a highly refined dendritic primary array. We also demonstrate that alloy composition can be tailored to increase or decrease the influence of MHD depending on the Seebeck coefficient and relative density of the primary phase and interdendritic liquid. This work paves the way towards novel computational and experimental methods of exploiting and optimising the application of MHD in solidification processes, together with the calculated design of novel alloys that utilise these forces.	Jun 2020
I12-JEEP: Joint Engineering, Environmental and Processing	Fundamental studies of ultrasonic melt processing D. G. Eskin , I. Tzanakis , F. Wang , G. S. B. Lebon , T. Subroto , K. Pericleous , J. Mi Ultrasonics Sonochemistry 52, 455-467 DOI: 10.1016/j.ultsonch.2018.12.028 Diamond Proposal Number(s): [8542, 12131] Open Access Show Abstract ▼ Abstract: Ultrasonic (cavitation) melt processing attracts considerable interest from both academic and industrial communities as a promising route to provide clean, environment friendly and energy efficient solutions for some of the core issues of the metal casting industry, such as improving melt quality and providing structure refinement. In the last 5 years, the authors undertook an extensive research programme into fundamental mechanisms of cavitation melt processing using state-of-the-art and unique facilities and methodologies. This overview summarises the recent results on the evaluation of acoustic pressure and melt flows in the treated melt, direct observations and quantitative analysis of cavitation in liquid aluminium alloys, in-situ and ex-situ studies of the nucleation, growth and fragmentation of intermetallics, and de-agglomeration of particles. These results provide valuable new insights and knowledge that are essential for upscaling ultrasonic melt processing to industrial level.	Apr 2019
I12-JEEP: Joint Engineering, Environmental and Processing	4D synchrotron X-ray tomographic quantification of the transition from cellular to dendrite growth during directional solidification Biao Cai , Jiang Wang , Andrew Kao , K. Pericleous , Andre Phillion , Robert Atwood , P. D. Lee Acta Materialia 117, 160 - 169 DOI: 10.1016/j.actamat.2016.07.002 Diamond Proposal Number(s): [10174] Open Access Show Abstract ▼ Abstract: Solidification morphology directly impacts the mechanical properties of materials; hence many models of the morphological evolution of dendritic structures have been formulated. However, there is a paucity of validation data for directional solidification models, especially the direct observations of metallic alloys, both for cellular and dendritic structures. In this study, we performed 4D synchrotron X-ray tomographic imaging (three spatial directions plus time), to study the transition from cellular to a columnar dendritic morphology and the subsequent growth of columnar dendrite in a temperature gradient stage. The cellular morphology was found to be highly complex, with frequent lateral bridging. Protrusions growing out of the cellular front with the onset of morphological instabilities were captured, together with the subsequent development of these protrusions into established dendrites. Other mechanisms affecting the solidification microstructure, including dendrite fragmentation/pinch-off were also captured and the quantitative results were compared to proposed mechanisms. The results demonstrate that 4D imaging can provide new data to both inform and validate solidification models.	Sep 2016
I13-2-Diamond Manchester Imaging	In Situ Synchrotron Radiography and Spectrum Analysis of Transient Cavitation Bubbles in Molten Aluminium Alloy I. Tzanakis , W. W. Xu , G. S. B. Lebon , D. Eskin , K. Pericleous , P. D. Lee Physics Procedia 70, 841 - 845 DOI: 10.1016/j.phpro.2015.08.172 Diamond Proposal Number(s): [9082] Show Abstract ▼ Abstract: The melt processing of conventional and advanced metallic materials with high-intensity ultrasonic vibrations significantly improves the quality and properties of molten metals during their solidification. These improvements are primarily attributed to ultrasonic cavitation: the creation, growth, pulsation, and collapse of bubbles in the liquid. However, the development of practical applications is limited by the lack of fundamental knowledge on the dynamics of the cavitation bubbles; it is very difficult to directly observe ultrasonic cavitation using conventional techniques in molten metals due their high temperature and opaqueness	Sep 2015

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