Liquid Metal Flow Studied by Positron Emission Tracking
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Liquid Metal Flow Studied by Positron Emission Tracking AGNIESZKA DYBALSKA, ADRIAN J. CADEN, DAVID J. PARKER, JOHN WEDDERBURN, and WILLIAM D. GRIFFITHS To improve the properties of castings, a new technique to observe the fluid flow and study the motion of oxygen-bearing inclusions has been developed. This new technique, Positron Emission Particle Tracking (PEPT), enabled a single radioactive tracer particle, moving inside a liquid metal casting, to be tracked with an accuracy of some millimeters, depending on the properties of the liquid metal and the mold. These novel experiments give promising results to observe the liquid metal flow and locate the tracked particle in a casting. Experiments have shown that various particle sizes (200 to 600 lm presented here) can be used to observe the liquid metal flow, if the particle has sufficiently initial radioactivity. Different sizes of particles are considered and their radioactivity compared in terms of their usefulness for tracking in flowing liquid aluminum according to the specific surface area. https://doi.org/10.1007/s11663-020-01897-7 Ó The Author(s) 2020
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INTRODUCTION
INCLUSIONS in castings are well known for their harmful role. Indigenous inclusions, which originate from the liquid metal, are almost impossible to avoid. For example, oxidation occurs naturally when liquid metal is in contact with the oxygen present in the atmosphere.[1–4] Such an oxide film can be entrained into the melt by surface turbulence and folded into bifilm defects of different sizes and shapes. These inclusions can cause major reductions in the strength or fatigue resistance of castings.[5] Oxide films lead to additional problems such as decreased fluidity and feeding,[6] creation of leakage paths due to connecting wall-to-wall defects in castings[5] and reduced machinability.[7,8] The means to eliminate such defects is limited, (although it has been suggested that with sufficient control on the oxide phase formation an improvement in the final properties of the Al alloy may be obtained.[9] One way to eradicate such defects may be the possibility to observe inclusion behavior during casting. In recent years, a new technique to observe fluid flow and study the motion of
AGNIESZKA DYBALSKA, ADRIAN J. CADEN, DAVID J. PARKER, JOHN WEDDERBURN, and WILLIAM D. GRIFFITHS are with the School of Metallurgy and Materials, University of Birmingham, B15 2TT, Birmingham, UK. Contact e-mail: [email protected] Manuscript submitted December 23, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
oxygen-bearing inclusions has been proposed. This new technique, Positron Emission Particle Tracking (PEPT), enables a single radioactive tracer particle moving inside a liquid metal casting to be tracked with an accuracy of some millimeters, depending on the liquid metal and mold properties. PEPT, developed at the University of Birmingham, is a variant of the standard imaging technique used to determine the spatial distribution of a fluid tracer, a technique known as Positron Emission Tomography (PET). PEPT does not requi
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