Transgranular liquation cracking of grains in the semi-solid state.
Grain refinement via semi-solid deformation is desired to obtain superior mechanical properties of cast components. Using quantitative in situ synchrotron X-ray tomographic microscopy, we show an additional mechanism for the reduction of grain size, via liquation assisted transgranular cracking of semi-solid globular microstructures. Here we perform localized indentation of Al-15wt.%Cu globular microstructures, with an average grain size of ∼480 μm, at 555 °C (74% solid fraction). Although transgranular fracture has been observed in brittle materials, our results show transgranular fracture can also occur in metallic alloys in semi-solid state. This transgranular liquation cracking (TLC) occurs at very low contact stresses (between 1.1 and 38 MPa). With increasing strain, TLC continues to refine the size of the microstructure until the grain distribution reaches log-normal packing. The results demonstrate that this refinement, previously attributed to fragmentation of secondary arms by melt-shearing, is also controlled by an additional TLC mechanism.
Manchester X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester M13 9PL, UK.|Research Complex at Harwell, Harwell Science &Innovation Campus, Didcot OX11 0FA, UK.
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Karagadde
Manchester X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester M13 9PL, UK.|Research Complex at Harwell, Harwell Science &Innovation Campus, Didcot OX11 0FA, UK.
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Lee
Manchester X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester M13 9PL, UK.|Research Complex at Harwell, Harwell Science &Innovation Campus, Didcot OX11 0FA, UK.
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Cai
Swiss Light Source, Paul Scherrer Institut, Villigen PSI 5232, Switzerland.
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Fife
Manchester X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester M13 9PL, UK.|Research Complex at Harwell, Harwell Science &Innovation Campus, Didcot OX11 0FA, UK.
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Azeem
Department of Materials, Imperial College London, London SW7 2AZ, UK.
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Kareh
Department of Metallurgical Engineering, Chulalongkorn University, Bangkok 10330, Thailand.
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Puncreobutr
Manchester X-ray Imaging Facility, School of Materials, The University of Manchester, Manchester M13 9PL, UK.
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Tsivoulas
Diamond Light Source Ltd, Harwell Science &Innovation Campus, Didcot OX11 0DE, UK.
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Connolley
Diamond Light Source Ltd, Harwell Science &Innovation Campus, Didcot OX11 0DE, UK.
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Atwood