Beauty of science: dendrites forming in a molten alloy

19-03-2014

This radiograph was collected at beamline BM05 during the in situ solidification of a nickel-based superalloy (CMSX4) in a high temperature furnace.

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During solidification, solid dendrites form (light colours), grow competitively and move in the melt (dark colours) with various velocities. They are visible because the solid has a slightly different density to the liquid. These particular dendrites are strikingly long and narrow. They also deform, bending and/or twisting, influenced by their neighbours. These deformations may be permanent or transient, localised or cumulative. Radiography was combined quasi-simultaneously with X-ray diffraction imaging (topography), which is sensitive to crystallographic orientation and deformation.  The X-ray observations were correlated with results from electron backscattered diffraction, and finite element modelling was used to investigate the mechanical response of dendrites in the “mushy zone” to thermal contraction, taking into account various physical parameters of the alloy.
 

Dendrites forming in a molten alloy


Publication
Dendrite bending during directional solidification, J.W. Aveson, G. Reinhart, H. Nguyen‐Thi, N. Mangelinck‐Noël, A. Tandjaoui, B. Billia, K. Goodwin, T.A. Lafford, J. Baruchel, H.J. Stone and N. D'Souza, Proceedings of the International Symposium on Superalloys, 615-624 (2012).
 

Top image: Dendrites forming in a molten alloy. Credit: J.W. Aveson, University of Cambridge.