Disorder trapping and grain refinement during solidification of undercooled Fe–18 at% Ge melts

Abstract

The electromagnetic levitation technique has been used to systematically study microstructure evolution and growth rate as a function of undercooling in concentrated Fe–18 at% Ge alloy. The samples are undercooled to a maximum of 240 K. Growth-rate analysis and transmission electron microscopy reveal that, beyond an undercooling of 120 K, the primary phase to solidify is disordered. Microstructural investigations show a decrease in grain size with increasing undercooling. Orientation-imaging microscopy using electron back-scattered diffraction (EBSD) and microhardness measurements have been used to show that recovery and recrystallization play a significant role in the evolution of final microstructure. Microstructural evolution has also been discussed in light of current models of dendrite growth and grain refinement.

Acknowledgements

One of the authors (GP) would like to thank the AvH Foundation for support through a research fellowship. This research was supported by a project between Department of Science and Technology (DST), Government of India and Bundesministerium für Bildung und Forschung (BMBF), Germany. The authors would like to thank Dr Peter Galenko for making his code available for computation of dendrite growth velocity and dendrite tip radius. The manuscript preparation was completed during K.B.'s stay at Tohoku University. K.B. would like to thank the Japan Society for Promotion of Sciences (JSPS) for a research followship.