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

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.