Microstructural evolution during laser resolidification of Fe-25 atom percent Ge alloy

Abstract

The microstructural evolution of concentrated alloys is relatively less understood both in terms of experiments as well as theory. Laser resolidification represents a powerful technique to study the solidification behavior under controlled growth conditions. This technique has been utilized in the current study to probe experimentally microstructural selection during rapid solidification of concentrated Fe-25 atom pct Ge alloy. Under the equilibrium solidification condition, the alloy undergoes a peritectic reaction between ordered α₂ (B2) and its liquid, leading to the formation of ordered hexagonal intermetallic phase ε (DO₁₉). In general, the as-cast microstructure consists of ε phase and ε-β eutectic and α₂ that forms as a result of an incomplete peritectic reaction. With increasing laser scanning velocity, the solidification front undergoes a number of morphological transitions leading to the selection of the microstructure corresponding to metastable α ₂/β eutectic to α₂ dendrite + α₂/β eutectic to α ₂dendrite. The transition velocities as obtained from the experiments are well characterized. The microstructural selection is discussed using competitive growth kinetics.