Metastable coupled-growth kinetics between primary and peritectic phases of undercooled hypoperitectic Fe_(54.5)Ti_(45.5) alloy

摘要

The metastable coupled-growth kinetics between the primary Fe_2Ti and peritectic FeTi phases of undercooled Fe_(54.5)Ti_(45.5) alloy was systematically investigated by both electromagnetic levitation and drop tube techniques. Employing a high-speed camera, the rapid crystallization processes of levitated bulk alloy were recorded in the undercooling range of 34-187 K. In small undercooling regime below 143 K, peritectic solidification proceeded and the dependence of primary Fe_2Ti dendritic growth velocity Ⅴ on the bulk undercooling ΔT satisfied a power relation of V=2.43 × 10~(-14) ×ΔT~(7.72) (mm s~(-1)). Once liquid undercooling increased beyond 143 K, the metastable coupled-growth was induced and the microstructure was characterized by the Fe_2Ti rods embedded in FeTi phase. Furthermore, the coupled-growth velocity decreased linearly with the rise in undercooling according to V=1.47×10~3-7.44ΔT (mm s~(-1)). In drop tube experiment, peritectic solidification characteristics of small alloy droplets disappeared and the primary and peritectic phases directly nucleated from undercooled liquid and grew cooperatively to form spherical coupled-growth cells if droplet diameter decreased below 481 μm.