In Situ Observation of the Competition Between Metastable and Stable Phases in Solidification of Undercooled Fe-17at. pctB Alloy Melt

摘要

High-speed video (HSV) technique was used to investigate the solidification behavior of undercooled Fe-17at. pctB alloy melt. Competitive growth between Fe/Fe3B (metastable eutectic) and Fe/Fe2B (stable eutectic) was captured, which is correlated with the critical nucleation undercooling [=104 K (104 A degrees C)] and the critical growth undercooling [=151 K similar to 183 K (151 A degrees C similar to 183 A degrees C)]. For the initial undercooling, , only the stable eutectic reaction (L -> Fe/Fe2B) occurs during solidification, whereas, for , the metastable eutectic reaction (L -> Fe/Fe3B) occurs firstly, followed by the stable eutectic reaction. Nevertheless, does not guarantee that the metastable phase (Fe3B) appears finally. Only if , Fe3B phase can be found in the room microstructure, as the growth velocity of metastable eutectic (Fe/Fe3B) is larger than stable eutectic (Fe/Fe2B) from HSV results; otherwise, the final structure consists of Fe2B and alpha-Fe. Accordingly, not only the competitive nucleation, but the competitive growth also determines the final microstructure of Fe-17at. pctB alloy. (C) The Minerals, Metals & Materials Society and ASM International 2015