Phase selection in undercooled peritectic Fe-Mo alloys

The change of the primary solidification mode of undercooled peritectic Fe-Mo melts has been studied by in situ observation of recalescence events during electromagnetic levitation. A maximum melt undercooling up to 380 K has been achieved. Levitated drops of controlled undercooling were quenched onto chill substrates and subjected to phase and microstructure analysis. A transition from the primary bcc-Mo to the peritectic sigma-phase solidification mode beyond a critical undercooling of 345 K was revealed for the Fe47Mo53 alloy and in a similar way for other compositions between Fe45Mo55 and Fe54Mo46. The suppression of the properitectic bcc-Mo phase was also achieved for subcritical undercooling in substrate-quenched Fe45Mo55 samples. In Fe61Mo39 a transition from the primary sigma- to the peritectic R-phase solidification mode beyond a critical undercooling of 150 K was inferred from recalescence processes and Xray investigation of as-quenched undercooled samples. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.