Phase selection in undercooled binary peritectic alloy melts

The change of the primary solidification mode in undercooled peritectic Fe–Mo, Co–Si and Al–Co melts has been revealed by in situ observation of recalescence events during electromagnetic levitation. Levitated drops of controlled undercooling up to 380 K were quenched onto chill substrates and subjected to phase and microstructure analysis. Beyond a critical undercooling, the equilibrium solidification can be replaced by the direct growth of the peritectic phase. This was ascertained from sudden changes in growth velocity at a critical undercooling and the ultimate recalescence temperature. Metastable phases were detected in Co75Si25 and Al74.4Co25.6 as-quenched samples. The direct growth of the peritectic phase from the undercooled melt considerably improves the sample homogeneity.