Solidification of peritectic alloys

Abstract

The solidification of peritectic alloys is reviewed, including both nucleation and growth. The introduction defines various compositions associated with binary peritectic alloys, their ‘equilibrium’ solidification, multicomponent peritectic systems, and metastable phases in peritectic systems. Nucleation studies are reviewed according to the rate of cooling and the type of specimen. Some comparisons are made with observations in eutectic alloys. At fast cooling rates metastable events can occur, as reviewed for alloys based on the Al-Ti and other systems. Growth studies in peritectic alloys have identified three stages: the ‘reaction’ (three phases in contact); the ‘transformation’ (the peritectic phase thickens by solid state diffusion); and ‘direct solidification’ of the peritectic phase. Models of the stages are outlined and compared with experiment for various binary alloys, followed by a summary of observations of peritectic solidification in multicomponent Fe-Cr-Ni and Fe-C-X alloys. Recent advances of single phase solidification are reviewed and applied to phase selection with increased velocity, in peritectic alloys such as in Fe-Cr-Ni, Co-Sm-Cu, and Fe-Nd-B alloys. Independent growth of the two solid phases also is discussed, as illustrated by superconducting Y-Ba-Cu-O alloys. Attempts to produce coupled structures in peritectic alloys are reviewed, followed by a discussion of low velocity banding. Limitations in current experimental or theoretical work are pointed out to aid future work in this important area.