Phase separation and subsequent solidification of peritectic Fe–Cu–Ge alloys subjected to substantial undercooling processing

Abstract Liquid ternary Fe 50- x /2 Cu 50- x /2 Ge x ( x = 5 and 15) alloys were highly undercooled by glass fluxing technique, and the achieved maximum undercoolings are 300 K (0.18 T L ) and 268 K (0.16 T L ), respectively. At small undercoolings, these two alloys solidify in a normal pathway of peritectic solidification. If the alloy undercooling continues to increase beyond a certain value, metastable liquid phase separation takes place. The critical undercooling for Fe 47.5 Cu 47.5 Ge 5 alloy is 70 K and that for Fe 42.5 Cu 42.5 Ge 15 alloy is 110 K. At larger undercoolings, the homogeneous liquid alloy separates into an Fe-rich zone and a Cu-rich zone. In such a case, the undercooled alloy displays a monotectic solidification structure. The rapid solidification of the Fe-rich zone is the keystone of alloy solidification, and the growth velocity of the primary phase rises with increasing alloy undercooling according to a power law relation. Within the experimental undercooling ranges, the primary γ Fe phase of Fe 47.5 Cu 47.5 Ge 5 alloy attains a maximum growth velocity of 19 m/s, while the growth velocity of the primary Fe 0.84 Ge 0.16 phase reaches 11 m/s in undercooled Fe 42.5 Cu 42.5 Ge 15 alloy. Moreover, energy dispersive spectroscopy (EDS) analysis shows that the Fe-rich and Cu-rich liquid phases have a similar affinity with solute Ge.