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

Abstract

Liquid ternary Fe50-x/2Cu50-x/2Gex (x = 5 and 15) alloys were highly undercooled by glass fluxing technique, and the achieved maximum undercoolings are 300 K (0.18TL) and 268 K (0.16TL), 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 Fe47.5Cu47.5Ge5 alloy is 70 K and that for Fe42.5Cu42.5Ge15 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 γFe phase of Fe47.5Cu47.5Ge5 alloy attains a maximum growth velocity of 19 m/s, while the growth velocity of the primary Fe0.84Ge0.16 phase reaches 11 m/s in undercooled Fe42.5Cu42.5Ge15 alloy. Moreover, energy dispersive spectroscopy (EDS) analysis shows that the Fe-rich and Cu-rich liquid phases have a similar affinity with solute Ge.