Rapid solidification behaviour of Ag-Cu-Ge ternary eutectic alloy

Ag38.5Cu33.4Ce28.1 ternary eutectic alloy was undercooled and solidified by glass fluxing method and drop tube technique, respectively, and its growth mode and phase selection in these two processes were investigated. By usin g B2O3 as a denucleating agent, this ternary eutectic alloy is undercooled by a maximum of 185 K (0.228 T-m). It is found that with the increase of un dercooling, a transition from the cooperative growth of three eutectic phas es, namely the semiconducting phase (Ge), the solid solution phase (Ag), an d the intermetallic compound phase eta (Cu5Ge2), to the preferential growth of (Ge) phase followed by that of the (Ag) and eta phases occurs. The fact that the latter two phases easily form lamellar structure indicates that t hese two phases have a good affinity. In addition, as undercooling increase s, the macrosegregation of semiconducting phase (Ge) becomes weak and the s olubilities of three eutectic phases are all extended. Under containerless processing conditions in drop tube, the solidification behaviour is signifi cantly influenced by droplet size which can usually determine the actual ma gnitude of undercooling. The cooling rate and undercooling level in this pr ocess are estimated and their effect on growth kinetics and structural morp hology of semiconducting phase (Ge) is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.