Characteristics of liquid-liquid immiscibility in Al-Bi-Cu, Al-Bi-Si, and Al-Bi-Sn monotectic alloys: Differential scanning calorimetry, interfacial tension, and density difference measurements

Abstract

Phase separation in ternary monotectic alloys ${({\mathrm{Al}}_{0.345}{\mathrm{Bi}}_{0.655})}_{90}{X}_{10}$ ($X=\mathrm{Cu},\mathrm{Si},\mathrm{Sn}$; wt %) has been investigated. Experimental work included differential scanning calorimetry and measurements of the liquid-liquid $(l\text{\ensuremath{-}}l)$ interfacial tension and difference in densities of coexisting phases. It is established that the interfacial tension between Al-rich and Bi-rich liquid phases increases when either Cu or Si is added and it decreases when Sn is added to the ${\mathrm{Al}}_{34.5}{\mathrm{Bi}}_{65.5}$ binary. This is related to the size of miscibility gap and is explained by increasing composition gradient across the $(l\text{\ensuremath{-}}l)$ interface upon addition of either Cu or Si and its decreasing upon addition of Sn to the Al-Bi binary. The drop of interfacial tension in liquid ${({\mathrm{Al}}_{0.345}{\mathrm{Bi}}_{0.655})}_{90}{\mathrm{Sn}}_{10}$ against ${\mathrm{Al}}_{34.5}{\mathrm{Bi}}_{65.5}$ is also caused by adsorption of Sn at the interface. Temperature dependences of the interfacial tension and density difference in the alloys studied follow a power law in reduced temperature $({T}_{C}\ensuremath{-}T)$ at approach of the critical point with exponents close to the values predicted by the renormalization group theory of critical behavior.