Model of Temperature-Induced Liquid–Liquid Transition in Metallic Melts

Temperature-induced liquid–liquid transition (TI-LLST) occurs widely in many liquid metallic melts and plays an important role in the final microstructure and properties of hard alloys. The paper presents a model of this physical phenomenon with a method of theoretical estimation of the temperature t* correspondent to TI-LLST. The TI-LLST model is based on “heterogeneous liquid–homogeneous liquid” concept and is interpreted as a structure transition from a heterogeneous system to a homogeneous solution when the melt is heated to t* temperature. The idea of the model is to theoretically determine the t* temperature, at which the viscosity of a heterogeneous system becomes equal to the viscosity of a homogeneous liquid solution with a uniform atomic distribution. The viscosity of a heterogeneous melt was calculated using the expression by Dul’nev for inhomogeneous media based on the unit cell method for a geometric model of isolated inclusions, the viscosity of a homogeneous melt—according to the additive dependence. The model is demonstrated by the example of TI-LLST in the Al81Sn19 melt. An inhomogeneous liquid alloy Al81Sn19 melt was understood as a set of clusters of aluminum atoms within the medium of tin atoms. The calculated t* = 1000 °C is close to the value of t* = 950 °C, which has been obtained experimentally. The possibility of percolation phenomena in heterogeneous Al–Sn melts has been investigated; the limiting ratio between the viscosity of medium and inclusion, at which the percolation transition is possible, has been established.