The α-factor is used to predict the solid–liquid interface type of a material during solidification.
Method
According to John E. Gruzleski in his book Microstructure Development During Metalcasting (1996):
α = (L/k*TE)*(η/v)
where L is latent heat of fusion; k is Boltzmann’s constant; TE is equilibrium freezing temperature; η is the number of nearest neighbours an atom has in the interface plane; and v is the number of nearest neighbours in the bulk solid.
Since L/TE = ΔSf
where ΔSf is the molar entropy of fusion of the material.
α = ΔSf/k(η/v)
According to Martin Glicksman in his book Principles of Solidification: An Introduction to Modern Casting and Crystal Growth Concepts (2011):
α = ΔSf/Rg(η1/Z)
where Rg is the universal gas constant. (η1/Z) is similar to previous, always 1/4 < (η1/Z) < 1.