Thermodynamic coupling and interfacial non-equilibrium in a finite-diffusion model of microsegregation

We introduce both CALPHAD coupling and interfacial non-equilibrium to a model of microsegregation that accounts for finite diffusion. The approach can also be used to perform Gulliver–Scheil calculations using a kinetic phase diagram, which would normally involve solving an underdetermined system of equations. The non-equilibrium finite-diffusion model is first applied to the Ag–15wt.%Cu system, where we find that previously reported experimental measurements can be completely described with the full non-linear phase diagram and the choice of appropriate kinetic constitutive parameters, indicating that the effects of finite liquid diffusion remain significant under processing conditions relevant to additive manufacturing. The model is enhanced to account for multiple phases forming from the liquid and then applied to a multicomponent Co-base superalloy, showing that finite liquid diffusion can influence both the compositions and fractions of secondary solid phases.