Oscillative surface morphology in peritectic NiAl using phase-field modeling

The NiAl-gamma-gamma'-system is numerically modeled using a multi-phase-field approach near its peritectic. The free energies are approximated as second order polynomials of the concentration. The parameters of these functions are fitted using experimentally determined values for the peritectic equilibrium concentrations and the liquidus/solidus slopes at the peritectic temperature. A study on lateral growth of a peritectic phase (gamma') layer on a primary (gamma) substrate reveals an oscillation of the layer interfaces at very low undercoolings (0.08 K). This morphology has its seeds in an oscillatory rotation of the triple junction. A mechanism for the origin of rotation is described and a reason for its disappearance at higher undercoolings is discussed. While the 'gamma-gamma' surface energy as well as the gamma interdiffusion constant are unknown, the influence of these parameters on the oscillation morphology is investigated.