An integrated model for dendritic and planar interface growth and morphological transition in rapid solidification

Rapid solidification can be achieved by quenching a thin layer of molten me tal on a cold substrate, such as in melt spinning and thermal spray deposit ion. An integrated model is developed to predict microstructure formation i n rapidly solidified materials through melt substrate quenching. The model solves heat and mass diffusion equations together with a moving interface t hat may either be a real solid/liquid interface or an artificial dendrite t ip/melt interface. For the latter case, a dendrite growth theory is introdu ced at the interface. The model can also predict the transition of solidifi cation morphology, e.g., from dendritic to planar growth. Microstructure de velopment of Al-Cu alloy splats quenched on a copper substrate is investiga ted using the model. Oscillatory planar solidification is predicted under a critical range of interfacial heat-transfer coefficient between the splat and the substrate. Such oscillatory planar solidification leads to a banded solute structure, which agrees with the linear stability analysis. Finally , a microstructure selection map is proposed for the melt quenching process based on the melt undercooling and thermal contact conditions between the splat and the substrate.