Mechanism of controlled diffusion solidification: Mixing, nucleation and growth

Abstract

Controlled diffusion solidification (CDS) is a novel process. It depends on mixing two precursor alloys that have different thermal masses to make another alloy, and then, the mixture is poured into a near net-shaped mold. The process changes the microstructure of the product to a non-dendritic structure. The mechanism of CDS depends on three considerations: mixing two precursor alloys, nucleation and growth. It has been found that the turbulence that occurs during the mixing blends the two precursor alloys and results in a mixture that has a matrix and morphologies. The matrix forms of the precursor alloy that has a higher mass (Alloy1), while the morphologies form of the alloy that has a lower mass (Alloy2). Nucleation occurs in the alloy that has the higher liquidus temperature near the boundary with the second alloy, thus forming the primary Al phase that grows away from the second alloy. The temperature of the second alloy strongly affects the stability of the solid–liquid interface. A two-dimension model was built using the heat, diffusion and Navier stokes equations to understand the probability of the nucleation, the growth rate and the stability of the solid–liquid interface. The results show that the solid–liquid interface is stable during the CDS process compared to during conventional casting processes. The numerical results were supported by experimental results and scanning electron microscopy (SEM).