Bernard, D.

Lee, P. D.

Ness, D.

Thuinet, L.

The formation of freckle chains during the directional solidification of Ni-base superalloys results from convective flow of the liquid in the mushy zone. This flow depends on the permeability and the density inversion in the interdendritic liquid. It has been hypothesized that carbide particles within the mushy zone may affect the permeability and reduce the propensity for defect formation. However, this effect has never been quantified. Experimental permeability measurements are very difficult to perform, especially at low volume fraction solid levels, due to the changing morphology of the dendritic microstructure over time and high temperatures. Therefore, a numerically determined value for the permeability of directionally solidified alloys is proposed. This was achieved by first simulating solidification microstructures by means of an in-house microstructural model. The permeability was then numerically calculated using the predicted microstructures. The impact of carbides on permeability and freckle formation is discussed.</p

Simulation of the influence of carbides on the permeability of NI-base superalloys

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