Abstract
In the present work the impact of curvature effects on freckle formation in CMSX-4 during directional solidification was modelled and simulated. Modelling work is based on a four-step criterion function for predicting freckles. First, only surface elements are taken into account. Second, critical cross-sectional areas are identified where freckle formation is possible. As a new aspect, third, curvature effects are taken into account for predicting freckles in radiation shadow. Fourth, the Rayleigh number is calculated based on a permeability function of dendrite arm spacing and fraction of liquid. In the thus identified areas sufficient thermo-solutal convection takes place to initiate freckle formation. With the new model freckles can only appear in areas where the thermal temperature profile is concave, that is, at locations where the temperature gradient is positive against the surface normal. The present model was tested simulating step samples. For that, the individual parts of our industrial Bridgman furnace were input and joined in one FEM model. The thermal results clearly show concave solidus isothermal at the shadow faces of the step sample in the cluster. Freckles are predicted at the corresponding locations. When comparing simulated freckle formation with experimental findings, good correlation was found. Furthermore, we could predict both the transition length that occurs when the cross-sectional area increases stepwise and the run length when the cross-sectional area is reduced.
Highlights
Related contentCriterion function for predicting freckles in CMSX-4 during directional solidification
Solidified or single crystal castings of superalloys are characterized by their excellent high temperature properties
Auburtin [3] examined freckle formation in directionally solidified rods made of the three superalloys (Waspaloy, Mar-M247, CMSX-4)
Summary
Criterion function for predicting freckles in CMSX-4 during directional solidification. To cite this article: B Pustal et al 2016 IOP Conf. View the article online for updates and enhancements. - Freckle Formation in Directionally Solidified Superalloy Components with Expanding Cross-Section D Ma, J Ziehm, W Wang et al. - Tertiary dendritic instability in late stage solidification of Ni-based superalloys M M Franke, R F Singer and I Steinbach. - Investigation on macrosegregation and dendrite morphology during directional solidification of Al-Cu hypereutectic alloys under a strong magnetic field Xi Li, DaFan Du, Yves Fautrelle et al. This content was downloaded from IP address 134.130.184.25 on 14/11/2017 at 14:52
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