Thermosolutal convection and macrosegregation during directional solidification of TiAl alloys in centrifugal casting

The microstructure evolution of Ti-Al peretectic system in transient stage and steady state in directional solidification was predicted via theoretical analysis. The solute distribution controlled by diffusion at and ahead the solid-liquid interface will determine whether the properitectic and peritectic phases can nucleate and grow ahead of the opposing solid phase. The formation of banding structure is possible in a certain composition range. At the steady state, a microstructure selection map was set up based on interface response function model. The microstructure of TiAl alloys with different aluminum content was studied with Bridgman directional solidification method. Some evidence in the experiment has been found to support the theoretical prediction.

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Simulations of the Effects of Mold Properties on Directional Solidification

Volume 2B: Advanced Manufacturing ◽

10.1115/imece2013-66830 ◽

2013 ◽

Cited By ~ 3

Author(s):

Mark A. Lauer ◽

David R. Poirier ◽

Robert G. Erdmann ◽

Luke Johnson ◽

Surendra N. Tewari

Keyword(s):

Finite Element ◽

Thermal Properties ◽

Mushy Zone ◽

Phase Change ◽

Directional Solidification ◽

Cross Section ◽

Cross Sections ◽

Mold Wall ◽

Solidification Process ◽

Thermosolutal Convection

The mold geometry and its thermal properties greatly influence the solidification process. Finite element simulations of directional solidification in various molds are presented. These simulations were performed using volume averaged properties in the mushy zone in order to model the convection, transport of solute and energy, and phase change occurring during solidification. These simulations show the interactions of the mold and alloy with the resultant solidification phenomena, including steepling. Mold geometries can cause macrosegregation because of shrinkage flows, by interrupting the development of the mushy zone, and by causing or influencing thermosolutal convection. Mold materials with different thermal properties result in different macrosegregation patterns even for the same geometries. Changes in cross section and the thermal properties of the mold also affect the gradients and solidification rates obtained in the alloy, as opposed to those measured on the mold wall. Simulations are compared qualitatively to a verification experiment of directionally solidifying a hypoeutectic Al-7wt%Si alloy in a mold with changing cross sections.

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Traveling Waves Induced by Sweeping Flows on Solidification Interfaces

Materials Science Forum ◽

10.4028/www.scientific.net/msf.941.1546 ◽

2018 ◽

Vol 941 ◽

pp. 1546-1551

Author(s):

Alain Pocheau ◽

Tania Jiang ◽

Marc Georgelin

Keyword(s):

Directional Solidification ◽

Traveling Waves ◽

Thermal Gradient ◽

Large Scale ◽

Solid Phase ◽

Travelling Waves ◽

Thermosolutal Convection ◽

Solidification Interface

Solidification of alloys in a thermal gradient usually involves the generation of flows by thermal or thermosolutal convection. We experimentally study their effects on the dynamics of a solidification interface by inducing a controlled sweeping flow in a directional solidification device. Flow is induced in the sample from an external thermosiphon. Downstream inclination of microstructures and downstream sidebranch development are observed. However, the major outcome is the evidence of large scale travelling waves on the solidification interface. They are induced by the coupling between solidification and flow and yield repetitive striations of the solid phase. Two waves are observed and characterized.

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