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Modeling of solidification of TiAl alloys in centrifugal casting

Abstract : TiAl alloys are an important material for automotive and aerospace industries due to their low density and high strength at high temperatures. However, due to their high reactivity in liquid state, low superheat must be used in casting in order to limit contamination. Centrifugal casting is an option to enhance mold filling at low superheat. In centrifugal casting the buoyancy driven flow is intensified and the flow structure is modified by the combined effect of the non-inertial accelerations – centrifugal and Coriolis – which appear in the rotating system. The consequence are particular patterns of macrosegregation and of distribution of microstructures in the solidified part. These patterns are not well understood. The objective of this thesis is to explain the flow structure, as well as the transport of solid grains and of chemical species during solidification of TiAl alloys in centrifuged systems. In the framework of this thesis a 3D finite-volume implementation of a multiscale solidification model was developed, which was required due to the inherently three-dimensional nature of the flow. The model was then used to simulate dedicated experiments of directional solidification of cylindrical samples of the TiAl GE alloy (Ti-47Al-2Cr-2Nb) that were previously conducted in the frame of the ESA GRADECET project. These experiments were carried out in the ESA “Large Diameter Centrifuge” at centrifugation levels between 5g and 20g, where g is the normal terrestrial gravity acceleration. The results of the simulations show that the Coriolis acceleration entirely modifies the liquid flow structure during solidification and lead to a one-vortex fluid flow pattern in the domain. On the contrary, it is shown that the Coriolis acceleration has only a weak impact on the motion of equiaxed grains. At high gravity level the grain motion is mainly controlled by the balance between the apparent gravity and the drag force. It is also shown that the final aluminum macrosegregation pattern show a strong enrichment on the flight velocity side of the sample due to the asymmetry of the liquid flow induced by the Coriolis force.
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  • HAL Id : tel-02528906, version 1

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Martín Cisternas Fernández. Modeling of solidification of TiAl alloys in centrifugal casting. Materials. Université de Lorraine, 2019. English. ⟨NNT : 2019LORR0218⟩. ⟨tel-02528906⟩

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