An In Situ High-Energy Synchrotron X-Ray Diffraction Study of Directional Solidification in Binary TiAl Alloys


Phase formation and microstructure selection during solidification in γ‐TiAl alloys are highly relevant, both with respect to the microstructure and texture of cast alloys and to directional solidification, which allows to obtain a unique combination of properties. However, during cooling to room temperature the solidifying phases transform to low temperature phases which mask the prior situation during solidification. A new inductive crucible‐free zone melting furnace has been used in this work which has been specially designed for in situ investigations of solidification using synchrotron radiation. In this work, alloys with 45 and 48 at.% Al have been studied and it could be shown, that with varying withdrawal rate a change from α solidification to synchronous β + α solidification occurred in Ti‐48Al as it has been predicted in literature. Further, it was observed that by increasing the withdrawal rate a preferred <001> growth of the β phase occurred in alloys with 45 at.% Al, which is interpreted as a transition to dendritic solidification. The observations are compared with a microstructure selection map calculated according to the nucleation and constitutional undercooling (NCU) model proposed in literature.
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