Heterogeneous Nucleation Sequence at the Interface of TiB2 to Form AlThursday (09.11.2017) 09:35 - 09:55 Part of:
Refinement of Al alloys by TiB2 has been extensively studied in both industry and academia for several decades [1-10]. The presence of solutes (e.g. Ti) enhances the TiB2 grain refinement potency by tailoring the heterogeneous nucleation interface of TiB2 . To date, there is still a lack of atomic scale experimental investigations of the heterogeneous nucleation interface of TiB2 under industrial solidification conditions (e.g. conventional die casting). In order to address these open issues, a combination of atomic scale high angle annular dark field (HAADF) imaging and electron energy loss spectroscopy (EELS) in the dedicated aberration corrected scanning transmission electron microscope (STEM) is used for the characterization of the heterogeneous nucleation interface of TiB2 in Al alloys, with a special focus on the partitioning of non-interacting solute elements (e.g. Ti and Cu) to TiB2. Experiments were carried out on two distinct material systems in order to more accurately elucidate the multiple roles of Ti in Al alloys and to determine the dominant mechanism for grain refinement in Al alloys. Firstly, as a reference, the heterogeneous nucleation interface of TiB2 in a commercial Al-Ti-B grain refiner (i.e. Al-5Ti-1B) was studied. Secondly, the grain refinement of Al-Cu based alloys with varying Ti content (but with identical growth restrictions to the reference case) was investigated. The heterogeneous nucleation interface of TiB2 in Al-Cu based alloys was also studied. The effect of the solidification path (i.e. peritectic reaction and subsequent peritectic transformation) on the observed nucleation phenomena is also discussed.