5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

Inoculation with exogenous particles has been widely used in industry to grain refine various alloys during solidification. Among a series of Al-Ti-B based grain refiners developed for Al-alloys, the Al-5Ti-1B master alloy, which contains potent TiB2 particles for enhancing heterogeneous nucleation of α-Al grains, has been most widely used for decades. However, it has been reported that, in the presence of certain alloying or impurity elements in Al-alloys, the effectiveness of Al-Ti-B master alloys for grain refinement can be dramatically reduced, resulting in a coarse and columnar grain structure in some cases. This adverse effect on grain refinement is often referred to as “poisoning” in the literature. When its content exceeds 2-3 wt.%, Si is one such element that poisons the Al-Ti-B based grain refiner. So far, the exact mechanisms for Si poisoning have not been fully understood, although significant research effort on the subject has been made. In this work, state-of-the-art electron microscopy, including aberration (Cs)-corrected high resolution STEM, has been carried out focusing on the Al/TiB2 interface at the atomic scale, in order to reveal any possible modification of TiB2 substrates caused by interaction between Si and TiB2 at the interface. In this contribution, we present the mechanism underlying Si poisoning in the context of Si segregation at the Al/TiB2 interface and its consequence on the potency of TiB2 particles as substrates for heterogeneous nucleation of Al.