| Summary: | In the present work, the structure and properties of Ti<sub>n</sub>B<sub>n</sub> (<i>n</i> = 2–12) clusters were studied, and the microstructure of a Al-Ti-B system was simulated by molecular dynamics to determine the grain refinement mechanism of an Al-Ti-B master alloy in Al alloy. Based on the density functional theory method, the structural optimization and property calculations of Ti<sub>n</sub>B<sub>n</sub> (<i>n</i> = 2–12) clusters were carried out. The clusters at the lowest energy levels indicated that the Ti and B atoms were prone to form TiB<sub>2</sub> structures, and the TiB<sub>2</sub> structures tended to be on the surface of the clusters. The Ti<sub>10</sub>B<sub>10</sub> cluster was determined to be the most stable structure in the range of <i>n</i> from 2 to 12 by average binding energy and second-order difference energy. The analysis of HOMOs and LUMOs suggested that TiB<sub>2</sub> was the active center in the cluster; the activity of Ti was high, but the activity of B atoms decreased as the cluster size <i>n</i> increased. Meanwhile, the prediction of reaction sites by Fukui function, condensed Fukui function, and condensed dual descriptor identify that Ti atoms were more active than B atoms. Furthermore, TiB<sub>2</sub> structures were found in the Al-Ti-B system simulated by the ab initio molecular dynamics method, and there were Al atoms growing on the Ti atoms in the TiB<sub>2</sub>. Based on the above analysis, this study suggests that TiB<sub>2</sub> may be a heterogeneous nucleation center of α-Al. This work helps to further understand the mechanism of Al-Ti-B induced heterogeneous nucleation in Al alloys, which can provide theoretical guidance for related experiments.
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