Ultrafine single‐phase aluminium nitride (AlN) particles were successfully synthesized by the vacuum carbothermal reduction nitridation (VCRN) method at shorter times and lower temperatures. The mechanism of the process was investigated. By analyzing the X‐ray diffraction (XRD) patterns and thermodynamic calculations, the main reaction path was determined to be Al2O3→Al2CO→Al4C3→Al5C3N→AlN. By investigating the kinetics mechanism, the process was a gas–solid reaction model, which was controlled by the crystalline chemical reaction from 0.5  to 1.5 h, combination control from 1.5 to 2 h, and gas diffusion control from 2 to 2.5 h. Moreover, the apparent activation energy (Ea) was calculated from the nitridation ratio, the value obtained, 237.71 kJ mol–1, is 31% of the energy reported for the conventional synthesis method. These results show that ultrafine AlN could be effectively synthesized at 1823–1873 K and 300 Pa N2 pressure for 2.5 h.

Herein, Al n Ti n (n = 2–12) clusters are studied by density‐functional theory method. The evolution of the geometric structure shows that Ti atoms tend to gather inside the clusters. The analysis of the relative stability and highest occupied molecular orbital–lowest unoccupied molecular orbital (HOMO–LUMO) gap show that Al n Ti n (n = 2–12) clusters tend to be stable and the bonding probability increases when n > 8. Nature bond orbitals (NBO) results show that the strong d‐orbital effect between Ti atoms results in the formation of TiTi bonds more easily than AlTi bonds, which leads to the enrichment of Ti atoms inside the Al n Ti n (n = 2–12) clusters. When n ≥ 8, Al atoms that surround the core formed by Ti atoms tend to form stable triangular configuration, which is stable adsorption site for Al atoms. Herein, the grain‐refining effect of TiAl3 grain refiners in Al alloys at the atomic level can be explained.

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