First-principles study of Ti adsorption on Al4C3 (0001) surface

Abstract

Al4C3 phase is hypothesized to undergo a solid–solid phase transition into TiC, thereby facilitating the heterogeneous nucleation of α-Al. However, capturing this transition process experimentally is challenging, which undermines the credibility of this transition theory. In this study, first-principles calculations are employed to investigate the feasibility of Ti atom adsorption on the exposed (0001) surface of the Al4C3 crystal, providing theoretical support for the phase transition hypothesis. The findings indicate that Ti adatoms can effectively adsorb on the C-terminated (0001) surface, whereas adsorption on the Al-terminated surface is thermodynamically unfavorable. Upon structural optimization, Ti adatoms at bridge site B, top site T, and hollow site H1, irrespective of coverage, migrate towards the most stable hollow H2 site. Electronic structure analysis reveals that the bonding between the Ti adatom at the H2 site and the surface layer C atoms is primarily covalent, while the bonding with subsurface layer Al atoms is metallic. Additionally, Ti atom adsorption induces polarization of the bonding electron cloud between Al and C atoms. This study provides theoretical support for the Ti-induced transformation of the Al4C3 to TiC phase via surface adsorption, paving the way for the development of high-performance master alloys based on phase transition theory.