Formation mechanisms of Ti2AlC MAX phase on SiC-4H using magnetron sputtering and post-annealing

Highlights: • A two-step process to obtain an epitaxial Ti₂AlC thin film onto SiC substrate is proposed. • The mechanisms involved in Ti₂AlC phase formation are described for 800 °C annealing temperature. • Interdiffusion between TiAl₂ nanocrystalline film and SiC monocrystalline during annealing is enhanced. • Thickness of Ti₂AlC phase can be controlled by annealing time or temperature. In the present work we focus on the mechanisms involved in Ti₂AlC MAX phase thin-film formation. The TiAl₂ thin-film was deposited by magnetron sputtering on a SiC-4H [0001] substrate. Samples were annealed at various temperatures (700–800 °C) for various times and analysed by XRD and TEM. The epitaxial Ti₂AlC phase was formed as follows: [0001]_MAX//[0001]_SiC and (11−20)_MAX//(11–20)_SiC which is in a good agreement with thermodynamic considerations. The presence of TiC structures at the interface indicates that the formation of this structure is necessary to obtain Ti₂AlC. Moreover, the formation of a liquid AlSi alloy was highlighted due to the interdiffusion of Al and Si respectively from TiAl₂ and SiC during TiC formation. Finally, we assume that, during the cooling, the AlSi alloy separates and Al diffuses to the surface of the TiAl₂ layer leading to the formation of an Al-rich layer. The remaining Si reacts with Ti from TiAl₂ to form a Ti₅Si₃ layer following this epitaxial relation: [0001]_Ti2AlC//[0001]_Ti5Si3 and (11–20)_Ti2AlC//(3−210)_Ti5Si3. These mechanisms lead to the stacking of four different layers. Between 700 and 800 °C, the nature of the formation mechanism is not time-dependent. However, the kinetics of the reactions are both temperature and time dependent.