Formation mechanisms of Ti 2 AlC MAX phase on SiC-4H using magnetron sputtering and post-annealing
Résumé
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.