Influence of the deposition process on the Cr2AlC phase formation during heat treatment of Cr-Al-C thin films

This paper focuses on the Cr2AlC phase formation during annealing post-treatment, with amorphous Cr-Al-C and (Cr,Al)2C as initial phases in the as-deposited state. The influence of the deposition process on the Cr2AlC formation, texture, and phase composition is investigated and an in-depth discussion of the intermediate phase is carried out. Cr-Al-C thin films were deposited by Direct Current Magnetron Sputtering and High Power Pulsed Magnetron Sputtering with the variation of the deposition temperature. To investigate the microstructure, phase composition, and texture, in situ synchrotron and high-temperature X-ray diffraction experiments were conducted and accompanied by electron microscopy. The Cr2AlC formation can be described as a temperature and time-dependent process with one intermediate state characterized by the formation of the disordered-Cr2AlC phase. Disordered-Cr2AlC shows a similar unit cell to Cr2AlC with an increased c/a ratio. The ratio decreases during the phase formation resulting from an ordering process. Formation temperatures depend on the initial phase, with a decreased formation temperature for (Cr,Al)2C, and the deposition process. While the (002) fiber texture of (Cr,Al)2C inherited to Cr2AlC, Cr2AlC originated from amorphous Cr-Al-C showed no preferred orientation. The coatings contained Cr7C3 as an additional phase, dependent on the deposition process and initial phases.