Constitution and microstructure of magnetron sputtered nanocomposite coatings in the system Ti-Al-N-C

An ambitious objective in the development of self-lubricating wear-resistant coatings is to make use of lubricious phases such as graphite, amorphous carbon or MoS2 incorporated into coatings. A series of (Ti,Al)(N,C) coatings with different carbon contents (0-28 at.%) have been deposited by reactive magnetron sputtering of TiAl in a mixture of Ar, N2 and CH4 gases. The microstructure and constitution of these coatings have been investigated using electron microprobe analysis, atomic force microscopy, X-Ray photoelectron spectroscopy, cross sectional transmission electron microscopy, Raman spectroscopy, X-ray diffraction and pole figure analyses. Starting from a pure TiAlN coating significant changes in the microstructure of the coatings were observed dependent on the carbon concentration. Under optimum conditions nanocomposite coatings with a structure of a coexisting metastable hard, nanocrystalline fcc TiAlNC phase and an amorphous carbon phase (a-C) have been deposited. The localization of an amorphous carbon phase has been shown by high-resolution transmission electron microscopy.