Microstructure of (Ti,Si,Al)N nanocomposite coatings

(Ti,Si,Al)N nanocomposite coatings were prepared by a combination of r.f. and d.c. reactive magnetron sputtering. The composition of the films was evaluated by electron probe microanalysis (EPMA) and Rutherford backscattering spectrometry (RBS) and structure by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). XRD experiments showed the development of crystalline phases whose structure is very similar to that of bulk TiN. Diffracted peak positions revealed changes of the lattice parameter from 0.418 to 0.429 nm when the ion adatom mobility was enhanced. The lowest lattice parameter corresponds to a Ti–Si–Al–N phase where some of the Si and Al atoms are occupying Ti positions in the fcc TiN lattice, while the highest corresponds to a system where a partial Si segregation has occurred being enough to nucleate and develop a Si3N4 amorphous phase. Cross-sectional HRTEM images of samples grown under high adatom mobility shown grains with a diameter between 3 and 10 nm surrounded by an amorphous layer, while for the samples grown under limited adatom mobility conditions grains with a diameter between 18 and 28 nm were observed. Furthermore, through the visualization of bright field images it was possible to discern a columnar structure.