Characterization of low temperature deposited nanolayered TiN/NbN multilayer coatings by cross-sectional transmission electron microscopy

Multilayer coatings of TiN/NbN with a modulation wavelength of about 8 nm were prepared on silicon (100) and tool steel substrates at low deposition temperature (approximately 100 °C) using a reactive DC magnetron sputtering system. These coatings were characterized using X-ray diffraction (XRD), X-ray reflectivity, nanoindentation, atomic force microscopy (AFM), cross-sectional transmission electron microscopy (XTEM), and high-resolution transmission electron microscopy (HRTEM) techniques. The XRD data of the coatings showed B1 NaCl structure with {111} texture. The nanoindentation hardness of the multilayer coatings was about 38 GPa, whereas TiN and NbN coatings exhibited hardnesses of about 23 and 17 GPa, respectively. The XTEM studies showed multilayers of TiN and NbN with an average modulation wavelength of about 7.7 nm, without noticeable microcracks and porosity. Detailed XTEM investigations showed that these layers had columnar growth along the growth direction with an average column size of about 100 nm. The layers appeared to exhibit non-planar structure. The selected area diffraction studies indicated that the coatings were polycrystalline and textured. The HRTEM studies showed non-planar nature of the lattice planes in the columnar grains. The non-planar nature of the lattice planes is attributed to the presence of a sub-grain structure with lattice misorientations arising from the lattice mismatch between TiN and NbN. The multilayers were found to be free from amorphous regions.