A comparative study on the structure and properties of nanolayered TiN/NbN and TiAlN/TiN multilayer coatings prepared by reactive direct current magnetron sputtering

Nanolayered multilayer coatings of TiN/NbN and TiAlN/TiN were deposited on Si (100) substrates at various modulation wavelengths (i.e. bilayer thickness, Λ) using a reactive direct current magnetron sputtering system. These coatings were characterized using X-ray diffraction (XRD), X-ray reflectivity, nanoindentation tester and micro-Raman spectroscopy. For TiN/NbN multilayer coatings, at low Λ, the XRD data showed well-resolved first-order negative satellite reflection along (111) principal reflection, whereas, a weak first-order positive satellite reflection was observed for TiAlN/TiN multilayer coatings. Similarly, the X-ray reflectivity data showed well-resolved satellite reflections of second-orders for TiN/NbN multilayer coatings and diffused satellite reflections for TiAlN/TiN multilayer coatings, indicating broad interfaces for TiAlN/TiN multilayers. TiN/NbN and TiAlN/TiN multilayers showed maximum nanoindentation hardness values of 4000 and 3750 kg/mm2, respectively. Single layer coatings of TiN, NbN and TiAlN showed hardness values of 2600, 1800 and 3850 kg/mm2, respectively. The low hardness of TiAlN/TiN multilayers is attributed to diffused interfaces. Raman spectroscopy measurements on the multilayer coatings after heat treatment in air showed that TiN/NbN multilayers were thermally stable (with respect to oxidation) up to 500 °C, whereas TiAlN/TiN multilayers were stable up to 800 °C. The nanoindentation measurements performed on the heat-treated coatings showed that TiN/NbN multilayer hardness reduced to about 2000 kg/mm2 after heating up to 600 °C. On the other hand, TiAlN/TiN multilayers retained hardness as high as 2500 kg/mm2 even after heating up to 700 °C.