Structure and properties of reactive DC magnetron sputtered TiN/NbN hard superlattices

Nanostructured TiN/NbN superlattices at various modulation wavelengths (Lambda) were deposited on silicon (111) and tool steel substrates using a reactive DC magnetron sputtering process. Structural characterization of the coatings was done using X-ray diffraction (XRD) in Bragg-Brentano theta-2theta geometry. All the multilayer coatings exhibited (111) preferred orientation in the XRD data. Appearance of satellite reflections (SR) along (111) principal reflection (PR) was used to check the quality of the superlattice coatings. The coatings exhibited superlattice structure for 106 Angstrom greater than or equal to Lambda greater than or equal to30 Angstrom. The mechanical properties of the coatings were measured using a nanoindentation technique. The multilayer coatings exhibited hardness as high as 4000 kg/mm(2) at a modulation wavelength of 48 Angstrom, which was similar to2.4 times the value of the rule-of-mixture. Thermal stability of the TiN/NbN multilayer coating was studied by vacuum annealing the coating for 30 min in the temperature range of 100-850 degreesC. Subsequent structural changes in the coating were measured by an in situ high-temperature X-ray diffractometer. Coating exhibited thermal stability up to 700 degreesC and subsequently showed reduction in the superlattice character. The corrosion behavior of 1.5 mum thick single layer TiN and NbN, and multilayer TiN/NbN (A = 50 Angstrom) coatings deposited on tool steel substrates were investigated using potentiodynamic polarization in 0.5 M NaCl and 0.5 M HCl solutions under non-deaerated conditions. The microstructural changes, as a result of corrosion, were investigated by atomic force microscopy (AFM). The results indicated that the multilayer coatings exhibited superior corrosion resistance as compared to the single layer coatings. (C) 2003 Elsevier B.V. All rights reserved.