Growth and characterization of TiAlN∕CrAlN superlattices prepared by reactive direct current magnetron sputtering

Abstract

TiAlN and CrAlN coatings were prepared using a reactive direct current magnetron sputtering system from TiAl and CrAl targets. Structural characterization of the coatings using x-ray diffraction (XRD) revealed the B1 NaCl structure of TiAlN and CrAlN coatings with a prominent reflection along the (111) plane. The XPS data confirmed the bonding structures of TiAlN and CrAlN single layer coatings. Subsequently, nanolayered multilayer coatings of TiAlN∕CrAlN were deposited on silicon and mild steel (MS) substrates at different modulation wavelengths (Λ) with a total thickness of approximately 1.0μm. The modulation wavelengths were calculated from the x-ray reflectivity data using modified Bragg’s law. TiAlN∕CrAlN multilayer coatings were textured along (111) for Λ<200Å and the XRD patterns showed the formation of superlattice structure for coatings deposited at Λ=102Å. The x-ray reflectivity data showed reflections of fifth and seventh orders for multilayer coatings deposited at Λ=102 and 138Å, respectively, indicating the formation of sharp interfaces between TiAlN and CrAlN layers. The cross-sectional scanning electron microscopy image of TiAlN∕CrAlN multilayer coatings indicated a noncolumnar and dense microstructure. A maximum hardness of 39GPa was observed for TiAlN∕CrAlN multilayer coatings deposited at Λ=93Å, which was higher than the rule-of-mixture value (30GPa) for TiAlN and CrAlN. Study of thermal stability of the coatings in air using micro-Raman spectroscopy indicated that the TiAlN∕CrAlN multilayer coatings were stable up to 900°C in air. TiAlN∕CrAlN multilayer coatings also exhibited improved corrosion resistance when compared to the MS substrate.