B. Deepthi

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

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<200A and the XRD patterns showed the formation of superlattice structure for coatings deposited at Λ=102A. The x-ray reflectivity data showed reflections of fifth and seventh orders for multilayer coatings deposited at Λ=102 and 138A, respectively,...

Stabilization of tetragonal and cubic phases of ZrO2 in pulsed sputter deposited ZrO2/Al2O3 and ZrO2/Y2O3 nanolayered thin films

We have prepared nanolayered thin films of ZrO2/Al2O3 and ZrO2/Y2O3 using pulsed sputtering to study the feasibility of stabilization of various polymorphs of ZrO2. These films have been deposited at various substrate temperatures (350–700 °C), individual layer thicknesses (1.9–25.2 nm), and modulation wavelengths (Λ, 9.6–32.7 nm). The cross section of ZrO2 and Y2O3 films consisted of microcolumns, whereas the ZrO2/Al2O3 and ZrO2/Y2O3 multilayer systems exhibited a less columnar microstructure. X-ray diffraction (XRD) data showed monoclinic, cubic, and amorphous structures for ZrO2, Y2O3, and Al2O3 thin films, respectively. The tetragonal phase of ZrO2 (t-ZrO2) was stabilized for ZrO2/Al2O3 nanolayered thin films prepared at Λ≤13.8 nm. Our studies demonstrated that a critical ZrO2 thickness (≤10.5 nm at a substrate temperature of 700 °C) is required in order to stabilize the t-ZrO2 phase, which was in agreement with thermodynamically derived critical radius for the stabilization of the tetragonal phase. I...

Structure and properties of reactive direct current magnetron sputtered niobium aluminum nitride coatings

A reactive direct current magnetron sputtering system was used to prepare NbAlN coatings at different nitrogen flow rates and substrate bias voltages. Various properties of NbAlN coatings were studied using x-ray diffraction, scanning electron microscopy, atomic force microscopy, x-ray photoelectron spectroscopy, nanoindentation, the four-probe method, a solar spectrum reflectometer and emissometer, spectroscopic ellipsometry, micro-Raman spectroscopy, and potentiodynamic polarization techniques. Single-phase NbAlN with B1 NaCl structure was obtained for the coatings prepared at a nitrogen flow rate in the range of 1.5–3 sccm, a substrate bias voltage of −50 to −210 V, and a substrate temperature of 300 °C. Nanoindentation data showed that the optimized NbAlN coating exhibited a maximum hardness of 2856 kg/mm2. An approximately 100-nm-thick NbAlN–NbAlON tandem on copper substrate exhibited a high absorptance (0.93) and a low emittance (0.06), suitable for solar-selective applications. The spectroscopic ellipsometry and resistivity data established the metallic nature of NbAlN and the semitransparent behavior of NbAlON coatings. The corrosion resistance of NbAlN coatings was superior to that of the mild steel substrate. The addition of aluminum in NbN coatings increased the onset of oxidation in air from 350 to 700 °C. Vacuum-annealed NbAlN coatings were structurally stable up to 700 °C and retained their high hardness up to a temperature of 650 °C.