National Aerospace Laboratories

About: National Aerospace Laboratories is a facility organization based out in Bengaluru, India. It is known for research contribution in the topics: Coating & Corrosion. The organization has 1838 authors who have published 2349 publications receiving 36888 citations.

Angular solar absorptance and thermal stability of W/WAlN/WAlON/Al2O3-based solar selective absorber coating

Abstract: In this paper, we report the solar absorptance property of a new tandem absorber consisting of layers W/WAlN/WAlON/Al2O3 that holds promise for solar thermal energy harvesting. The coating was prepared by DC/RF magnetron sputtering on stainless steel substrate. The performance of the film was investigated by measuring the reflectance spectra in the wavelength range of 250-2500 nm and most importantly by varying the incident angle from 18 degrees to 68 degrees. The effect of thermal annealing on the optical properties, microstructure and morphology of the solar selective absorber coating was also explored. The thermal annealing of the coating at 350 degrees C till 550 h in air did not result in any significant change in the spectral properties of the absorber coating. The excellent thermal stability and wide range of angular absorptance of this multilayer coating indicate the potential for application as selective coating in mid temperature photothermal conversion systems. (C) 2016 Elsevier Ltd. All rights reserved.

Vibro-acoustic response of sandwich plates with functionally graded core

Abstract: This paper presents the vibro-acoustic modeling and analysis of sandwich plateswith metal–ceramic functionally graded (FG) core using a simplified first-order shear deformation theory and elemental radiator approach. A simply supported rectangular plate having functionally graded core, metal and ceramic facesheets is considered with aluminum as metal and alumina as ceramic. The material properties of the core are assumed to vary according to a power law distribution of the volume fraction of the constituents. The sound radiation due to point load and uniformly distributed load is computed by numerically solving the Rayleigh integral. The effective material properties of the sandwich plate are presented as a function of core thickness. The vibration parameters in terms of natural frequencies, plate displacement and velocity, and acoustic parameters such as radiated sound power level, radiated sound pressure level and radiation efficiency are computed for various values of the power law index. A comprehensive study of the influence of core thickness on vibro-acoustic performance is presented in terms of mean-squared velocity and overall sound power level. It is found that, for the plate being considered, the sound power level increases with increase in the power law index of the core at lower frequency segment. Increased vibro-acoustic response is observed in the high-frequency band for ceramic-rich FG core and in the low-frequency band for metal-rich FG core, respectively. A sandwich plate with metal-rich FG core configuration has shown improved flexural stiffness, compared to an FG plate with no significant rise in overall radiated sound. It is possible with this analysis to suitably tailor and optimize the sandwich FG plates for multifunctional performance and desired vibro-acoustic interaction.

Deposition of TiN/CrN hard superlattices by reactive d.c. magnetron sputtering

Abstract: Multilayer superlattice coatings of TiN/CrN were deposited on silicon substrates using a reactive d.c. magnetron sputtering process. Superlattice period, also known as modulation wavelength (?), was controlled by controlling the dwell time of the substrate underneath Ti and Cr targets. X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the films. The XRD data showed 1st and 2nd order satellite reflections along the principal reflection for films having 132 A? ? ? ? 84 A?, thus confirming the formation of superlattice. The multilayer coatings exhibited hardness (H) as high as 3200 kg/mm2, which is 2 times the rule-of-mixtures value (i.e. HTiN = 2200 kg/mm2 and HCrN = 1000 kg/mm2). Detailed investigations on the effect of various process parameters indicated that hardness of the superlattice coatings was affected not only by modulation wavelength but also by nitrogen partial pressure and ion bombardment during deposition.