Microstructural, phase evolution and corrosion properties of silicon carbide reinforced pulse electrodeposited nickel-tungsten composite coatings

Silicon carbide (SiC) reinforced nickel-tungsten (Ni-W) coatings were successfully fabricated on steel substrate by pulse electrodeposition method (PED) and the amount of SiC was varied as 0 g/l, 2 g/l, and 5 g/l in Ni-W coating. Effect of subsequent addition of SiC on microstructures, phases and on corrosion property of the coating was investigated. Field emission scanning electron microscopy (FE-SEM) image of the surface morphology of the coating showed the transformation from the dome like structure to turtle shell like structure. X-ray diffraction (XRD) of Ni-W-5 g/l SiC showed the disappearance of (220) plane of Ni(W), peak splitting in major peak of Ni(W) and formation of distinct peak of W(Ni) solid solution. Absence of (220) plane, peak splitting and presence of W(Ni) solid solution was explained by the high resolution transmission electron microscopy (HR-TEM) images. Tafel polarization plot was used to study the corrosion property of the coatings in 0.5 M NaCl solution. Ni-W-5 g/l SiC coating was showed higher corrosion resistance (i.e. similar to 21% increase in corrosion potential, E-corr) compared to Ni-W coating. Two simultaneous phenomena have been identified for the enhanced corrosion resistance of Ni-W-5 g/l SiC coating. (a) Presence of crystallographic texture (b) formation of continuous double barrier layer of NiWO4 and SiO2. (C) 2015 Elsevier B.V. All rights reserved

A Time Resolved Spectroscopic Study of Laser Generated Plasmas in Air at High Pressures

We present time resolved spectroscopic measurements of 1064 nm laser produced plasma in air at pressures from 0.85 to 48.3 bar. This paper reports on the measurement of temperature and electron number density of the plasmas at times between 100 ns and 3000 ns from the plasma onset. Neutral atomic oxygen lines at 715 nm and 777 nm are used for temperature measurement through a Boltzmann analysis. Electron number density is measured using Stark broadened atomic hydrogen (Hα) line at 656 nm. We employ Taylor-Sedov blast wave theory to calculate initial plasma pressures and utilize thermo-chemical computations of the plasma to determine plasma compositions. Both ideal and non-ideal behaviors of the plasma are considered. In the former case, plasma composition is computed by minimizing the specific Gibbs free energy and solving the system of nonlinear coupled equilibrium equations. The non-ideal behaviour is taken into account by considering Coulomb interactions between charged particles within the framework of the Debye-Hückel model. © 2010 by the American Institute of Aeronautics and Astronautics, Inc