Showing papers by "U. Kamachi Mudali published in 2019"

Weld overlay coating of Inconel 617 M on type 316 L stainless steel by cold metal transfer process

Abstract: A study of microstructure and volumetric dilution of Cold Metal Transfer (CMT) clad of Nickel based super alloy, Inconel 617M on type 316L stainless steel (SS) substrate was carried out. Overlay coatings were deposited at three different current inputs (80, 90 and 100 A) to synergetic CMT welding set while the wire feed rate and pulse frequency were pre-programmed. The ability of CMT to produce very low dilution and low heat input with the minimal heat affected zone (HAZ), when compared to conventional Tungsten Inert Gas welding (TIG) process was successfully demonstrated. Detailed microstructural evaluation of the cross sections revealed porosity and crack free Inconel 617M overlay with complete fusion, making a metallurgical bonding at the interface. Transverse micro Vickers hardness evaluation from clad to substrate showed the absence of significant HAZ for overlay produced by CMT. Calculation of percentage volumetric dilution, based on elemental Energy Dispersive Spectroscopy (EDS) of Fe-K counts, revealed that the cladding deposited at 100 A current exhibited low dilution value of 6.3% at 100 μm away from the interface while clad produced by TIG show significantly higher dilution value of ~50% at 100 μm from interface. Electron Backscattered Diffraction (EBSD) studies revealed morphology similar to epitaxial growth, with same crystallographic orientation of grains across the interface for CMT overlaid coatings.

Development of Superhydrophobic Coating on Copper for Enhanced Corrosion Resistance in Chloride Medium

Abstract: In this paper, a simple and economic method of superhydrophobic (SHP) surface modification of copper surfaces with water contact angle (WCA) of 147° ± 0.1° and roll-off angle of 5° is reported. SHP copper surfaces were synthesized by annealing copper foil in air and then coated with silica nanoparticles dispersed in silane solution. Scanning electron microscopy analysis of the SHP Cu surfaces showed the uniform distribution of spherical micron-sized CuO particles throughout the surface. Atomic force microscopy images of silane-coated surfaces showed increased valleys and peaks with higher root mean square and average roughness contributed by the silica nanoparticles. X-ray photoelectron spectroscopy results further confirmed the micron-sized CuO particles in the outer layer with silane containing silica nanoparticles, which contributed to the micro-/nano-roughness causing a phenomenal improvement in the WCA values. Electrochemical studies carried out in aqueous chloride environments demonstrated the corrosion resistance of superhydrophobic copper surface as evident from the shift in open-circuit potential values towards the nobler direction, increase in the charge transfer resistance and lower anodic current as compared with the fresh copper foil.

Enhanced anti-microbial activity in green concrete specimens containing fly ash, nanophase modifiers, and corrosion inhibitor

Abstract: This study reports the anti-bacterial properties of green concrete containing fly ash, nanoparticle modifiers, and a corrosion inhibitor. Four different concrete specimens, namely control concrete containing ordinary portland cement (CC), fly ash concrete containing 40 wt % fly ash (CF), modified fly ash concrete containing nano-TiO2 and nano-CaCO3 (1 wt % each) called CFN, and CFN with 2 wt % corrosion inhibitor (CFNI) are used in the present study. Among the four specimens exposed to microbial culture, CFNI showed minimal bacterial attachment and biofilm density, which is further corroborated from Epifluorescence microscopy and 3D confocal laser scanning microscopy. The CFNI specimens showed the least pH reduction among the four, which resulted in the enhanced microbial resistance. The results unambiguously confirm the synergetic effects of nanophase modifiers and NaNO2 based inhibitor in controlling microbial activity in concrete specimens. The results have promising applications in formulating concrete structures that are exposed to harsh environmental conditions. © 2018 American Institute of Chemical Engineers Environ Prog, 2018

Probing the Stability of Superhydrophobic (SHP) Silane Coating on Anodized Ti Substrate Using Kelvin Probe Force Microscope (KPFM)

Abstract: The present work aims at probing the stability of superhydrophobic (SHP) silane coating on anodized Ti substrate in different environmental conditions using Kelvin probe force microscope (KPFM) technique. The measurements were carried out for anodized silane-coated SHP Ti samples before and after exposure to UV light and flowing water systems. The KPFM mapping results (surface potential measurements) revealed that the SHP silane coating from anodized Ti surface was partially removed after exposure to the UV light and flowing water system. Moreover, reduction in surface roughness and contact angle was observed after exposure resulting in the conversion of the sample surface from SHP to hydrophobic condition indicating the stability of the coating in the aggressive environments. The results clearly showed that the SHP silane-coated Ti is highly suitable for applications in cooling water system.