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K.S. Rajam

Bio: K.S. Rajam is an academic researcher from National Aerospace Laboratories. The author has contributed to research in topics: Sputter deposition & Nanoindentation. The author has an hindex of 42, co-authored 83 publications receiving 4765 citations.

Papers published on a yearly basis

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TL;DR: In this article, the structural and mechanical properties of CrN and CrAlN coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively.
Abstract: Approximately 1.5 μm thick CrN and CrAlN coatings were deposited on silicon and mild steel substrates by reactive direct current (DC) magnetron sputtering. The structural and mechanical properties of the coatings were characterized using X-ray diffraction (XRD) and nanoindentation techniques, respectively. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy (XPS). The surface morphology of the coatings was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The XRD data showed that the CrN and CrAlN coatings exhibited B1 NaCl structure. Nanoindentation measurements showed that as-deposited CrN and CrAlN coatings exhibited a hardness of 18 and 33 GPa, respectively. Results of the surface analysis of the as-deposited coatings using SEM and AFM showed a more compact and dense microstructure for CrAlN coatings. The thermal stability of the coatings was studied by heating the coatings in air from 400 to 900 °C. The structural changes as a result of heating were studied using micro-Raman spectroscopy. The Raman data revealed that CrN coatings got oxidized at 600 °C, whereas in the case of CrAlN coatings, no detectable oxides were formed even at 800 °C. After annealing up to 700 °C, the CrN coatings displayed a hardness of only about 7.5 GPa as compared to CrAlN coatings, which exhibited hardness as high as 22.5 GPa. The potentiodynamic polarization measurements in 3.5% NaCl solution indicated that the CrAlN coatings exhibited superior corrosion resistance as compared to CrN coatings.

277 citations

Journal ArticleDOI
Abstract: Ni–Co alloys with varying cobalt content were electrodeposited employing sulphamate electrolyte. The changes in microstructure and corrosion behavior of electrodeposited nickel with respect to cobalt addition were studied. Scanning electron microscope, optical microscope and energy dispersive X-ray analysis were used to characterize the alloy coatings. The alloy co-deposition was observed to be anomalous type. The cross-section microhardness measurement indicated that the hardness reached the maxima for a cobalt content of 50 wt.% and then dropped with the increase in cobalt content. A correlation between microhardness and microstructure has been attempted. The optical micrographs indicated a change in microstructure from mixed columnar-fibrous to lamellar and finally to fibrous with increase in cobalt content. The X-ray diffraction (XRD) studies indicated the crystal structure to be cubic for cobalt content in the range of 0–50 wt.%. A transition to hexagonal structure was observed for a cobalt content of 70 wt.% and beyond. A change in preferred orientation was also observed with respect to cobalt addition. Potentiodynamic polarization and electrochemical impedance studies were used to study the corrosion behavior of Ni–Co alloys. The physical behavior was quantified with equivalent circuit. These studies indicated that the Ni–20% Co alloy exhibited better corrosion resistance in comparison to other Ni–Co alloys, plain nickel and plain cobalt coatings irrespective of the substrate (mild steel, brass) employed for deposition.

199 citations

Journal ArticleDOI
TL;DR: In this article, the effect of copper and tungsten in alkaline electroless nickel baths has been studied in depositing Ni-Cu-P and Ni-W-P alloys.
Abstract: Interest in electroless plating of nickel-based ternary alloys has increased because of their excellent corrosion, wear, thermal and electrical resistance. They also possess good magnetic properties. In the present investigation, the effect of copper and tungsten in alkaline electroless nickel baths has been studied in depositing Ni–Cu–P and Ni–W–P alloys and also the synergistic effect of ions in depositing Ni–W–Cu–P alloys. Deposits were characterized using XRD, scanning electron microscopy (SEM), energy-dispersive analysis of X-ray (EDX) and atomic force microscopy (AFM) techniques. XRD results revealed that not much variation in structure and grain size has been found in Ni–Cu–P deposit. A decrease in phosphorus content and a marginal increase in grain size have been observed due to the tungsten addition in the Ni–P deposit. Addition of copper in Ni–W–P baths has resulted in a quaternary deposit, Ni–W–Cu–P, with increased crystallinity. SEM studies showed that presence of coarse nodules in ternary Ni–Cu–P and Ni–W–P deposits. Addition of copper in Ni–W–P baths has resulted in a very smooth deposit. Studies by AFM on deposits have proved that the copper has suppressed coarse nodules by inhibiting their growth in quaternary deposit. No considerable change in hardness has been noticed in both as-plated and heat-treated deposits due to the inclusion of copper in Ni–W–P deposit. A marginal improvement in corrosion resistance has been observed in quaternary alloy compared to ternary (Ni–Cu–P or Ni–W–P) alloys.

197 citations

Journal ArticleDOI
17 Jan 2005-Vacuum
TL;DR: In this article, nanolayered TiAlN/CrN multilayer films were deposited on silicon substrates from a TiAl target using a reactive DC magnetron sputtering process in Ar+N 2 plasma.

193 citations

Journal ArticleDOI
TL;DR: In this paper, the authors used x-ray diffraction (XRD) and micro-Raman spectroscopy to characterize the structural properties of nanolayered multilayer coatings.
Abstract: About 1.5-um-thick single-layer TiN, CrN, TiAlN coatings and nanolayered TiN/CrN, TiAlN/CrN multilayer coatings were deposited on silicon (111) substrates using a13; reactive direct current magnetron sputtering process. Structural characterization of the coatings was done using x-ray diffraction (XRD) and micro-Raman spectroscopy. All13; the coatings exhibited NaCl B1 structure in the XRD data. Raman spectroscopy data of as-deposited coatings exhibited two broad bands centered at 230x2013;250 and 540x2013;630 cmx2212;1.13; These bands have been assigned to acoustical and optical phonon modes, respectively. Thermal stability of the coatings was studied by heating the coatings in air in a13; resistive furnace for 30 min in the temperature range 400x2013;900 xB0;C. Structural changes as a result of heating were characterized using Raman spectroscopy and XRD. Raman13; data showed that TiN, CrN, TiN/CrN, TiAlN, and TiAlN/CrN coatings started to oxidize at 500, 600, 750, 800, and 900 xB0;C, respectively. To isolate the oxidation-induced spectral changes as a result of heating of the coatings in air, samples were also annealed in vacuum at 800 xB0;C under similar conditions. The Raman data of vacuum-annealed coatings showed no phase transformation, and intensity of the optical phonon mode increased and shifted to lower frequencies. The origin of these spectral changes is discussed in terms of defect structure of the coatings. Our results indicate that the thermal stability of nanolayered multilayer coatings is superior to the13; single-layer coatings.

186 citations


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TL;DR: In this paper, the recent developments and trends in combustion science towards the synthesis of nanomaterials are discussed, and different modifications made to conventional combustion approaches for preparation of nano-materials are critically analyzed.
Abstract: The recent developments and trends in combustion science towards the synthesis of nanomaterials are discussed. Different modifications made to conventional combustion approaches for preparation of nanomaterials are critically analyzed. Special attention is paid to various applications of combustion synthesized nanosized products.

842 citations

Journal ArticleDOI
TL;DR: The development of metal deposition processes based on electroless nickel, alloy and composite coatings on various surfaces has witnessed a surge in interest among researchers, with many recent applications made possible from many excellent properties as mentioned in this paper.

680 citations

Journal ArticleDOI
TL;DR: In this paper, the state-of-the-art physical vapor deposited solar selective coatings used for solar thermal applications with an emphasis on sputter deposited coatings for high-temperature applications.

543 citations

Journal ArticleDOI
TL;DR: In this paper, the Advanced Research Projects Agency-Energy (ARPA-Energy) gave DE-AR0000471 and DE-ARM0000181 for the first time, respectively.
Abstract: United States. Advanced Research Projects Agency-Energy (Awards DE-AR0000471 and DE-AR0000181)

483 citations

Journal ArticleDOI
TL;DR: In this article, the authors reviewed the tribological advancement of different electroless nickel coatings based on the bath types, structure and also the tribo testing parameters in recent years.

477 citations