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Sankara Narayanan  TSN

    Sankara Narayanan TSN

    Electroless Ni–Co–P ternary alloy deposits were prepared by varying the metallic ratio and were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and vibration sample... more
    Electroless Ni–Co–P ternary alloy deposits were prepared by varying the metallic ratio and were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and vibration sample magnetometer. The plating rate of electroless ...
    Abstract Surface mechanical attrition treatment (SMAT) was carried out on Ti-6Al-4 V. Fretting wear tests were conducted using two counterbody materials (alumina and steel). SMAT resulted in surface nanocrystallization. Due to high... more
    Abstract Surface mechanical attrition treatment (SMAT) was carried out on Ti-6Al-4 V. Fretting wear tests were conducted using two counterbody materials (alumina and steel). SMAT resulted in surface nanocrystallization. Due to high hardness, low tangential force coefficient (TFC) and more TiO 2 layer, fretting wear resistance of SMAT treated samples was higher than that of the untreated samples. TFC values obtained with alumina counterbody were higher than those obtained with steel counterbody. The fretting wear ...
    Abstract Microarc oxidation (MAO) of magnesium is performed in a single stage using an alkaline silicate electrolyte and acidic zirconate electrolyte as well as in two stages, sequentially using the alkaline silicate followed by the... more
    Abstract Microarc oxidation (MAO) of magnesium is performed in a single stage using an alkaline silicate electrolyte and acidic zirconate electrolyte as well as in two stages, sequentially using the alkaline silicate followed by the acidic zirconate electrolyte. The morphological characteristics, surface roughness, phase content, corrosion behaviour and bioactivity were compared. The surface morphology, thickness, average surface roughness (Ra), and phase composition of the MAO coatings show a strong dependence on the type of electrolytes used and the methodology employed for deposition. Based on the corrosion protective ability in Hank’s balanced salt solution, the uncoated and MAO coated Mg are ranked as follows: Uncoated Mg
    The idea of codepositing various second-phase particles in electrodeposited (ED) or electroless deposited (EL) metal or alloy matrix and thereby taking advantage of their desirable qualities, such as hardness, wear and abrasion... more
    The idea of codepositing various second-phase particles in electrodeposited (ED) or electroless deposited (EL) metal or alloy matrix and thereby taking advantage of their desirable qualities, such as hardness, wear and abrasion resistance, and corrosion resistance, has led to the development of ED and EL composite coatings with a wide range of possible combinations and properties [1–3]. ED and EL composite coatings can be prepared by codepositing various second-phase particles in the respective metal or alloy ...
    ABSTRACT The effect of surface mechanical attrition treatment (SMAT) and its duration on fatigue lives of alloy 718 has been studied. The SMAT process was carried out in vacuum (−0.1 MPa) with SAE 52100 steel balls of 5 mm diameter for 30... more
    ABSTRACT The effect of surface mechanical attrition treatment (SMAT) and its duration on fatigue lives of alloy 718 has been studied. The SMAT process was carried out in vacuum (−0.1 MPa) with SAE 52100 steel balls of 5 mm diameter for 30 and 60 min at a vibrating frequency of 50 Hz. SMAT resulted in surface nanocrystallization, higher surface roughness, higher surface hardness, higher compressive residual stress, higher tensile strength, reduced ductility and superior fatigue lives. The enhancement in the fatigue lives of treated samples can be attributed to the positive influence of nanostructured surface layer, compressive residual stress and work hardened layer, which surpassed the negative effect of increased surface roughness. There was no significant difference between the fatigue lives of samples treated for 30 and 60 min.
    The effectiveness of hydroxyapatite (HA) coating prepared by electrodeposition technique in improving the corrosion resistance of commercially pure magnesium (CP-Mg) in simulated body fluid (SBF) is addressed. The coating formed in... more
    The effectiveness of hydroxyapatite (HA) coating prepared by electrodeposition technique in improving the corrosion resistance of commercially pure magnesium (CP-Mg) in simulated body fluid (SBF) is addressed. The coating formed in as-deposited condition is identified as dicalcium phosphate dehydrate (DCPD) (Brushite), which is converted to HA after immersion in 1 M NaOH at 80°C for 2 h. The XRD patterns and FTIR spectra confirm the formation of DCPD and HA. During electrodeposition, the H2PO4− ion is reduced and the reaction between Ca2+ ions and the reduced phosphate ions leads to the formation of DCPD, which is converted to HA following treatment in NaOH. The deposition of HA coating enables a threefold increase in the corrosion resistance of CP-Mg. The ability to offer a significant improvement in corrosion resistance coupled with the bioactive characteristics of the HA coating establish that electrodeposition of HA is a viable approach to engineer the surface of CP-Mg in the development of Mg-based degradable implant materials.
    Abstract The present study investigates the influence of gum ghatti (GG) concentration on the porosity of hydroxyapatite (HAP), where the final composite has been tested for the effects of drug delivery, antibacterial activity, and in... more
    Abstract The present study investigates the influence of gum ghatti (GG) concentration on the porosity of hydroxyapatite (HAP), where the final composite has been tested for the effects of drug delivery, antibacterial activity, and in vitro cytotoxicity. Following the synthesis of GG-HAP composite by a simple chemical precipitation method, the various analyses were employed to understand the crystallinity, morphology, chemical composition, surface functionality and internal bonding, etc. From the comparison of physical properties among the sintered and un-sintered GG-HAP composites and that too with different concentrations of GG (1%, 5%, and 10%), we observed the superior properties for the samples formed from higher GG concentration (10%) with sintering. We observed the lowest crystal size of 30 nm with 95% crystallinity, a surface area of 108 m2/g, a total pore volume of 0.2 mL/g, an average pore diameter of 33 A for the Sin-10% GG-HAP composite. In addition, the biocompatibility test performed on the Sin-GG-HAP pellet confirmed the in-built bioactivity and biostability of the composites in simulated body fluid. Further, the Naringenin drug delivery profiles confirmed for the stable and controlled release of loaded drug from the Sin-GG-HAP composites (with 1, 5, and 10% of GG). We observed the highest release of 96% from the Sin-10% GG-HAP matrix in just 90 min and T50% of 416 h, and a mean diffusion time period of 459 h. Finally, the antimicrobial (using both gram-positive and gram-negative bacteria) and cytotoxic activities (with the use of healthy normal and diseased cells) of the drug-loaded and un-loaded GG-HAP composites confirm the potential role of the formed Sin-10% GG-HAP composite towards biomedical applications.
    The present study reports the development of multi-functional coatings on titanium for orthopaedic implant applications.
    Faster degradation of iron based degradable implants in physiological media, particularly during the initial stages of implantation, poses difficulties in directly using them for clinical applications.
    Abstract The effects of surface mechanical attrition treatment (SMAT) of EN8 steel on the growth of phosphate coatings, morphological features and corrosion resistance of the resultant coatings have been studied. SMAT enabled the... more
    Abstract The effects of surface mechanical attrition treatment (SMAT) of EN8 steel on the growth of phosphate coatings, morphological features and corrosion resistance of the resultant coatings have been studied. SMAT enabled the formation of a uniform surface profile although the average surface roughness is increased after treatment. SMAT increased the extent of metal dissolution and the rate of growth of phosphate coating. In spite of the similarity in phase composition, the phosphate crystallite size is relatively high for samples treated by SMAT. Compared to the untreated one, a cathodic shift in Ecorr with a corresponding decrease in icorr is observed for SMAT treated EN8 steel after phosphating. For all tested samples, zinc phosphate coatings deposited on EN8 steel after SMAT using 8 mm Ø balls for 30 min offers the highest corrosion resistance. The increase in surface roughness by SMAT is partly compensated by the expected improvement in corrosion resistance.
    Résumé/Abstract A cold zinc phosphating bath was formulated and optimized to study the effect of some cotionic surfactants viz.. Dodecylamine (DDA), Tetradecylamine (TDA), Hexadecylamine (HDA) and Octadecylamine (OCA) on the growth and... more
    Résumé/Abstract A cold zinc phosphating bath was formulated and optimized to study the effect of some cotionic surfactants viz.. Dodecylamine (DDA), Tetradecylamine (TDA), Hexadecylamine (HDA) and Octadecylamine (OCA) on the growth and the crystal habit of zinc phosphote coating on mild steel. Studies have been carried out regarding the mode of adsorption and how these additives modify the crystallization kinetics. The properties of the coated layer and corrosion performance were also investigated to correlate with the effect ...
    Abstract The effect of SMAT on pack boronizing of EN8 steel is addressed. SMAT induced plastic deformation, enabled nanocrystallization at the surface, reduced the grain size and increased the volume fraction of non-equilibrium gain... more
    Abstract The effect of SMAT on pack boronizing of EN8 steel is addressed. SMAT induced plastic deformation, enabled nanocrystallization at the surface, reduced the grain size and increased the volume fraction of non-equilibrium gain boundaries, accumulation of defects and dislocations at the grain boundaries and within the grains. These features helped to promote the diffusion of boron. The present study demonstrates for the first time that SMAT treated EN8 steel can be boronized with a reasonable case depth at 923 K for 7 h. It also addresses the benefits of duplex treatment methodology to achieve the desired case depth and a dense boronized layer. Formation of an FeB phase along with an Fe 2 B phase for SMAT treated EN8 steel has also been reported for the first time. The findings of the study recommend that SMAT can be used as a pretreatment for boronizing of steel, provided necessary precautions are made on boron concentration, to control the volume fraction of the deleterious FeB phase.
    ABSTRACT The influence of surface mechanical attrition treatment (SMAT) on pack boronizing of AISI 304 stainless steel (304 SS) is addressed. SMAT of 304 SS was performed using 8 mm Ø 316L stainless steel balls for 60 min. Untreated and... more
    ABSTRACT The influence of surface mechanical attrition treatment (SMAT) on pack boronizing of AISI 304 stainless steel (304 SS) is addressed. SMAT of 304 SS was performed using 8 mm Ø 316L stainless steel balls for 60 min. Untreated and SMATed 304 SS samples were pack boronized by single stage (at 1223 K for 1, 3 5 and 7 h) and duplex (973 K for 1 h and 1223 K for 1 h) treatments. SMATed 304 SS increased the kinetics of boron diffusion, enabled the formation of a higher volume fraction of alloy borides and increased the hardness of the borided layer. Duplex treatment increased the case depth than the single stage treatment. The findings of this study suggest that SMAT can be used as an effective pretreatment for boronizing of 304 SS.
    The formation of Ni-B alloy films by electrodeposition route and evaluation of their structural characteristics, phase transformation behavior and corrosion resistance are discussed. The Ni-B alloy films were prepared using... more
    The formation of Ni-B alloy films by electrodeposition route and evaluation of their structural characteristics, phase transformation behavior and corrosion resistance are discussed. The Ni-B alloy films were prepared using Watt's nickel bath containing dimethylamine borane (DMAB) as the source of boron. The ratio of rate of reduction of nickel and rate of decomposition of DMAB determines the boron content of the films. The Ni-B films electrodeposited in the current density range of 1-4 A/dm (2) are found to be crystalline in ...

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