Papers by Sankara Narayanan TSN
Journal of Coatings Technology and Research, Jun 15, 2011
Galvanic coupling technique is capable of producing coatings of desired thickness. Good quality c... more Galvanic coupling technique is capable of producing coatings of desired thickness. Good quality coatings can be produced at low temperature. Galvanic coupling of mild steel (MS) with the other cathode materials such as titanium (Ti), copper (Cu), brass (BR), nickel (Ni), and stainless steel (SS) accelerates iron dissolution, enables quicker consumption of free phosphoric acid and facilitates an earlier attainment of point of incipient precipitation, resulting in a higher amount of coating formation. In the present investigation, potentiodynamic polarization and electrochemical impedance spectra on MS substrates phosphated using galvanic coupling are studied. This study reveals that MS substrates phosphated under galvanically coupled condition possess better corrosion resistance than the substrates phosphated under uncoupled condition.
Surface and Coatings Technology, 2006
The formation of electroless NiB coatings obtained using a low temperature bath and evaluation of... more The formation of electroless NiB coatings obtained using a low temperature bath and evaluation of their characteristic properties are addressed in this paper. An alkaline bath having nickel chloride as the source of nickel and borohydride as the reducing agent was used to prepare the electroless NiB coatings. The influence of concentration of sodium borohydride in bath on the plating rate and the nickel/boron content of the resultant NiB coatings was studied. Selected coatings were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively, for assessing the phase content, phase transformation behaviour and magnetic properties. XRD patterns reveal that the structure of electroless NiB coatings in as-plated condition is a function of the boron content of the coating: higher the boron content, greater the amorphous nature of the coating and vice-versa. DSC traces exhibit two exothermic peaks around 300 and 420°C, corresponding to the phase transformation of crystalline nickel and Ni 3 B phases at 300°C and the transformation of a higher phase compound to Ni 3 B at 420°C. VSM studies indicate that the magnetic properties of the coating is also a function of the boron content of the coating: higher the boron content, lesser the saturation magnetization.
Surface and Coatings Technology, 2003
Electroless NiCoP ternary alloy deposits were prepared by varying the metallic ratio and were c... more Electroless NiCoP 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 ...
Tribology International, 2013
Abstract Surface mechanical attrition treatment (SMAT) was carried out on Ti-6Al-4 V. Fretting we... 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 ...
Journal of Colloid and Interface Science, Feb 1, 2016
The objectives of the present study are to ascertain, particle incorporation during the initial s... more The objectives of the present study are to ascertain, particle incorporation during the initial stages of microarc oxidation (MAO), feasibility of increasing the level of particle incorporation through manipulation of process variables and, the use of MgO-ZrO 2 composite coatings either as a pre-treatment or as a post-treatment for MAO coated Mg. Experiments Anodic oxide coatings were prepared using 0.3 M NaOH + 15 g/l ZrO 2 and 3 M NaOH + 15 g/l ZrO 2 at 10 V under direct current, pulsed current (PC) unipolar and PC bipolar modes. MAO coatings were prepared using 5 g/l NaOH + 15 g/l Na 2 SiO 3 at 250 V under direct current mode for 2 min. Findings The study reveals that it is possible to incorporate ZrO 2 particles in the anodic oxide layer, suggesting such a possibility during the initial stages of MAO. When the MgO-ZrO 2 composite coating is used as a pre-treatment, it helps to reduce the size and density of the pores of the MAO coatings and increased the corrosion resistance. When it is used as a post-treatment, lamellar shaped Mg(OH) 2 with a very high surface area is formed on the surface, which would be beneficial to impart a better bioactivity and to facilitate immobilization of biomolecules.
Journal of Alloys and Compounds, Dec 1, 2016
Abstract Microarc oxidation (MAO) of magnesium is performed in a single stage using an alkaline s... 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
International Journal of Electrochemical Science, 2014
대한치과재료학회 학술대회, Nov 1, 2014
대한치과재료학회 학술대회, Apr 1, 2012
대한치과재료학회 학술대회, Nov 1, 2012
Wiley Encyclopedia of Composites, Jul 20, 2012
The idea of codepositing various second-phase particles in electrodeposited (ED) or electroless d... 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 ...
Advanced Materials Research, Feb 1, 2012
The low carbon Co28Cr6Mo alloy used for artificial joints like hip and knee prostheses is subject... more The low carbon Co28Cr6Mo alloy used for artificial joints like hip and knee prostheses is subjected to a surface treatment called SMAT (surface mechanical attrition treatment). The purpose of this treatment is to modify the surface mechanical properties of the treated alloy. Since the SMAT impacts the surface of materials, its influence on the corrosion behavior of the CoCrMo alloy has to be assessed in a physiological solution as Ringer's solution. Furthermore, a specific biomedical polishing is coupled with the SMAT in order to finalize the production of a hip prosthesis ready for use. The corresponding corrosion behavior is also studied. The corrosion behavior of CoCrMo alloy samples is investigated using electrochemical techniques (potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS)) in physiological liquid and simulated by an equivalent circuit. The polarization results show the reduction of the corrosion current density and the increase of the corrosion potential after the SMAT. The EIS analyses also show the benefit of the SMAT on the corrosion resistance of the CoCrMo alloy. The surface morphology modification and the phase's transformation induced by the SMAT are evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD).
Applied Surface Science, Nov 1, 2015
Ti-15Mo alloy has received considerable attention for biomedical applications (currently listed b... more Ti-15Mo alloy has received considerable attention for biomedical applications (currently listed by ASTM) due to its non-toxic nature, good mechanical properties and better corrosion resistance. Thermal oxidation is an effective method to form a thicker oxide layer on Ti and its alloys. In the present study, thermal oxidation of Ti-15Mo alloy is explored for the first time. The objective of the study is to ascertain the surface, structural and morphological characteristics of Ti-15Mo alloy subjected to thermal oxidation at different temperatures (500, 650 and 800 °C), for various periods of time (8, 16, 24 and 48 h). It is also aimed at to evaluate their corrosion behaviour in Ringer's solution in order to assess their suitability for biomedical applications. Thermal oxidation increased the average surface roughness (Ra) and microhardness, while decreasing the water contact angle of the Ti-15Mo alloy. The phase contents of the oxide layer show a strong dependence on treatment conditions with a predominance of the rutile phase over the anatase phase at temperatures > 650 °C and for time periods > 16 h. A more positive Ecorr and a lower ipass are observed for the thermally oxidized Ti-15Mo alloys when compared with the untreated alloy. For the experimental conditions employed in the present study, it is clear that Ti-15Mo alloy subjected to thermal oxidation at 650 °C for 8 to 48 h offers a better corrosion resistance than those treated at 800 °C for 8 h.
대한치과재료학회 학술대회, Nov 1, 2013
Additive manufacturing, May 1, 2020
Enhancement of the surface properties of selective laser melted maraging steel by large pulsed el... more Enhancement of the surface properties of selective laser melted maraging steel by large pulsed electron-beam irradiation, Additive Manufacturing (2020),
RSC Advances, 2016
A simple strategy to modify the porous structure of the oxide coating formed on Mg by plasma elec... more A simple strategy to modify the porous structure of the oxide coating formed on Mg by plasma electrolytic oxidation (PEO) is addressed. Post-treatment of PEO coated Mg using 3 M NaOH at 60 C for 1 h modifies its porous structure, helps to seal the smaller pores and decrease the size of medium and bigger size pores, increases the surface roughness but provides a better homogeneity of the surface, changes its chemical nature, improves its corrosion resistance in Hank's balanced salt solution, facilitate apatite growth in simulated body fluid and promotes cell viability and growth in cell culture media.
Journal of Magnesium and Alloys, 2022
The thin and porous Fluoride Conversion Coating FCC with many cracks could not offer a significan... more The thin and porous Fluoride Conversion Coating FCC with many cracks could not offer a significant improvement in corrosion resistance for Mg. Magnesium phosphate coating improves the corrosion resistance of Mg, good bioactivity, promotes cell viability and cyto-compatibility and exhibits antibacterial activity. However, rapid dissolution in Mg in acidic magnesium phosphate containing solutions leads to the development of an inhomogeneous coating. The present study attempts to prevent the excessive dissolution of Mg by forming a fluoride conversion coating as a pre-treatment in the first stage followed by deposition of magnesium phosphate coating in the second stage to develop magnesium fluoride-magnesium phosphate duplex coatings. The morphological features, structural characteristics, nature of functional groups, corrosion behavior in Hanks' balanced salt solution and bioactivity in simulated body fluid are assessed to ascertain the suitability of the magnesium fluoride-magnesium phosphate duplex coating in controlling the rate of degradation of Mg and improving its bioactivity using uncoated Mg and fluoride conversion coated Mg as reference. The findings of the study reveal that the magnesium fluoride-magnesium phosphate duplex coating could offer an excellent corrosion resistance and improve the bioactivity of Mg.
Transactions of the Indian Institute of Metals, Jul 27, 2012
ABSTRACT The effect of surface mechanical attrition treatment (SMAT) and its duration on fatigue ... 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.
Applied Surface Science, Feb 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Papers by Sankara Narayanan TSN