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Thiruvikraman C.,Annamalai University | Balasubramanian V.,Annamalai University | Sridhar K.,Naval Materials Research Laboratory NMRL
Journal of Thermal Spray Technology | Year: 2014

High velocity oxygen fuel (HVOF)-sprayed cermet coatings are extensively used to combat erosion-corrosion in naval applications and in slurry environments. HVOF spray parameters such as oxygen flow rate, fuel flow rate, powder feed rate, carrier gas flow rate, and spray distance have significant influence on coating characteristics like adhesion bond strength and shear strength. This paper presents the use of statistical techniques in particular response surface methodology (RSM), analysis of variance, and regression analysis to develop empirical relationships to predict adhesion bond strength and lap shear bond strength of HVOF-sprayed WC-CrC-Ni coatings. The developed empirical relationships can be effectively used to predict adhesion bond strength and lap shear bond strength of HVOF-sprayed WC-CrC-Ni coatings at 95% confidence level. Response graphs and contour plots were constructed to identify the optimum HVOF spray parameters to attain maximum bond strength in WC-CrC-Ni coatings. © 2014 ASM International.


Majhi S.M.,CSIR - Institute of Minerals And Materials Technology | Behura S.K.,CSIR - Institute of Minerals And Materials Technology | Bhattacharjee S.,CSIR - Institute of Minerals And Materials Technology | Singh B.P.,CSIR - Institute of Minerals And Materials Technology | And 3 more authors.
International Journal of Hydrogen Energy | Year: 2011

Solid oxide fuel cells (SOFC), with its ability to use hydrocarbon fuels and capability to offer highest efficiency, have attracted great attention in India in recent years as an alternative energy generation system for future. But a great deal of problems associated with SOFC is needed to be solved before it can find commercial application. The relatively high operating temperature of 800-1000 °C of SOFC imposes a stringent requirement on materials that significantly increases the cost of SOFC technology. Reducing the operating temperature of an SOFC to below 800 °C can reduce degradation of cell components, improve flexibility in cell design, and lower the material and manufacturing cost by the use of cheap and readily available materials such as ferritic stainless steel. The operating temperature can be reduced by two possible approaches: (i) developing alternative electrolyte materials with high ionic conductivity at lower temperature, and (ii) developing much thinner and denser electrolyte layer such that the ohmic losses are minimised. In this work we report the use of inexpensive Electrophoretic deposition (EPD) technique in making about 10 micron thin and dense YSZ electrolyte on NiO-YSZ substrate. The effect of different operating parameters such as applied voltage, deposition time etc have been optimised during deposition from YSZ suspension in acetylacetone. The YSZ/NiO-YSZ bi-layers were then co-sintered at 1450 °C for 5 h. The single SOFC cells were then fabricated by brush painting LSM:YSZ (50:50) paste on the electrolyte layer followed by sintering at 1200 °C for 2 h. The single SOFC cell when tested using H2 as fuel and ambient air as oxidant exhibited an open circuit voltage (OCV) of 1.03 V and the peak power density of about 624 mW/cm2 at 800 °C. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Chouhan D.K.,Indian Defence Institute of Advanced Technology | Rath S.K.,Naval Materials Research Laboratory NMRL | Kumar A.,Indian Defence Institute of Advanced Technology | Alegaonkar P.S.,Indian Defence Institute of Advanced Technology | And 3 more authors.
Journal of Materials Science | Year: 2015

The present work attempts at a relative deduction of correlations between structure-reinforcement and chain dynamics in Laponite- and graphene oxide (GO)-dispersed epoxy nanocomposites. The fillers were reasonably well dispersed in the epoxy matrix as revealed by wide-angle X-ray diffraction, transmission electron microscopy and small-angle X-ray scattering studies. The scattering from the nanocomposites exhibited power-law behaviour at low q region with fractal dimensions, implying presence of platelets and tactoids of varying thicknesses. A comprehensive study on the thermomechanical properties of the nanocomposites was made in terms of tensile, dynamic mechanical analysis and flexural and fracture toughness measurements. The studies revealed simultaneous reinforcement as well as toughening effects in the nanocomposites; ~42 and ~34 % increases in flexural strength and mode I fracture toughness (KIC), respectively, with 0.1 wt% GO; and ~25 and ~20 % enhancements in flexural modulus and KIC with 0.1 and 0.3 wt% Laponite, respectively. A unique phenomenon of bimodal distribution of glass transition temperatures was observed as two overlapped peaks in terms of Gaussian contributions in the tan δ versus temperature profiles of the nanocomposites (from dynamic mechanical analysis) and derivative of reversible heat capacity with respect to temperature, dCp,rev/dT versus temperature profiles (from modulated differential scanning calorimetric measurements); as against a single symmetric profile for the unfilled matrix. We attempt to understand the nanofiller-induced alteration in the primary relaxation mechanisms as well as notable reinforcement and toughening effects by invoking the filler/polymer interactions, filler dispersion and fractographic investigations. © 2015, Springer Science+Business Media New York.


Kumar S.,Indian Institute of Technology Roorkee | Chaudhari G.P.,Naval Materials Research Laboratory NMRL | Nath S.K.,Indian Institute of Technology Roorkee | Basu B.,Naval Materials Research Laboratory NMRL
Materials and Manufacturing Processes | Year: 2012

13/4 low carbon martensitic stainless steel is conventionally used for turbine blades in hydroelectric power plants. Due to silt erosion and cavitation, heavy damage often occurs in this material. In order to enhance the life of hydro-turbine components, repair welding is needed. Selection of proper welding parameters during repair welding is therefore essential in order to control any possible deterioration of its mechanical properties. This work deals with heat affected zone (HAZ) simulation of 13/4 martensitic stainless steel using a thermomechanical simulator, Gleeble® 3800. Assessment of Charpy impact toughness, tensile properties, and hardness of HAZ simulated specimens is done. Peak temperatures of 1,000°C, 1,200°C, and 1,325°C and preheat temperatures of 30°C and 121°C are used. High impact toughness (52.8J) and ductility (19.3%) is observed in steel specimens simulated with peak temperature of 1,000°C along with 121°C preheat temperature. The observed results are explained based on the microstructural changes resulting from different welding parameters. © 2012 Copyright Taylor and Francis Group, LLC.


Ragu Nathan S.,Annamalai University | Balasubramanian V.,Annamalai University | Malarvizhi S.,Annamalai University | Rao A.G.,Naval Materials Research Laboratory NMRL
International Journal of Refractory Metals and Hard Materials | Year: 2016

A non-consumable tool is a vital requirement for friction stir welding (FSW) of high melting point alloys such as steel and titanium. In this investigation, an attempt was made to understand the pre-weld and post-weld microstructural characteristics of three tungsten based alloy FSW tools viz. 90%W, 95%W and 99%W. A naval grade high strength low alloy (HSLA) steel plates of 5 mm thickness were welded using the above tools with a tool rotational speed of 600 rpm and welding speed of 30 mm/min. Microstructural characteristics of the FSW tools, before and after welding, were analyzed using optical microscopy (OM) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS). From this investigation, it is found that the tool made of 99% W doped with 1% La2O3 exhibited microstructural stability at elevated temperatures during FSW process. © 2015 Elsevier Ltd. All rights reserved.


Nathan S.R.,Annamalai University | Malarvizhi S.,Annamalai University | Balasubramanian V.,Annamalai University | Rao A.G.,Naval Materials Research Laboratory NMRL
Engineering Failure Analysis | Year: 2016

A non-consumable tool is a vital requirement for friction stir welding (FSW) of high melting point alloys such as steel and titanium. In this investigation, an attempt was made to understand the pre-weld and post-weld microstructural characteristics of three tungsten based alloy FSW tools viz. 90%W, 95%W and 99%W. High strength low alloy (HSLA) steel plates of 5 mm thickness were welded using the above tools with a tool rotational speed of 600 rpm and welding speed of 30 mm/min. Microstructural characteristics of the FSW tools, before and after welding, were analyzed using optical microscopy (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) techniques. From this investigation, it is found that the tool made of 99%W doped with 1% La2O3 exhibited microstructural stability due to absence of Fe-Co-Ni phase formation at elevated temperatures during FSW process. © 2016 Elsevier Inc.


Tiwari V.K.,Banaras Hindu University | Prasad A.K.,Banaras Hindu University | Singh V.,Banaras Hindu University | Jana K.K.,Banaras Hindu University | And 3 more authors.
Macromolecules | Year: 2013

Process and nanoparticle induced piezoelectric super toughened poly(vinylidene fluoride) (PVDF) nanohybrids have been demonstrated. The nanohybrids have been prepared by incorporating organically modified nanoclay through melt extrusion and solution route. The solution processed nanohybrid exhibit 1100% improvement in toughness as well as adequate stiffness as compared to pure PVDF without any trade-off. The structural and morphological origins of super toughening phenomena have been worked out. The unique crystallization behavior of PVDF on top of the silicate layers (β-phase, planar zigzag chain conformation, and subsequent polar γ-phase and α-phase as layered type) has been revealed to create an island type of structure, which in turn is responsible for greater toughness. The extent of piezoelectric β-phase has been enhanced by controlled stretching of the nanohybrid at moderately high temperature for better disentanglement, and 90% of the piezoelectric phase has been stabilized. The structural change over has been confirmed through XRD, FTIR, and DSC studies. The nanohybrids possess β-phase with a small amount of α-phase and distorted γ-phase (T3G-T6G) before stretching which convert into predominantly β-phase with increasing the draw ratio, whereas pure PVDF converted directly into β-phase from pure α-phase. The piezoelectric coefficient (d33) exhibits significant increase with draw ratio, and the relative enhancement is more in nanohybrid vis-à-vis pure PVDF arising from the presence of greater β-phase leading to super toughened lightweight piezoelectric material. © 2013 American Chemical Society.


Ragu Nathan S.,Annamalai University | Balasubramanian V.,Annamalai University | Malarvizhi S.,Annamalai University | Rao A.G.,Naval Materials Research Laboratory NMRL
Transactions of the Indian Institute of Metals | Year: 2016

In this study, the effect of tool shoulder diameter (primary heat generating source) to the plate thickness ratio on tensile and impact toughness properties of friction stir welded high strength low alloy (HSLA) steel was investigated. A naval grade HSLA steel of 5 mm thick plates were welded with tool rotational speed of 600 rpm and welding speed of 30 mm/min using five tungsten based alloy tools having shoulder diameter varying from 20 to 30 mm. Microstructural characteristics of the weld joints were analyzed using optical microscopy along with the evaluation of tensile properties. From this investigation, it was found that the joint fabricated using a tool shoulder diameter of 25 mm (5 times the plate thickness) exhibited superior mechanical properties compared to other joints. © 2016 The Indian Institute of Metals - IIM


Rath S.K.,Naval Materials Research Laboratory NMRL | Dubey S.,CSIR - National Chemical Laboratory | Kumar G.S.,Indian Defence Institute of Advanced Technology | Kumar S.,Indian Institute of Technology Kharagpur | And 5 more authors.
Journal of Materials Science | Year: 2014

A simple two-step process was used to disperse acid functionalized multi-walled carbon nanotubes (CNTs) in poly(vinylidene fluoride) (PVDF). While the neat solvent-cast PVDF showed coexistence of α- and β-phases; the composite films exhibited only β-phase crystals. Further studies on the crystalline behaviour, using differential scanning calorimetry and small-angle X-ray scattering techniques showed an increase in the percentage of crystalline phase with CNT. The network formed by CNTs in the matrix reduced the macroscopic electrical resistivity of composite films. The dielectric constant increased with CNT loading. Further, these composites were investigated for its electromagnetic wave absorbance (EWA) and strain sensing properties. The EWA properties were studied in the X-band (6-12 GHz) region. A maximum of ∼37 dB reflectivity loss at ∼9.0 GHz was obtained in a ∼25 μm thick PVDF film containing only 0.25 wt% of functionalized CNT. Preliminary studies showed a systematic change in electrical resistance by the application of dynamic bending strain in nanocomposite film. The film also showed a significant improvement in mechanical stiffness owing to efficient stress transfer from matrix to filler, the property desirable for a good strain sensor. In view of the unique combination of EWA and electro-mechanical properties, the nanocomposite films are expected to serve as a multifunctional material for strain sensing in health monitoring as well as in radar absorption. © 2013 Springer Science+Business Media New York.


Prabhuraj P.,Aarupadai Veedu Institute of Technology | Prabhuraj P.,Annamalai University | Rajakumar S.,Annamalai University | Balasubramanian V.,Annamalai University | Sridhar K.,Naval Materials Research Laboratory NMRL
International Journal of Applied Engineering Research | Year: 2015

High strength aluminum alloys have been widely used in marine and aircraft industries due to the attractive combined properties, such as low density, high yield stress, ductility, and fatigue resistance. However, these series alloys are susceptible to stress corrosion cracking (SCC) in sea environment which substantially restricts their further development and application. The mechanism of SCC in the high strength aluminum series alloy is generally attributed to anodic dissolution of the grain boundary region exacerbated by the tensile stress. In this article reviewed the stress corrosion cracking high strength series aluminum alloy. An extensive failure occurred in the aircraft industry, and what kind of mechanism led to initiate and propagate the stress corrosion cracks. The article covered most of the results of stress corrosion crack test with 7XXX series of aluminium alloys that have been obtained to date with fracture mechanics and stress corrosion crack growth rate measurement with the results from various testing specimens. The major part of the article is reviewed the SCC behavior of high strength aluminium alloys and it is still in a research area of high interest due to the favorable behavior in the aircraft industry. The article brings out the general understanding of the SCC mechanism and the critical metallurgical aspects and issues affecting the SCC behavior of high strength heat treatable alloy. © Research India Publications.

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