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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.

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.

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.

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

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