Showing papers by "A. K. Gupta published in 2021"

Study on Microstructural Characterization, Mechanical Properties and Residual Stress of GTAW Dissimilar Joints of P91 and P22 Steels

Abstract: This article deals with the dissimilar joining of two different grade Cr-Mo steel (2.25Cr-1Mo: P22 and modified 9Cr-1Mo: P91) for power plant application. The dissimilar butt-welded joint was produced for conventional V groove design by using the gas tungsten arc welding (GTAW) process with the application of an ERNiCrMo-3 Ni-based super alloy filler. A microstructure characterization was performed to measure the inhomogeneity in the microstructure and element diffusion across the interface in a welded joint. The experiments were also performed to evaluate the mechanical properties of the dissimilar welded joint in as-welded (AW) and post-weld heat treatment (PWHT) conditions. An acceptable level of the mechanical properties was obtained for the AW joint. After PWHT, a significant level of the element diffusion across the interface of the weld metal and P22 steel was observed, resulting in heterogeneity in microstructure near the interface, which was also supported by the hardness variation. Inhomogeneity in mechanical properties (impact strength and hardness) was measured across the weldments for the AW joint and was reduced after the PWHT. The tensile test results indicate an acceptable level of tensile properties for the welded joint in both AW and PWHT conditions and failure was noticed in the weak region of the P22 steel instead of the weld metal.

Room temperature hydrogen sensing with Polyaniline/SnO2/Pd Nanocomposites

Abstract: In this work, we report unique hybrid composite film fabricated with the amalgamation of metal, semiconductor and polymers for hydrogen sensing application at room temperature. Fabrication of a novel nanocomposite film based on tin oxide (SnO2) nanosheets with polyaniline (PANI) doped with palladium (Pd) is performed using the hydrothermal synthesis technique. Functional aspects of the fabricated films are investigated with XRD, Raman spectra, FESEM, and FTIR spectral analysis. Interactions of the H2 gas molecules with SnO2, SnO2-Pd, PANI, PANI-SnO2, PANI-SnO2-Pd nanocomposite are also theoretically studied. Using first-principles density functional theory, the effects of gas adsorption on the electronic and transport properties of the sensor are examined. The computations show that the sensitivity of the SnO2 to the H2 gas molecules is considerably improved after hybridisation with Pd and, the sensitivity of the PANI to the H2gas molecules is considerably improved after hybridisation with SnO2.Gas sensing characteristics of fabricated films of SnO2, PANI and composite of SnO2/PANI/Pd are also experimentally investigated at room temperature with varying concentration level ranging from 50 to 400 ppm. The highest sensitivity among all the films at room temperature has been observed as ~540% for the SnO2/Pd film at 0.4% of the target gas and performance factor (the ratio of response percentage to total cycle time) is evaluated highest in Pd doped PANI-SnO2 film. Our results reveal the promising future of SnO2, PANI and Pd associated hybrid films in the development of ultra-high sensitive gas sensors.

Study on Microstructure and Mechanical Properties of Laser Welded Dissimilar Joint of P91 Steel and INCOLOY 800HT Nickel Alloy.

Abstract: This investigation attempts to explore the weld characteristics of a laser welded dissimilar joint of ferritic/martensitic 9Cr-1Mo-V-Nb (P91) steel and Incoloy 800HT austenitic nickel alloy. This dissimilar joint is essential in power generating nuclear and thermal plants operating at 600–650 °C. In such critical operating conditions, it is essential for a dissimilar joint to preserve its characteristics and be free from any kind of defect. The difference between the physical properties of P91 and Incoloy 800HT makes their weldability challenging. Thus, the need for detailed characterization of this dissimilar weld arises. The present work intends to explore the usage of an unconventional welding process (i.e., laser beam welding) and its effect on the joint’s characteristics. The single-pass laser welding technique was employed to obtain maximum penetration through the keyhole mode. The welded joint morphology and mechanical properties were studied in as-welded (AW) and post-weld heat treatment (PWHT) conditions. The macro-optical examination shows the complete penetrations with no inclusion and porosities in the weld. The microstructural study was done in order to observe the precipitation and segregation of elements in dendritic and interface regions. Solidification cracks were observed in the weld fusion zone, confirming the susceptibility of Incoloy 800HT to such cracks due to a mismatch between the melting point and thermal conductivity of the base metals. Failure from base metal was observed in tensile test results of standard AW specimen with a yield stress of 265 MPa, and after PWHT, the value increased to 297 MPa. The peak hardness of 391 HV was observed in the P91 coarse grain heat-affected zone (CGHAZ), and PWHT confirmed the reduction in hardness. The impact toughness results that were obtained were inadequate, as the maximum value of impact toughness was obtained for AW P91 heat-affected zone (HAZ) 108 J and the minimum for PWHT Incoloy 800HT HAZ 45 J. Thus, difficulty in obtaining a dissimilar joint with Incoloy 800HT using the laser beam welding technique was observed due to its susceptibility to solidification cracking.

Palladium-Functionalized Graphene for Hydrogen Sensing Performance: Theoretical Studies

Abstract: The adsorption characteristics of H2 molecules on the surface of Pd-doped and Pd-decorated graphene (G) have been investigated using density functional theory (DFT) calculations to explore the sensing capabilities of Pd-doped/decorated graphene. In this analysis, electrostatic potential, atomic charge distribution, 2D and 3D electron density contouring, and electron localization function projection, were investigated. Studies have demonstrated the sensing potential of both Pd-doped and Pd-decorated graphene to H2 molecules and have found that the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), i.e., the HOMO-LUMO gap (HLG), decreases to 0.488 eV and 0.477eV for Pd-doped and Pd-decorated graphene, respectively. When H2 is adsorbed on these structures, electrical conductivity increases for both conditions. Furthermore, chemical activity and electrical conductivity are higher for Pd-decorated G than Pd-doped G, whereas the charge transfer of Pd-doped graphene is far better than that of Pd-decorated graphene. Also, studies have shown that the adsorption energy of Pd-doped graphene (−4.3 eV) is lower than that of Pd-decorated graphene (−0.44 eV); a finding attributable to the fact that the recovery time for Pd-decorated graphene is lower compared to Pd-doped graphene. Therefore, the present analysis confirms that Pd-decorated graphene has a better H2 gas sensing platform than Pd-doped graphene and, as such, may assist the development of nanosensors in the future.

Study on the Variation in Mechanical Properties along the Dissimilar Weldments of P22 and P91 Steel

Abstract: The aim of the present work was to examine the microstructure and mechanical aspects of the Gas Tungsten Arc Welded dissimilar joint of P22 and P91 steel in as-welded (AW) and post-weld heat-treatment (PWHT) conditions. The weldments' optical and scanning electron microscopy characterization showed the heterogeneous microstructure formation along the weldments, which led to the variation in mechanical properties. After the PWHT, a carbon depleted soft and carbon enriched hard zone was observed near the interface of P22 steel and weld metal (WM) due to the diffusion of the carbon elements across the interface. A variation in hardness was observed along the weldments, and maximum was measured in WM (430 HV) and CGHAZ (408 HV) and reduced as move from the WM to base metal. A significant reduction in hardness of WM (333 HV) and CGHAZ (308 HV) was measured after the PWHT. Tensile strength of AW and PWHT conditions was measured 611 ± 9 MPa and 650 ± 13 MPa, respectively, which was higher than the tensile strength of P22 steel. The tensile test of the welded joint showed the failure in P22 steel base metal in AW and in P22 HAZ after PWHT, which indicates that welded joint is stronger than the base material. The impact toughness results also showed that the variation along the weldments and minimum impact toughness was measured 41 J in WM, which was lower than the impact toughness of the P22 and P91 base metal. The poor impact toughness of the WM was attributed to the untempered martensitic microstructure present in WM. In AW condition, maximum impact toughness of 184 J was measured in P22 HAZ; however, it was lower than the P22 base metal. The PWHT showed a significant increase in impact toughness of the WM and HAZ of P22 and P91 steel.

Triethanolamine–ethoxylate (TEA-EO) assisted hydrothermal synthesis of hierarchical β-MnO2 nanorods: effect of surface morphology on capacitive performance

Abstract: In this study we are presenting the synthesis of MnO2 nanorods using hydrothermal method assisted by facile tri-ethanolamine-ethoxylate. Structural (x-ray diffraction, Rietveld refinement), functional (Fourier Transform Infrared spectroscopy and x-ray Photoelectron Spectroscopy) and morphological (Field emission scanning electron microscope, Transmission electron microscopy) characterization conform the β-MnO2 nanostructure with a rod-like morphology and uniform thickness. The morphological variations of the nanorod thickness can be easily controlled by simply monitoring the reaction temperature. Comparative investigations of β-MnO2 samples synthesized at two different reaction temperatures (viz. 100 °C and 120 °C) used as a supercapacitive electrode material have been performed with the aid of different electrochemical techniques. With different electrolytes (Li2SO4 and Na2SO4), supercapacitor device is tested using Cyclic voltammetry, impedance spectroscopy and galvanostatic charge discharge. Interestingly, the low temperature synthesized β-MnO2 nanorods sample exhibit superior electrochemical performance in 1 mol l−1 Li2SO4 electrolyte in terms of high specific capacitance (462 Fg−1 at10 mVs−1), energy density (9.72 WhKg−1), and outstanding cyclic stability (90.26% over 2000 cycles).

Functional characterization of nano-porous silicate-polymer composite for bovine serum albumin immobilization

Abstract: The paper dwells upon the elaboration of a simple and energy-efficient approach for the “bottom-up” fabrication of porous polymeric film, which possesses unique surface, structural and bulk properties, followed by its comprehensive study through various characterization techniques. The fabricated film is multi-layered methyl silsesquioxane and suitably modified with the help of several treatments making the film compatible for biosensing applications. Film characterization reports the self- organized topography of the film deposited over the substrate and confirms the successful bonding between the polymers. The influence of the concentration of polypropylene glycol, which itself acts as thermally labile dendrimer, is studied by observing its bond formation ensuring polymer mixing by using FTIR. Energy dispersive x-ray analysis has been performed for the confirmation of elements. In addition to this, the nanoporous film is also studied with the help of variable angle spectroscopic ellipsometry for the determination of film porosity and refractive index. In this analysis, Cauchy model and graded-index model were chosen for data analysis and the Bruggeman effective medium approximation method was used for evaluating the optical constant. The surface of the porous film has been treated with different silane surfaces, characterized with the help of FTIR, UV-VIS, and AFM and envisioned for protein immobilization.

Facile synthesis of CuO nanobricks for high combustion characteristics with nanoaluminum and catalytic thermal decomposition of lithium perchlorate

Abstract: Reactive metal/metal-oxide based nanoenergetic materials find tremendous applications in propellants, explosives, and pyrotechnics. This paper reports on the synthesis of CuO nanobricks (CuOnb) usi...