Browsing by Author "Anita Mohan"

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A Study on Mechanical Properties and Strengthening echanisms of AA5052/ZrB2 in Situ Composites
(American Society of Mechanical Engineers (ASME), 2017) Narendra Kumar; Gaurav Gautam; Rakesh Kumar Gautam; Anita Mohan; Sunil Mohan
In the present study, in situ reaction technique has been employed to prepare AA5052 matrix composites reinforced with different vol. % of ZrB2 particles (i.e., 0, 4.5, and 9 vol. %). Composites have been characterized by X-ray diffraction (XRD) to confirm the in situ formation of ZrB2 particles in the matrix. Optical Microscopy (OM) studies reveal the refinement of aluminum-rich phase due to the presence of ZrB2 particles. Scanning electron microscopy (SEM) studies reveal size and distribution of ZrB2 particles while transmission electron microscopy (TEM) reveals the presence of dislocations in the matrix around ZrB2 particles. Hardness and tensile testing of composites have been carried out at room temperature to evaluate the mechanical properties. The results reveal the improvement in hardness and strength with increased amount of ZrB2 particles. Strength of AA5052/ZrB2 in situ composites has been analyzed by various strengthening mechanism models. The analysis revealed that Orowan and Solid solution strengthening mechanisms are the predominant mechanism for high strength composites. Theoretical yield strength is about 6-10% higher than the experimental values due to clustering tendency of ZrB2 particles. © Copyright VC 2017 by ASME.
Effect of Primary Silicon Refinement on Mechanical and Wear Properties of a Hypereutectic Al-Si Alloy
(Springer Netherlands, 2018) Khushubo Tiwari; Gaurav Gautam; Narendra Kumar; Anita Mohan; Sunil Mohan
This study explores the effect of primary silicon refinement of hypereutectic Al-Si alloy on the mechanical and wear properties. Refinement has been carried out by purging N2 into hypereutectic Al-Si alloy melt for different period of time. Hypereutectic Al-Si alloy with 16.2 wt.% of Si was taken for the study and purged by N2 gas for different time. Hypereutectic alloy under different conditions was characterised for various properties. X-ray diffractometer (XRD) analysis doesn’t show formation of any nitride but optical microscopy (OM) and scanning-electron microscopy (SEM) results show modified/refined morphology of silicon. Mechanical and dry sliding wear properties were evaluated at ambient temperature and results reveal improvement in these properties. Worn surfaces were also studied under SEM and 3D-profilometer for surface analysis. Results indicate that at low load/sliding velocity, wear is oxidative/mild in nature, whereas, oxidative-metallic/severe wear is observed at high load/sliding velocity. © 2018, Springer Science+Business Media B.V., part of Springer Nature.
Energy Efficient Composite Materials
(Elsevier, 2020) Anita Mohan
After a brief background of the materials/metals/alloys, this article deals with the working of certain tribological parts of automobiles, their working environment and typical property requirement for a specific application. This articles also deals with the conventional material used, their deficiencies according to modern age requirements and composites as alternative energy efficient material. © 2020 Elsevier Inc. All rights reserved
Enhancement of Multiferroic and Optical Properties in BiFeO3 Due to Different Exchange Interactions Between Transition and Rare Earth Ions
(John Wiley and Sons Inc, 2023) Seema Kumari; Khyati Anand; Mohd Alam; Labanya Ghosh; Srishti Dixit; Rahul Singh; Anil Kumar Jain; Seikh Mohammad Yusuf; Chetna Gautam; Anup K Ghosh; Anita Mohan; Sandip Chatterjee
An experimental analysis of the Bi0.90Tb0.1Fe0.90Mn0.1O3 system synthesized via the solid-state method is presented in this report. UV–visible measurements are carried out and a smaller bandgap (i.e., semiconductor-type behavior) is obtained. The structural phase of the present system is analyzed with X-ray diffraction and neutron diffraction measurement. Structural-phase analysis reveals that the system contains two nuclear phases (rhombohedral structure [R3c space group] with orthorhombic [Pn21a space group]). Moreover, also more bending in the bond angle is found, and the existence of a magnetic phase with a nuclear phase for the Bi0.90Tb0.1Fe0.90Mn0.1O3 system is also confirmed by neutron diffraction. The magnetic moment versus temperature (M–T) curve demonstrates that the system's Néel transition temperature is at 568 K. The magnetization data show enhancement in the magnetic property by displaying the weak ferromagnetic-type behavior at room temperature in the magnetic field versus magnetic moment (M–H) curve as compared to the parent compound. From dielectric measurement, the dielectric constant increases while the loss decreases. © 2023 Wiley-VCH GmbH.
High-Temperature Tribology of AA5052/ZrB2 PAMCs
(American Society of Mechanical Engineers (ASME), 2017) Narendra Kumar; Gaurav Gautam; Rakesh Kumar Gautam; Anita Mohan; Sunil Mohan
AA5052/ZrB2 particulate aluminum matrix composites (PAMCs) have been produced by in situ reaction of K2ZrF6 and KBF4 compounds with molten alloy at about 860 °C. Dry sliding wear and friction of composites have been investigated for a particular sliding velocity and sliding distance at different loads from ambient temperature to 200 °C. It is revealed that for a particular load and temperature, wear rate and normalized wear rate decrease with increase in the volume percentage of ZrB2 particles whereas coefficient of friction (COF) shows a reverse trend. Wear rate and COF also increase with increase in temperature for a constant load and composition. Whereas with load for a particular temperature, wear rate and wear rate per unit vol. % ZrB2 increase while COF decreases. Worn surface and wear debris morphology examined under scanning electron microscopy (SEM) and profilometer to understand the wear mechanism revealed that wear mode transition takes place from mild-oxidative to severe-metallic at 100°C for unreinforced alloy, whereas a shifting is observed in transition temperature from 100 to 150°C for composite with 9 vol. % ZrB2 particles. Energy dispersive spectroscopy (EDS) analysis of worn surface confirms the oxidative wear mode. Profilometry results indicate that wear surface has higher surface roughness at higher values of load and temperatures. Prior to wear and friction studies, composites were also characterized by X-ray diffraction (XRD) and SEM for morphology and microstructural characteristics to correlate with wear results. The findings are very helpful to make the AA5052/ZrB2 composites suitable for the applications, where high-temperature wear is a limiting factor. Copyright © 2017 by ASME.
Line diagnostics for Ne V and Mg V solar ions
(Kluwer Academic Publishers, 1995) B.N. Dwivedi; Anita Mohan
Spectroscopic diagnostics for the Ne v and Mg v solar ions have been investigated. The theoretical forbidden line ratios from these ions are presented for estimating the Ne/Mg variation in different solar structures. Calculations for density and temperature line diagnostics of these ions are given for the several spectral line ratios and their applications are discussed with the help of available solar observations in space. Future observations from the CDS and the SUMER experiments aboard the SOHO satellite are also discussed. © 1995 Kluwer Academic Publishers.
Spontaneous exchange bias and large dielectric constant in Bi0.8Tb0.2Fe0.8Mn0.2O3multiferroic
(American Institute of Physics Inc., 2022) Seema Kumari; Khyati Anand; Mohd Alam; Labanya Ghosh; Swayangsiddha Ghosh; Prince Gupta; Rahul Singh; A.K. Jain; S.M. Yusuf; Anup K. Ghosh; Anita Mohan; Sandip Chatterjee
The structural, dielectric, and magnetic properties of Bi0.8Tb0.2Fe0.8Mn0.2O3 have been studied in detail. A structural shift from rhombohedral (space group R3c) to orthorhombic (space group Pn21a + Pnma) phase is observed with doping. The substitution of Mn and Tb gives a very large value of the dielectric constant. It has been demonstrated that the observed spontaneous exchange bias is larger than the conventional exchange bias at room temperature. Moreover, doping reduces the Neel temperature from 643 to 521 K and magnetization increases. Thermoremanent magnetization studies at room temperature show that the system is composed of an interfacial layer of an antiferromagnetic core and a two-dimensional diluted antiferromagnet shell with a net magnetization under the field. Furthermore, the system's reasonable HEB and HC values at room temperature make it intriguing and appealing for a variety of multifunctional devices. © 2022 Author(s).
Synthesis and statistical modelling of dry sliding wear of Al 8011/6 vol.% AlB2 in situ composite
(Institute of Physics Publishing, 2017) Narendra Kumar; Sandeep Kumar Singh; Gaurav Gautam; Aditya Kumar Padap; Anita Mohan; Sunil Mohan
The present study has used response surface methodology (RSM) and central composite design (CCD) for modelling, using wear parameters to predict the wear performance of an Al 8011/6.0 vol.% AlB2 composite. The effect of applied load and sliding velocity was studied at five levels for a fixed sliding distance. To understand wear behaviour, sliding wear tests were planned according to CCD and performed on a pin-on-disc apparatus at ambient temperature. An analysis of variance (ANOVA) was conducted to show the relative significance of the parameters. A second-order regression model was developed to predict the wear loss and to establish the relationships between wear parameters. Response surface and contour plots were drawn to analyse the wear results. Worn surfaces were examined under scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) was used to interpret the operative wear mechanisms. Validation tests results show good agreement between experimental and predicted data. As an initial step of this study, AlB2 particles were reinforced in Al 8011 alloy by an in situ technique to synthesise an Al 8011/6.0 vol.% AlB2 composite. During synthesis an in situ reaction takes place between molten alloy and inorganic salt KBF4 at 850 °C, which leads to the formation of AlB2 particles. The composite was analysed by x-ray diffractometer (XRD) to detect the phases present, while optical and scanning electron microscopy (OM & SEM) were carried out to ascertain morphology and particle distribution. Hardness was evaluated by a Vickers hardness testing machine. © 2017 IOP Publishing Ltd.
Synthesis and tribological properties of AA5052-base insitu composites
(Taylor and Francis Ltd., 2016) Anita Mohan; Gaurav Gautam; Narendra Kumar; Sunil Mohan; R.K.C. Gautam
It is important to optimize the properties of a material for a particular application, hence, to find the suitable material for tribological applications, the wear and friction behaviour of AA5052 in situ composites with different kind of reinforcements have been investigated. For present study, three in situ formed composites have been produced with different reinforcements namely Al3Zr, ZrB2 and combination of both (Al3Zr + ZrB2) by direct melt reaction (DMR) technique. The as-cast composites and base alloy have been characterized by X-ray diffraction (XRD), optical microscopy, electron microscopy, tensile testing, hardness and dry sliding wear and friction tests. XRD results indicate the successful formation of second phase reinforcement particles in all composites. Wear test results indicate that the cumulative volume loss increases with an increase in sliding distance while coefficient of friction shows a fluctuating tendency, whereas with increasing applied load, wear rate shows an increasing trend while coefficient of friction shows decreasing trend. The variation of wear rate with composites indicates that the composite with multiple reinforcement (Al3Zr + ZrB2) has lowest wear rate among all as-cast composites and base alloy, while coefficient of friction is higher. The responsible mechanisms concerned with wear and friction results have been discussed in detail with the help of the observation on worn surface analysis by scanning electron microscope (SEM) and 3D-profilometer. All tribological results have been correlated with the microstructural properties, strength parameters and bulk hardness of the composites. © 2016 Informa UK Limited, trading as Taylor & Francis Group.
Theoretical Ne VI/Mg VI line diagnostics for SUMER
(Kluwer Academic Publishers, 1995) B.N. Dwivedi; Anita Mohan
Theoretical Ne vi/Mg vi EUV line emissivity ratios, suitable for density-measurements in various solar features such as active regions, sunspots, umbrae and flare plasmas and to be observed in the SUMER spectral range, are presented and their applications discussed with the help of available observational data. © 1995 Kluwer Academic Publishers.
ZrB2 nanoparticles transmuting tribological properties of Al3Zr/AA5052 composite
(Springer Verlag, 2019) Gaurav Gautam; Narendra Kumar; Anita Mohan; Sunil Mohan; Devendra Singh
Good work hardenability, moderate to high strength of AA5052 alloy and high melting point and elastic modulus of Al3Zr with limited wear resistance have been the driving force to transmute Al3Zr/AA5052 composite by generations of ZrB2 nanoparticles. For this purpose, the varying amounts of ZrB2 particles in Al3Zr/AA5052 composite have been produced by direct melt reaction in situ technique. The phase identification, microstructural studies and wear testing have been performed for all the composites. The phase identification and microstructural studies indicate that the ZrB2 particles are formed successfully in the Al3Zr/AA5052Al composite with hexagonal and rectangular morphology within a size range of 10–190 nm. Wear testing results show that friction coefficient (COF) fluctuates with sliding distance, whereas it decreases with normal load. For the composite without ZrB2, the COF is exhibited increasing trend with sliding velocity, while for the hybrid composites initially it decreases, but beyond 2 m/s sliding velocities it starts increasing. Wear studies also show that with ZrB2 generation in Al3Zr/AA5052 composites can be used up to larger loads and higher sliding velocities while being in mild wear regime. It is observed that the mild wear regime extends and COF increases with the increase in vol% of ZrB2 particles. Texture analysis of worn surfaces is in agreement with the results. The present investigation shows that in situ (ZrB2 + Al3Zr)/AA5052 hybrid composites could be a promising material in the applications requiring high wear resistance and high COF such as braking system. © 2019, The Brazilian Society of Mechanical Sciences and Engineering.