Browsing by Author "Sunil 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.
Dry Sliding Wear Behavior of Chemically Treated Sisal Fiber Reinforced Epoxy Composites
(Taylor and Francis Ltd., 2022) Sudhakar Behera; Rakesh Kumar Gautam; Sunil Mohan; Arghya Chattopadhyay
The effect of fiber surface treatment on the structural, thermal, and tribological properties of sisal fibers and their epoxy composites were investigated in this research work. Sisal fibers were modified with alkali (NaOH), glutamic acid, and a combination of both alkali and glutamic acid. To analyze the effect of chemical modification on the properties of sisal fibers, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA) were performed. It is observed from the experimental results that there is an improvement in the surface roughness, crystallinity, and thermal stability of chemically treated fibers in comparison to untreated fibers. Microhardness properties of chemically treated sisal fiber reinforced epoxy composites (SFREC) also showed minor improvement. The dry sliding wear experiments were carried out according to Taguchi design of experiment (DOE) methods. The results of the wear test showed an increase in the wear resistance of chemically modified SFREC relative to untreated SFREC. The best wear properties were demonstrated by alkali treated SFREC. It is also observed from the findings of ANOVA that the applied load and sliding distance have the most defining effect on wear volume loss of SFREC. © 2021 Taylor & Francis.
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.
Hemp fiber surface modification: Its effect on mechanical and tribological properties of hemp fiber reinforced epoxy composites
(John Wiley and Sons Inc, 2021) Sudhakar Behera; Rakesh Kumar Gautam; Sunil Mohan; Arghya Chattopadhyay
In this research work, the effects of sodium carbonate and hydrogen peroxide treatment of hemp fiber on the water absorption, mechanical, and tribological properties of hemp fiber reinforced epoxy composites (HFREC) were investigated. The change in surface roughness and fiber size after chemical treatment was confirmed by the scanning electron microscopy (SEM) images. Fourier transform infrared analysis confirmed the removal of hemicellulose and lignin content of the fiber after both the chemical treatment. X-ray diffraction analysis showed an increase in the crystallinity index of the chemically treated fiber. The experimental results also revealed that both sodium carbonate and peroxide modification have resulted in enhancement of water resistance and mechanical properties such as tensile strength and tensile modulus and reduction in impact properties of treated HFREC. Tribological test results revealed that the treated HFREC have improved wear and frictional properties in comparison with untreated HFREC. The best tribological and mechanical properties were exhibited by peroxide treated HFREC, which was also confirmed through the SEM images of worn and fractured surfaces of the composites. © 2021 Society of Plastics Engineers.
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.
In-situ development of ZrB2 particles and their effect on microstructure and mechanical properties of AA5052 metal-matrix composites
(Elsevier Ltd, 2015) Narendra Kumar; Rakesh Kumar Gautam; Sunil Mohan
AA5052/ZrB2 composites with different volume percent (i.e. 0, 3, 6, 9 and 10vol.%) ZrB2 particles were developed by in-situ reaction of molten AA5052 alloy with two inorganic salts K2ZrF6 and KBF4 at a temperature of 860°C. The in-situ composites were characterized by DTA, XRD, SEM, TEM for reaction analysis and morphology. Their mechanical properties like hardness and tensile properties were evaluated using standard methods. Morphology studies show that grain size of Al-rich phase reduces due to the presence of ZrB2 particles. Microstructural studies also reveal the uniform distribution of second phase particles, clear interface, good bonding, dislocations and morphology of ZrB2 particles. It is found that ZrB2 particles are mostly in nano size with hexagonal or rectangular shape, however, few particles in micron size are also observed. Density and hardness of the composites increases with increase in the amount of reinforcement. Ultimate tensile strength and 0.2% yield strength (YS) also improved continuously with increase in the volume fraction of ZrB2 particles up to 9vol.% but beyond this composition strength reduced. It is important to note that with dispersion of ZrB2 particles in base alloy an improvement in ductility is observed which is contrary to many other composites. © 2015 Elsevier Ltd.
Mechanical and tribological properties of chemically modified jute/epoxy composites
(Taylor and Francis Ltd., 2023) Sudhakar Behera; Rakesh Kumar Gautam; Sunil Mohan; Arghya Chattopadhyay
The purpose of the present work is to assess the effectiveness of low-cost and environmental friendly chemical modification of jute fibres based on the usage of sodium hydroxide (AT), sodium carbonate (ST) and sodium hydrogen carbonate (SHT) on the morphological, water absorption, mechanical and tribological characteristics of jute fibre-reinforced epoxy composites (JFREC). Mechanical properties like tensile strength, tensile modulus and impact strength showed appreciable improvement for the AT JFREC (38.08%, 30.56% and 31.66%), ST JFREC (70.03%, 33.06% and 41.30%) and SHT JFREC (24.69%, 8.88% and 22.61%) when compared to untreated JFREC. The experimental results also confirmed that the improved fibre-matrix adhesion, attained by chemical modification, increased the water absorption resistance and the tribological properties of chemically modified JFREC. Improved mechanical and tribological properties attained by the chemically modified JFREC can be found as a potential application in automotive and packaging industries. © 2023 Institute of Materials, Minerals and Mining Published by Taylor & Francis on behalf of the Institute.
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.
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.