Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
5 results
Search Results
Item Microstructural characterization of low temperature plasma-nitrided 316L stainless steel surface with prior severe shot peening(Elsevier Ltd, 2016) Jayalakshmi, M.; Huilgol, P.; Badekai Ramachandra, B.R.; Bhat, K.U.Surface nanocrystallization by severe deformation has proven beneficial as pre-treatment to plasma nitriding. It aids in achieving thicker nitride layers at lower temperatures thus making the process more economical. In austenitic stainless steels, severe deformation leads to formation of strain induced martensite on the surface while plasma nitriding alone forms expanded austenite. However, structural characteristics of surface layer of pre-deformed steel after plasma nitriding is still a matter of debate. In present study, 316L stainless steel was subjected to severe shot peening: followed by plasma nitriding at 400 °C for 4 h. Characteristics of sample surface before and after treatment were analyzed by scanning electron microscopy, X-ray diffractometry and transmission electron microscopy techniques. Results showed that, this duplex treatment leads to formation of about 45 ?m thick nitride layer; without CrN precipitation. This is significantly high compared to reported data considering the temperature and duration of nitriding treatment employed. Selected area electron diffraction pattern from topmost surface confirmed the co-existence of austenite and martensite while subsurface layer was predominantly consisting of lath martensite. This indicates that major phase in the nitrided layer is martensitic in nature and nitrogen supersaturation leads to transformation of small fraction of martensite to expanded austenite. © 2016 Elsevier LtdItem Photoluminescence Quenching in Metal Ion (Cu2+, Co2+) Interacted Graphene Quantum Dots(Wiley-VCH Verlag info@wiley-vch.de, 2017) Mishra, P.; Badekai Ramachandra, B.R.Graphene quantum dots (GQD) are nanosized fragments of graphene with finite band gap. Thus, GQDs show excellent photoluminescence (PL) and also possess good electrochemical properties. In the present study, we synthesized GQDs via hydrothermal (HT) method using Graphene oxide as prepared from improved Hummer's method as a precursor with several modifications. The effect of the variation in the photoluminescence and electrochemical properties of the as-prepared GQDs were studied. Average particle size of the as-synthesized GQDs was roughly 30 nm and produced blue PL on excitation with a wavelength of 365 nm. On reacting the GQDs with Cupric Nitrate and Cobalt Nitrate in separate batches, a significant decrease in the intensity of PL was observed. This quenching of PL of GQDs has been utilized in the qualitative estimation of Metal ion (Cu2+ and Co2+) species in aqueous media. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Synthesis and characterization of graphene quantum dots and their size reduction using swift heavy ion beam(Taylor and Francis Inc. 325 Chestnut St, Suite 800 Philadelphia PA 19106, 2018) Mishra, P.; Badekai Ramachandra, B.R.Graphene quantum dots (GQDs) are nanosized fragments of graphene displaying quantum confinement effect. They have shown to be prepared from various methods which include ion beam etching of graphene. However, recently the modification of the GQDs has garnered tremendous attention owing to its suitability for various applications. Here, we have studied the effect of swift ion beam irradiation on the properties of GQDs. The ion beam treatment on the GQDs exhibited the change in observed photoluminescence of GQDs as they exhibited a blue luminescence on excitation with longwave UV (?365 nm) due to the reduction in size and removal of the ethoxy (–C–O–C–) groups present on the quantum dots. This was confirmed by transmission electron microscopy, particle size analysis, and Fourier transform infrared spectroscopy. © 2018 Informa UK Limited, trading as Taylor & Francis Group.Item Insights into formation of gradient nanostructured (GNS) layer and deformation induced martensite in AISI 316 stainless steel subjected to severe shot peening(Elsevier B.V., 2018) Jayalakshmi, M.; Huilgol, P.; Badekai Ramachandra, B.R.; Udaya Bhat, K.Severe peening is a well-accepted top-down approach to engender surface nanocrystallization in austenitic stainless steels. In the present study, AISI 316 grade austenitic stainless steel is subjected to severe peening through air blast shot peening technique. Study is aimed at analyzing the microstructural features of the peened layer and deformation induced martensite through transmission electron microscopy technique. Gradient nanostructured (GNS) layer formed as a result of high strain rate, multi-directional deformation during severe peening found to extend to about 500 ?m from the surface. Nucleation of deformation induced martensite is not limited to shear band intersections as affirmed by the published literature related to severe peening. It is observed to nucleate at multiple locations in the austenite matrix. Martensite units thus formed, coalesce with each other to form continuous layer of lath martensite layer at about 15–20 ?m from the surface. Upon further deformation, lath morphology transforms to dislocation cell-type; resulting in fine martensite crystallites at the topmost layer of the peened surface. © 2018 Elsevier B.V.Item Aggregative ways of graphene quantum dots with nitrogen-rich edges for direct emission spectrophotometric estimation of glucose(Elsevier B.V., 2019) Mishra, P.; Badekai Ramachandra, B.R.We report a facile one step in-situ synthesis of amino-functionalized graphene dots. These quantum dots were employed for the detection of glucose in both standard aqueous solutions and commercially available fruit juice to assess its practicability. The characterization of the quantum dots revealed that they were decorated with amine functionality. Additionally, the interaction between glucose and amine functionalized graphene quantum dots gave enhancement in the UV–vis absorption and photoluminescence (PL) due to aggregation of quantum dots via glucose link. Therefore, the quantum dots were able to detect the concentration of glucose in solution exhibiting linearity from 0.1 to 10 mM and 50–500 mM with a sensitivity transition from 10 mM to 50 mM. The limit of detection for the determination of glucose was found to be 10 ?M. This determination was agreed from both UV–Vis absorption and PL spectroscopy. However, the PL emission method of determination was most suited with its very high accuracy of 98.04 ± 1.96% and 97.33 ± 2.67% for the linear range of glucose concentration within 0.1–10 mM and 50–500 mM, respectively. The PL enhancement was highly selective towards glucose in mixture of other form of sugars making it suitable for determining glucose in food samples. © 2019