Faculty Publications
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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 Effect of shot peening coverage on surface nanostructuring of 316L stainless steel and its influence on low temperature plasma-nitriding(ASTM International, 2017) Jayalakshmi, M.; Badekai Ramachandra, B.; Bhat, K.U.Air-blast shot peening (ABSP) is a cost effective and industrially viable technique to produce nanostructured surface layer on metallic materials. In the present study, 316L stainless steel samples were subjected to shot peening at different peening coverage, from conventional to severe peening. Nanocrystalline structure was observed on the sample surface after peening and mechanical twins; intersection of multidirectional twins producing rhombic blocks were observed in the subsurface layer. Peening process led to the formation of strain induced martensite (?'), and its fraction was found to increase with the coverage. Depth of nanostructured layer and surface microhardness also increased with the increase in coverage, whereas surface roughness followed an opposite trend. Both peened and un-peened samples were subjected to plasma nitriding at 400°C for 4 h. Uniform and appreciably high case depth of about 45 ?m was observed in severely pre-peened (1000 % coverage) sample after nitriding treatment. No precipitation of CrN was observed. This highlights the marked influence of severe shot peening as a pre-treatment for low temperature plasma nitriding of austenitic stainless steels. © © 2017 by ASTM International.Item Assessment of triboelectricity in colossal-surface-area-lanthanum oxide nanocrystals synthesized via low-temperature hydrothermal process(Springer, 2021) Meti, S.; Hosangadi Prutvi, H.P.; Rahman, M.R.; Bhat, K.U.Triboelectric nanogenerators (TENGs) have marked their applications in various fields, most importantly, in medical devices. The electrical output of the TENGs mainly concentrated on parameters such as electrode separation distance, applied mechanical pressure, surface charge density, and overlapping surface area. The surface area of the active layer in TENGs plays a crucial role. Given this, the present contribution is the first report on the utilization of lanthanum oxide (La2O3) as an active material with a large surface area (~ 72.33 m2/g) in TENGs. The nanocrystals of La2O3 have been successfully embedded into TENGs architecture through a high-quality screen-printed film with a Teflon-counter surface. The in-house test-rig of TENGs resulted in an output open-circuit voltage of 120 V and a short-circuit current of 23.7 ?A. Further, the maximum power density is 7.125 W/m2 at an external load resistance of 30 M?. These results suggest that La2O3 is a suitable contender in various self-powered devices. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.