Faculty Publications
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Item Plasma nitriding of AISI 2205 steel: Effects of surface mechanical attrition treatment and chemical etching(Maney Publishing michael.wagreich@univie.ac.at, 2016) Gatey, A.M.; Hosmani, S.S.; Arya, S.B.; Figueroa, C.A.; Singh, R.P.In the present study, surface mechanical attrition treatment (SMAT) and plasma nitriding were conducted on AISI 2205 steel. SMAT was effective in enhancing the surface hardness of the steel by about 80%. The influence of SMAT on the corrosion behaviour of the steel was studied in a 3.5 wt-% NaCl solution. Due to the stable and thicker passive layer, improved corrosion resistance was observed for the SMATed steel. However, nitrogen diffusion during plasma nitriding was impeded by the improved passivation, especially for the lower duration (30 min) of chemical etching/cleaning (i.e. sputter cleaning in hydrogen plasma) of the specimen's surface. Furthermore, high chemical etching duration (120 min) resulted in improved surface hardness and nitriding kinetics. © 2016 Institute of Materials, Minerals and Mining.Item Role of surface mechanical attrition treatment and chemical etching on plasma nitriding behavior of AISI 304L steel(Elsevier B.V., 2016) Gatey, A.M.; Hosmani, S.S.; Figueroa, C.A.; Arya, S.B.; Singh, R.P.In the present study, the effect of surface mechanical attrition treatment (SMAT) on corrosion resistance and plasma nitriding behavior of AISI 304L stainless steel (SS) was investigated. Mechanical twins and deformation induced martensite phase were observed in the SMAT affected region. SMAT improved the corrosion resistance and nitriding kinetics of AISI 304L SS. Effective nitriding time and hence, the thickness of the nitrided layer were increased with increase in the duration of chemical etching and a decrease in the stability of passive layer on the SMATed specimens. Surface hardness of the nitrided specimens was dependent on the formation of expanded austenite (?N) and its decomposition (especially, at higher effective nitriding time). © 2016 Elsevier B.V.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 Cumulative effect of FexN phases, roughness parameters, and asperity geometry on the anti-wear properties of low-temperature plasma nitrided Ti-Nb stabilized IF steel(Elsevier Ltd, 2025) Sahoo, B.; Bhat, K.U.Plasma-driven surface modification techniques like plasma nitriding (PN) are trending, especially for steel products. It is advantageous due to the higher order of process control and superior quality of property enhancement of the surface. This technique often employs a high processing temperature, which is one of its metallurgical and economical limitations. One of the renowned solutions is the implementation of lower processing temperatures. The current work is based on the low-temperature plasma nitriding of Ti-Nb stabilized interstitial-free steel at different processing temperatures ranging from 400 ºC to 500 ºC. The role of FexN phases, surface roughness parameters, and asperities geometry are thoroughly studied with respect to the anti-wear properties of the surface. The formation of ??-Fe4N and ?-Fe2–3N are detected in the XRD plot, whereas ??-Fe16N2 is confirmed in microscopy. The sample treated at 450 ºC presents the best anti-wear properties compared to other samples, primarily due to the presence of prominent ?-Fe2–3N phase and blunt surface asperities. A maximum reduction in wear volume of about 3 times the base value is recorded in the wear test. The microscopic and elemental analyses are conducted on the wear scars, wear debris, and counter-body worn-out surfaces to study the wear mechanism comprehensively. The work tries to illustrate the wear mechanisms schematically to understand the conceptual grounds associated with such theories. The spectrometric analysis in the depth direction is also performed, and it detects the trace of nitrogen up to about 7 µm depth for 500 ºC nitriding conditions. © 2025Item Synergistic investigation on Fe[sbnd]N phases and gradient microstructure supported anti-indentation and anti-scratch performance of low-temperature plasma ion nitrided Ti[sbnd]Nb stabilized IF steel(Elsevier B.V., 2025) Sahoo, B.; Udaya Bhat, K.Plasma ion nitriding (PIN) is a remarkable surface modification process that utilizes a thermochemical environment to treat the substrate by diffusion-induced phenomena, allowing it to modify complex-shaped objects, especially steel components. However, the foremost shortcoming of PIN is the higher processing cost, which can be minimized by reducing the nitriding temperature. This leads to a prominent variation in the sample's microstructure, often resulting in a gradient microstructure in the depth direction, which can be beneficial for specific industrial applications like scratch resistance, abrasion resistance, etc. The current investigation performs an extensive study to extrapolate the gradient microstructure-induced indentation and scratch resistance of low-temperature PINed (400 °C to 500 °C) interstitial-free steel through microscopy, diffractometry, spectroscopy, microhardness test, indentation test, and scratch test (constant and progressive loading). The transmission electron microscopy and scanning electron microscopy findings suggested a clear trace of gradient microstructure containing various Iron nitride phases (?-Fe2-3N, ?'-Fe4N, and ??-Fe16N2), size and distribution of which affect the scratch resistance. The sample treated at 450 °C shows the best result, with an overall improvement in scratch hardness of 3.2 times the base value. The coefficient of friction, track depth, traction force variation, etc., are also studied and correlated with spectroscopy and microscopy findings. © 2025 Elsevier B.V.