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    Effect of reversion heat treatment on the mechanical properties of thermally embrittled UNS S32760 duplex stainless steel
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Natesh, M.; Shamanth, V.; Ravishankar, K.S.
    Duplex Stainless Steels contain very high chromium contents (19-30% by weight) and exhibit excellent corrosion resistance and extremely good mechanical properties. Embrittlement of duplex stainless steels due to precipitation of αʹ upon prolonged exposure in the temperature range of 280°C to 500°C has been a serious limiting factor for its long term usage in the nuclear industry, where the operating temperatures of cooling pipes is around 300°C. In this investigation, the effect of reversion heat treatment on the mechanical properties of a thermally embrittled duplex stainless steel has been studied. The specimens were solutionized, aged and then reversion treated for varying periods. The aged specimens showed significant increase in tensile strength and decrease in ductility in comparison to the ones in solutionized condition. The specimens which were reversion treated showed marginal decrease in tensile strength and significant increase in ductility after 5 minutes of holding time. As the holding time increased, the tensile strength rapidly decreased and ductility increased initially up to 30 minutes of reversion, after which there was no significant change in strength and ductility. © (2015) Trans Tech Publications, Switzerland.
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    Effect of Sigma (σ) phase on Mechanical and Dry sliding wear
    (Elsevier Ltd, 2017) Davanageri, M.; Narendranath, S.; Kadoli, R.
    In this paper, the wear behaviour of heat treated (oil and water quenched) super duplex stainless steel (SDSS) AISI 2507 was studied using dry sliding wear test rig. Initially as received materials was solution treated at 1050°C for duration of 2 h to achieve a balanced austenite (γ) and ferrite (δ) microstructure. The effect of different heat treatment techniques on microstructure and wear behaviour was studied by heat treating specimen at 850°C for duration of 1 h and was followed by oil and water quenching. The microstructure and crystal structure were studied through scanning electron microscope (SEM) and X-ray diffraction. The sliding wear test was employed with variation in load and speed at constant sliding distance. The results reveal that wear rate increased with increase in wear parameters. The oil quenched exhibited better wear resistance than water quenched and solution treated specimen. The worn surface morphology were analysed through SEM micrographs. © 2017 Elsevier Ltd.
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    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.
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    Dry Sliding Wear Behavior of Super Duplex Stainless Steel AISI 2507: A Statistical Approach
    (De Gruyter Open Ltd peter.golla@degruyter.com, 2016) Davanageri, M.; Narendranath, S.; Kadoli, R.
    The dry sliding wear behavior of heat-treated super duplex stainless steel AISI 2507 was examined by taking pin-on-disc type of wear-test rig. Independent parameters, namely applied load, sliding distance, and sliding speed, influence mainly the wear rate of super duplex stainless steel. The said material was heat treated to a temperature of 850°C for 1 hour followed by water quenching. The heat treatment was carried out to precipitate the secondary sigma phase formation. Experiments were conducted to study the influence of independent parameters set at three factor levels using the L27 orthogonal array of the Taguchi experimental design on the wear rate. Statistical significance of both individual and combined factor effects was determined for specific wear rate. Surface plots were drawn to explain the behavior of independent variables on the measured wear rate. Statistically, the models were validated using the analysis of variance test. Multiple non-linear regression equations were derived for wear rate expressed as non-linear functions of independent variables. Further, the prediction accuracy of the developed regression equation was tested with the actual experiments. The independent parameters responsible for the desired minimum wear rate were determined by using the desirability function approach. The worn-out surface characteristics obtained for the minimum wear rate was examined using the scanning electron microscope. The desired smooth surface was obtained for the determined optimal condition by desirability function approach. © 2016 M. Davanageri et al., published by De Gruyter Open 2016.
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    Influence of ageing time on hardness, microstructure and wear behaviour of AISI2507 super duplex stainless steel
    (Institute of Physics Publishing helen.craven@iop.org, 2017) Davanageri, M.; Narendranath, S.; Kadoli, R.
    The effect of ageing time on hardness, microstructure and wear behaviour of super duplex stainless AISI 2507 is examined. The material was solution treated at 1050 °C and water quenched, further the ageing has been carried out at 850 °C for 30 min, 60 min and 90 min. The chromium (Cr) and molybdenum (Mo) enriched intermetallic sigma phase (?) were found to precipitate at the ferrite/ austenite interface and within the ferrite region. The concentration of intermetallic sigma phase (?), which was quantified by a combination of scanning electron microscopy and image analysis, increases with increasing ageing time, leading to significant increase in the hardness. The x-ray diffraction (XRD) and energy dispersive x-ray (EDX) was employed to investigate the element distribution and phase identification. Wear characterstics of the aged super duplex stainless steel were measured by varying normal loads, sliding speeds, sliding distance and compared with solution treated (as-cast) specimens. Scanning electron microscopy was used to assist in analysis of worn out surfaces. The outcomes suggested that the increase in percentage of sigma phase increases hardness and wear resistance in heat-treated specimens compared to solution treated specimens (as-cast). © 2017 IOP Publishing Ltd.
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    Corrosion resistance and in-vitro bioactivity of BaO containing Na2O-CaO-P2O5 phosphate glass-ceramic coating prepared on 316 L, duplex stainless steel 2205 and Ti6Al4V
    (Institute of Physics Publishing helen.craven@iop.org, 2018) Edathazhe, A.B.; Shashikala, H.D.
    The phosphate glass with composition 11Na2O-15BaO-29CaO-45P2O5 was coated on biomedical implant materials such as stainless steel 316 L, duplex stainless steel (DSS) 2205 and Ti6Al4V alloy by thermal enamelling method. The structural properties and composition of glass coated substrates were studied by x-ray diffraction (XRD), Scanning electron microscopy (SEM) and Energy dispersive x-ray spectroscopy (EDS) analysis. The coatings were partially crystalline in nature with porous structure and pore size varied from micro to nanometer range. The polarization curve was obtained for uncoated and coated substrates from electrochemical corrosion test which was conducted at 37 °C in Hank's balanced salt solution (HBSS). The corrosion resistance of 316 L substrate increased after coating, whereas it decreased in case of DSS 2205 and Ti6Al4V. The XRD and SEM/EDS studies indicated the bioactive hydroxyapatite (HAp) layer formation on all the coated surfaces after electrochemical corrosion test, which improved the corrosion resistance. The observed electrochemical corrosion behavior can be explained based on protective HAp layer formation, composition and diffusion of ions on glass coated surfaces. The in-vitro bioactivity test was carried out at 37 °C in HBS solution for 14 days under static conditions for uncoated and coated substrates. pH and ion release rate measurements from the coated samples were conducted to substantiate the electrochemical corrosion test. The lower ion release rates of Na+ and Ca2+ from coated 316 L supported its higher electrochemical corrosion resistance among coated samples. Among the uncoated substrates, DSS showed higher electrochemical corrosion resistance. Amorphous calcium-phosphate (ACP) layer formation on all the coated substrates after in-vitro bioactivity test was confirmed by XRD, SEM/EDS and ion release measurements. The present work is a comparative study of corrosion resistance and bioactivity of glass coated and uncoated biomedical implants such as 316 L, DSS and Ti6Al4V. © 2018 IOP Publishing Ltd.