Jitendra Kumar Sahu

Bio: Jitendra Kumar Sahu is an academic researcher from Council of Scientific and Industrial Research. The author has contributed to research in topics: Superalloy & Creep. The author has an hindex of 12, co-authored 49 publications receiving 533 citations. Previous affiliations of Jitendra Kumar Sahu include Folkwang University of the Arts & Academy of Scientific and Innovative Research.

Effect of 475 ◦ C embrittlement on the mechanical properties of duplex stainless steel

Abstract: The binary iron–chromium alloy embrittles in the temperature range of 280–500 °C limiting its applications to temperatures below 280 °C. The embrittlement is caused by the decomposition of the alloy to chromium-rich phase, α′ and iron-rich phase, α. This phenomenon is termed 475 °C embrittlement as the rate of embrittlement is highest at 475 °C. Primarily the investigations on 475 °C embrittlement were confined to binary iron–chromium alloys and ferritic stainless steels. Duplex stainless steel grades contain varying proportions of ferrite and austenite in the microstructure and the ferritic phase is highly alloyed. Moreover, this grade of steel has several variants depending on the alloy composition and processing route. This modifies the precipitation behaviour and the resulting change in mechanical properties in duplex stainless steels when embrittled at 475 °C as compared to binary iron chromium systems. The precipitation behaviour of duplex stainless steel at 475 °C and the effect on tensile, fracture and fatigue behaviour are reviewed in this article.

Phase transformations and numerical modelling in simulated HAZ of nanostructured P91B steel for high temperature applications

Abstract: This paper critically assesses phase transformations occurring after welding and subsequent post weld heat treatments in simulated sub-heat affected zones (HAZ) of P91B steel. Samples for weld-HAZ simulation were produced corresponding to grain-coarsened HAZ, grain-refined HAZ and inter-critical HAZ. Analyses revealed diverse phase transformation mechanisms (for GCHAZ = pipe-diffusion and for GR/ICHAZ = GB-diffusion) owing to manipulation in grain size and boron-enriched nanosized particles as regards virgin steel after welding. However, after PWHT, same phase transformation mechanism (interface diffusion) in all simulated sub-HAZs is observed. Hardness evaluations and prior austenite grain boundaries dissolution confirm GB embrittlement after welding. Boron segregation, the presence of borides and boron-enriched particles heads to ~ 50% drop in hardness deviations enhancing GB hardening after PWHT. Particle refinement is observed after PWHT which is further validated by numerical modelling. In addition, particle evolution during cooling from peak temperature of weld thermal cycle and isothermal holding of PWHT is analysed. Apparent activation energy of nucleation/growth follows descending order, i.e. GC/GR/ICHAZ for nanosized particles during welding.

Fatigue behavior of a thermal barrier coated superalloy at 800°C

Abstract: Fatigue testing of thermal barrier coated (TBC), bond coated only and bare Superni C263 superalloy was conducted at 800 °C in air. Results reveal that the endurance limits for the TBC and bond coated substrate was substantially higher than that of the base alloy, while the opposite was found for high stress, low cyclic life times. It appears that the increase in endurance limit for the TBC and bond coated superalloy is due to load shifting to the bond coat, and the premature failure for these two materials is possibly due to high stress crack imitation/growth in the TBC/bond coat layers.

Recent advancements in optical DNA biosensors: Exploiting the plasmonic effects of metal nanoparticles

Abstract: The emerging field of plasmonics, the study of electromagnetic responses of metal nanostructures, has revealed many novel signal enhancing phenomena. As applied to the development of label-free optical DNA biosensors, it is now well established that plasmon-based surface enhanced spectroscopies on nanostructured metal surfaces or metal nanoparticles can markedly improve the sensitivity of optical biosensors, with some showing great promise for single molecule detection. In this review, we first summarize the basic concepts of plasmonics in metal nanostructures, as well as the characteristic optical phenomena to which plasmons give rise. We will then describe recent advances in optical DNA biosensing systems enabled by metal nanoparticle-derived plasmonic effects, including the use of surface enhanced Raman scattering (SERS), colorimetric methods, "scanometric" processes, and metal-enhanced fluorescence (MEF).

Materials corrosion for thermal energy storage systems in concentrated solar power plants

Abstract: The current commercial deployment of concentrating solar power (CSP) relies on a system of thermal energy storage (TES) for round the clock generation of electricity. The heat harvested by a system of collectors, either parabolic troughs or a heliostat field, is transferred by means of heat transfer fluid (HTF) to a storage tank, where it is kept until required for power generation. In the implemented systems, the storage of heat is accomplished by a mixture of salts characterized by an optimum set of properties required at the desired temperatures of operation. In liquid phase, the salt mixture represents an ionic conductor providing conditions for electrochemical degradation of materials when in direct contact. The risk of materials failure is further increased by thermal cycling and the possibility of mechanical stress. This paper describes the possible corrosion issues that might affect a TES system considering generalized and localized corrosion, as well as flow accelerated and mechanically assisted corrosion for the specific operation conditions of CSP plants. A comprehensive summary of uniform corrosion rates determined for common and less common alloys considered for application in TES is provided, along with discussion of the applicability for evaluation of possible corrosion damage in an actual CSP plant.

Low temperature embrittlement of duplex stainless steel: Correlation between mechanical and electrochemical behavior

Abstract: The low temperature embrittlement behavior of duplex stainless steel 2205 was investigated on the basis of changes in mechanical and electrochemical properties after aging for 5000 h at 335, 365 and 400 °C. Aging leads to increase in the hardness of δ-ferrite phase. The ferrite hardening was very rapid in the initial stages of aging; thereafter the hardness increase was more gradual at all the aging temperatures. Charpy impact test of the aged samples showed drastic decrease in impact toughness. The value of Charpy impact energy saturated after aging to 5000 h at all the aging temperatures. The embrittlement in the material is known to be caused by spinodal decomposition reaction in which the δ-ferrite decomposes into iron-rich α and chromium-enriched α′. For the purpose of non-destructive evaluation of thermal aging embrittlement, double loop electrochemical potentiokinetic reactivation (DL-EPR) test and anodic polarizations in acetic acid and HCl solution were carried out. The peak current density during the anodic scan in DL-EPR test and the peak anodic current density for secondary passivation during polarization in acetic acid increased with increase in aging time. A good linear correlation was observed between the peak anodic current density for secondary passivation during polarization in acetic acid and the microhardness of δ-ferrite phase.