Browsing by Author "Thakare J.G."

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    An assessment for mechanical and microstructure behavior of dissimilar material welded joint between nuclear grade martensitic P91 and austenitic SS304 L steel
    (2019) Thakare J.G.; Pandey C.; Mahapatra M.M.; Mulik R.S.
    The microstructural evolution and mechanical properties of gas tungsten arc welded creep strength enhanced martensitic (CSEM) and austenitic stainless steel (SS) dissimilar welded joint is explored in the as welded (AW) and post weld heat treated (PWHT) conditions. The as received normalized and tempered P91 steel has been welded with SS304 L by preparing a conventional groove and employing a P91 GTAW filler wire. The welded plate is subjected to PWHT at 760 �C for 120 min followed by air cooling. The P91 steel in as received condition exhibited fully martensitic (tempered) structure with lathe morphology and prior austenite grain boundaries while SS304 L have austenitic structure with twins. The heterogeneity (as-welded condition) across the welded joint were produced in terms of microstructure and mechanical properties (hardness, Charpy toughness and tensile strength). The variation in mechanical properties has been minimized after the PWHT. PWHT has observed a drastic influence on mechanical properties and microstructure of weld fusion zone and HAZ of P91 side however, remain unaffected for the SS304 L side HAZ. The strength of the welded joint have been measured 1016 � 2.5 MPa and 906 � 6.5 in as-welded and PWHT condition with joint efficiency of 140 % and 125 %, respectively. � 2019 The Society of Manufacturing Engineers
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    Characterization of slurry-based mullite coating deposited on P91 steel welds
    (2019) Kanwal S.; Thakare J.G.; Pandey C.; Singh I.; Mahapatra M.M.
    Ceramic coatings are widely used as thermal and environment barrier coatings due to their inert properties and capability to withstand high temperature. Ceramic coatings are commonly deposited by air plasma spray process and electron beam physical vapor deposition. In the present work, a cost-effective, slurry-based dip coating technique was developed to deposit mullite-based ceramic coating on the P91 steel substrate. The coating has been characterized by X-ray diffraction technique and scanning electron microscopy. Sintering of coatings was carried out in the temperature range of 900�1000��C. Sintering time was varied between 0.5 and 1�h. Energy dispersive spectroscopy was carried out to study the distribution and diffusion of constituent elements during high-temperature sintering. Potentiodynamic polarization tests and thermo-gravimetric analysis were performed to investigate the corrosion behavior of the coating. The coating sintered at 1000��C was found to be free from cracks and other microdefects. The corrosion rate of coating sintered at 1000��C was found to be 26.06�mpy whereas the uncoated sample showed a higher corrosion rate of 153.7�mpy. � 2018, Australian Ceramic Society.
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    Characterization of weld fusion zone for TIG welded p91 and P92 steels
    (2018) Pandey C.; Mohan Mahapatra M.; Kumar P.; Kumar P.; Thakare J.G.
    The welding of nuclear grade P91 and P92 steel plate of thickness 5.2 mm were performed using the autogenous tungsten inert gas (TIG) welding process. The welded joint of P91 and P92 steel plate were subjected to the varying post weld heat-treatment (PWHT) including the post weld heat treatment (PWHT) and re-austenitizing based tempering (PWNT). A comparative study was performed related to the microstructure evolution in fusion zone (FZ) of both the welded joint using the scanning electron microscope and optical microscope in a different condition of heat treatment. The hardness test of the FZ for both joints was also conducted in a different condition of heat treatment. P92 steel welded joint have observed the higher tendency of the ? ferrite formation that led to the great variation in hardness of the P92 FZ. The homogeneous microstructure (absence of ? ferrite) and acceptable hardness was observed after the PWNT treatment for both the welded joint. � 2018 Polish Academy of Sciences. All Rights Reserved.
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    Effect of carbon nanotubes and aluminum oxide on the properties of a plasma sprayed thermal barrier coating
    (2018) Thakare J.G.; Mulik R.S.; Mahapatra M.M.
    To protect the structural components of a power generating unit from the corrosive environment, thermal spray coatings are applied to the components. In the present work, four different types of thermal barrier coating (TBC) viz. partially stabilised zirconia (8YSZ), zirconia-20% alumina (ZA) composite coating without carbon nanotube (CNT) reinforcement, and ZA with 1% and 3% CNT reinforcement. The coating was deposited on NiCrAlY coated P91 steel using a plasma spraying process. The coating microstructure and phases were characterised using field emission scanning electron microscope (FE-SEM) with energy dispersive spectroscopy (EDS). The phases of the coating were analyzed using X-ray diffraction technique. The effect of CNT reinforcement on the thermal conductivity, porosity, and hardness of the composite coatings was investigated. The protective behavior of the coatings was characterised by potentiodynamic polarization testing and electrochemical impedance measurements. The thermal conductivity of the composite coating was found to be increased with increasing CNT content. Hardness was found to be highest for 3% CNT reinforcement and the thermal conductivity was found to increase with decreasing porosity. The electrochemical measurements indicate that reinforcement of CNT in zirconia alumina composite coating improved its corrosion resistance. � 2017 Elsevier Ltd and Techna Group S.r.l.
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    Effect of grit blasting and thermal spraying on microstructure evolution of P91 weldment
    (2018) Thakare J.G.; Pandey C.; Mulik R.S.; Mahapatra M.M.; Narang H.K.
    In the present work, studies have been carried out on the variations in the microstructure and hardness of P91 base-metal and welded joint. This variations result from the grit blasting and thermal cycle experienced during the thermal spraying process. The microstructural effects have been analyzed in terms of the depth of the deformation zone. Scanning Electron Microscopy and X-ray diffraction were used as characterization techniques. The grit blasting carried out prior to thermal spraying has resulted in the highest change in sub-surface hardness of the heat affected zone (HAZ). However, flame treatment further reduced the subsurface hardness of the heat affected zone. The depth of deformation zone was highest for inter-critical heat affected zone (IC-HAZ). The overall coating process resulted in an increase in subsurface hardness of various regions of HAZ and fusion zone (FZ). The base metal showed a 7% increase in subsurface hardness due to the overall coating process. The IC-HAZ showed maximum variation with 36% increase in subsurface hardness. The coarse grained heat affected zone (CG-HAZ) and FZ did not show any change in subsurface hardness. As a whole, the hardness and microstructure of the welded joint was observed to be more sensitive to the thermal spray coating process as compared to the base metal. � 2018 Polish Academy of Sciences. All Rights Reserved.
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    Hot corrosion behavior of plasma sprayed 8YSZ-alumina- CNT composite coating in Na2SO4�60% V2O5 molten salt environment
    (2018) Thakare J.G.; Mulik R.S.; Mahapatra M.M.; upadhyaya R.
    Hot corrosion (HC) behavior of air plasma sprayed 8% yttria stabilized zirconia (8YSZ) -alumina (YA) composite thermal barrier coating has been evaluated in the present work. Three variants of YA coatings were produced, two by reinforcing 1%, 3% multiwall carbon nanotube (MCNT) and one coating was obtained without any MCNT reinforcement. The creep strength enhanced ferritic P91 steel was used as substrate material for coating. Na2SO4 and V2O5 salts mixed in 2:3 ratio was applied to the coating and subjected to 800 �C for 120 h in an electric furnace. The microstructure and phase characterization of the coating was carried out before and after HC using scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. Energy dispersive spectroscopy (EDS) integrated with the SEM was used for elemental analysis of the coating. The investigation reveals improved isothermal HC behavior of 1% MCNT reinforced coating. The dominating effect of the HC was recognized as depletion of yttria leading to destabilization of 8YSZ. The formation of YVO4 was the corrosion product containing the depleted Y2O3 of YSZ. The 1% and 3% MCNT reinforced coating exhibited monoclinic phase percentage of around 9% and 34% respectively. Nanoindentation was carried out along the cross-section before and after the isothermal HC. The Youngs modulus after HC increased by 46%, 42%, 12.5% and 38% for 8Y, 8YA, 8YA1C and 8YA3C coating, respectively. Weibull modulus of Youngs modulus of bond coats was used to identify the efficiency of top coat in retarding the infiltration of molten salt. The bond coat of 8YA1C coating exhibited lowest modulus value (m = 8.55) indicated non-uniform infiltration of detrimental species. The 1% MCNT reinforced thermal barrier coating (TBC) system was more resistant to degradation than the conventional 8YSZ and YA composite coatings. � 2018 Elsevier Ltd and Techna Group S.r.l.
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    Mechanical property evaluation of carbon nanotubes reinforced plasma sprayed YSZ-alumina composite coating
    (2018) Thakare J.G.; Pandey C.; Mulik R.S.; Mahapatra M.M.
    Yttria (8%) stabilized zirconia (8YSZ)-alumina-carbon nanotube (CNT) composite coatings were deposited using air plasma spray (APS) technique. Three zirconia alumina (ZA) composite coatings, without CNT reinforcement, and with 1%CNT, 3%CNT reinforcement were deposited using identical process parameters (500 A and 66 V). Indentation method was used to characterize mechanical behavior of coatings. The CNT reinforced composite coating showed superior mechanical properties as compared to the conventional 8YSZ coating. The addition of alumina and 1%CNTs increased the Young's modulus by around 25% and 40%, respectively. However, the increase in CNT content decreased the Young's modulus as a result of CNT agglomeration. The hardness, fracture toughness increased with addition of alumina and CNT. The fracture toughness increased from 0.55 � 0.26 MPa m1/2 for 8YSZ to 1.76 � 0.65 MPa m1/2 for 17%alumina-3%CNT reinforcement due to various toughening mechanisms like crack deflection, bridging etc. The maximum displacement of indenter was found to decrease from ~ 176 nm for conventional YSZ coating to ~ 120 nm for 3% CNT reinforced coating. The surface roughness (Ra) was found to be decrease with alumina addition and CNT reinforced coating. The CNT reinforced coating showed surface roughness of around 6 �m. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was used to characterize the coating microstructure and elemental composition respectively. � 2018 Elsevier Ltd and Techna Group S.r.l.
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    Microstructure and mechanical properties of D-Gun sprayed Cr3C2-NiCr coating on P91 steel subjected to long term thermal exposure at 650 �c
    (2019) Thakare J.G.; Pandey C.; Mulik R.S.; Mahapatra M.M.
    Thermally sprayed 75Cr3C2-25NiCr coating is applied on structural components to improve corrosion, oxidation and erosion behaviour at high temperature. In order to understand the microstructural and mechanical behaviour of coating a long term investigation was carried out at 650 �C. The Objective of the present work is to study the effect of long term heat treatment (i.e. 650 �C/ 3000 h) on various characteristics of the detonation gun sprayed 75Cr3C2-25NiCr coating. Hardness and nanoindentation studies were carried out on Cr3C2-NiCr coating after fixed time intervals. The morphological and microstructural features of the coated surface were characterized using scanning electron microscope (SEM). The phases formed during the long term exposure were identified by x-ray diffraction (XRD) technique. The coating showed the presence of various Cr, Ni, based oxides, Fe and Ni based spinels. Vanadium, niobium, and molybdenum showed maximum tendency to diffusion from substrate to the coating. Hardness of the coating reached a maximum value of 870 HV after 2160 h of exposure. The hardness of coating observed an initial drop in hardness due to carbide coarsening which was recovered by precipitation of carbides from the solid solution. � 2019 IOP Publishing Ltd.
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    Study on effect of double austenitization treatment on fracture morphology tensile tested nuclear grade P92 steel
    (2019) Pandey C.; Mahapatra M.M.; Kumar P.; Kumar P.; Saini N.; Thakare J.G.; Kumar S.
    Effect of �conventional normalizing and tempering� (CNT) and �double austenitization based normalizing and tempering� (DNT) process on microstructure characteristic and mechanical behavior was studied forP92 steel. In CNT heat treatment, P92 steel is normalized at 1040 �C/air cool and tempered with 760 �C/2 h/air cool. In DNT heat treatment, initially normalizing was performed at 1040 �C for 1 h followed by water quenching. After that sample was normalized in the temperature range of 950�1150 �C for 1 h and tempered at 760 �C/2 h/air cool (950 �C-DNT1, 1050 �C-DNT2, 1150 �C-DNT3).Grain size for CNT and DNT1 treatment were measured 17 � 7 ?m and 12 � 5 ?m. A DNT treatment resulted in homogeneous microstructure formation that led to improved mechanical properties as compared to CNT treatment. The DN based heat treatment produced complete martensitic microstructure formation by complete dissolution of carbide precipitates. The optimized room temperature condition was obtained for the DNT 1 heat treatment. � 2018 Elsevier Ltd
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    Thermomechanical analysis of tungsten inert gas welding process for predicting temperature distribution and angular distortion
    (2019) Narang H.K.; Pandey C.; Thakare J.G.; Saini N.; Mahapatra M.M.; Jha P.K.
    In present research work, discussions have been made to predict the bead geometries and shape profiles of weldments using statistical regression modeling and fuzzy logic techniques. However, the regression and fuzzy logic modeling techniques do not take into account the actual physical properties and phenomena that occur in welding. Moreover, techniques such as regression and fuzzy logic modeling are not suitable for predicting the transient temperature distribution and distortion of arc welded joints. To predict the transient temperature distributions, peak temperature distribution, and residual deformation in welding, deterministic modeling techniques such as thermomechanical analysis are preferred. However, while performing thermomechanical analysis of welded joints, size and reinforcement dimensions of the weld bead need to be incorporated into the model for accurate prediction of transient temperature distributions and distortions. In this work, circularly spread moving heat source has been used for transient thermal modeling of tungsten inert gas (TIG) welding process. In the subsequent sections of this article, the weld thermomechanical analyses for TIG square butt joints are discussed to predict the temperature distributions and angular distortion. The weld dimensions such as weld width, weld depression, and weld bulging have shown great influence on the angular distortion patterns. � 2019 Society of Naval Architects and Marine Engineers. All rights reserved.