Department of Mechanical Engineering

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Energies

Palladium-functionalized graphene for hydrogen sensing performance: theoretical studies

Freckle formation during directional solidification of binary alloy is a well-researched subject area. However, the influence of shrinkage induced flow (SIF) on freckling phenomena is barely reported. The focus of this work is to investigate this effect during bottom-up solidification of binary alloys. A fixed grid-based numerical scheme involving volume averaging of conserved parameters is proposed. The solidification geometry under consideration is a two-dimensional mold cavity with a central riser allowing continuous melt flow into the cavity. Model validation is obtained against existing numerical results involving directional solidification of Al-4.1 wt. % Cu alloy. However, heavier solute (Cu) rejection in the melt during solidification renders the validation case study devoid of freckling phenomena. The postvalidation investigations involve bottom up solidification of Al-30 wt. % Mg alloy with lighter solute (Mg) rejection, leading to solutal instability and freckle formation. The effect of SIF on solutal instability, channel formation, and overall macro-segregation is investigated. The intensity of SIF hinges on both cooling condition and opening size. The penetration depth of SIF into the solidification domain gives rise to either early or late onset of solutal instability. SIF penetration depth till the melt domain adjacent to the mushy layer promotes early onset of solutal instability. However, SIF penetration into the mushy layer itself triggers redistribution of solute-rich melt inside this layer, leading to delayed onset of solutal instability. Since the macro-segregation is a direct consequence of advection of solute inside and adjacent to the mushy region, the influence of SIF is manifested by unprecedented macro-segregation pattern. © 2021 Author(s).

Fulltext

Physics of Fluids

Binary alloy solidification and freckle formation: Effect of shrinkage induced flow on solutal instability and macro-segregation

Machined components deviate in size, form, and orientation in comparison to actual features realized by the designer. The deviations originate from several process-related factors and can be specified as per the Geometric Dimensioning and Tolerancing standards (ASME Y14.5-2009 or ISO 1101:2017). According to these standards, the deviation of planar or flat components is expressed in the form of flatness error. This article presents an overall framework to estimate static deflection–induced flatness errors during end milling of thin-walled planar components. The framework incorporates the Mechanistic force model, finite element analysis–based workpiece deflection model, and particle swarm optimization–based algorithm to estimate flatness-related parameters. The individual elements of the proposed framework are implemented in the form of computational tools, and a set of experiments are conducted on thin-walled parts. It has been observed that the static deflections of the thin-walled component have considerable influence on flatness error, and the same can be captured effectively using the proposed framework. The study also investigates the effect of inevitable aspects of the thin-walled machining, such as workpiece rigidity and thinning on the flatness error. The findings of the present study aid process planners in devising appropriate machining strategies to manufacture thin-walled components within tolerances specified by the designer. © IMechE 2020.

Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture

Modeling of flatness errors in end milling of thin-walled components

We have demonstrated a highly sensitive novel platform for real-time detection of Mercury (Hg2+) ions after successfully making silver nanowires (AgNWs)-MoS2 nanocomposite and functionalizing it over ungated AlGaN/GaN high electron mobility transistor (HEMT). The AlGaN/GaN HEMT structures were grown over the sapphire substrate using Molecular Beam Epitaxy. AgNWs-MoS2 nanocomposites were optimized for the device functionalization and 1:4 ratio was found highly sensitive for Hg2+ ions. The sensor exhibits high sensitivity towards Hg2+ ions of 1.604 mA/ppb and calculated its Limit of Detection (LoD) up to the range of 20 ppt. The observed sensitivity is highest among previously reported AlGaN/GaN fabricated HEMT based sensors for Mercury (Hg2+) ions detection and is well below the standard permissible limits as set by World Health Organization (WHO) and Environmental Protection Agency (EPA). The enhancement in sensitivity is due to the enhanced surface to volume ratio of AgNW-MoS2 nanocomposite and the highly conductive nature of silver nanowires incorporated in MoS2. Moreover, we also performed sensing on real water samples of tap water and lake water. Further, we showed the smart sensing capability of our developed sensor by illustrating the Internet of Things (IoT) enabled system for next-generation heavy metal ion sensing. IEEE

Department of Electrical Engineering

IEEE Internet of Things Journal

Mercury (II) Ion Detection using AgNWs-MoS2 Nanocomposite on GaN HEMT for IoT Enabled Smart Water Quality Analysis

This review article presents an overview of the dissimilar welded joint's microstructure and mechanical behavior. Dissimilar metal weldings are generally employed in high-pressure tubing/tubing-coupler assembly generally functional in subsea oil-gas production instruments and a wide range of geothermal plants and piping systems for subsea manifolds. Thus, dissimilar metal welding has an essential role in enhancing the subsea oil-gas drilling system's structural integrity. Dual-phase super duplex stainless steel 2507 (super DSS 2507) comprises a balanced phase of austenite and ferrite, establishing great attention of manufacturers and researchers due to its mechanical strength and corrosion resistance properties in several hostile surroundings like marine, offshore, petrochemical, and nuclear power plant. The other most frequently used material in the marine application is nitronic steel (N50), primarily used in subsea oil and gas developments in tube and couplers for its corrosion resistance, high strength, and resistance to galling. Nickel-based superalloy Inconel 625 has significant application in the aviation, petrochemical, and marine industry due to its high tensile, yield, and creep strength with excellent corrosion properties in an unfavorable environment. The dissimilar joining of these materials is repeatedly required in marine and offshore industries. This review focuses on the significant difficulties related to the dissimilar welding of super DSS 2507 with nitronic steel (N50) and Inconel 625. Unlike chemical composition, metallurgical properties, mechanical and physical properties of these steel and nickel alloys lead to the problem like stress corrosion cracking, hydrogen embrittlement, ductility dip cracking and migration of carbon. The other metallurgical problems are deleterious secondary phase formation, carbon diffusion-related problem, δ-ferrite phase present in the fusion zone, and residual stresses are required to be removed or decrease their intensity for the qualification of the weld. The effect of intermetallic phases such as sigma phase, FCC carbides like (M23C6, M6C, and M7C3), laves phase, R and χ-phase, Z-phase on the mechanical property of dissimilar welded joints of each material are reviewed in detail. After the extensive literature review, proper selection of filler metal has also been covered in this article because it plays an essential role in decreasing some of the dissimilar welded joint problems. Heterogeneity across the weldment, unmixed zone formation including peninsula, island, beaches, and filler deficient region, grain boundaries related problems during the dissimilar welded joint of these materials is also discussed thoroughly in this article. The effect of residual stresses in the dissimilar welded joint's distinct condition has also been discussed in detail. © 2021 Elsevier Ltd

International Journal of Pressure Vessels and Piping

Dissimilar welding of duplex stainless steel with Ni alloys: A review

This article investigates the hot corrosion behavior of P22/P91 dissimilar welds used in power plant applications. The hot corrosion behavior of P22/P91 dissimilar welds was observed under the exposure of molten salts Na2SO4 + 60% V2O5 (SM1) and Na2SO4 + 50% NaCl (SM2) at the temperature of 650°C and 750°C. The welds were fabricated by shielded metal arc welding (SMAW) process using the laboratory developed electrode. This study is an attempt to develop welding electrodes which provide better mechanical and hot corrosion properties as compared to the commercially available electrodes for joining P22/P91 alloys. Thermogravimetric analysis was used to study the oxidation kinetics. XRD, SEM/EDS characterization has been performed to analyze the oxide scale morphology. Results obtained indicate that the welds exposed to SM2 gain more weight as compared to that of SM1. A significant gain in weight was observed with an increase in the exposure temperature. Dissimilar welds fabricated using laboratory-made electrodes (CM1, CM2) show enhanced corrosion resistance in all the exposed environments. © IMechE 2020.

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

High temperature molten salt corrosion investigations on P22/P91 power plant dissimilar welds

This research investigates the effect of CaO–CaF2–SiO2–Al2O3 based flux coating constituents of nickel-based electrodes on the weld chemistry of power plant applications. Extreme vertices design approach was used to prepare electrode coatings and extruded on FM-182 (Nickel based) core wire. TiO2 is added in a fixed amount to enhance the arc stability during welding and slag detachability. Weld beads were deposited on P22 alloy steel plate and examined for weld chemistry in terms of Cr, Ni, Nb and Fe. The microhardness of the deposited welds was also observed using Vicker's microhardness tester. Regression analysis was applied to develop a relationship between the weld chemistry and flux constituents. The results obtained from the regression analysis were then optimized to choose the best suitable electrode coating composition with higher desirability. © 2021 Elsevier Ltd and Techna Group S.r.l.

Ceramics International

CaO–CaF2–SiO2–Al2O3 system for development of SMAW electrodes with Ni alloy core wire

Materials

Study on microstructural characterization, mechanical properties and residual stress of gtaw dissimilar joints of p91 and p22 steels

The dissimilar welding of nuclear grade P91 and P92 steel was carried out using the shielded metal arc welding (SMAW) process. The dissimilar welded joint (DWJ) was subjected to mechanical and metallographic testing for as welded and post-weld heat treatment (PWHT) conditions. The SMAW joint was produced using the different filler composition (P91 filler and P92 filler). For the mechanical behavior of the DWJ, room temperature tensile tests, and Charpy toughness test was conducted for as welded and PWHT state. PWHT of the DWJ contributed a good amount of the ductility of the welded joint. The W and Mo-enriched P92 filler showed a higher tendency to unwanted δ ferrite phase formation as compared to the P91 filler. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Lecture Notes in Mechanical Engineering

Filler Composition Effect on the Mechanical Behavior of the Dissimilar Welds Joint

The work described the effect of the grain refinement in virgin P92 steel plate on the microstructural and mechanical behavior of the P92 welded joint. The as-received P92 steel plate was subjected to varying heat-treatment, i.e., conventional heat treatment (CNT) and double normalized heat treatment (DNT) to refine the grain structure. The DNT is mainly done for the grain refinement in the as-received P92 steel plate. The autogenous gas tungsten arc welding (GTAW) process was utilized to prepare the P92 steel welds joint. Four set of the welds joint were prepared, two by using the CNT plate, termed as AW1 and two by using the DNT plate, termed as AW2. The welded plate has been subjected to heat treatment at 760 °C for 3 h (T1, T2) for both the conditions to stabilize the microstructure of weldments, i.e., tempering of the fresh martensite. The grain growth, particle size, and particle distribution in P92 weldments have been studied. For mechanical characterization, tensile tests, hardness tests and Charpy toughness tests (CTT) have been carried out. Soft δ ferrite formation was observed in weld fusion zone (WFZ) and coarse-grained heat-affected zone (CGHAZ) for AW and T condition and formation is attributed to high heat input and presence of the ferrite stabilizer like W and Mo. Heterogeny in microstructure and mechanical properties was measured across the weldments for AW condition and get minimized as a result of the PWHT. The average hardness for WFZ was measured 363 and 358 HV for AW1 and AW2 conditions, respectively. The difference in the hardness of WFZ can be neglect. The peak hardness of CGHAZ was measured at 358 and 397 HV for AW1 and AW2, respectively and it is attributed to the solid solution strengthening mechanism. The variation in hardness along the welded joint was reduced to a minimum level as a result of the heat treatment. The AW 2 welds joint showed maximum tensile strength of 943 MPa and get reduced drastically after the heat-treatment (T2) (700 MPa) but still showed a higher value as compared to T1 (602 MPa). A significant improvement in tensile strength without any loss in ductility was obtained for the welds joint prepared using the DNT plate as compared to CNT plate. © 2021 Elsevier Ltd