Department of Metallurgical and Materials Engineering

In this study, we investigated the influence of cold rolling reduction on microstructural evolution and slip behavior in Ta-10W alloy fabricated by vacuum arc melting (VAM). As the reduction increased, both single and multiple slips were observed within some grain interiors. At reductions of 20% and 40%, deformation bands, primarily consisting of γ-fiber components, formed within the grain interiors. The fraction of deformation bands (DBs) increased with higher reduction. Conversely, at 60% reduction, in addition to DBs, experimentally observed shear bands (SBs) with a herringbone pattern were formed. Both DBs and SBs predominantly formed in regions of concentrated strain (areas with high kernel average misorientation (KAM) and geometrically necessary dislocations (GND)). As the reduction increased, the misorientation angle between the matrix and the DBs or SBs gradually increased, while the width of the DBs decreased. To investigate the violation of Schmid’s law in Ta-10W alloy, slip trace and resolved shear stress (RSS) analyses were performed on observed slip lines within deformed grains. Contrary to conventional slips, where slip typically occurs on the plane with the highest RSS, slips in the Ta-10W alloy were confirmed to occur even on planes with lower RSS in certain grains. Hence, this study provides experimental evidence of Schmid’s law violation in Ta-10W alloy. Copyright

This study investigates the effect of filler materials on the structural integrity of dissimilar welded joints (sDSS 2507/IN625) employed in marine subsea manifold applications. Multi-pass gas tungsten arc welding (GTAW) using ER2594 and ERNiCrMo-3 fillers investigates microstructure evolution, solidification mechanisms, mechanical characteristics, residual stresses, and corrosion behavior. Optical and scanning electron microscopy revealed an unmixed zone (peninsula/island-shaped) at the weld interface and weld zone (WZ) in both filler weldments. Segregation of Mo, Nb, and Ni was observed in the interdendritic region of ERNiCrMo-3 filler WZ, whereas the skeletal ferrite matrix of ER2594 filler WZ revealed the existence of the Laves phase (Fe2Nb form). Electron beam scattered diffraction (EBSD) investigation showed austenitic solidification for ERNiCrMo-3 and fully ferritic solidification for ER2594 with distinct dendrite formations. Inhomogeneity has been observed in microhardness maps, with ER2594 and ERNiCrMo-3 WZ averaging 310 ± 7 Hv0.5 and 270 ± 10 Hv0.5, respectively. ERNiCrMo-3 (165 ± 5 J and 180 ± 3 J) and ER2594 (100 ± 3 J and 110 ± 6 J) fillers exhibited distinct effects on toughness in the weld cap and root due to laves phase precipitation. Additionally, ER2594 (750 ± 6 MPa) and ERNiCrMo-3 (790 ± 7 MPa) fillers exhibited lower tensile strength than base metals. The structural integrity of WZ can be better understood by residual stress analysis, which showed compressive cap pass and tensile root pass residual stresses for both fillers. In a 3.5 wt% NaCl solution, both fillers exhibited outstanding corrosion resistance in marine conditions. These findings improve subsea manifold structure integrity and performance in corrosive marine environments.

Lightweight alloys are known to improve the fuel efficiency of the structural components due to high strength-to-weight ratio, however, they lack formability at room temperature. This major limitation of poor formability is most of the time overcome by post-fabrication processing and treatments thereby increasing their cost exponentially. We present a novel Ti50V16Zr16Nb10Al5Mo3 (all in at. %) complex concentrated alloy (Ti-CCA) designed based on the combination of valence electron concentration theory and the high entropy approach. The optimal selection of constituent elements has led to a density of 5.63 gm/cc for Ti-CCA after suction casting (SC). SC Ti-CCA displayed exceptional room temperature strength (UTS ∼ 1.25 GPa) and ductility (ε ∼ 35 %) with a yield strength (YS) of ∼ 1.1 GPa (Specific YS = 191 MPa/gm/cc) without any post-processing treatments. The exceptional YS in Ti-CCA is attributed to hetero grain size microstructure, whereas enormous strength-ductility synergy is due to the concurrent occurrence of slip and deformation band formation in the early stages of deformation followed by prolonged necking event due to delayed void nucleation and growth. The proposed philosophy of Ti-CCA design overcomes the conventional notion of strength-ductility trade-off in such alloy systems by retaining their inherent characteristics.

The technique of micro-exfoliation has gained prominence as a highly effective and adaptable method for exploiting two-dimensional (2D) materials, such as graphene Transition metal dichalcogenides (TMDCs), Borophene, Molybdenum disulfide (MoS2), among others. This paper presents an analysis of optical images and the micro exfoliation technique, focusing on the application to MoS2 and graphene. Additionally, the study investigates the exfoliated sheet of graphene, MoS2, and their hybrid on a (111) crystal plane of silicon wafer. The micro-exfoliation technique employed for MoS2 involves a mechanical process that gently disentangles the layers of MoS2 from the larger crystal structure, resulting in the formation of ultrathin two-dimensional nanosheets. This paper comprehensively analyses the exfoliation processes' mechanisms, emphasizing the intricate relationship between van der Waals forces, interlayer bonding, and external forces. The micro-mechanical exfoliation, a fundamental technique, entails the utilization of adhesive scotch tape to remove monolayers from a large MoS2 crystal delicately. The integration of MoS2 into various applications such as electronics, optoelectronics, sensors, and energy storage devices has been driven by its exceptional properties, including its distinctive electronic, optical, and mechanical characteristics. Furthermore, the ability to adjust the bandgap of MoS2 has created novel opportunities for potential applications in the field of semiconductors. This paper provides a succinct summary of recent studies, that have concentrated on the optical characterization of MoS2 monolayers. Optical and Raman spectroscopy was employed to characterize the 2D sheets of MoS2 and its hybrid materials.

Industrial applications and fundamental scientific research involving the scalable development of high-quality Molybdenum disulfide (MoS2) nanosheets continue to present significant challenges. MoS2 is a material with a two-dimensional (2D) structure consisting of a single layer of molybdenum atoms positioned between two layers of sulfur atoms. The primary type of bonding present within each layer is primarily covalent in nature, characterized by the formation of robust chemical bonds between the atoms of molybdenum and sulfur. Nevertheless, the predominant driving force behind the interactions among the layers of MoS2 is attributed to van der Waals forces. This study utilizes a top-down approach to synthesize MoS2 nanomaterials from their bulk counterpart. This is achieved through the implementation of grinding via liquid exfoliation and ball milling methods. These methods effectively mitigate the influence of weak van der Waals forces that exist between the layers of MoS2, resulting in the production of nanomaterials derived from their bulk counterparts. This study compared the above methods using Field Emission Scanning Electron Microscopy (FESEM) and X-ray Diffraction (XRD).

The sol-gel methodology has been extensively utilized in the production of metal oxide solutions, commonly known as sols. This technique represents a cost-effective and facile approach to the production of metal oxide solutions, achieved through the utilization of lower temperatures. Here, this paper presents a cost-effective and straightforward method, referred to as 'gel-cast,' for fabricating tape/film composed of a composite material consisting of alumina (Al2O3) and molybdenum disulfide (MoS2). The composite material was synthesized through the even distribution of MoS2 powder within an alumina sol, which was developed using the sol-gel method. The morphological investigations were undertaken to ascertain the characteristics of the tape/film subsequent to the introduction of additives. The composition of the tape/film was also examined both prior to and following the annealing process.

The detrimental effects of climate change and global warming have become major concerns due to an increase in carbon footprints across the globe. One of the techniques to minimize carbon emissions is the use of clean and green energy while limiting the use of fossil fuels. Interestingly, rechargeable batteries based on lithium-ion technology serve the purpose due to their stability and reliability. In particular, lithium-ion batteries have gained more attention due to their higher energy density, high coulombic efficiency, high discharge power, and longer cycle life. Graphite is still employed as an anode material because of its simple and highly ordered carbon structure. However, the search for new materials and their hybrids cannot be ignored, as graphite's interaction with electrolytes leads to poor performance on prolonged usage. MWNTs (Multi Wall Nano Tubes) exhibit exceptional electrical conductivity, a large surface area, and mechanical strength, contributing to an enhanced lithium storage capacity and rate capability, ultimately leading to improved battery performance. Additionally, we have investigated the material using various characterization techniques to ensure that the materials have been synthesized in the correct phase and purity.

This study primarily focused on forming pure single-phase FeSb and explored its thermoelectric, mechanical, and electrochemical properties since no reports are available. The FeSb binary alloy has been synthesized through the vacuum melting method, and the phase formation has been confirmed through powder X-ray diffraction (PXRD). The PXRD results show that the synthesized FeSb binary alloy belongs to the hexagonal crystal structure with space group P63/mmc, which coincides with ICSD no. 53971. The pure single phase has been formed by creating a deficiency of 10 % in antimony. The High-Resolution Scanning Electron Microscopy (HR-SEM) and Energy Dispersive X-ray (EDX) analysis have been used to identify the pure single-phase and various elemental components of the hot-pressed pellet of FeSb0.9. The atomic wt.% of iron (Fe) and antimony (Sb) have been identified through EDX spectral analysis. The highest Seebeck coefficient value of −5.4 μV/K is achieved at 497 K, and the lowest electrical conductivity value of 24049 S/m is achieved at 447 K. The hardness of the material is found to be 6.076 GPa, which is much more sufficient for thermoelectric material during industrial handling. The magnetic characteristics of the prepared pure phase FeSb compound have also been measured by Vibrating Scanning Magnetometer (VSM) analysis, which has a weak ferromagnetic nature. Furthermore, three electrodes were employed to study the electrochemical properties, and the alloy has attained the appreciable specific capacitance of 169.5 F/g at 2 A/g.

The objective of this study is to develop and examine coating fluxes for SMAW electrodes intended for use in nuclear power plant steel welding. A set of 21 unique flux compositions is created using the extreme vertices design methodology. These compositions predominantly consist of SrO-CaO-Al2O3-CaF2 fluxes. At a temperature of 1373 K, an in-depth investigation is carried out to assess key properties, including the work of adhesion, spread area, contact angle and floatation coefficient. Additionally, the surface tension of these flux compositions is estimated. XRD and FTIR analysis methodologies have been employed for the purpose of examining and identifying the phases that exist within both the flux and slag. Furthermore, structural analysis of the molten material is conducted through the examination of quenched slag powder. Results reveal that the individual components CaO, CaF2 and binary interaction of Al2O3 × SrO have a significant effect on the contact angle and floatation coefficient. Individual interactions of CaO, SrO, Al2O3 and CaF2 exert a positive impact on the spread area. The individual components Al2O3 and SrO were found to have a significant effect on the work of adhesion.

In the current study, 7 wt.%Ni alloy steel was prepared, hot rolled, and heat treated according to popular quenching, lamellarization, and tempering treatments. The inter-critical lamellarization temperature was varied and the microstructure-property correlation was evaluated in each stage of heat treatment to understand the metallurgical aspects. Optical and detailed electron microscopic techniques were used to characterize and quantify the microstructures. Mechanical responses under uniaxial and impact loading were also recorded for all the studied samples. Tempered martensite with blocky and lamellar morphology, along with retained austenite and ɛ-martensite, were observed in the microstructures after the above-mentioned heat treatment. The lamellarization at 700 ℃ leads to a more uniform distribution of alloying elements and, therefore, promotes the formation of finer retained austenite with uniform distribution, compared to 650 °C lamellarization temperature. The presence of lower matrix strain and uniformly distributed fine retained austenite provides the highest toughness with moderate strength in the 700 °C samples. ɛ-martensite is expected to provide the necessary strength to balance the softening arising due to tempered martensite and retained austenite. Moreover, the uniformly distributed fine and filmy-shaped retained austenite provides thermal stability, and arrests crack propagation, enhancing toughness. The XRD results after impact toughness show that the γ-ε-α transformation takes place during the -196 °C temperature, and during impact toughness testing, ε-α transformations also provide the toughening in the Ni-700+590 sample.