Department of Metallurgical and Materials Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

The structure of the chaotic potential caused by the electrostatic field of charged dislocations in group III-nitride heterojunctions is investigated. Taking into account the spatial dispersion of the dielectric response of a two-dimensional electron gas, the amplitude and scale of the chaotic potential in the junction plane are determined. It is shown that the parameters of the chaotic potential depend on the density of surface states and the concentration of dislocations. © 2021, Pleiades Publishing, Ltd.

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Technical Physics Letters

A Chaotic Potential of Charged Dislocations in Group III-Nitride Heterojunctions

In this study, investigations on stretch flangeability were carried out on as-received DP 600 steel which had 22 volume % of martensite. Stretch flangeability is normally characterized by the hole expansion test and refers to the ability to avoid cracking during stretch flanging or hole expansion. Two intercritical annealing treatments (soaking temperatures of 760 °C and 800 °C followed by water quenching) were selected in order to obtain lower and higher volume fractions of martensite respectively. The influences of four different hole preparation techniques, electrical discharge machining, drilling, drilling + reaming, and punching, on the hole expansion ratios were investigated. Higher surface roughness at the surface of the hole showed inverse correlation with HER values. The highest hole expansion ratio of 156% was obtained for the as-received DP 600 steel with the hole prepared by electrical discharge machining. The HER values observed for various hole preparation conditions can be normalized with respect to the electrical discharge condition so that the HER values can be estimated when one of the HER values is known. © 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.

International Journal of Advanced Manufacturing Technology

Evaluation of stretch flangeability of dual-phase steels by hole expansion test

engrXiv

Reduction in Charge Requirements of Hismeltiron-Making Process in Indian Context

Phase diagram calculation of Fe–Ti system is obtained by coupling of CALPHAD with first principle methods. Single Gibbs energy model is used for FeTi to take care of order-disorder transition. First principle calculation shows that Laves phase is ferromagnetic nature with the magnetic moment of 1.417μB which is incorporated in the modelling. For extrapolation to higher order system, Laves phase is mostly expressed with two sublattice model. From crystallographic view, 3 sublattice model is appropriate one for description of Laves phase. Hence, two different models are used for Laves phase. Wagner-Schottky model used to describe the homogeneity region of Laves phase in two sublattice model. Using the first principle method, the energies of formation of unstable end members of FeTi phase and three sublattice model of Laves phase are calculated and incorporated as experimental data in optimisation. Calculated phase diagram and the thermochemical properties using 3 sublattice model of Laves phase shows good agreement with the experimental data. © 2020 Elsevier Ltd

Intermetallics

Thermodynamic modelling of magnetic laves phase in Fe–Ti system using first principle method

This study examines the joining of a 4 mm thick plate of alloy C-2000 by continuous current gas tungsten arc welding (CCGTAW) and pulsed current gas tungsten arc welding (PCGTAW) techniques by using ERNiCrMo-4 (filler-4) and ERNiCrMo-17 (filler-17) as filler wires. This article aims to present a comprehensive structure-property relationship of these welded joints. Weld microstructure was characterized with optical microscope and scanning electron microscope. The results show that PCGTA weldments possess a refined microstructure compared to the CCGTA weldments in both filler wires. Energy-dispersive x-ray spectroscopy study divulged the existence of chromium (Cr)-rich and slight molybdenum (Mo)-rich segregation in the fusion zone interdendritic region of all the four weldments. However, the extent of microsegregation is very low in PCGTA-filler-4 weldment when compared with the other weld joints. Significant grain refinement (8.9 to 9.77%) was observed when shifting the welding mode from CCGTAW to PCGTAW. Weldment produced with PCGTAW-filler-4 offers higher tensile strength ( 4 to 6%), higher toughness ( 5 to 7.5%), and higher hardness ( 3 to 6%) compared to other weldments. © 2021, ASM International.

Journal of Materials Engineering and Performance

Influence of Filler Wire and Welding Process to Mitigate the Microsegregation of Alloy C-2000 Using Continuous and Pulsed Current Gas Tungsten Arc Welding Techniques

In this work, we report the results of a systematic study on the evolution of the precipitates during aging in a Ni-based superalloy (Alloy 617) and their effect on the high-temperature hot corrosion (HTHC). It was observed that the extent of Cr-rich precipitation increased with the aging time while the other microstructural parameters such as grain size, retained strain, and Σ3n (n ≤ 3) boundaries fraction did not change in comparison to the as-received (AR) condition. To evaluate the role of precipitation on hot corrosion, the AR and the aged specimens were subjected to the HTHC test involving complete immersion of the specimens in a 75 wt% Na2SO4 + 20 wt% NaCl + 5 wt% V2O5 salt mixture at 1273 K for 24 h. The characterization of surface and cross-section morphologies of the corroded layers through scanning electron microscopy revealed that the oxide film formed on the AR specimen is highly porous and loose. In contrast, the layer formed on the specimen aged for 100 h (AR-100 h) is significantly thinner and dense. Post-HTHC analysis aided with the thermodynamic and diffusion calculations revealed that the improved HTHC performance of the AR-100 h specimen is due to the rapid formation of an oxide layer owing to the enhanced supply of Cr as a consequence of carbide dissolution. Also, the undissolved carbides at the grain boundaries acted as a potential obstruction to the inward transport of corrosive species, resulting in a significantly lower percolation depth in the AR-100 h specimen (~66 ± 6 µm) than the AR condition (~305 ± 15 µm). © 2021 Elsevier B.V.

Journal of Alloys and Compounds

Precipitate evolution during aging and its individual role on high-temperature hot corrosion response in Alloy 617

Herein, we present a simple, large-scale and low-cost process to develop hierarchically porous N–S co-doped 3D wrinkled graphene like nanosheets (3D H-GNS) from carbonization of biomass Tender palm shoots and NaHCO3. Non-corrosive and non-toxic Na2CO3 acts as a reaction mean to control the activation process, developing 3D H-GNS with a high specific surface area of 2095 m2 g−1. A 3D H-GNS-900 electrode exhibits a high specific capacitance of 529 F g−1 (1.5 A g−1) and 330 F g−1 (1 A g−1) in 1 M H2SO4 for 3-electrode and 2-electrode systems respectively. Further, a longer cycle life with 93% capacitance retention over 10,000 cycles at 5 A g−1 is realized. Also, we are successful in fabricating biocompatible solid-state flexible supercapacitor device with 3D H-GNS-900 electrodes in organic electrolyte with 3 V voltage range, demonstrating to run a toy fan and lightning a LED for 15 min after charging for 60 s. © 2020 Hydrogen Energy Publications LLC

Department Of Physics

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International Journal of Hydrogen Energy

Large-scale single-step synthesis of wrinkled N–S doped 3D graphene like nanosheets from Tender palm shoots for high energy density supercapacitors

The objective of the present work is to investigate the microstructural evolution during hot deformation of nano oxide dispersion strengthened (n-ODS) Fe – 18Cr ferritic steel over a wide range of temperatures 1273–1573 K and strain rates 10−2 – 10 s−1. Electron backscatter diffraction analysis was performed extensively on deformed samples to investigate the restoration mechanisms operating in the material. Small angle X-ray scattering (SAXS) analysis was performed on the deformed samples to investigate the nanoprecipitate characteristics. Flow curves obtained in the current study exhibit initial strain hardening followed by flow softening for all the studied deformation conditions. An inflection point was noticed in the plot between strain hardening rate [Formula presented] and flow stress for almost all test conditions except the ones corresponding to 1573 K and at 10−2 and 10−1 s−1, which is an obvious indication for the occurrence of dynamic recrystallization (DRX) in the n-ODS-18Cr steel. Microstructural analysis revealed the occurrence of continuous DRX and it is responsible for the grain refinement in the present steel. Grain growth was dominant in the samples deformed at 1423 K (and above) and 10−2 s−1. SAXS analysis revealed considerable coarsening of nanoprecipitates with bimodal particle distribution in the sample deformed at 1573 K and 10−2 s−1. It showed that the average size of fine nanoprecipitates increased to 6.2 nm from 3.8 nm and coarse precipitates of size 20–30 nm. © 2020 Elsevier B.V.

Materials Science and Engineering A

On the understanding of microstructural evolution during hot deformation of n-ODS-18Cr ferritic steel containing heterogeneous microstructure

Conversion of Cr(VI) to Cr(III) in mitigating pollution of water bodies is of significant importance to public health due to the fact that Cr(VI) is known to be a potent carcinogen, while Cr(III) is relatively low in toxicity. Photocatalytic approaches are considered as important means to achieve this reduction. Here, TiO2/SnS2 core-shell nanostructures have been produced using a single-step hydrothermal method and its photocatalytic activity is tested for the reduction of aqueous Cr(VI). The structural and optical properties of the as-synthesized products are characterized by XRD, HRTEM, Raman, FTIR, XPS and DRS techniques. The present work reveals that by calcining the core-shell nanoparticles in Ar atmosphere a defective Ti3O5 phase is formed as the core with low band gap, and hence, offers improved light absorption in the visible range. However, its photoactivity was found to be lower than that of the core-shell nanoparticles annealed in oxidizing atmosphere. The observed lower photoreduction was due to the presence of midgap states which acted as recombination centres and hence, reduced the photocatalytic activity. © 2021 University of Novi Sad, Faculty of Technology. All rights reserved.

Processing and Application of Ceramics

Effect of calcination atmosphere on structural, optical and photocatalytic activity of TiO2/SnS2 core-shell nanostructures in the reduction of aqueous Cr(VI) to Cr(III)

Indium oxide (In2O3) nanocubes modified by ruthenium oxide (RuO2) on the surface are successfully prepared through hydrothermal method, calcination and impregnation in turn. The sensing properties of RuO2-modified In2O3 sensing material are significantly enhanced even with low loading amount. The response values of RuO2-modified In2O3 sensing material to TXM vapor containing benzyl group (including toluene, xylene and mesitylene) increase rapidly when compared to various volatile organic compounds (VOCs). Therein the RuO2-modified In2O3 sensor displays a 36-times increase in response value to mesitylene (100 ppm) in contrast to un-modified one at 255 °C. The optimum operating temperature (OOT) decreases obviously from 375 °C of pristine In2O3 one. The gas sensing enhancement mechanism can be explained by electronic and chemical sensitization. However, the reason for selectivity change will be (temporarily) investigated further later. © 2021