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

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.

World University root node

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

Fulltext

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

In the present study, using ICME approach, the development of Co-Cr-Fe-Ni-V based single-phase FCC high entropy alloy (HEA) has been explored. The simulation guided composition was arc melted and verified using microstructure characterization. The as-cast sample was subjected to deformation at a strain rate of 0.1 s−1in the temperature range of 1073–1373 K. The flow stress behavior in this temperature range could be correlated with the evolution of microstructure using EBSD. Based on these results, the deformation behavior of the alloy at elevated temperature is rationalized. The current study realizes the ICME approach to develop novel single-phase FCC HEA. © 2021 Elsevier B.V.

Design and deformation characteristics of single-phase Co-Cr-Fe-Ni-V high entropy alloy

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)

Crystal structure classification of perovskites (ABO3) is done using the Light Gradient Boosting Machine (Light GBM) algorithm. In this work, we have identified features such as electronegativity, ionic radius, valence, and bond lengths of A-O and B-O pairs that enable a priori crystal structure prediction. We have taken 5329 ABO3 perovskites and applied the proposed model to 675 compounds. It successfully categorized the compounds into cubic, tetragonal, orthorhombic, and rhombohedral structures with 80.3% best accuracy using 5-fold cross-validation. Therefore, the model can be used as a preliminary, fast, and inexpensive method to classify perovskites into their respective crystal systems. Feature importance graph and SHapley Additive exPlanations (SHAP) are used in feature ranking and crystal structure prediction. These composition-structure predictions will find applications in ceramic engineering and solid-state chemistry. © 2020 Elsevier B.V.

Computational Materials Science

Crystal structure classification in ABO3 perovskites via machine learning

Quantitative treatment of microstructure data is the first step in establishing the structure–property linkages using materials informatics. However, the microstructure data are often huge and require dimensionality reduction techniques to use it in a computationally meaningful way. In this paper, we present a simple and unique approach to estimate the intrinsic dimensionality of microstructure data. By using principal component analysis (PCA) and multi-dimensional scaling (MDS), we demonstrate the effects of global and local metrics on various classes of 2D and 3D synthetic two-phase microstructure data on the intrinsic dimensionality (ID). Further, we establish the influence of the phase fraction and the inherent stochastic nature of the microstructure on ID estimation. It is observed that 2-point spatial correlation statistics greatly influence intrinsic dimensionality. A change in the intrinsic dimensionality is observed with an increase in the volume fraction of the phase. Considerable variation is observed in metric values for MDS compared to PCA, with an increase in dimensions. We also provide a reduced-order phase fraction benchmark of intrinsic dimensionality (ID) for high dimensional microstructure data. The presented framework is based on a simple and effective trade-off between property preservation and complexity reduction. © 2021, The Minerals, Metals & Materials Society.

Integrating Materials and Manufacturing Innovation

Intrinsic Dimensionality of Microstructure Data

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

Sensors and Actuators, B: Chemical

In2O3 nanocubes modified with RuO2 for detection of TXM vapors containing benzyl group

The flow stress reduction during plastic deformation superposed with electric current, commonly referred as 'electroplasticity' has been actively researched over the past few decades. While the existence of an electron-dislocation interaction, independent of Joule heating is established, the exact rate controlling mechanism of the observed behaviour lacks consensus. Understanding the governing mechanism is complex due to the combined effect of Joule heating and electron-dislocation interaction. The present work attempts to establish the electroplastic mechanism in AA 6063 alloy and its nanocomposites. The role of microstructure on the electron interaction is investigated by preparing four distinct microstructure from the base alloy. All the samples were subjected to constant amplitude direct current during plastic deformation. The Joule heating effect is decoupled using the experimentally measured temperature history. The potential electroplastic mechanism for the alloy is elucidated by analysing the trend of flow stress reduction with strain and strain rate. It is inferred that micro Joule heating and electron wind effect cannot completely explain the observed electroplastic behaviour in AA 6063. The SiC particles in nano-composites suppressed the electroplastic effect. The observed mechanical behaviour under electric current is in agreement with the trend predicted assuming magnetic depinning mechanism. The reduction of dislocation density quantified using X-ray diffraction is found to concur with the inferred mechanism. © 2021 The Author(s).

Department of Mechanical Engineering

Journal of Materials Research and Technology

Microstructure dependent electroplastic effect in AA 6063 alloy and its nanocomposites

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

Spring-back of sheet metal affects the dimensional accuracy of the components after stamping and has to be eliminated or corrected. Advanced high strength steels (AHSS) are prone to spring-back while forming at ambient temperatures. Hot stamping process is an effective technique to reduce the spring-back upon forming. The forming temperatures and the phase transformations associated with quenching are known to influence the spring-back. However, the detailed experimental analysis on spring-back behaviour is limited due to the difficulty in physically simulating the thermal-mechanical conditions prevailing in a typical hot forming process. In the present work, a novel V-bending technique is presented for effectively measuring the spring-back using a thermal-mechanical simulator, Gleeble™. V-bending is carried out by applying a compressive force along the longitudinal plane of AHSS steel strips at forming temperatures. Upon V-bending, samples were cooled at different cooling rates while maintaining the forming loads to simulate die quenching. Results indicate that the spring-back decreases and becomes close to zero (at a cooling rate of 20 K s-1) with an increase in cooling rate for a hot stamping steel. Further, an increase in cooling rate results in spring-forward owing to the formation of an increased volume fraction of martensite. © 2021 The Authors.