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 tensile fracture behavior of oxide dispersion strengthened 18Cr (ODS-18Cr) ferritic steels milled for varying times was studied along with the oxide-free 18Cr steel (NODS) at 25, 200, 400, 600, and 800 °C. At all the test temperatures, the strengths of ODS–18Cr steels increased and total elongation decreased with the duration of milling time. Oxide dispersed 18Cr steel with optimum milling exhibited enhanced yield strength of 156 pct at room temperature and 300 pct at 800 °C when compared to oxide-free 18Cr steel. The ductility values of ODS-18Cr steels are in the range 20 to 35 pct for a temperature range 25 to 800 °C, whereas NODS alloy exhibited higher ductility of 37 to 82 pct. The enhanced strength of ODS steels when compared to oxide-free steel is due to the development of ultrafine grained structure along with nanosized dispersion of complex oxide particles. While the pre-necking elongation decreased with increasing temperature and milling time, post-necking elongation showed no change with the test temperature. Fractographic examination of both ODS and NODS 18Cr steel fractured tensile samples, revealed that the failure was in ductile fracture mode with distinct neck and shear lip formation for all milling times and at all test temperatures. The fracture mechanism is in general followed the sequence; microvoid nucleation at second phase particles, void growth and coalescence. The quantified dimple sizes and numbers per unit area were found to be in linear relation with the size and number density of dispersoids. It is clearly evident that even nanosized dispersoids acted as sites for microvoid nucleation at larger strains and assisted in dimple rupture. © 2021, The Minerals, Metals & Materials Society and ASM International.

World University root node

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Role of Microstructure and Temperature on the Tensile Fracture Behavior of Oxide Dispersion Strengthened 18Cr Ferritic Steel

Carbide-free bainite (CFB) microstructures containing a mixture of nano-sized retained austenite laths and bainitic ferrite exhibit a good combination of strength, ductility, and toughness. In this work, an attempt was made to identify welding electrode compositions with a carbon content of about 0.35 to 0.5 wt.% to achieve carbide-free bainite microstructures in multi-pass shielded metal arc welds. Suitable alloy compositions were designed using a commercial neural network–based database, considering thermodynamic parameters such as allotropic phase boundary (XTo), ΔGɣ-ɑ (driving force for transformation) and martensite start temperatures. Three different alloy compositions were identified using this approach. Shielded metal arc welding (SMAW) electrodes were fabricated with the compositions identified and the samples extracted from the weld deposits were used for dilatometer studies, metallurgical characterisation, and mechanical property evaluation. Based on the results, an optimised electrode composition and welding parameters were identified to stabilise the carbide-free bainitic microstructures in weld metal. © 2020, International Institute of Welding.

Fulltext

Welding in the World

Development of shielded metal arc welding electrodes to achieve carbide-free bainitic weld microstructures

Microstructural evolution during the strain-induced phase transformation of austenite in an Austempered ductile iron (ADI) under various thermomechanical processing conditions is studied in the present study. An alloyed ductile iron is taken as the base material, and thermomechanical treatment is carried out on a Gleeble 3800 thermomechanical simulator coupled with dilatometry. The effect of deformation on the austempering process has been studied by microstructure characterization using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) techniques. The variations in retained austenite volume fraction and its carbon content with respect to different austempering times are analyzed to study the effect of strain-induced transformation of austenite. It has been observed that the thermomechanical treatment significantly influences the phase transformation kinetics during the austempering process. The thermomechanical treatment produced a martensite free ausferritic microstructure for all austempering times with a high volume fraction of carbon enriched retained austenite as compared to the conventional heat treatment. © 2021 Trans Tech Publications Ltd, Switzerland.

Department of Mechanical Engineering

Materials Science Forum

Microstructure evolution during strain-induced transformation of austenite in an austempered ductile iron (ADI)

Efficient electrocatalysts for water splitting are essential for viable generation of highly purified hydrogen. Hence there is a need to develop robust catalysts to eliminate barriers associated with sluggish kinetics associated with both anodic oxygen and cathodic hydrogen evolution reactions. Herein, we report a two-step nanocasting-solid phase phosphorization approach to generate ordered mesoporous triphasic phosphides CoP@Cu2P-Cu3P. We show that it is a highly efficient bifunctional electrocatalyst useful for overall water splitting. The mesoporous triphasic CoP@Cu2P-Cu3P only requires a low overpotential of 255 mV and 188 mV to achieve 10 mA cm−2for oxygen and hydrogen evolution reactions, respectively. The combination of mesoporous pores (∼5.6 nm) with very thin walls (∼3.7 nm) and conductive networks in triphasic CoP@Cu2P-Cu3P enable rapid rate of electron transfer and mass transfer. In addition, when CoP@Cu2P-Cu3P is used to fabricate symmetric electrodes, the high surface area mesoporous structure and synergetic effects between phases together contribute to a low cell voltage of 1.54 V to drive a current density 10 mA cm−2. This performance is superior to noble-metal-based Pt/C-IrO2/C. This work provides a new approach for the facile design and application of multiphase phosphides as highly active bifunctional and stable electrocatalysts for water-alkali electrolyzers. © The Royal Society of Chemistry 2021.

Sustainable Energy and Fuels

Interface engineering of mesoporous triphasic cobalt-copper phosphides as active electrocatalysts for overall water splitting

To evaluate the heat transfer performance (HTP) of hybrid nanofluids, numerical simulations are carried out in an industrial length single pass shell and tube heat exchanger. In shell, ISO VG 68 oil enters with 75°C and with 30°C, the coolant passes into the tube. CNT-TiO2/water and CNT-TiO2/sodium alginate (SA) are used as Newtonian and non-Newtonian hybrid nanofluid, respectively. The influence of base fluid and nanoparticles on thermal performance of heat exchanger is studied. The chosen nanoparticles are reliable to the industrial deployment. The current numerical procedure is validated with the earlier experimental results. Volume fraction of nanoparticles is optimized for an effective HTP of the heat exchanger. About 60% increment in heat transfer coefficient is observed when hybrid nanofluid is employed. By using Newtonian hybrid nanofluid, 50% improvement in Nusselt number is marked out. Effectiveness and heat transfer rate of heat exchanger are higher with the employment of Newtonian hybrid nanofluid. Results indicated that, even though Newtonian hybrid nanofluid shows higher thermal performance, non-Newtonian hybrid nanofluid is preferable for energy consumption point of view. © 2021 World Scientific Publishing Company.

International Journal of Modern Physics C

Modeling of Newtonian and non-Newtonian-based coolants for deployment in industrial length-scale shell and tube heat exchanger

The phosphorus partition between the unkilled liquid crude steel and the high basicity (CaO/SiO2 = 4.2), basic oxygen furnace (BOF) slags with varying compositions of Al2O3, TiO2, and MnO is studied at temperatures 1600 and 1650 °C. The tests are conducted in both “slag-to-metal” and “metal-to-slag” directions and for durations of 30 and 60 min. The measured results are compared with the values reported in literature and found to be in good agreement with some of them. It is found in the investigation of high-basicity BOF slags, that Al2O3, MnO, and TiO2 lower the phosphorus partition. The phosphorus partition increases with increasing optical basicity. The phosphorus partition shows a maximum when the FeO content is in range of 25–30 mass%. The MgO content slightly increases the phosphorus partition. © 2021 The Authors. Steel Research International published by Wiley-VCH GmbH

Steel Research International

Phosphorus Partition Between Liquid Crude Steel and High-Basicity Basic Oxygen Furnace Slags

Combined role of microconstituents (particles, eutectic fraction and its morphology) on the damage accumulation of three as-cast Mg–Ca–Sn alloys having distinctive microstructural features is studied. Flow stress normalized with that of a solid solution alloy brought out the sole contribution of microconstituents to the deformation. For identifying the influence of microconstituents on strain hardening rate, Kocks-Mecking analysis is utilized together with intermittent post-deformation microstructures. Comprehensive microstructural characterization as a function of strain facilitated to unravel the distinction in internal damage accumulation among the alloys. Further, the internal damage accumulation variation due to distinct variation in the microconstituents is attributed to the differences in hardening rate trends among the three alloys. The reduction in hardening rate is analyzed to occur due to damage accumulation through eutectic fracture or interphase cracking. Thus, the damage mechanism and its influence on strain hardening in cast magnesium alloys is proposed. © 2020 Elsevier B.V.

Materials Science and Engineering A

Synergetic influence of microconstituents on the damage accumulation and consequent effect on the flow behaviour in cast Mg–Ca–Sn alloys

Travel time is a variable that varies over both time and space. Hence, an ideal formulation should be able to capture its evolution over time and space. A mathematical representation capturing such variations was formulated from first principles, using the concept of conservation of vehicles. The availability of position and speed data obtained from GPS enabled buses provide motivation to rewrite the conservation equation in terms of speed alone. As the number of vehicles is discrete, the speed-based equation was discretized using Godunov scheme and used in the prediction scheme that was based on the Kalman filter. With a limited fleet size having an average headway of 30 min, availability of travel time data at small interval that satisfy the requirement of stability of numerical solution possess a big challenge. To address this issue, a continuous speed fill matrix spatially and temporally was developed with the help of historic data and used in this study. The performance of the proposed Advanced Time-Space Discterization (AdTSD) method was evaluated with real field data and compared with existing approaches. Results show that AdTSD approach was able to perform better than historical average approach with an advantage up to 11% and 5% compared to Base Time Space Discretization (BTSD) approach. Also, from the results it was observed that the maximum deviation in prediction was in the range of 2–3 min when it is predicted 10 km ahead and the error is close to zero when it is predicted a section ahead i.e. when the bus is close to a bus stop, indicating that the prediction accuracy achieved is suitable for real field implementation. © 2020, Springer Science+Business Media, LLC, part of Springer Nature.

Department Of Civil Engineering

International Journal of Intelligent Transportation Systems Research

Numerical Stability of Conservation Equation for Bus Travel Time Prediction Using Automatic Vehicle Location Data

The sensitive ecosystem of the central Himalayan (CH) region, which is experiencing enhanced stress from anthropogenic forcing, requires adequate atmospheric observations and an improved representation of the Himalaya in the models. However, the accuracy of atmospheric models remains limited in this region due to highly complex mountainous topography. This article delineates the effects of spatial resolution on the modeled meteorology and dynamics over the CH by utilizing the Weather Research and Forecasting (WRF) model extensively evaluated against the Ganges Valley Aerosol Experiment (GVAX) observations during the summer monsoon. The WRF simulation is performed over a domain (d01) encompassing northern India at 15 km-15 km resolution and two nests (d02 at 5 km-5 km and d03 at 1 km-1 km) centered over the CH, with boundary conditions from the respective parent domains. WRF simulations reveal higher variability in meteorology, e.g., relative humidity (RHD70.3 % 96.1 %) and wind speed (WSD1.1 4.2ms-1), compared to the ERA-Interim reanalysis (RHD80.0 % 85.0 %, WSD1.2 2.3ms-1) over northern India owing to the higher resolution. WRF-simulated temporal evolution of meteorological variables is found to agree with balloon-borne measurements, with stronger correlations aloft (r D0.44 0.92) than those in the lower troposphere (r D0.18 0.48). The model overestimates temperature (warm bias by 2.8 C) and underestimates RH (dry bias by 6.4 %) at the surface in d01. Model results show a significant improvement in d03 (P D827.6 hPa, T D19.8 C, RHD92.3 %), closer to the GVAX observations (P D801.4 hPa, T D19.5 C, RHD94.7 %). Interpolating the output from the coarser domains (d01, d02) to the altitude of the station reduces the biases in pressure and temperature; however, it suppresses the diurnal variations, highlighting the importance of well-resolved terrain (d03). Temporal variations in near-surface P, T , and RH are also reproduced by WRF in d03 to an extent (r>0:5). A sensitivity simulation incorporating the feedback from the nested domain demonstrates the improvement in simulated P, T , and RH over the CH. Our study shows that the WRF model setup at finer spatial resolution can significantly reduce the biases in simulated meteorology, and such an improved representation of the CH can be adopted through domain feedback into regional-scale simulations. Interestingly, WRF simulates a dominant easterly wind component at 1 km-1 km resolution (d03), which is missing in the coarse simulations; however, the frequency of southeasterlies remains underestimated. The model simulation implementing a highresolution (3 s) topography input (SRTM) improved the prediction of wind directions; nevertheless, further improve- ments are required to better reproduce the observed localscale dynamics over the CH. © 2021 EDP Sciences. All rights reserved.

Department Of Chemistry

Geoscientific Model Development

Effects of spatial resolution on WRF v3.8.1 simulated meteorology over the central Himalaya

A number of creep tests were performed on a Ni-base superalloy DS CM 247 specimens at three temperatures viz. 850, 950 and 1050 °C and over a range of stresses. Three-dimensional (3D) maps of creep curves (creep strain–time-stress) were generated by using the ‘in-house developed code’ based on θ-projection methodology. These 3D maps with overlaid experimental creep curves show a very good agreement with the predicted creep behaviour at different stresses and at a given temperature. Also, the ability of the method in deducing the stress relaxation curves at different strains derived from 3D maps of creep curves has been demonstrated. Further, the relative performance of the LMP approach and the θ-projection approach in prediction of time to rupture has been reported. © 2021, The Indian Institute of Metals - IIM.