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

This paper proposes a Phononic crystal (PnC) device formed by embedding spheres in a polymer matrix for energy harvesting, an application that has drawn much research interest recently. A parametric study is performed to evaluate the optimal radius to lattice parameter ratio r/a = 0.4 to obtain a large bandgap as well as gap to mid-gap ratio. By removing a sphere from the central lattice point, a defect is created within an otherwise perfect PnC. The supercell technique is employed to compute defect modes and band structure of defect PnC. These defect bands show strong vibrational modes within the spatial arrangement of the defect point and these defect frequencies appear to be flat (dω/dk = 0) in the band structure confirming energy localization at these modes. Also, while varying the radius of the defect sphere rd in the range of [0.1a–0.5a], the number of defect modes within the bandgap tend to decrease, vanishing when rd equals 0.4a and 0.5a. To utilize the defect mode for energy harvesting, a small patch made of a piezoelectric material is attached onto the PnC device exactly above the defect. Introduction of this patch renders the band structure and defect modes to shift upwards compared to the defect PnC without the patch. A highly localized vibrational eigen mode is observed around 662 kHz in the band structure for the defect PnC with patch. The voltage response of this device is simulated by connecting a high resistance (open-circuit) to the patch and sweeping frequencies around the defect mode. This process produced a voltage of 2.8 V at 656.7 kHz for a 0.3 µm displacement excitation, thus demonstrating the usefulness of the proposed concept. © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

World University root node

Department of Mechanical Engineering

Lecture Notes in Civil Engineering

Spherical Inclusions Based Defect Modes in a Phononic Crystal for Piezoelectric Energy Harvesting

Self-assembled chessboard-like (CB-like) nanostructures in oxides are potential candidate materials for high density memory and energy storage devices. The evolution of CB-like nanostructures has been studied by combining transmission electron microscopy and 3D atom probe tomography in spinel-forming CoFeMn oxide. CB-like nanostructures evolve through a complex process of twinning, subdomain formation through recurrent pseudo-spinodal decomposition and domain coalescence along specific crystallographic axes. It initiates with the cross-penetration of compound deformation twins with subtle chemical composition separation between different domains, which ultimately results in the polymorphic transformation of cubic and tetragonal phases. The requirement of interfacial strain minimization leads to the formation of two tetragonal and two cubic spinel domains of different compositions which are rotationally orientated. In the CB-like nanostructure, cubic and tetragonal domains are connected along 〈022〉 directions. Cubic with cubic domains, and tetragonal with tetragonal domains, are connected along 〈040〉 or 〈004〉 directions. Recurring pseudo-spinodal decomposition within the CB-like domains leads to the formation of finer CB-like nanodomains. The formation of cuboid shaped domains of the cubic and tetragonal phases to rod shape morphology with four {220} and two {001} faces can give rise to 2D CB-like nanostructures. Combined transmission electron microscopy and atom probe tomography analysis indicates that CB-like nanostructures can also form in 3D, and a new model for this has been proposed based on the octahedral/cuboidal shape of the compositionally separated domains. The coalescence of such nanostructures along 〈004〉 directions gives rise to a rod-like morphology. The proposed model is expected to lead to a paradigm shift in the current understanding of CB-like nanostructures. © 2022

Acta Materialia

Nanoarchitectonics of self-assembled chessboard-like structures by recurrent phase separation and coalescence of nano domains in CoFeMn oxide

Amorphous silicon oxycarbides are known to be an effective anode material for lithium-ion batteries. Despite their exceptional properties and high charge capacities, however, their practical uses are limited by their significant first-cycle loss, considerable hysteresis, and low cyclic ability. Comparatively, SiOC/metal oxide materials have demonstrated increased rate capability and cyclic stability. This study utilized a liquid precursor-derived ceramic method to modify SiOC with titanium (IV) butoxide precursor to synthesize SiOC/TiOxCy. X-ray diffractograms confirmed the amorphous nature of SiOC/TiOxCy. The elemental composition and bonding properties were investigated using X-ray photoelectron spectroscopy, and electron microscopy was used to explore morphological features. In the first cycle, the reversible capacity of pyrolyzed SiOC/TiOxCy was 520 mAh g−1, which then increased to 736 mAh g−1 for the 1200°C annealed SiOC/TiOxCy due to the increased free carbon network and TiC conductive phases. The irreversible capacity of the first cycle was 568 mAh g−1, which was lower than the annealed SiOC irreversible capacity of 695 mAh g−1. Interestingly, the rate stability of the pyrolyzed SiOC/TiOxCy performed more stability than the annealed sample. Localized carbothermal reactions between amorphous SiOC/TiOxCy and free carbon at annealing temperatures resulted in loss of structure stability. © 2022 The American Ceramic Society.

International Journal of Applied Ceramic Technology

Single source precursor-derived SiOC/TiOxCy as an anode component for Li-ion batteries

In this work, we studied the effect of initial grain size on the hot compression characteristics of super-304H austenitic stainless steel in a range of strain rates (0.001–1 s−1) at a fixed temperature of 1223 K. Analysis of the flow curves reveals that the flow stress is inversely proportional to the average sub-grain diameter in both coarse and fine-grained specimens at higher strain (≥0.5) levels. Further, the fine-grained specimen following deformation at a low strain rate (0.001 s−1) reveals the occurrence of both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) mechanisms. In this condition, the CDRX is characterized by a progressive increase of boundary misorientation, while the DDRX is characterized by bulging and strain-induced boundary migration. In contrast, the CDRX characterized by the formation of microbands is majorly responsible for the grain refinement in the fine-grained specimen at higher strain rates (∼1 s−1) and in the coarse-grained specimen at all strain rates (0.001–1 s−1). The superposition of different DRX mechanisms leads to significant variations in grain refinement kinetics with strain rates and initial grain sizes. The findings of this investigation provide a foundation for the accurate control of the microstructures in the studied alloy with different initial grain sizes during the hot working at various strain rates. © 2021 Elsevier B.V.

Materials Science and Engineering A

Implication of initial grain size on DRX mechanism and grain refinement in super-304H SS in a wide range of strain rates during large-strain hot deformation

At present, additively manufactured biomedical materials find extensive applications in a wide range of avenues ranging from orthopaedics to urology. Additive manufacturing (AM) techniques based on the layerwise deposition of materials allow fabrication of complex-shaped biomedical components with a high level of accuracy. In this context, the major challenge is to obtain robust and functional engineering components. This may be attributed to a large-scale microstructural inhomogeneity arising due to the aforementioned deposition methodology followed in the AM-based techniques. In addition, the other challenges include size limitations, quality inconsistency, scaling issues and the high cost of manufacturing of final parts. This leads to a major limitation of AM-based biomedical components in terms of their mechanical biocompatibility with the adjoining bones and tissues. One of the ways to overcome the aforementioned challenges is to engineer the microstructure in these materials to optimise the parameters involved in AM-based fabrication techniques. The present chapter is aimed to provide an overview of the different AM-based techniques involved in the fabrication of commonly used biomaterials and the common characterisation techniques for establishing a systematic structure–property correlation in these materials. Moreover, future outlooks and challenges associated with these materials have been addressed from the authors’ viewpoints at the end of the chapter.

Advanced Materials for Biomechanical Applications

Additive Manufacturing and Characterisation of Biomedical Materials

While descending through different layers of atmosphere with tremendously high velocities, hypersonic re-entry nosecones fabricated using ultra-high temperature ceramic matrix composites (UHTCMCs) are subjected to repeated thermal shocks. This necessitates extensive investigations on the cyclic oxidation behaviour of UHTCMCs at temperatures ranging from 1100°C to 1300°C (service temperature of the nosecones). To this end, the present work is aimed at investigating the cyclic oxidation behaviour of ZrB2 -20 vol.%MoSi2 (ZM20) UHTCMC (a very widely investigated ZM CMC) by carrying out cycles for 6h, at 1cycle/h and estimating oxidation kinetic law. This has been followed by extensive characterisation using X-Ray Diffraction (XRD) to indicate the phases formed during oxidation and Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), in order to determine the chemical composition of the oxides formed between 1100°C and 1300°C.

Cyclic oxidation behaviour of ZrB2-20 vol.% MoSi2 based ultra-high temperature ceramic matrix composite between 1100 C and 1300 C

Solute decoration at grain boundaries (GB) leads to a number of phenomenon such as changes in interface structure, mobility, cohesion etc. Recent experimental investigations on interfacial segregation in steels are based on microstructural characterisation using two correlative methodologies, namely, Transmission Electron Microscopy-Atom Probe Tomography (APT) and Electron Backscatter Diffraction-APT. Considering the growing interest in this avenue, the present review is aimed at addressing the common adsorption isotherms used for quantifying interfacial segregation and providing an overview of the present state of experimental research in the area of GB segregation in steels. The areas where an understanding of GB segregation may be utilised have also been highlighted with a focus on the experimental challenges associated with understanding GB segregation in steels.

arXiv preprint arXiv:2202.

Grain boundary segregation in steels: Towards engineering the design of internal interfaces

In this work, a novel idea of combining two established microstructural engineering approaches viz., grain boundary engineering (GBE) and grain boundary serration (GBS) through optimization of thermomechanical and thermal processing in Alloy 617 is investigated and the superior resistance of GBE+GBS microstructure to the high-temperature hot corrosion is demonstrated. To achieve the GBE+GBS microstructure, the GBS treatment was introduced as a part of the GBE processing schedule (i.e., incomplete GBE+GBS) and following the GBE treatment (i.e., complete GBE+GBS). The extent of GBS is found to be similar in all the processed specimens. However, the extent of GBE is observed to be lower in the specimens undergoing incomplete GBE+GBS. This is due to the occurrence of recrystallization and consequent infrequent multiple twinning. On the other hand, a higher extent of GBE is achieved in the specimens subjected to complete GBE+GBS owing to the retention of the optimized GBE microstructure following the GBS treatment. The synergistic influence of GBE and GBS on the hot corrosion behavior is assessed by exposing the as-received (AR) as well as optimized grain boundary engineered and serrated (GBES) specimens to a salt mixture at 1273 K. The percolation depth after 24h and 48h exposure is significantly lower in the GBES specimen (∼55 µm and ∼115 µm, respectively) than the AR condition (∼305 µm and ∼630 µm, respectively). This is ascribed to the incorporation of Σ3n (n ≤3) and serrated boundaries in the GBES microstructure which obstructed the infiltration of harmful species into the alloy. © 2022 Acta Materialia Inc.

Materialia

A novel approach combining grain boundary engineering and grain boundary serration to enhance high-temperature hot corrosion resistance in Alloy 617

Formation of nano-twinned domains associated with ferro-elastic transformation in 2 mol.% ZrO2 alloyed YTaO4 has been investigated using a correlative microscopy approach. Transmission Kikuchi diffraction reveals the presence of two phases, monoclinic (M) and tetragonal (T) in the material sintered at 1485 °C for 3 hr. The microstructure comprises of alternate nano-twinned domains with an average spacing of 154.07 ± 42.52 nm. Crystallographic symmetry based spontaneous strain analyses support the observation of single domain state. Ab-initio calculations further indicate the propensity of stabilizing both M and T phases at room temperature as a function of ZrO2 alloying, without any change in chemical composition, as is evidenced by atom probe tomography. © 2022 Acta Materialia Inc.

Scripta Materialia

On the correlative microscopy analyses of nano-twinned domains in 2 mol% zirconia alloyed yttrium tantalate thermal barrier material

The structure-property(S-P) correlation,especially in the context of high-temperature oxidation, in ZrB2-MoSi2 based Ultra High-Temperature Ceramic Matrix Composites (UHTCMCs) have been extensively investigated for quite some time since the last 25 years and a countless amount of published data is presently available in this field.On the other hand,emergence of correlative microscopy [1] has completely revolutionised the world of materials research, in a number of ways.However,owing to the challenges of sample preparation, there has hardly been a literature aimed at understanding the aforesaid phenomenon of understanding S-P correlation,based on oxidation in ZrB2-MoSi2 UHTCMCs,which,in future, may open up new frontiers of research in UHTCMCs.The present review intends to discuss some of the most interesting data published existing in this field and intends to provide a brief overview of the challenges associated along with some of the currently unexplored avenues in this field,especially in terms of fundamental research.However,in view of the enormous amount of research already done in understanding oxidation-based S-P correlation in these materials,the author does not claim to address all the issues which may be associated with understanding the same.