Department of Metallurgical & Materials Engineering

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Recent metastable alloy designs have demonstrated simultaneous attainment of high ultimate tensile strength (UTS) and ductility in high entropy alloys but with low yield strength. Here we present new strategy for improving the work hardenability and yield strength (YS) together in Fe38.5Mn20Co20Cr15Si5Cu1.5 high entropy alloy (Cu-HEA). Drastic increase in the YS (1.5 GPa) is attributed to the formation of γ/ε, ε/ε (twin type) and ε/ε (plate type) interfaces in the microstructure due to extreme grain refinement whereas high UTS-ductility synergy (2.2 GPa, 15%) is attained by dynamic Hall-Petch hardening across these interfaces (i.e. massive interface strengthening) and transformation induced plasticity in γ phase. Thus, this harmonious combination of YS and UTS-ductility synergy in Cu-HEA outperform all structural materials till date. Therefore, deformation-induced massive interface strengthening is a new, yet cost-effective pathway for synergizing the benefits of advanced steels and high entropy alloys together in a material by conventional processing route. © 2021 Acta Materialia Inc.

World University root node

Scripta Materialia

Transformative high entropy alloy conquers the strength-ductility paradigm by massive interface strengthening

Deciphering the role of multiple generations of annealing twins on texture evolution in cold-rolled high entropy alloys during annealing

Martensitic transformations in the body-centered cubic beta-phase (Im (3) over barm) of zirconium are studied using first-principles calculations, grouptheoretical methods, and symmetry analysis. Phonon dispersion relations in the beta-phase calculated within the harmonic approximation predicted an unstable phonon at wave vector 2 pi/a {[}1/2, 1/2, 0] (N) and a soft phonon at wave vector 2 pi/a {[}2/3, 2/3, 2/3] (Lambda). The symmetry of the unstable phonon is the same as the symmetry of the N-4(-) irreducible representation, and the symmetry of the soft phonon is the same as the symmetry of the Lambda(1) irreducible representation. Martensitic transformations are simulated considering two steps. Frozen phonon calculations are used to determine the first step, i.e., the transformation of the beta-phase to an intermediate phase due to phonon motion. Structure relaxation is used to determine the second step, i.e., the transformation of the intermediate phase to the final phase. The unstable N-4(-) phonon transforms the beta-phase into an intermediate orthorhombic phase (Cmcm), which further transforms to a hexagonal close packed alpha-phase (P6(3)/mmc) after structure relaxation. The soft Lambda(1) phonon transforms the beta-phase into an intermediate trigonal phase (P (3) over bar m1), which further transforms to a hexagonal close packed omega-phase (P6/mmm) after structure relaxation. The intermediate phase space group (Cmcm/P (3) over bar m1) is a common subgroup of the parent phase (beta) space group and the final phase (alpha/omega) space group. Therefore, the martensitic transformations in zirconium are reconstructive transformations of the second kind. Symmetry characterization of the martensitic transformations is also presented. Published under an exclusive license by AIP Publishing.

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JOURNAL OF APPLIED PHYSICS

Martensitic transformations of beta-phase in zirconium

The electrocatalytic nitrogen reduction reaction (ENRR) to ammonia is a potentially sustainable alternative to the Haber-Bosch (HB) process, but low Faradaic efficiencies and rates hinder its implementation. Perovskite oxynitrides are a tunable class of materials with unique chemistry for ENRR. Elucidating structure–property–mechanism relations for perovskite oxynitrides will aid ENRR catalyst design. © 2021 Elsevier Inc.

Trends in Chemistry

Perovskite oxynitrides as tunable materials for electrocatalytic nitrogen reduction to ammonia

Worldwide infections and fatalities caused by the SARS-CoV-2 virus and its variants responsible for COVID-19 have significantly impeded the economic growth of many nations. People in many nations have lost their livelihoods, it has severely impacted international relations and, most importantly, health infrastructures across the world have been tormented. This pandemic has already left footprints on human psychology, traits, and priorities and is certainly going to lead towards a new world order in the future. As always, science and technology have come to the rescue of the human race. The prevention of infection by instant and repeated cleaning of surfaces that are most likely to be touched in daily life and sanitization drives using medically prescribed sanitizers and UV irradiation of textiles are the first steps to breaking the chain of transmission. However, the real challenge is to develop and uplift medical infrastructure, such as diagnostic tools capable of prompt diagnosis and instant and economic medical treatment that is available to the masses. Two-dimensional (2D) materials, such as graphene, are atomic sheets that have been in the news for quite some time due to their unprecedented electronic mobilities, high thermal conductivity, appreciable thermal stability, excellent anchoring capabilities, optical transparency, mechanical flexibility, and a unique capability to integrate with arbitrary surfaces. These attributes of 2D materials make them lucrative for use as an active material platform for authentic and prompt (within minutes) disease diagnosisviaelectrical or optical diagnostic tools orviaelectrochemical diagnosis. We present the opportunities provided by 2D materials as a platform for SARS-CoV-2 diagnosis. © The Royal Society of Chemistry 2021.

Journal of Materials Chemistry B

2D materials as a diagnostic platform for the detection and sensing of the SARS-CoV-2 virus: a bird's-eye view

Abnormal features of VOC dependence on temperature and illumination are probed for p-n+-n++ heterojunction family of solar cell devices. Thin-film solar cells of CIGS, CZTS, CdTe, SnS have p-n+-n++ configuration. VOC plots associated with the device configuration/defect scenarios give identifiable features in a one-sided abrupt heterojunction. These features could be assigned to their generating causes akin to high surface recombination velocity, hole mobility, conduction band offset, resistance, Schottky barrier height and bulk defects. This analysis helps make a general prediction of defects or shortcomings present in the device by observing the VOC-temperature and VOC-illumination plots. An individual defect/shortcoming is introduced at a time in the simulated device model and a comparative study for temperature-VOC and illumination-VOC is performed. Features associated with various device shortcomings (high SRV, hole mobility, conduction band offset, resistance, Schottky barrier height, and bulk defects) are summarized. Finally based on the simulation of VOC-temperature and VOC-illumination plots characterization could diagnose and distinctly identify the defect present in the device. © 2021 International Solar Energy Society

Solar Energy

Defects signature in VOC characterization of thin-film solar cells

The relation between microstructure and mechanical properties of carbide-free bainitic steel 0.2% C – 1.53% Mn – 1.1% Si – 1% Cr – 0.3% Mo – 0.5% N under thermomechanical treatment is studied under isothermal conditions and under continuous air cooling. Impact tests of Charpy specimens, metallographic and x-ray diffraction analyses of the steel deformed by different variants are conducted. The size of the initial austenite grains and the Vickers hardness of the steel are determined. The hot plastic deformation is shown to affect positively the impact toughness of the steel treated for bainite. © 2021, Springer Science+Business Media, LLC, part of Springer Nature.

Metal Science and Heat Treatment 63 (7-8)

Thermomechanical Treatment of Carbide-Free Bainitic Steel

Nowadays, secondary batteries based on sodium (Na), potassium (K), and magnesium (Mg) stimulate curiosity as eventually high-availability, nontoxic, and eco-friendly alternatives of lithium-ion batteries (LIBs). Against this background, a spate of studies has been carried out over the past few years on anode materials suitable for post-lithium-ion battery (PLIBs), in particular sodium-, potassium- and magnesium-ion batteries. Here, we have consistently studied the efficiency of a 2D α-phase arsenic phosphorus (α-AsP) as anodes through density functional theory (DFT) basin-hopping Monte Carlo algorithm (BHMC) and ab initio molecular dynamics (AIMD) calculations. Our findings show that α-AsP is an optimal anode material with very high stabilities, high binding strength, intrinsic metallic characteristic after (Na/K/Mg) adsorption, theoretical specific capacity, and ultralow ion diffusion barriers. The ultralow energy barriers are found to be 0.066 eV (Na), 0.043 eV (K), and 0.058 eV (Mg), inferior to that of the widely investigated MXene materials. During the charging process, a wide (Na+/K+/Mg2+) concentration storage from which a high specific capacity of 759.24/506.16/253.08 mAh/g for Na/K/Mg ions was achieved with average operating voltages of 0.84, 0.93, and 0.52 V, respectively. The above results provide valuable insights for the experimental setup of outstanding anode material for post-Li-ion battery. © 2021 American Chemical Society. All rights reserved.

ACS Applied Energy Materials

High-Specific-Capacity and High-Performing Post-Lithium-Ion Battery Anode over 2D Black Arsenic Phosphorus

Direct electrochemical nitrogen reduction for ammonia production is necessary to reduce the use of fossil fuels from conventional Haber–Bosch methods. Applications of nitrogen reduction electrocatalysts remain inhibited by slow reaction kinetics and low faradaic efficiencies because of competitive H2 production pathways. Current strategies to address this challenge in selectivity have focused on catalyst design, reactor configuration, and electrolyte conditions. This brief review discusses the thermodynamic and kinetic challenges in the field as well as current underused approaches for selective catalyst development including bimetallic catalysts, transition metal nitrides, and carbon supports. © 2021 Elsevier B.V.

Current Opinion in Electrochemistry

Roads less traveled: nitrogen reduction reaction catalyst design strategies for improved selectivity

For thermodynamics reasons, most liquids crystallize when they are cooled below their liquidus temperature. However, crystallization can be obstructed if the cooling occurs faster than some critical cooling rate (102 −1010 K/s). Under such conditions, it is suggested that atoms are forced to ‘freeze-in’ at their positions [1,2] with some local short-range order, due to the finite nature of diffusion kinetics, i.e. the rigid state that is produced maintains the disordered or amorphous structure of the liquid. In this short-communication, using CALPHAD (CALculation of Phase Diagrams), we ask, can the underlying atomic interactions within the liquid state be a valid measurement of a material's glass-forming ability? © 2021 Elsevier Ltd