Department of Metallurgical & Materials Engineering

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IIT Jodhpur

Misorientation angle distribution gives information about the type and fraction of grain boundaries present in a material. Since grain boundaries affect various mechanical and functional properties of the material, the distribution of grain boundary misorientation is important in order to evaluate these properties. This becomes particularly important when we want to study the microstructure in finer detail, such as understanding the average misorientation within a grain. One of the techniques increasingly used in past two decades for characterization of grain boundary misorientation is electron back scatter diffraction (EBSD). Reliable detection of very small misorientation angles using conventional EBSD system is quite challenging due to the presence of measurement error. This makes the comprehensive characterization of microstructures difficult and prone to error. In order to prevent such problems, it is important to understand the nature of measurement error and find ways to minimize it. The present work aims to elucidate the effect of measurement error on the observed misorientation angle and its statistical distribution in low misorientation angle regime. A true strain of 0.3 was imposed during cold-rolling of Cu-5%Zn alloy sample. The rolled sample was then subjected to in-situ heating from room temperature to 500 °C (∼0.58 Tm). It was found that the overall measurement error in misorientation distribution consists of random error caused by limited angular precision and systematic error which manifests primarily in the statistical distribution of low angle misorientation. In this work, we show a way to deconvolute this overall error based on the measurement technique. We further show that this systematic error is not limited to any particular measurement technique, rather related to the presence of a lower bound in the measurement. © 2018

World University root node

Micron

Deconvoluting error in measurement of low angle misorientation distribution

The CZTS films are made by direct liquid coating of solution precursors. A benign solution of propanol and polyethylene glycol as solvent is used. Films of CZTS are prepared by drop casting and spin coating followed by annealing and sulfurisation. The present synthesis need as low as 350°C to form the kesterite phase CZTS films. The presence of secondary phase in CZTS films are not conclusively detectable using X-ray diffraction and hence the role of Raman spectroscopy for the same is emphasized. © 2017 Elsevier Ltd.

Materials Today: Proceedings

Secondary Phases in CZTS Thin Films Grown Using Direct Liquid Coating Approach

We report hydrogen peroxide (H2O2)sensing using free standing graphene oxide thin films prepared using a cost effective scalable approach. Such sensors may find application in pharmaceutical and food processing industries.

AIP Conference Proceedings

Free standing graphene oxide film for hydrogen peroxide sensing

A low cost, non-explosive process for the synthesis of graphene oxide (GO) is demonstrated. Using suitable choice of reaction parameters including temperature and time, this recipe does not require expensive membranes for filtration of carbonaceous and metallic residues. A pre-cooling protocol is introduced to control the explosive nature of the highly exothermic reactions during the oxidation process. This alleviates the requirement for expensive membranes and completely eliminates the explosive nature of intermediate reaction steps when compared to existing methods. High quality of the synthesized GO is corroborated using a host of characterization techniques including X-ray diffraction, optical spectroscopy, X-ray photoemission spectroscopy and current-voltage characteristics. Simple reduction protocol using ultra-violet light is demonstrated for potential application in the area of photovoltaics. Using different reduction protocols together with the proposed inexpensive method, reduced GO samples with tunable conductance over a wide range of values is demonstrated. Density functional theory is employed to understand the structure of GO. We anticipate that this scalable approach will catalyze large scale applications of GO.

Fulltext

Scientific Reports

A Low-Cost Non-explosive Synthesis of Graphene Oxide for Scalable Applications

Biodegradable materials suitable for medical application with improved corrosion resistance and good biocompatibility along with enhanced mechanical properties are the need of the hour. Such properties in Mg-Zn-Ca glass forming alloy used as a metal matrix can be obtained through proper reinforcement. Hydroxyapatite (HA) which is a mineral constituent of natural bone has a wide range of medical applications because of its excellent biocompatibility and bioactivity. They promote bone cell adhesion and osteoblastic proliferation. In the present study, the influence of HA particle (HAp) addition on the glass forming ability, corrosion resistance, mechanical behavior and cytocompatibility of Mg66Zn30Ca4 alloy has been investigated. The addition of HAp decreases the glass forming ability of Mg66Zn30Ca4 alloy. Significant improvement in corrosion resistance along with marginal improvement in mechanical properties is observed upon addition of HAp. Moreover, HAp incorporation into Mg66Zn30Ca4 metallic glass has enhanced the cell viability and cell adhesion of human osteoblast-like cell (MG63) cells, complementing the excellent biocompatibility, bioactivity, osteoconductivity and osteoinductivity of hydroxyapatite mineral due to its biomimetic nature. HA reinforcement is not only a promising approach to improve the corrosion resistance, but also offers a biomimitic interface to enhance osseointegration and overall competence of orthopedic implants. © 2018 IOP Publishing Ltd.

Biomedical Physics and Engineering Express

Hydroxyapatite particle (HAp) reinforced biodegradable Mg-Zn-Ca metallic glass composite for bio-implant applications

Rolling/sliding wear behaviour of two newly designed low-carbon, continuously cooled, carbide-free bainitic rail steels has been studied and compared with pearlitic rail steel. Bainitic rail steels showed higher wear resistance than pearlitic rail steel and wear resistance increases with increasing starting hardness. Detailed microstructural characteristics of the steels undergoing wear were investigated. Wear resistance of carbide-free bainitic rail steels has been found to increase with increasing retained austenite content and decreasing bainitic ferrite lath thickness. © 2018 Elsevier B.V.

Wear

Dry rolling/sliding wear behaviour of pearlitic rail and newly developed carbide-free bainitic rail steels

A long-standing effort has been devoted for the development of high energy density cathodes both for Li- and Na-ion batteries (LIBs and SIBs). The scientific communities in battery research primarily divide the Li- and Na-ion cathode materials into two categories: layered oxides and polyanionic compounds. Researchers are trying to improve the energy density of such materials through materials screening by mixing the transition metals or changing the concentration of Li or Na in the polyanionic compounds. Due to the fact that there is more stability in the polyanionic frameworks, batteries based on these materials mostly provide a prolonged cycling life as compared to the layered oxide materials. Nevertheless, the bottleneck for such compounds is the weight penalty from polyanionic groups that results into the lower capacity. The anion engineering could be considered as an essential way out to design such polyanionic compounds to resolve this issue and to fetch improved cathode performance. In this topical review we present a systematic overview of the polyanionic cathode materials used for LIBs and SIBs. We will also present the computational methodologies that have become significantly relevant for battery research. We will make an attempt to provide the theoretical insight with a current development in sulfate (SO4), silicate (SiO4) and phosphate (PO4) based cathode materials for LIBs and SIBs. We will end this topical review with the future outlook, that will consist of the next generation organic electrode materials, mainly based on conjugated carbonyl compounds. © 2018 IOP Publishing Ltd.

Journal of Physics: Condensed Matter

Current computational trends in polyanionic cathode materials for Li and Na batteries

The ever-increasing consumption of energy storage devices has pushed the scientific community to realize strategies toward organic electrodes with superior properties. This is owed to advantages such as economic viability and eco-friendliness. In this context, the family of conjugated dicarboxylates has emerged as an interesting candidate for the application as negative electrodes in advanced Li-ion batteries due to the revealed thermal stability, rate capability, high capacity and high cyclability. This work aims to rationalize the effects of small molecular modifications on the electrochemical properties of the terephthalate anode by means of first principles calculations. The crystal structure prediction of the investigated host compounds dilithium terephthalate (Li2TP) and diethyl terephthalate (Et2Li0TP) together with their crystal modification upon battery cycling enable us to calculate the potential profile of these materials. Distinct underlying mechanisms of the redox reactions were obtained where Li2TP comes with a disproportionation reaction while Et2Li0TP displays sequential redox reactions. This effect proved to be strongly correlated to the Li coordination number evolution upon the Li insertion into the host structures. Finally, the calculations of sublimation enthalpy inferred that polymerization techniques could easily be employed in Et2Li0TP as compared to Li2TP. Similar results are observed with methyl, propyl, and vinyl capped groups. That could be a strategy to enhance the properties of this compound placing it into the gallery of the new anode materials for state of art Li-batteries. © 2018

Nano energy

Identifying the tuning key of disproportionation redox reaction in terephthalate: A Li-based anode for sustainable organic batteries

Design of multi-phase high entropy alloys uses metastability of phases to tune the strain accommodation by favoring transformation and/or twinning during deformation. Inspired by this, here we present Si containing dual phase Fe42Mn28Co10Cr15Si5 high entropy alloy (DP-5Si-HEA) exhibiting very high strength (1.15 GPa) and work hardening (WH) ability. The addition of Si in DP-5Si-HEA decreased the stability of f.c.c. (γ) matrix thereby promoting pronounced transformation induced plastic deformation in both as-cast and grain refined DP-5Si-HEAs. Higher yet sustained WH ability in fine grained DP-5Si-HEA is associated with the uniform strain partitioning among the metastable γ phase and resultant h.c.p. (ϵ) phase thereby resulting in total elongation of 12%. Hence, design of dual phase HEAs for improved strength and work hardenability can be attained by tuning the metastability of γ matrix through proper choice of alloy chemistry from the abundant compositional space of HEAs. © 2018 The Author(s).

Extremely high strength and work hardening ability in a metastable high entropy alloy

Material processing plays a vital role in fabrication of appliances and components of specific properties by selecting a right kind of material. In today's context, the widely used structural steels must have properties of high strength and environmental corrosion resistance to overcome the limitations of iron-carbon plane steels, which show pitting resistance of zero equivalent number (PREN). Therefore, towards overcoming the limitations and enhancing the strength, various notch wavy rolling techniques were developed for environmental friendly austenitic stainless steel (ASS) sheets, especially, for thin sections to have light weight. The ASS material shows good corrosion resistance (PREN > 18 for AISI 304 SS) but it also shows low yield strength and high ductility after solution annealing treatment. Furthermore, it has a drawback of undergoing phase transformation from austenite (fcc-crystalline structure) to martensite (bcc/bct) when subjected to large plastic deformation at ambient temperature. By applying the notch wavy rolling techniques, the yield strength of such 304 ASS material can be increased from 300 MPa to 750 MPa, along with the optimized ductility ranging from 52% to 25%, respectively. These are considered to be very important and favorable properties for advanced structural applications. Strain hardening ratio after the process was also determined. The microstructural changes responsible for such improvements in properties of the processed material were studied using optical microscopy and AFM techniques. © 2018 Elsevier Ltd.