Department of Metallurgical & Materials Engineering

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IIT Jodhpur

CuCrZr alloy (Cu-0.8wt-%Cr-0.1wt-%Zr) and 316L stainless steel (Fe-0.03wt-%C-16wt-%Cr-10wt-%Ni) plates were successfully friction stir lap welded resulting in significant mechanical mixing of the two matrix elements, Cu and Fe, in the stir zone. The severe mixing not only led to improved load bearing response but also leads to form Cu-rich and Fe-rich regions in the weld nugget. The formation of these phases governs the failure mechanism of the joint. Tensile properties of the weld showed promising response when compared with joints made for the similar alloy pair by other welding techniques. This suggests strong feasibility of applying FSW for joining Cu and steel for nuclear applications. © 2018, © 2018 Institute of Materials, Minerals and Mining. Published by Taylor & Francis on behalf of the Institute.

World University root node

Science and Technology of Welding and Joining

Towards attaining dissimilar lap joint of CuCrZr alloy and 316L stainless steel using friction stir welding

Metastability-based high entropy alloy design opens a new strategic path for designing high-strength materials. However, high strength is always coupled with poor damage tolerance under cyclic loading conditions (fatigue). To overcome this drawback, here we present grain-refined Fe42Mn28Cr15Co10Si5 exhibiting significantly high fatigue strength as compared with leading transformation induced plasticity steels upon friction stir processing. The enhanced fatigue behavior is attributed to the metastability-promoted γ→ϵ transformation that caused local variation in work-hardening activity near the crack tip, and subsequent crack branching. Thus, decreased γ phase stability assisted not only in attaining strength but also in making the alloy fatigue-resistant. © 2018, © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.

Fulltext

Materials Research Letters

Metastability-assisted fatigue behavior in a friction stir processed dual-phase high entropy alloy

Metal-ion batteries are key for energy storage in both portable electronics and large-scale applications. As the ion capacity of the widely used graphite electrodes is limited, 2D materials, in particular silicene, are considered for possible replacement. Here, the effects of B/Al doping on the ion capacity of silicene are studied and it is demonstrated that complex charge transfer leads to ultra-high Na capacity. Low Na/K diffusion barriers open potential for fast charge and discharge. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Advanced Theory and Simulations

Potential of B/Al-Doped Silicene Electrodes in Na/K-Ion Batteries

Efficient charge separation of photo-generated electrons and holes is critical to achieve high solar to hydrogen conversion efficiency in photoelectrochemical (PEC) water splitting. N-type doping is generally used to improve the conductivity by increasing the majority carrier density and enhance the charge separation in the photoanode. However, minority carrier transport is also very important in the process of charge separation, especially in materials that possess inadequate minority carrier mobility. Herein, we take a BiVO4 PEC water splitting cell as an example to demonstrate how to analyze the limiting factor and to formulate the corresponding solutions to improve the hole mobility. The benefits and problems caused by n-type doping (W-doping here) of BiVO4 are analyzed. Codoping with Ti further enhances the charge separation by improving the hole transport and leads to a cathodic shift of the photocurrent onset potential. A high charge separation efficiency (79% at 1.23 VRHE) in a compact BiVO4 photoanode has been achieved without any nanostructure formation. Theoretical results show that W-Ti codoping has decreased the hole polaron hopping activation energy by 11.5% compared with mono-W doping, and this has resulted in a hole mobility increase by 29%. The calculated adsorption energy and reaction Gibbs free energies indicate that the Ti site is energetically more favorable for water splitting. Moreover, the Ti site possesses a lower overpotential in the W-Ti codoped sample compared with the mono-W doped sample. The current study indicates that in order to improve the solar energy conversion efficiency, there should be a balanced charge transport of both majority and minority charge carriers. This can be achieved by simply choosing appropriate codoping elements. © 2018 The Royal Society of Chemistry.

Journal of Materials Chemistry A

Simultaneous enhancement in charge separation and onset potential for water oxidation in a BiVO 4 photoanode by W–Ti codoping

First principles electronic structure calculations based on the density functional theory (DFT) framework are performed to investigate hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) on two-dimensional Al2C monolayers. In addition to the pristine Al2C monolayer, monolayers doped with Nitrogen (N), Phosphorous (P), Boron (B), and Sulphur (S) are also investigated. After determining the individual adsorption energy of hydrogen and oxygen on the different functionalized Al2C monolayers, the adsorption free energies are predicted for each of the functionalized monolayers in order to assess their suitability for HER or OER. The density of states and optical absorption spectra calculations along with the work function of the functionalized Al2C monolayers enable us to gain a profound understanding of the electronic structure for the individual system and their relation to the water splitting mechanism. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

ChemPhysChem

Theoretical Evidence behind Bifunctional Catalytic Activity in Pristine and Functionalized Al2C Monolayers

In this study, the photocatalytic degradation of seven sulfur compounds (2-methylthiophene, 3-methylthiophene, 2-phenylthiophene, 3-phenylthiophene, 2,5-diphenylthiophene, 2-(2-thienyl) pyridine, and 2-(3-thienyl) pyridine in semiaqueous medium are compared to thiophene. The apparent-reaction-rate constant (k) is found to decrease in the following order: 2,5-diphenylthiophene &gt; 2-(2-thienyl) pyridine &gt; 2-penhylthiophene &gt; 3-penhylthiophene &gt; 2-(3-thienyl) pyridine &gt; 3-methylthiophene &gt; 2-methylthiophene &gt; thiophene. From the data obtained by UV light absorption (Λmax) measurements and electronic structure calculations (frontier orbitals energy, global hardness, and global softness), the kinetic parameters of the reaction have been determined. Among the studied compounds, thiophene with a high Λmax and low calculated LUMO-HOMO gap energy has showed higher activity under UV irradiation. Interestingly, a lower activity is observed with low Λmax and high LUMO-HOMO gap energy. This demonstrates, for the first time, that the reactivity depends essentially on the thermodynamic stability of the sulfur compound rather than on the nature or the position of the substituent on the ring. © 2018 American Chemical Society.

The Journal of Physical Chemistry C

New concept on photocatalytic degradation of thiophene derivatives: experimental and DFT studies

Despite continued interest in the multiferroic BiFeO3 for a diverse range of applications, use of this material is limited by its poor electrical leakage. This work demonstrates some of the most resistive BiFeO3 thin films reported to date via defect engineering achieved via high-energy ion bombardment. High leakage in as-grown BiFeO3 thin films is shown to be due to the presence of moderately shallow isolated trap states, which form during growth. Ion bombardment is shown to be an effective way to reduce this free carrier transport (by up to ≈4 orders of magnitude) by trapping the charge carriers in bombardment-induced, deep-lying defect complexes and clusters. The ion bombardment is also found to give rise to an increased resistance to switching as a result of an increase in defect concentration. This study demonstrates a systematic ion-dose-dependent increase in the coercivity, extension of the defect-related creep regime, increase in the pinning activation energy, decrease in the switching speed, and broadening of the field distribution of switching. Ultimately, the use of such defect-engineering routes to control materials will require identification of an optimum range of ion dosage to achieve maximum enhancement in resistivity with minimum impact on ferroelectric switching. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Advanced Materials Interfaces

Electronic Transport and Ferroelectric Switching in Ion-Bombarded, Defect-Engineered BiFeO3 Thin Films

The new generation γ-TiAl alloys contain higher amount Nb because of its effect on oxidation, strength and creep properties. This paper presents the effect of Nb addition in microstructure, oxidation behaviour and compression strength of two γ-TiAl alloys Ti-45Al-2Cr-7.5Nb-0.3B, Ti-45Al-2Cr-10Nb-0.3B and comparison with the properties of a standard gamma alloy Ti-48Al-2Nb-2Cr. The microstructural evolution was studied in as-cast, solutionized and aged conditions. The oxidation studies were carried out at 900°C in air for various time intervals up to 200 hrs and the type of oxide layer formed have been characterized by X-ray diffraction (XRD). The composition and phase analysis in all the three alloys were studied out electron probe micro analysis (EPMA). Finally the strength and oxidation behaviour were correlated with both the composition and microstructure. © 2017 Elsevier Ltd.

Materials Today: Proceedings

The Effect of Nb addition on microstructure, oxidation behavior and strength of some γ-TiAl alloys

Mg–Zn–Sr alloys are suitable for biodegradable orthopaedic implants due to excellent biocompatibility and bone regeneration effect of Sr. For Sr additions exceeding 0.2 wt%, ternary phases are observed in the microstructure contrary to binary MgxZny and Mg17Sr2 intermetallics predicted by the existing phase diagrams and corrosion and mechanical properties reduce drastically. Thermal analysis employed for Mg–4Zn–xSr alloys (0 ≤ x≤2) recorded two peaks, hitherto unreported, at temperatures of ~ 514 and 409 °C with 2 wt%, and ~ 549 and 428 °C with 1 wt% of Sr added to Mg–4Zn alloy. In conjunction with SEM–EDAX and XRD analysis, one of these phases is identified as Mg11Zn4Sr3, with second one an unknown intermetallic (IM2). Formation of Mg17Sr2 phase is suppressed in the presence of Zn, and the ternary phase is favoured beyond the solid solubility of Sr in Mg. Solidification pathway of L → α-Mg + Mg11Zn4Sr3 + unknown intermetallic (IM2) has been proposed for the ternary compositions with Sr &gt; 0.2 wt% investigated in the current study. © 2018, The Indian Institute of Metals - IIM.