Department of Metallurgical & Materials Engineering

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The microstructures and mechanical properties of friction stir processed 2507 super duplex stainless steel were examined. Experimental results revealed that there is an optimum traverse speed for a given rotational speed that gives minimum grain size. The individual and synergistic effects of FSP parameters such as heat input, strain rate and strain on the grain size of the material were evaluated. The results indicate that counteracting effect of heat input and the combined effect of strain rate and strain results in achieving minimum grain size at an intermediate traverse to rotation speed ratio. The twin boundaries (particularly Σ3 CSL boundaries) in the stir zone of friction stir processed material reduced considerably compared to that in the base material. Both the base material and the friction stir processed material with the smallest grain size achieved were subjected to tensile testing at ambient and elevated temperatures under different strain rates. The results obtained are presented and discussed here. © 2018 Elsevier B.V.

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Materials Science and Engineering A

On the microstructure evolution in friction stir processed 2507 super duplex stainless steel and its effect on tensile behaviour at ambient and elevated temperatures

The ability to synthesize high-quality, complex-oxide heterostructures has created a veritable playground in which to explore emergent phenomena and exotic phases which arise from the interplay of spin, charge, orbital, and lattice degrees of freedom. Of particular interest is the creation of artificial heterostructures and superlattices built from two or more materials. Through such approaches, it is possible to observe new phases and phenomena that are not present in the parent materials alone. This is especially true in ferroelectric materials where the appropriate choice of superlattice constituents can lead to structures with complex phase diagrams and rich physics. In this article, we review and explore future directions in such ferroic superlattices wherein recent studies have revealed complex emergent polarization topologies, novel states of matter, and intriguing properties that arise from our ability to manipulate materials with epitaxial strain, interfacial coupling and interactions, size effects, and more. We focus our attention on recent work in (PbTiO3)n/(SrTiO3)n superlattices wherein exotic polar-vortex structures have been observed. We review the history of these observations and highlights of recent studies and conclude with an overview and prospectus of how the field may evolve in the coming years. © 2018 Author(s).

Fulltext

APL Materials

Perspective: Emergent topologies in oxide superlattices

In this study, the electrodeposition of nickel foam by dynamic hydrogen bubble-template method is optimized, and the effects of key deposition parameters (applied voltage and deposition time) and bath composition (concentration of Ni2+, pH of the bath, and roles of Cl− and SO4 2− ions) on pore size, distribution, and morphology and crystal structure are studied. Nickel deposit from 0.1 M NiCl2 bath concentration is able to produce the honeycomb-like structure with regular-sized holes. Honeycomb-like structure with cauliflower morphology is deposited at higher applied voltages of 7, 8, and 9 V; and a critical time (&gt;3 minutes) is required for the development of the foamy structure. Compressive residual stresses are developed in the porous electrodeposits after 30 seconds of deposition time (−189.0 MPa), and the nature of the residual stress remains compressive upto 10 minutes of deposition time (−1098.6 MPa). Effect of pH is more pronounced in a chloride bath compared with a sulfate bath. The increasing nature of pore size in nickel electrodeposits plated from a chloride bath (varying from 21 to 48 μm), and the constant pore size (in the range of 22 to 24 μm) in deposits plated from a sulfate bath, can be ascribed to the striking difference in the magnitude of the corresponding current–time profiles. © 2018, The Minerals, Metals & Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

A Study on the Effect of Electrodeposition Parameters on the Morphology of Porous Nickel Electrodeposits

This paper communicates stabilization of a Sn anode by impregnating it within the porous framework of a Ni-scaffold. The impregnation is carried out by electrodeposition Sn on Ni-foam followed by heating at 300 °C for 1 h. The Ni-foam was also electrodeposited on a Cu foil prior to deposition of Sn. The melting step leads to the formation of Ni–Sn and Cu–Sn intermetallics within pores of the Ni-scaffold. Sn–Cu/Ni intermetallics lithiate following the active-inactive strategy in which the inactive Cu/Ni buffers the volume expansion while Sn lithiates. Furthermore, this entire process takes place within Ni-scaffold which resists material pulverization and delamination and provide better electronic pathway for charge transfer. This active-inactive Sn:Sn–Cu/Ni intermetallic within a protected Ni-scaffold assembly results in 100 th cycle discharge capacity of 587.9 mA h/g at a rate of 500 mA/g (0.5 C), and superior rate capability delivering 463 mAh/g at a rate of 2 A/g (2 C) while retaining structural integrity as compared to pure Sn electrodeposited (without heat-treatment) on the nickel scaffold. © 2018 Elsevier B.V.

Applied Surface Science

Melt impregnation as a post processing treatment for performance enhancement in high capacity 3D microporous tin-copper-nickel intermetallic anode for Li-ion battery supported by electrodeposited nickel scaffold: A structural study

This work reports the development of a novel bilayered Zn–Ni/Ni–Co–SiC nanocomposite coating on mild steel (MS) by electrodeposition. The top Ni-Co-SiC nanocomposite layer, when deposited directly on MS (monolayer) shows a hardness of 734 HV and a corrosion current density of ∼28μA/cm2 in 3.5 wt% NaCl. However, the lack of adherence of the coating with MS results in poor wear and scratch resistance. Mild steel is anodic to Ni–Co–SiC nanocomposite and any kind of discontinuity in the coating may lead to severe galvanic corrosion. This problem has been successfully overcome with the incorporation of an anodic (with respect to mild steel)Zn–12%Ni under-layerin between the electrodeposited Ni–Co–SiC nanocomposite coating and MS, which is adherent to both the materials. This bilayer coating has a hardness of 760 HV and corrosion current density of ∼19μA/cm2 in 3.5 wt% NaCl which are slightly better than that of the monolayer. Further, the bilayer coating assembly exhibits exceptionally low volume loss under wear (∼350 mm3) compared to bare mild steel (∼1700 mm3). This Zn–Ni/Ni–Co–SiC nanocomposite bilayercoating has the potential to emerge as hard, wear resistant and anti-corrosive coating which is essential in the field of heavy duty machines. © 2017 Elsevier B.V.

Journal of Alloys and Compounds

Novel bilayer Zn–Ni/Ni–Co–SiC nanocomposite coating with exceptional corrosion and wear properties by pulse electrodeposition

We have synthesized free-standing films of graphene oxide (GO), reduced graphene oxide (rGO) and graphene oxide-manganese oxide composite (GMC) for humidity and hydrogen peroxide sensing applications. Structural and morphological characterizations of these free-standing films were performed using X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). The presence of anionic sites in the form of oxygen functional groups (OFGs) at the surface of GO along with its hydrophilic nature makes GO a unique candidate as a suitable material for humidity and hydrogen peroxide sensing. In contrast, rGO has a relatively lower fraction of OFGs, higher electrical conductivity and hydrophobicity compared to GO. We estimate the response time, recovery time and stability of free-standing films over multiple sensing-degassing cycles of the as chemically prepared GO, rGO and GMC films for humidity sensing. We observed a dramatic improvement in both the response and recovery times for rGO and GMC films compared to GO film at relatively low humidity, while at higher humidity percentages, rGO film has the best response and recovery times compared to GMC and GO films. Regarding stability, GO was found to be more stable over multiple sensing cycles compared to rGO and GMC at high humidity values. In addition to this, we observed that the addition of metal oxide to GO makes GMC film more selective for hydrogen peroxide sensing in comparison to GO and rGO film at a lower concentration. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.

Journal of Materials Science: Materials in Electronics

Graphene oxide based free-standing films for humidity and hydrogen peroxide sensing

Scientific Reports

Erratum to: A Low-Cost Non-explosive Synthesis of Graphene Oxide for Scalable Applications (Scientific Reports, (2018), 8, 1, (12007), 10.1038/s41598-018-30613-4)

Deformation and fracture behaviors of AZ31 and E-form Mg alloys sheets were investigated during Erichsen test. Formability of Mg alloys was discussed in terms of Erichsen index (IE) and tests were conducted at room temperature using conventional Erichsen tester. The role of difference in initial textures and grain sizes in Mg alloys sheets was investigated to understand the deformation and fracture mechanisms in Mg alloys during Erichsen test. The evolution of the microstructure and microtexture of the deformed Mg alloys was analyzed via an electron back-scattered diffraction (EBSD) technique. Crystal plasticity finite element method (CPFEM) was used to predict the micromechanical deformation behavior of Mg alloys during Erichsen test. EBSD analysis revealed that deformation twins along with shear localization by dislocation slip were the main deformation mechanisms during Erichsen test. E-form Mg alloys with a weaker basal texture show higher IE compared to AZ31 alloy with a stronger basal texture. © The Minerals, Metals & Materials Society 2018.

Minerals, Metals and Materials Series

The effect of initial texture on deformation behaviors of Mg alloys under erichsen test

An analytical model was developed to determine the stress distribution over thickness for a multilayered thermal barrier coating (TBC) system deposited within a cylindrical reaction vessel. Temperature dependent material properties were used to estimate the stress values. It was found that, even for small lattice misfits, very high compressive elastic stresses could exist at the ceramic-bond coat interface immediately after deposition. Furthermore, this interfacial stress could ultimately relax to a lower value with increasing film thickness by dislocation nucleation. In the presence of a Thermally Grown Oxide (TGO), however, a tensile stress was generated within the oxide layer and discrete changes in stress profile were predicted at ceramic-TGO and TGO-bond coat interfaces. While the stress-change was higher at the ceramic-TGO interface for a high deposition temperature, the change was greater at the TGO-bond coat interface at a lower deposition temperature. A high compressive stress was predicted within the TGO layer upon cooling down the TBC system to room temperature and the stress-change was highest at the TGO-bond coat interface. Finally, when the TGO layer was subjected to fatigue loading under compressive mean stress during thermal cycling, the model predicted that the internal pressure of the cylindrical vessel reduces the magnitude of mean stress and increases the stress-range in the thermal stress cycle. The effects of evolved stresses on the context of interfacial failure of TBCs should provide fundamental insight into material selection and component design. © 2018

Mechanics of Materials

Modeling of thermal and lattice misfit stresses within a thermal barrier coating

Pressure tube spools fabricated from Zr-2.5%Nb alloy, were subjected to gaseous hydrogen charging and stress reorientation treatment to form radial hydrides in a specially designed fixture. Curved Compact Tension specimens of 17 mm width containing 100 wppm of hydrogen were made using electro discharge machining. Some of the samples were annealed at 300, 325 and 350 °C followed by furnace cooling. Metallographic examination of the samples revealed 100% radial hydride in the samples to which stress reorientation treatment was imparted. The radial hydride fraction decreased with increase in the temperature of annealing that followed stress reorientation. Fracture toughness of samples with variable radial hydride fraction was evaluated as per ASTM E1820-13 procedure between 25 and 300 °C. All the samples exhibited a sharp ductile to brittle transition behavior and the transition temperature was observed to increase with increase in the radial hydride fraction. © 2018 Elsevier B.V.