Mechanical Properties, Microstructure, and Actuation Behavior of Wire Arc Additive Manufactured Nitinol: Titanium Bimetallic Structures.

Nitinol (NiTi) is well known for its corrosion resistance, shape memory effect, superelasticity, and biocompatibility, whereas Titanium (Ti) is well known for its high specific strength, corrosion resistance, and biocompatibility. The bimetallic joint of NiTi and Ti is required for applications that require tailored properties at different locations within the same component, as well as to increase design flexibility while reducing material costs. However, because of the formation of brittle intermetallic phases, connecting NiTi and Ti is difficult. In the present study, a systematic experimental investigation is carried out to develop NiTi-Ti bimetallic joint using wire arc additive manufacturing (WAAM) for the first time and to evaluate its microstructure, mechanical properties, martensitic transformation, and actuation behavior in the as-built condition. The defect-free joint is obtained through WAAM and microstructural studies indicate the formation of intermetallics at the NiTi-Ti interface leading to higher microhardness values (600 HV). Shape recovery behavior and phase transformation temperature were also enhanced in comparison to NiTi. An improved actuation and bending angle recovery is observed in comparison with NiTi. The present study lays the way for the use of WAAM in the construction of NiTi and Ti bimetallic structures for engineering and medicinal applications.

Characterisation of AZ31 metal matrix composites reinforced with carbon nanotubes.

The focus of this study revolves around the synthesis of AZ31 metal matrix composites (MMCs) reinforced with carbon nanotubes (CNTs) using the powder metallurgy technique. Various compositions of CNTs were incorporated into the AZ31 alloy matrix. The sintered specimens were analysed using microstructural characterization and Fourier transform infrared (FTIR) spectroscopy. Furthermore, differential scanning calorimetry (DSC) were conducted to investigate the impact of sintering on the processed composites. Corrosion studies were performed in a sodium chloride (NaCl) medium, and Tafel curves were plotted to assess corrosion behaviour. It was observed that composites enriched with 0.5 wt.% CNTs demonstrated the highest level of corrosion resistance among the synthesized AZ31 metal specimens.

Enhancement of patterned triboelectric output performance by an interfacial polymer layer for energy harvesting application.

Efficaciously scavenging waste mechanical energy from the environment is an emerging field in the self-powered and self-governing electronics systems which solves battery limitations. It demonstrates enormous potential in various fields such as wireless devices, vesture, and portable electronic devices. Different surface textured PET triboelectric nanogenerators (TENGs) were developed by the laser pattern method in the previous work, with the line textured TENG device showing improved performance due to a larger surface contact area. Here, a polyethylene oxide (PEO) and polyvinyl alcohol (PVA) coated line patterned PET-based TENG was developed for the conversion of mechanical energy into useful electric energy. The PEO layer boosted the TENG output to 4 times higher than that of the PA6-laser patterned PET TENG device (our previous report) and 2-fold higher than that of a pristine line patterned TENG. It generated an open-circuit voltage, short circuit current, and instantaneous power density of 131 V, 2.32 µA, and 41.6 µW cm-2, respectively. The as-fabricated device was tested for 10 000 cycles for reliability evaluation, which shows no significant performance degradation. In addition, the device was deployed to power 10 LEDs with high intensity. Thus, this device can be used for ambient mechanical energy conversion and to power micro and nano-electronic devices.

Development of Sn-doped ZnO based ecofriendly piezoelectric nanogenerator for energy harvesting application.

In this work, we have a demonstrated zinc oxide (ZnO) polymer-based ecofriendly piezoelectric nanogenerator (PENG) on a paper substrate for an energy harvesting application. The ZnO thin film is developed on the paper substrate, where different doping concentrations of Sn have been investigated systematically to validate the effect of doping towards enhancing the device performance. The piezoelectric potential of the fabricated device is evaluated by applying three different loads (4 N, 8 N, 22 N), where the source of the corresponding mechanical loads is based on the object of a musical drum stick. The results suggest that the pristine ZnO PENG device can generate a maximum output voltage and current of 2.15 V and 17 nA respectively. Moreover, the ZnO PENG device doped with 2.5% Sn achieved an even higher voltage (4.15 V) and current (36 nA) compared to pristine ZnO devices. In addition, the hydrothermal growth technique used to develop Sn-doped ZnO has the benefits of high scalability and low cost. Hence, the Sn-doped PENG device is a suitable candidate for energy harvesting applications operating in both uniform and non-uniform loading conditions.

Green synthesis of near-infrared absorbing eugenate capped iron oxide nanoparticles for photothermal application.

Nanomaterials exhibit different interesting physical, chemical, electronic and magnetic properties that can be used in a variety of biomedical applications such as molecular imaging, cancer therapy, biosensing, and targeted drug delivery. Among various types of nanoparticles, super paramagnetic iron oxide nanoparticles (SPIONs) have emerged as exogenous contrast agents for in vitro and in vivo deep tissue imaging. Here, we propose a facile, rapid, non-toxic, and cost-effective single step green synthesis method to fabricate eugenate (4-allyl-2-methoxyphenolate) capped iron oxide nanoparticles (E-capped IONPs). The magnetic E-capped IONPs are first time synthesized using a medicinal aromatic plant, Pimenta dioica. The Pimenta dioica leaf extract was used as a natural reducing agent for E-capped IONPs synthesis. The crystalline structure and size of the synthesized spherical nanoparticles were confirmed using the x-ray diffraction and electron microscopic images respectively. In addition, the presence of the functional groups, responsible for capping and stabilizing the synthesized nanoparticles, were identified by the Fourier transform infra-red spectrum. These nanoparticles were found to be safe for human cervical cancer (HeLa) and human embryonic kidney 293 (HEK 293) cell lines and their safety was established using MTT[3-(4, 5-Dimethylthiazol-2-yl)-2, 5-Diphenyltetrazolium Bromide] assay. These green synthesized E-capped IONPs display a distinct absorbance in the tissue transparent near-infrared (NIR) wavelength region. This property was used for the NIR photothermal application of E-capped IONPs. The results suggest that these E-capped IONPs could be used for deep tissue photothermal therapy along with its application as an exogenous contrast agent in biomedical imaging.

Multi-Response Optimization of WEDM Process Parameters for Machining of Superelastic Nitinol Shape-Memory Alloy Using a Heat-Transfer Search Algorithm.

Nitinol, a shape-memory alloy (SMA), is gaining popularity for use in various applications. Machining of these SMAs poses a challenge during conventional machining. Henceforth, in the current study, the wire-electric discharge process has been attempted to machine nickel-titanium (Ni55.8Ti) super-elastic SMA. Furthermore, to render the process viable for industry, a systematic approach comprising response surface methodology (RSM) and a heat-transfer search (HTS) algorithm has been strategized for optimization of process parameters. Pulse-on time, pulse-off time and current were considered as input process parameters, whereas material removal rate (MRR), surface roughness, and micro-hardness were considered as output responses. Residual plots were generated to check the robustness of analysis of variance (ANOVA) results and generated mathematical models. A multi-objective HTS algorithm was executed for generating 2-D and 3-D Pareto optimal points indicating the non-dominant feasible solutions. The proposed combined approach proved to be highly effective in predicting and optimizing the wire electrical discharge machining (WEDM) process parameters. Validation trials were carried out and the error between measured and predicted values was negligible. To ensure the existence of a shape-memory effect even after machining, a differential scanning calorimetry (DSC) test was carried out. The optimized parameters were found to machine the alloy appropriately with the intact shape memory effect.

A Comparative Analysis of ZnO Nanorods and Nanopencils Towards Amperometric Biosensing Applications.

In this work, ZnO Nanorods (ZNR) and Nanopencils (ZNP) were synthesized over Platinum (Pt) coated glass substrate by simple and low-temperature hydrothermal process for large-scale fabrication towards biosensing applications. The two types of morphologies have been obtained by using strong oxidizing agent viz KMnO4 as an additive and replenishing the growth solution during the hydrothermal growth process. It was observed that incorporation of additive and replacement of growth solution has greatly influenced structural and electrochemical properties of ZNR/ZNP in terms of morphology, aspect ratio, and charge transfer hindrance. The aspect ratio has been found to increase by approximately three times from ZNR to ZNP which facilitated higher enzyme loading over ZNP as compared to ZNR. Moreover, electrochemical charge transport resistance was found to decrease by 36 times with changes in morphology and aspect ratio. Hence, significant variation in performance of as-fabricated enzymatic biosensor was observed. Amidst both the types of biosensors four-fold increment in sensitivity was found from ZNR to ZNP along with fast response time of 5s and a linear range of operation of 0.5-7.5 mM. The obtained results revealed that aspect ratio could be tuned efficiently by replacing the growth solution during hydrothermal growth which cognitively effects enzyme loading thereby influencing different figure of merits of the biosensor.

Life cycle analysis of electrically actuated SMA spring using Talbot interferometry.

Electrically actuated shape memory alloys (SMAs) find widespread applications in engineering and science. Such materials are known to retain/remember their state. In the stressed/deformed state, when activated by the application of a suitable excitation mechanism, such as the use of heat or potential, they return to their original unstressed state. To test their reliability, it is a standard procedure to undertake a life cycle analysis. In this paper, the life cycle analysis of a SMA spring using the Talbot interferometric technique is reported. The life cycle of the SMA spring is analyzed in terms of the displacement drift, which sets in because of the functional fatigue generated due to its repeated use. Collimated light from a He-Ne laser transmitted through a beam splitter is converged through a focusing lens onto a plane mirror attached to the spring. Backreflected light from the mirror is incident on a set of two Ronchi gratings separated by the Talbot distance, forming a moiré pattern. The resulting interferograms are analyzed using a fringe rotation mechanism. The angle of orientation is a function of displacement drift. There is deterioration in the SMA property because of repeated cycles, and the spring loses its ability to return to its original unstretched position. The values of the displacement drift generated after 1, 1000, 2000, 3000, 4000, and 5000 such cycles as measured using a Talbot interferometer are 0, 0.875, 1.275, 1.459, 1.720, and 1.859 mm, respectively. It is observed that the SMA effect deteriorates as the number of stretching/contraction cycles increases. The uncertainty analysis is also reported. The expanded uncertainty was determined to be 201.61 µm.

Enhancement of ZnO-based flexible nano generators via a sol-gel technique for sensing and energy harvesting applications.

Zinc oxide (ZnO) is a remarkable inorganic semiconductor with exceptional piezoelectric properties compared to other semiconductors. However, in comparison to lead-based hazardous piezoelectric materials, its properties have undesired limitations. Here we report a 5∼6 fold enhancement in piezoelectric features via chemical doping of copper matched to intrinsic ZnO. A flexible piezoelectric nanogenerator (F-PENG) device was fabricated using an unpretentious solution process of spin coating, with other advantages such as robustness, low-weight, improved adhesion, and low cost. The device was used to demonstrate energy harvesting from a standard weight as low as 4 gm and can work as a self-powered mass sensor in a broad range of 4 to 100 gm. The device exhibited a novel energy harvesting technique from a wind source due to its inherent flexibility. At three different velocities (10∼30 m s-1) and five different angles of attack (0∼180 degrees), the device validated the ability to discern different velocities and directions of flow. The device will be useful for mapping the flow of air apart from harvesting the energy. The simulation was done to verify the underlining mechanism of aerodynamics involved.

Insights into non-noble metal based nanophotonics: exploration of Cr-coated ZnO nanorods for optoelectronic applications.

Herein, the room temperature photoluminescence and Raman spectra of hydrothermally grown ZnO nanorods coated with Cr are investigated for optoelectronic applications. A thorough examination of the photoluminescence spectra of Cr coated ZnO nanorods showed the suppression of deep level emissions by more than twenty five times with Cr coating compared to that of pristine ZnO nanorods. Moreover, the underlying mechanism was proposed and can be attributed to the formation of Schottky contacts between Cr and ZnO resulting in defect passivation, weak exciton-plasmon coupling, enhanced electric field effect and formation of hot carriers due to interband transitions. Interestingly, with the increase in sputtering time, the ratio of the intensities corresponding to the band gap emission and deep level emission was observed to increase from 6.2 to 42.7, suggesting its application for UV only emission. Further, a planar photodetector was fabricated (Ag-ZnO-Ag planar configuration) and it was observed that the dark current value got reduced by more than ten times with Cr coating, thereby opening up its potential for transistor applications. Finally, Cr coated ZnO nanorods were employed for green light sensing. Our results demonstrated that ZnO nanorods decorated with Cr shed light on developing stable and high-efficiency non-noble metal based nanoplasmonic devices such as photodetectors, phototransistors and solar cells.

Influence of Parametric Variations on Hydrothermal Growth of ZnO Nanostructures for Hybrid Polymer/ZnO Based Photodetector.

Dumbbell and flower like ZnO nano-crystals were grown via hydrothermal process. The as-prepared dumbbells, with length of 0.8-10 µm and edge length of 0.3-0.8 µm possess a hexagonal structure, while flowers with lengths ranging from 1-6 µm with hexagonal structure have been synthesized. The effect of temperature, solution concentration and growth time on the size and shapes of the ZnO nanostructures has been studied using Field emission scanning electron microscope (FESEM) and X-ray diffractometer (XRD). Further the optical properties of nanostructures were investigated by Photoluminescence (PL) spectroscopy, which shows emission in UV and visible regions. From Diffused reflectance spectroscopic analysis (DRA) it was observed that ZnO nanodumbbells and nanoflowers have a direct band gap of 3.27 eV and 3.25 eV respectively. The I-V plot showed dependence of current values under dark and illumination over the annealing temperature during the growth stage. Thus we report a control over the shape and dimension of nanostructures by varying various parameters having implications for (opto)electronic devices.