I. A. Palani

Abstract: Among the various shaped memory alloys (SMA), nitinol (Ni–Ti alloy) finds applications in automotive, aerospace, biomedical and robotics The conventional route of fabrication of SMA has several limitations, like formation of stable secondary phases, fabrication of simple geometries, etc This paper reports a novel method of fabricating SMA using a laser based additive manufacturing technique Three different compositions of Ni and Ti powders (Ni-45% Ti-55%; Ni-50% Ti-50%; Ni-55% Ti45%) were pre-mixed using ball-milling and laser based additive manufacturing system was employed to fabricate circular rings The material properties of fabricated rings were evaluated using Scanning Electron Microscopy (SEM), Differential scanning calorimeter (DSC), X-ray diffraction (XRD) system and micro-hardness test All the characterized results showed that SMA could be manufactured using the laser based additive manufacturing process The properties of laser additive manufactured SMA (Ni-50% Ti-50%) were found to be close to that of conventionally processed SMA

Abstract: Texturing the rake face of the cutting tools has recently emerged as a promising and environment friendly method for reducing friction during machining. Laser surface texturing has been the most commonly used method for fabricating textures on the cutting tool. This paper reports the experimental study of fabricating an array of micro scale dimples on the rake face of high speed steel cutting tool using a pulsed Nd:YAG laser. The effect of the laser parameters like wavelength and fluence on the dimensions and form of individual dimples were studied. Analysis of results show that uniform circular shaped dimples with very little spatter can be obtained using low fluence levels at wavelength of 355 nm. An array of micro scale dimples were then fabricated on the cutting tool using the optimized parameter levels. A very low textured area density was used in order to understand the process of chip flow over the textures and study the effect of machining on individual dimples. This textured cutting tool was then used in orthogonal dry machining of Al7075-T6 aerospace alloy and compared with the performance of conventional tools. Use of textured cutting tools resulted in reduction of both cutting and thrust forces. The tool-chip contact length is also less in the case of textured tool. The results show that textured high speed steel tools can significantly improve the metal cutting process while dry machining ductile workpieces.

Abstract: In the present research, an approach of converting amorphous-silicon (a-Si) thin films into polycrystalline thin films using the third harmonics of an all-solid-state pulsed Nd 3+ :YAG laser (355 nm) is studied. Two different samples of a-Si thin films on alkali-free glass (a-Si/glass) substrates and a-Si thin film on crystalline-Si substrates (a-Si/c-Si) are laser treated at different laser fluences ranging from 170 to 960 mJ/cm 2 . The amount of heat incident on the surface has been analyzed theoretically by solving the one-dimensional heat-equation model. The ablation threshold, the region of crystallization and the depth of crystallization have been investigated theoretically. The influence of laser irradiation, ablation and crystallinity has been experimentally analyzed through in-situ reflectivity measurements, scanning electron microscopy (SEM) and Raman spectroscopy studies. In the case of a-Si/c-Si, the extent of crystallinity and the influence of structural characteristics on electronic properties are studied using the Hall-effect technique. The ablation threshold and the range of crystallization regime are in good agreement with the theoretical results. Laser fluence between 300 and 500 mJ/cm 2 is required for crystallization and the ablation threshold is estimated to be above 500 mJ/cm 2 for a-Si thin film with a thickness up to 400 nm.

Abstract: For the first time, NiTi shape memory alloy was successfully joined by Friction Stir Welding (FSW). The weld showed significant grain refinement without formation of detrimental phases. The yield strength of the weld joint increased by 17% as compared to the base metal without substantial change in shape memory behaviour.

Abstract: Photoluminescence spectra of metal (Al and Au)-coated ZnO nanorods synthesized by a facile low-temperature hydrothermal method with in situ addition of KMnO4 has been investigated. Further, dependence of defect density prior to metal coating on enhancement/suppression of UV and defect-related emissions have been investigated. The UV emission from metal-coated ZnO nanorods was greatly enhanced whereas the visible emission was significantly suppressed compared with the case of bare ZnO nanorods. Here, we have proposed a new mechanism elucidating the effect of Al and Au coating, incorporating the fact that nonradiative decay of surface plasmons to hot electrons and hot holes (generated through interband transitions) can be assigned for UV-emission enhancement and defect-related emission passivation, respectively. The recombination of electrons present at the defect level of ZnO to the hot holes generated with d–sp transition can be attributed for the suppression of deep level emission rather than the transfe...

Abstract: Driven by functionality and purity demand for applications of inorganic nanoparticle colloids in optics, biology, and energy, their surface chemistry has become a topic of intensive research interest. Consequently, ligand-free colloids are ideal reference materials for evaluating the effects of surface adsorbates from the initial state for application-oriented nanointegration purposes. After two decades of development, laser synthesis and processing of colloids (LSPC) has emerged as a convenient and scalable technique for the synthesis of ligand-free nanomaterials in sealed environments. In addition to the high-purity surface of LSPC-generated nanoparticles, other strengths of LSPC include its high throughput, convenience for preparing alloys or series of doped nanomaterials, and its continuous operation mode, suitable for downstream processing. Unscreened surface charge of LSPC-synthesized colloids is the key to achieving colloidal stability and high affinity to biomolecules as well as support materials,...

Abstract: Nickel-titanium (NiTi) is an attractive alloy due to its unique functional properties (i.e., shape memory effect and superelasticity behaviors), low stiffness, biocompatibility, damping characteristics, and corrosion behavior. It is however a hard task to fabricate NiTi parts because of the high reactivity and high ductility of the alloy which results in difficulties in the processing and machining. These challenges altogether have limited the starting form of NiTi devices to simple geometries including rod, wire, bar, tube, sheet, and strip. In recent years, additive manufacturing (AM) techniques have been implemented for the direct production of complex NiTi such as lattice-based and hollow structures with the potential use in aerospace and medical applications. It worth noting that due to the relatively higher cost, AM is considered a supplement technique for the existing. This paper provides a comprehensive review of the publications related to the AM techniques of NiTi while highlighting current challenges and methods of solving them. To this end, the properties of conventionally fabricated NiTi are compared with those of AM fabricated alloys. The critical steps toward a successful manufacturing such as powder preparation, optimum laser parameters, and fabrication chamber conditions are explained. The microstructural characteristics and structural defects, the influencing factors on the transformation temperatures, and functional properties of NiTi are highlighted to provide and overview of the influencing factors and possible controlling methods. The mechanical properties such as hardness and wear resistance, compressive behaviors, fatigue characteristics, damping and shock absorption properties are also reported. A case study in the form of using AM as a promising technique to fabricate engineered porous NiTi for the purpose of creating a building block for medical applications is introduced. The paper concludes with a section that summarizes the main findings from the literature and outlines the trend for future research in the AM processing of NiTi.

Abstract: Rational control over the morphology and the functional properties of inorganic nanostructures has been a long-standing goal in the development of bottom-up device fabrication processes. We report that the geometry of hydrothermally grown zinc oxide nanowires can be tuned from platelets to needles, covering more than three orders of magnitude in aspect ratio (~0.1-100). We introduce a classical thermodynamics-based model to explain the underlying growth inhibition mechanism by means of the competitive and face-selective electrostatic adsorption of non-zinc complex ions at alkaline conditions. The performance of these nanowires rivals that of vapour-phase-grown nanostructures, and their low-temperature synthesis (<60 °C) is favourable to the integration and in situ fabrication of complex and polymer-supported devices. We illustrate this capability by fabricating an all-inorganic light-emitting diode in a polymeric microfluidic manifold. Our findings indicate that electrostatic interactions in aqueous crystal growth may be systematically manipulated to synthesize nanostructures and devices with enhanced structural control.

Abstract: With large surface-to-volume ratios and Debye length comparable to their small sizes, one-dimensional inorganic nanostructures have extensively been investigated and widely used to fabricate high-performance nanoscale electronic and optoelectronic devices This feature article reviews the state-of-the-art research activities that focus on the one-dimensional inorganic nanostructures and their photodetector applications It begins with a survey of one-dimensional inorganic nanostructures and the fundamentals of photodetectors Some remarkable photoresponse characteristics are then presented, which are organized into sections covering several kinds of important nanostructures, such as ZnO, V 2 O 5 , ZnS, In 2 Se 3 , InSe, CdS, CdSe, ZnSe, Sb 2 Se 3 , ZrS 2 , Ag 2 S, and Zn x Cd 1-x Se Each section describes the corresponding photodetective properties in detail Finally, the article concludes with some perspectives and outlook on the future developments in the field