60 research outputs found

    WELDING OF NITINOL BY SELECTED TECHNOLOGIES

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    Nitinol is a perspective alloy that is difficult to weld because of its high sensitivity to heat, atmospheric gases and the NiTi phase instability. We evaluated several welding techniques with regard to their applicability to weld fine pseudoelastic NiTi wires. Namely, we tested the microplasma arc, laser, electron beam, resistance and capacitor discharge welding. In conclusion, the behaviour of the weld for any of the implemented welding techniques is similar; it leads to a loss of mechanical properties in the welded joint caused by a recrystallization and an increased amount of brittle intermetallic phases. Yet, under perfect shielding and with a minimum heat input, the welds could, as a whole, retain the majority of their properties, and, as such, have the desired properties close to the base metal

    Advances in Plasma Arc Welding: A Review

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    The nature of welding in the aeronautical industry is characterized by low unit production, high unit cost, extreme reliability and severe service conditions. These characteristics point towards more expensive and more concentrated heat sources such as plasma arc, laser beam and electron beam welding as the processes of choice for welding of critical components. Among various precision welding processes, Plasma Arc welding has gained importance in small and medium scale industries manufacturing bellows , diaphragms etc because of less expensive and easy to operate. This paper reviews the works on Plasma Arc welding and associated phenomena such as Micro Plasma Arc Welding, Variable Polarity Plasma Arc welding and Keyhole Plasma Arc Welding. The review covers works carried out by various researchers on various metals using different modes of plasma arc

    INFLUENCE OF WELDING TECHNIQUES ON MICROSTRUCTURE AND HARDNESS OF STEEL JOINTS USED IN AUTOMOTIVE AIR CONDITIONERS

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    Austenitic steels belong to a group of special-purpose steels that are widely used in highly aggressive environments due to their enhanced anticorrosive behavior and high mechanical properties. The good formability and weldability of these materials has made them very popular in automotive AC systems. This study presents the results of hardness tests and microstructure observations on plasma- and laser-welded joints. The examined joints consisted of two different stainless steel components; i.e., a nipple made from corrosion-resistant AISI 304 steel and a corrugated hose made from 316L steel. Microplasma welding was carried out on a workstation equipped with an MSP-51 plasma supply system and a BY-100T positioner. The laser-welded joint was made on a numerically controlled workstation equipped with an Nd:YAG laser (without filler material) with 1 kW of maximum power; the rotational speed of the welded component was n = 4 rpm. Microstructural observations were performed using a scanning electron microscope and an optical microscope. Vickers hardness was measured with a hardness tester. The obtained results proved that both the microplasma- and laser-welded joints were free from any visible welding imperfections. In the micro areas of the austenitic steel weld, crystals of intercellular ferrite appeared against a background of austenite. The crystallization front (depending on the welding technology) was running from the fusion line towards the weld axis. The grain size depended on the distance from the fusion line

    Welding Studies on a Near-alpha Titanium Alloy

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    The mechanical properties and microstructures of electron beam and friction welds of a near-alpha titanium alloy IMI 834 (presently TIMET 834) have been evaluated. Electron beam welds that contain micro pores and friction welds are free from such solidification-related defects. Porosity index in electron beam welds shows a decreasing trend with an increase in the welding speed. Electron beam welds contain coarse prior β grains and fine transformed β microstructure while, friction welds contain fine prior β grains and coarse transformed β microstructure. Electron beam welds with fine transformed β microstructure exhibited higher strength as compared to friction welds with coarse transformed β microstructure. The impact toughness of both the welds is comparable. Drastic reduction in impact toughness was observed when the welds were subjected to post-weld ageing as a result of inter-lath precipitation. Coarse-grained electron beam welds exhibited better creep and stress rupture properties as compared to friction welds.Defence Science Journal, 2011, 61(6), pp.590-596, DOI:http://dx.doi.org/10.14429/dsj.61.64

    An Overview of TIG Welding of Ti6Al4V : Recent Developments

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    Abstract: Titanium is a commonly used non-ferrous metal in the aerospace, chemical and nuclear industry, due to its unique structural and mechanical properties. Selection of suitable welding techniques and understanding of the effects of parameters corroboration to achieve a quality joint necessitated this article. The article presents recent researches in process parameters optimization done on Tungsten Inert Gas (TIG) welding of Ti6Al4V alloy. Furthermore, it discusses the effects of the parameters used in TIG welding technique on the weld quality, mechanical properties, and microstructure of joined plates. Pulsed TIG welding was found to be the most suitable type of welding for Ti6Al4V alloys based on its ease of use and reduced heat input compared to the conventional TIG welding

    Feasibility of remotely manipulated welding in space. A step in the development of novel joining technologies

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    In order to establish permanent human presence in space technologies of constructing and repairing space stations and other space structures must be developed. Most construction jobs are performed on earth and the fabricated modules will then be delivered to space by the Space Shuttle. Only limited final assembly jobs, which are primarily mechanical fastening, will be performed on site in space. Such fabrication plans, however, limit the designs of these structures, because each module must fit inside the transport vehicle and must withstand launching stresses which are considerably high. Large-scale utilization of space necessitates more extensive construction work on site. Furthermore, continuous operations of space stations and other structures require maintenance and repairs of structural components as well as of tools and equipment on these space structures. Metal joining technologies, and especially high-quality welding, in space need developing

    Design and manufacture of functional titanium–palladium devices for the activation of anti-cancer prodrugs

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    National health organisations and authorities have reported an increment in death cases due to cancer. To overcome this issue and improve the survival rate, it is needed to find new clinical methods, early diagnoses techniques and treatments. Radiation and chemotherapy have been used for years to treat cancer. However, these types of treatments have serious side effects such as hair loosing, the mortality of healthy cells and other organs. A new treatment based on prodrugs therapy is in development with the intention to reduce these side effects or to replace the harmful treatments completely. Prodrug treatments need an activation agent, i.e. a catalyst, to convert the prodrug delivered to the cancerous cells to an active drug in-situ. Metals such as palladium can be used as a catalyst to activate the prodrug in targeted cancer cells. In this PhD study, the research was divided into two major aspects. The first aspect was to design and manufacture a catalyst carrier with specific properties and specifications such as biocompatibility of the materials used as the carrier, suitable mechanical properties to withstand physiological loads and conditions, and cost efficiency of the production. Two different manufacturing methods were used, Powder Metallurgy technique and Arc Melting technique, to achieve the optimal fabrication method. The carriers were characterised via XRD, SEM, EDS, DSC methods and mechanical tests to ensure the carrier meets the requirements. In the second stage, the carriers were coated with Palladium in its metallic state (i.e. Pd0). The coating was required to meet the requirements of being unalloyed, pure and free of any contamination, and its deposition cost and time effective. Four coating methods were employed. Powder Metallurgy technique and sintering (with and without space holder), Magnetron Sputtering, Pulsed Laser Deposition and Supersonic Beam Cluster Deposition methods were used to apply Palladium coating onto the carriers. The coating was characterised by XPS, XRD, FIB, XRF, SEM, EDS, biochemical and in-situ biological tests. The results obtained confirmed that the devices achieve high biocompatibility of the materials, and an excellent superelasticity can withstand the loads inside the human body. Also, the Magnetron sputtering methods as a coating method demonstrated it is the most effective for achieving a uniform and long-lasting deposited layer. The devices were able to activate a clinically approved prodrug.</div

    Current Air Quality Issues

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    Air pollution is thus far one of the key environmental issues in urban areas. Comprehensive air quality plans are required to manage air pollution for a particular area. Consequently, air should be continuously sampled, monitored, and modeled to examine different action plans. Reviews and research papers describe air pollution in five main contexts: Monitoring, Modeling, Risk Assessment, Health, and Indoor Air Pollution. The book is recommended to experts interested in health and air pollution issues

    Welding Properties of Titanium Alloys Grade 5

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    Titanium alloys have attractive properties that have been widely used in various fields due to these properties. The biocompatibility of titanium has caused its usages in the pharmaceutical industry. Its good corrosion resistance has resulted in its many applications in petrochemical and marine industries. Meanwhile, the most important and major application of titanium and its alloys can be found in the aerospace industry in a variety of spacecraft, space rockets, and satellites. The most important reason for the widespread use of these alloys in the aerospace industry is the high ratio of strength to their weights. However, the most important factor limiting the usage of titanium and its alloys is its high price. In this chapter, we first introduced titanium and its alloys. Then, according to mainstream of the design, titanium alloy bonding methods and welding problems have been investigated. The purpose of this study is to investigate the processes of arc welding of tungsten electrode-neutral gas with different alloy heat inputs for a titanium alloy of Ti-6Al-4 V and to provide comprehensive welding instructions. So, after introducing the pure commercial titanium properties, we examined the properties, specifications and welding of Ti-6Al-4 V. Given the focus on the mentioned process, the generalities of this welding process have been described
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