FBE- Metalurji ve Malzeme Mühendisliği Lisansüstü Programı - Yüksek Lisans

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  • Öge
    Wear behaviour of multilayer coated WE43 magnesium alloy
    (Institute of Science and Technology, 2020) Kaba, Mertcan ; Malayoğlu, Uğur ; 638078 ; Department of Metallurgical and Materials Engineering
    Perspective on decreasing the weight of the components in order to reduce CO2 emission has led the manufacturers in automotive and aerospace industries to consider the application of magnesium alloys owing to their high specific strength (strength to weight ratio). However, the limited strength of the magnesium alloys, especially above 120 °C, restricts their extensive usage. For this reason, instead of widely-used aluminium and zinc containing alloys such as AZ31 and AZ91, WE series magnesium alloys containing yttrium and rare earth elements have been developed for high temperature application up to 300 °C. Considering its high temperature and creep resistances, WE series alloys are attractive for aerospace and automotive industries. However, similar to the most widely used ones, this new alloy also suffers from poor wear and corrosion resistance due to low hardness and high surface reactivity. Therefore, in order to enhance wear and corrosion resistance of WE series alloys, modification of the surfaces by various techniques appears as an essential technical solution. In this respect, micro-arc oxidation (MAO) process, which forms magnesium oxide-based coatings, has been successfully employed on many commercially available grades of magnesium alloys. In the open literature, a few numbers of MAO studies have been conducted on the WE series alloys with the aim of improving the corrosion resistance. To the author's best knowledge, only one study is available in the open literature stating improvement in room temperature wear resistance of WE43 alloy by MAO process, which formed a coating consisting of magnesium oxide and magnesium silicate. However, magnesium oxide-based coatings did not provide sufficient protection against corrosion and wear due to their lower hardness and poor compactness. From this point of view, higher hardness of aluminium oxide (alumina) as compared to magnesium oxide motivated some researchers to fabricate multilayer coatings on magnesium alloys by applying cold spray and MAO processes sequentially. Thus, after the coating of magnesium alloys with aluminium or aluminium matrix composites by cold spray technique, MAO process has been employed to form aluminium oxide-based coatings at the outermost surface. The multilayer coating composed of alumina and aluminium or aluminium matrix composite layer exhibited superior wear and corrosion resistance than that of monolayer magnesium oxide-based coating. In the scope of this study, which was initiated mainly with the aim of improving high temperature wear resistance, multilayer (aluminium matrix composite/alumina) coating was fabricated on the WE43 magnesium alloy by subsequently applying CS and MAO process. While commercially available alumina particle reinforced aluminium matrix powder was used in the cold spray process, MAO processes were conducted in an aluminate-based electrolyte. In order to compare the properties of multilayer coat-ing with monolayer magnesium oxide coating, WE43 alloy was also subjected to the MAO process. Structural characterization of the fabricated coatings was done by using an optical microscope, energy dispersive spectroscopy equipped scanning electron microscope, and a X-ray diffractometer.
  • Öge
    Ergitici olarak kullanılan farklı alkali kaynaklarının seramik duvar karosu bünyesindeki teknolojik özelliklere etkisinin incelenmesi
    (Fen Bilimleri Enstitüsü, 2020) Emir, Merih Anıl ; Arslan, Cüneyt ; 627642 ; Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
    Seramik karolar seramik malzemeden çeşitli ebatlarda levhalar halinde üretilen, zemin ve duvar kaplama malzemeleridir. Seramik karolar uluslararası ISO 14411 üretim yöntemi ve nihai ürünün su emme değerlerine göre bir çok grupta sınıflandırılmaktadır. Güncel ISO standartlarına göre seramik duvar karoları GRUP B III Su Emme Değeri %20>E> %10 olarak nitelendirilir. Teknik özellikleri açısından seramik duvar karoları genellikle %13-18 arasında su emme değerine sahip, eğme mukavemeti 200-250 kg/cm2 olan hammadde özellikleri açısından fırın çıkışında boyut küçülmeleri <%1'den az olan ve ticari kullanım alanına göre sınıflandırılan seramik kaplama malzemeleridir. Seramik sektöründe hammadde rezervlerinin belirli bölgelerde bulunmasından dolayı hammadde nakliyesi ürünlerin nihai oluşumunda maliyete etki eden en önemli etkenlerden bir tanesidir. Dolayısıyla hammadde seçiminde mevcut üretimin yapıldığı bölgelerden edinilecek hammaddeler maliyet anlamında da önemli oranda faydalar sağlayacaktır. Özellikle duvar karosu reçetelerinde kullanılan mikronize mermer ( CaCO3) 900 °C'de dekompozizasyonu ile CaO ve CO2'ye ayrışır. karbonatların dekompozisyonu sonucu bünyede porozite de artış gözlenir. Bununla birlikte ergime sıcaklıklarından dolayı duvar karosu reçetelerinde kullanılır. Ancak poroziteyi arttırıcı etki gösterdiklerinden dolayı reçetelerde kullanımı sınırlıdır. %20 >GRUP B III Su Emme Değeri > %10 aralığında olmalarından dolayı seramik yer karoları ve porselen karolara nazaran oldukça poroz bir yapıya sahiptir. Poroz yapısından dolayı nem alma kapasiteleri yüksektir. Bunun yanı sıra tek pişirim sıcaklıkları 1100-1150°C aralığındadır ve düşük üretim maliyetleri sebebiyle günümüzde kullanıcıların beğenisine sunulmaya devam etmektedir. Endüstriyel seramik üretiminde duvar karolarının en büyük problemi ise poröz bir yapıya sahip olmasından kaynaklı bünyenin nem alması sonucu oluşan düzlemden sapma hatalarıdır. Bununla birlitke zamanla oluşan boyut artışları ve bünye sır uyumsuzluklarından dolayı çatlaklar oluşabilir. Dolayısıyla seramik duvar karosu üretiminde teknolojik özellikler çok iyi irdelenmelidir. Seramik duvar karoları temel olarak yapısında kil, kaolen, feldspat ve kalsit barındırır. Ergitici olarak kullanılan feldspatların seramik bünyedeki görevi; ürünlerin sinterleşme sıcaklığını belirleyerek sıvı faza geçmesini sağlar ve aynı zamanda oluşturulan bünyelerin ergime sıcaklıklarını düşürürler. Doğada feldspat rezervlerinin çok fazla olmasına rağmen az sayıda oluşum ve seramik sektörüne uygun feldspatların az bulunması bu sebeple de maliyetlerinin fazla olması, reçetelerde feldpsat kullanımını sınırlandırmaktadır. Bu çalışmanın amacı; seramik bünyede ergitici olarak kullanılan ve Çanakkale yöresinden edinilen alternatif alkali içerikli ergiticilerin seramik duvar karosu bünyesindeki teknolojik özelliklere etkisini incelemek için yapılmıştır. Çalışmada standart reçeteyle birlikte 4 farklı ergitici kaynağı, oluşturulan reçetelere belirlenen oranlarla ilave edilerek toplamda 17 farklı reçete oluşturulmuştur.
  • Öge
    Development of iron-rich anode materials for lithium-ion battery technology from local FeCr alloys
    (Institute of Science and Technology, 2020) Gülcan, Mehmet Feryat ; Gürmen, Sebahattin ; 637664 ; Department of Metallurgy and Material Engineering
    Energy is an indispensable concept for all creatures to survive. Energy is also needed to increase the quality of lives. At this point, it can be said that secondary batteries become important because they play a critical role in the widespread use of portable devices that are employed in defence, home appliance and medical applications. Among the secondary batteries, lithium-ion batteries stand out in terms of their light in weight, high safety, theoretical capacity and energy density. However, their high costs restrict their extensive uses. History shows that after the industrial revolution steam machines replaced manpower and fossil fuels that were used to prefer as the energy source of the machines. However, mankind was greedy. Countries that became stronger with the acceleration of industrialization sought new resources in different geographies to meet their ever-increasing energy needs. This quest has led to various energy crises until this date. The positive opportunities provided by the use of energy obtained from renewable energy sources rather than the use of limited energy resources such as fossil have been expressed in many different platforms. The discontinuity of such renewable energy in question is overcome by the development of energy storage technologies. Following the works of Galvani and Volta in the 18th century, the first battery types were produced by Exxon in the 1970s where titanium disulphide and lithium metal were used as the cathode and the anode materials, respectively. Then in the 1990s, Goodenough et al. created a great milestone for studies on energy storage technologies with the secondary battery system that they proposed. In this battery (LIB) design transition metals were used as cathode and carbon was used as the anode materials. The fact that in 2019, they were awarded the Nobel Prize thanks to their LIB design, officially documented the importance of such technology in the world history. Then in 1980, Armand published the intercalation mechanism of lithium metal in LIB. In 1991, Sony announced the introduction of the LIB as a product into the market. Today, the market of lithium-ion batteries is growing day by day, while the researches to improve their energy and power densities as well as safety are also increasing exponentially. Simply, a lithium ion battery consists of four main elements: separator, negative electrode (Anode) , positive electrode (Cathode) and electrolyte. In charging, lithium ions of the cathode pass through the electrolyte and get in to the negative electrode, while electrons follow the ions and move on the external circuit to go to the anode. Then in discharging, lithium ions leave the anode material and return to their initial place in the cathode material. Meanwhile, electrons direct the stored energy to the desired application. Examples of positive electrodes include LiCoO2, LiFePO4 and LiMnO2, and the most widely used negative electrodes are silicon, transition metal oxide, and graphite. These electrode materials are produced by a wide variety of synthetic methods. However, in many of these production methods, since the starting material is of high purity, industrial scaled production processes often require working with a continuous maintenance of high quality raw materials. In this type of production process, where raw materials are dependent on foreign countries, the input value becomes unstable which causes financial difficulties in the production for long term business.
  • Öge
    Recycling of In2O3 from waste LCD panels & process design
    (Institute of Science and Technology, 2020-07-20) Tarı, Doğaç ; Gürmen, Sebahattin ; 506171227 ; Metallurgical and Materials Engineering ; Metalurji ve Malzeme Mühendisliği
    Indium's scarcity and increasing usage rate classifies it as a critical metal. As indium mines are depleted, recycling offers an alternative indium resource worldwide. Indium is used for various fields worldwide while electronics applications hold the biggest percentage. Specifically, optoelectronic applications are the most indium-consuming field. Our study aims to recycle In2O3 from scrap LCD and produce In2O3 particles by using different process routes. Indium based transparent conductive oxides (TCOs) offer higher transparency to visible light than their counterparts while having low electrical resistance. These properties enable In2O3 to be used on applications that require TCOs. While In2O3 thin films themselves can be used as TCOs, additions like zinc and tin help lower cost and improve properties. SnO2 addition is used for the most popular TCO on consumer products, Indium – Tin Oxide (ITO). Liquid crystal displays (LCD) are one of the devices that require a TCO, where TCO operates as an electrode. In LCD technology, electrodes (TCOs) are necessary to apply a voltage difference to liquid crystal and ITO is the most widely used TCO for LCD based screens. While LED screens are more dominant nowadays, this technology also depends on liquid crystals and uses TCOs, only difference being utilizing different backlight source. Display devices and other usage areas increase worldwide indium consumption. As consumption increases annually, mine capacities soon will not be able to match demand. This situation pushes researchers to study on different approaches to recycle indium from various sources. LCDs contain indium in the form of ITO thin films, which is found on smartphones, tablets, laptops, desktop monitors and televisions. These are commercial devices and have an average life cycle of 4-5 years or even shorter. After they complete their life cycles, they are collected as e-waste or waste electronic and electric equipment (WEEE). WEEEs are usually dismantled to reveal different parts like batteries, printed circuits, displays, magnets etc. Most parts of WEEE are recycled as they usually contain valuable elements. Therefore, indium-recycling methods can be included to existing e-waste recycling streams with ease as LCDs are already dismantled from their devices. In this study, we aimed to extract indium from End-of-life LCD glasses by leaching, cleaning the solution of impurities with solvent extraction and produce high-quality In2O3 particles by Ultrasonic Spray Pyrolysis (USP) method. LCD panels were obtained dismantled from their respective plastic housings and printed circuits. LCDs were split into front and back panels to expose ITO layers, which were in contact with liquid crystal sandwiched between front and back panels. Appropriate sizes were measured; glass was cut and weighed according to leach parameters. Leaching experiments involved multiple sections. First section utilized different acids (H2SO4 and HNO3) and same solid to liquid ratio (1:10). Aim was to test how indium and impurity concentration would change if solid weights were increased while maintaining solid to liquid ratio. The results showed that increased solid amount still yielded high indium concentration. Next two sections of leaching studies were done to increase the indium concentration in leach solutions while maintaining volume. H2SO4 and HNO3 with 1:10 solid to liquid ratio were used again. They were performed with multi-step approach (10 total steps), where same acid solutions were utilized to increase indium ion concentration remarkably. Leaching started with 1M H2SO4 and HNO3 separately; with each subsequent step leached solids were removed and a new set of solid (LCD pieces) was put into liquid (H2SO4 or HNO3, the acid solution from previous step). This resulted in a substantially higher concentration of indium compared to single step leaching, while maintaining volume. Last section of leach involved 1M H2SO4 as liquid media, 1:10 solid to liquid ratio and a custom tank design to maximize ITO – liquid interaction while minimizing liquid volume. Single piece, larger LCD glasses were used. This section also utilized the same multi-step approach as previous leachs. As a result, a high indium containing and relatively high volume solution was obtained. Afterwards, a model solution for multi-step leachate was prepared to conduct synthetic solvent extraction experiments for parameter optimization. D2EHPA diluted in kerosene was used for extraction; D2EHPA concentrations, shaking durations and O/A ratios were tested. 1M HCl was used to strip loaded D2EHPA solutions; shaking times and O/A ratios were tested. We determined optimized parameters from synthetic solution experiments and used them on high volume multi-step leachate. This leach solution was treated by parameter-optimized solvent extraction process to extract indium out and obtain indium-rich solutions for In2O3 production. Ultrasonic spray pyrolysis method is capable of producing particles with small, spherical size and homogeneous distribution. As commercial In2O3 particles are required to have good sinterability, USP was chosen as particle production method. Another reason was that USP requires a liquid solution as starting material and our planned solvent extraction experiments would yield indium-rich solutions. Our USP experiments included In2O3 production from synthetic nitrate salts with varying temperatures.
  • Öge
    Copper - diamond composite fabrication by electroforming process for thermal management applications
    (Institute of Science and Technology, 2020-07-07) Evren, Gökçe ; Ürgen, Mustafa ; 506171413 ; Metallurgical and Materials Engineering ; Metalurji ve Malzeme Mühendisliği
    Challenge in today's electronics world is miniaturization of electronic packages with suitable thermal management. Resistance against the conduction of electrons in electronic circuits causes heat generation. Generated heat should be dissipated quickly and reliably, or else device will encounter overheating related failures. Thermal management applications deals with heat dissipation. Simplest and most commonly applied thermal management method is conduction of the generated heat to air by means of a thermally conductive material, which is attached on heat generating component. For that purpose heat sinks or heat spreaders are commonly used in thermal management applications. Currently used heat sink materials are aluminum and copper; however, their usage in thermal management has a significant drawback that cannot be neglected. Despite being one of the highest thermally conductive metals, coefficient of thermal expansion (CTE) of copper is higher than the CTE of semiconductor on which heat sink is attached. For reliable heat dissipation and prevention of possible incompatible elongation related fractures, CTE of semiconductor material and heat sink material should match. Copper has a thermal conductivity of 398 W/m-1.K-1 and CTE of 17.10-6K.-1. Despite having satisfactory thermal conductivity, its CTE value is almost three times that of the semiconductor material. When copper is produced in composite form with diamond particles as reinforcement phase, not only a reduced CTE value is achieved, also an increased thermal conductivity is obtained. By adjusting the volume fraction of phases which constitute a composite material, material properties can also be adjusted. Diamond here is the reinforcing material of choice since having a thermal conductivity higher than 2000 W.m-1.K-1, highest among all known materials, and a CTE value of 1.1.10-6.K-1 makes diamond a unique material for thermal management applications. In this thesis, copper-diamond composite material to be used in thermal management applications is produced by electrochemical deposition method. Rather than conventional electrodeposition techniques, a modified sediment codeposition method is used. Particular electroforming system is designed for production of a near net shape and self-standing composite material. As electroforming electrolyte, traditional acidic copper sulfate plating bath containing 180 g/l copper sulfate, 30 g/l sulfuric acid, 0.1 g/l hydrochloric acid and 0.05 g/l Thiouera is prepared. 75 μm and 250 μm diamond particles are utilized in the codeposition process. Initial set of experiments are conducted without particles for optimization of operating conditions. After with optimized parameter smooth and bright copper is obtained, diamond is incorporated in copper matrix. First set of experiments are conducted 2-4 hours with 250 μm diamond particles. Particles are wetted in an electrolyte having identical composition with forming electrolyte prior to electroforming. Prior to electrodeposition process cathodic polarization curve is obtained potentiodynamically and the substrate surface potential required to be applied, corresponding to current density of 1 A/dm2, is derived from the polarization plot. As the deposit fills up the gaps between particles and grows further, available cathodic area changes. For that reason current density controlled deposition is not feasible. Therefore experiments were conducted potential controlled. Further experiments are conducted by optimized parameters with duration of 30 hours for copper to cover the particles entirely. After the surface coverage with homogeneous distribution of particles in matrix is obtained, reproducibility of method is examined using diamond particles with particle sizes of 75 and 250 μm. Annealing and cold isostatic pressing are applied for an improved copper-diamond interface. A group of samples are annealed for 2 hours at 650 °C, another group of samples are cold isostatic pressed for 10 minutes under the pressure of 1.5 x 106 N, a group of samples are both annealed and CIP'ed. Distribution of diamond particles, copper-diamond interface and morphology of copper deposit are investigated by Scanning Electron Microscopy. After cold isostatic pressing it is observed that copper morphology changed itself to an indented structure from a smooth morphology. X-Ray Diffraction patterns of samples with 75 μm diamond particles are plotted to investigate structural properties of as deposited samples and for observation of changes induced by annealing, cold isostatic pressing and both annealing and cold isostatic pressing. As deposited samples have copper peaks slightly shifted to smaller angles in respect of induced compression stresses while deposition. For annealed samples shifting to higher angles with a large extend is obtained. Cold isostatic pressing shifted the angles to smaller values. Copper peaks at smaller angles are also for the samples both exposed to cold isostatic pressing and annealing observed. Three point flexural test is conducted to as deposited and annealed samples to observe how mechanical properties are effected by annealing. Flexural strength test results indicated that flexural strength of copper-diamond composite is lowered by annealing. Flexural strength of annealed sample is 1.2 MPa while for as deposited sample it is 2.8 MPa. When there is a need for increased ductility regarding further forming processes material can be annealed. Copper-diamond composites produced with electroforming technique in desired shape and dimensions with enhanced diamond content. Material has void free structure and reliable interface.