Carbothermic production of hexagonal BN by using boric acid and ground colemanite mined from Bigadi&ccedil / Region in Turkey was investigated by subjecting pellets prepared from B2O3, activated carbon and colemanite mixtures to nitrogen gas at 1500&deg / C. Similar to CaCO3 addition, colemanite addition to the B2O3-C mixtures resulted in higher amounts of h-BN in the final products. As a result of the experiments conducted with colemanite and CaCO3 additions providing the same quantity of CaO to the initial mixtures, similar amounts of hexagonal BN in the reaction products were observed. As a result of the experiments conducted with different compositions of colemanite- B2O3- C mixtures, 5 wt % colemanite addition was determined to be the optimum composition giving the highest amount of hexagonal BN in the reaction products. Increasing duration of the experiments increased the amount and particle size of h-BN formed in the products. Optimum amount of colemanite addition resulted in higher amounts and coarser particles of h-BN in the products than the optimum amounts of CaCO3 addition.

In Diesel engine blocks properties such as tensile strength, heat conductivity, sound damping, engine vibration and noise are strongly influenced by graphite shape and volume percent in the matrix microstructure. In this study, the engine blocks were produced at ELBA Basin&ccedil / li D&ouml / k&uuml / m Od&ouml / ksan Cast iron foundry in Osmaneli Turkey by performing casting into furan resin sand and preparing cast iron liquid alloy in induction furnace that were treated with Mg by using ladle method. The main purpose of this study is to achive 0 &ndash / 25% volume nodularity and remaining is compacted graphite in the produced engine blocks. The shape and volume percent of graphite particles were characterized by an image analyze system. In the first part of this work, after the diesel engine blocks were produced at ELBA Basin&ccedil / li D&ouml / k&uuml / m Od&ouml / ksan Cast iron foundry in Osmaneli Turkey, the blocks were cut and samples were obtained from 14 different thicknesses of diesel engine blocks. Afterwards, the samples were examined under optical microscope, Soif XJP-6A. The nodularity and compacted graphite values were obtained numerically with the help of Materials Plus image analyzer systems, which is attached to the optical microscope. v In the second part of the study, the diesel engine blocks which are produced at Od&ouml / ksan were examined by ultrasonic test that was done by using USM 35 flaw detector test machine. Solidification &ndash / time and temperature &ndash / time simulations were also done by using NovaCast NovaFlow simulation code. Finally mathematical formulas for 13 different thickness of diesel engine blocks were obtained by using excel linest code. The compacted graphite volume percent observed at different sections of the diesel engine blocks were found to be a function of cooling rate and chemical composition. Best results were obtained when chemical Mg/S ratio was approximately 1 and C.E.V. was between 4.40 &ndash / 4.50.

High Pressure Die Casting (HPDC) is low-cost technique for the mass production of complex, non-ferrous parts. Despite its benefits such as dimensional accuracy, surface quality and high production rate / some mechanical drawbacks limit use of HPDC in production of critical parts especially under dynamical loads. This study aims to improve impact resistance and surface hardness of die cast parts by means of tool steel inserts. These inserts act as a barrier between the impactor and die casting alloy, in order to avoid surface deformation and reduce stress localization which leads crack formation. Except the impact surface, whole insert is embedded into the die casting alloy by placing them on specially machined die casting molds prior to the metal injection. The mentioned method was evaluated by mechanical test and micro-examinations which were applied on AISI D2 tool steel inserted A518.0, A413.2 and Zamak5 alloy samples. To see the effect of inserts on energy absorbance under single destructive loads, both monolithic (conventional) and inserted (produced by mentioned technique) samples were subjected to Charpy impact test. In order to observe its behavior under non-destructive, cyclic, low velocity impacts / a dedicated real rifle part was produced by this method and tested in the real service loads. Explicit Finite Elemental Analysis was also carried out to understand how the inserts increases the energy absorbance and protect the die cast body by simulating both destructive and non-destructive impact loads. In addition to these, micro-examinations were also conducted especially on insert-die casting alloy interface for chemical and physical interactions, defects and stability. In regards of experimental findings, mechanical feasibility of the method was achieved. It was proved that steel inserts improve energy absorbance, stress distribution and impact-surface hardness of die cast products.

Magnesium (Mg) thin films with various thicknesses ranging from 50 to 1000 nm capped with nominally 20 nm Palladium (Pd) were prepared by a thermal evaporation unit. A total of 25 glass substrates were used in each experiment. The unit had a rotatable macro shutter, rectangular in shape, rotation axes opposite to the Mg source, which allowed controlled exposure of the substrates. Thin films of 50, 100, 150, 200, 300, 400, 500, 600, 800 nm and 1000 nm were produced in a single experiment. Hydrogenation and dehydrogenation of the films were examined using a gas loading chamber which allowed in-situ resistance measurement. Samples were hydrogenated isochronally up to 453 K with a heating rate of 1.5 K/min. Samples cooled to room temperature were subjected to dehydrogenation test. The chamber was taken under vacuum (~10-2 mbar) and the sample was heated up to 453 K at a rate of 1.5 K/min. The results showed that the hydrogenation and dehydrogenation temperatures correlate with the film thickness, thinner films reacting with hydrogen at low temperatures. While 200 nm thin film hydrogenated at 420 K and desorbed it at 423 K, 50 nm thin film hydrogenated at room temperature and desorbed it at 405 K. Thicker films needed higher temperatures to react with hydrogen. It is concluded that films thinner than 200 nm react fully with hydrogen / while a considerable portion of the thicker films remain unreacted. Significance of this is discussed with reference to the design of hydrogen storage systems based on thin films or nanoparticles.

It is of great importance for a materials scientist both from fundamental and applicability aspects to have better understanding of solid-state phase transformations and its kinetics responsible for micro-/nano-structure development in alloys and corresponding physical and mechanical properties. Transformation kinetics can be analyzed by various experimental techniques such as thermal analysis, laborious electron microscopy combined with extensive image analysis or by measuring changes in electrical resistivity, specimen volume and relative intensities of diffraction lines caused by the phase transformation. Beyond these conventional techniques, this dissertation provides a novel magnetic monitoring approach to study the isothermal kinetics of phase transformations in multicomponent alloy systems involving measurable changes in overall magnetic moment as the transformation proceeds. This dissertation focuses on understanding the microstructural evolution, macro- and micro-alloying behavior, magnetic properties, thermal characteristics, mechanical properties and kinetics of solid-state transformations, i.e. nanoscale precipitation and nanocrystallization, in nickel aluminides and Fe-based bulk amorphous alloys. Microstructural characterization of alloys was done by X-ray diffraction, scanning electron microscopy and transmission electron microcopy techniques. Magnetic properties were analyzed by vibrating sample magnetometry whereas thermal characteristics were evaluated by differential scanning calorimetry. Mechanical properties of alloys were determined by microhardness measurements and compression tests. The influence of Fe macroalloying and 3d transition metal microalloying on the microstructure and properties of Ni-Al-Fe alloys were studied for as-cast and annealed states and it is shown that desired microstructure and related properties can be obtained by proper selection of the type and concentration of macro- or micro-alloying elements together with an appropriate annealing procedure. Thermomagnetic characterization reveals the nanoscale precipitation of a ferromagnetic second phase with annealing. In conjunction with saturation magnetization dependence on annealing, an optimum temperature is identified where nanoscale precipitates impart the highest extent of precipitation strengthening. The isothermal kinetics of ferromagnetic second phase precipitation reveals invariant Avrami exponents close to unity, indicating that nanoscale precipitation is governed by a diffusion-controlled growth process with decreasing growth rate, which closely resembles continuous precipitation kinetics. Appropriate annealing of the Fe-based bulk amorphous alloy precursor produced by suction casting demonstrated extremely fine microstructures containing uniformly distributed and densely dispersed nanocrystals inside a residual amorphous matrix. In order to have better understanding of nanocrystallization mechanisms, kinetic parameters were determined via isothermal magnetic monitoring and non-isothermal differential scanning calorimetry where excellent agreement was obtained in Avrami exponent and activation energy. Analyzing the local kinetics, the nanocrystalline phase was found to evolve through distinct transformation regimes during annealing which were discussed on the basis of transformation kinetics theory and microscopical investigations on each characteristic transformation regime.

Porous Ti-6Al-4V alloys are widely used in the biomedical applications for hard tissue implantation due to its biocompatibility and elastic modulus being close to that of bone. In this study, porous Ti-6Al-4V alloys were produced with a powder metallurgical process, space holder technique, where magnesium powders were utilized in order to generate porosities in the range of 50 to 70 vol. %. In the productions of Ti-6Al-4V foams, first, the spherical Ti-6Al-4V powders with an average size of 55 &mu / m were mixed with spherical magnesium powders sieved to an average size of 375 &mu / m, and then the mixtures were compacted with a hydraulic press under 500 MPa pressure by using a double-ended steel die and finaly, the green compacts were sintered at 1200

The aim of this thesis is to investigate the effects of Mn content and alloying additions such as Cr and Mo, and various heat treatment procedures on both microstructure and mechanical properties of austenitic manganese (Hadfield) steels. For this purpose, steels with two different Mn content were considered (12-14 Mn, 16-18 Mn). First, five different heat treatment procedures were applied to the as-cast 12-14 Mn specimens to decide the procedure resulting the optimum tensile properties. Then, the specimens having various amounts of Mn, Cr and Mo were cast and heat-treated to investigate the effect of alloy modifications on austenitic manganese steels. Optical and scanning electron microscopies were used for microstructural investigation. To determine the mechanical properties, tensile tests and hardness tests were carried out. In addition to correlation between microstructure and mechanical properties, ultrasonic velocity measurements were also done. The results show that both composition and heat treatment affect the performance of hadfield steels extensively, and these changes also affect the propogation velocity of the ultrasonic waves.

The effect of physical, chemical and mineralogical properties on reducibility of iron containing raw materials were studied with the use of two pellets, one sinter and one lump iron ore sample provided by Erdemir integrated iron and steel works. Although Erdemir lump iron ore contained hematite, it was found to be less reducible than Erdemir sinter since porous structures are easier to reduce and in general sinters have a higher porosity as compared to lump ores. Experimental findings indicated that Erdemir pellet with a code B had the highest reducibility. On the other hand, the results of Erdemir samples were compared with those results obtained from the projects carried out in the Metallurgical and Materials Engineering Department of METU in 1980&rsquo / s. In mentioned projects, samples of various lump iron ores and a concentrate, pellet and sinter from Turkish sources and imported lump iron ores of CVRD from Brazil and ISCOR from the Republic of South Africa were tested. Within the context of this thesis, a mathematical model that would fit to the reduction kinetics was studied and the porous solid model was found to be the best for Erdemir samples.

In this work, nozzle clogging in the submerged entry nozzle in continuous casting of Al killed steels has been studied. The study has been based on low silicon Al killed SAE 1006 (1.2006) and SAE 1008 (1.2008) grades. In this study, castabilities of 75 heats for 1.2006 steel grades and 75 heats for 1.2008 steel grades have been investigated. Castabilities of the experimental heats have been found to be affected by Al content in oxide form (Aloxy) and Ca content of the liquid steel. Castabilities have been found to decrease with increase in Aloxy and to increase with increase in Ca content and Ca/Aloxy ratio. Reoxidation has been found not to affect the castability appreciably.

This study is on the production and testing of an aluminum metal matrix composite. Metal Matrix Composites can be produced in several different ways. In this study, an aluminum matrix composite is produced by direct addition of the reinforcement ceramic into the liquid metal. The ceramic reinforcement for this process was a mixture of TiB2 and Al2O3 which was produced by means of a thermite reaction of reactants Al, B2O3 and TiO2 all in powder form with their respective stoichiometric amounts. This ceramic mixture was ground to fine powder size and then added to liquid aluminum in small percentages. After casting and taking samples of unreinforced alloy and reinforced alloys, their tensile strength and hardness as material properties were measured and compared. Another issue is the wetting of ceramic particles by molten Aluminum. The aim of the experiments in general is to find a better way to produce a composite material with desired mechanical properties.