The damage and deformation behaviour of particle reinforced aluminum matrix composites can be highly sensitive to local variations in spatial distribution of reinforcement particles, which markedly depend on melt processing and solidification stages during production. The present study is aimed at understanding the mechanisms responsible for clustering of SiC particles in an Al-Si-Mg (A356) alloy composite during solidification process and establishing a model to predict the risk of cluster formation as a function of local solidification rate in a cast component. Special emphasis has been given to spatial characterization methods in terms of their suitability to characterize composite microstructures. Result indicate that methods that present a summary statistics on the global level of heterogeneity have limited application in quantitative analysis of discontinuously reinforced composites since the mechanical response of such materials are highly sensitive to dimensions, locations and spatial connectivities of clusters. The local density statistics, on the other hand, was observed to provide a satisfactory description of the microstructure, in terms of localization and quantification of clusters. A macrotransport - solidification kinetics model has been employed to simulate solidification microstructures for estimation of cluster formation tendency. Results show that the distribution of SiC particles is determined by the scale of secondary dendrite arms (SDAS). In order to attain the lowest amount of particle clustering, the arm spacings should be kept within the limit of 2dSiC &gt / SDAS &gt / dSiC, where dSiC is the average particle diameter.

In this study the data taken from Outokumpu type Flash smelter of Eti-Bakir Plant (Samsun, Turkey) was used to write a computer program in Visual Basic with interface to Excel. Flash smelting is the pyrometallurgical process for smelting metal sulfide concentrates, used in Eti-Bakir plant. In this plant, copper flash smelting consists of blowing fine, dried copper sulfide concentrate mixtures, silica flux, lignite with air into the furnace and natural gas as main fuel. The molten matte is the principal product of the furnace and slag contains 0.5-2% Cu. It is sent to a slag treatment (flotation) process for Cu recovery. This flash furnace off-gas contains from 8-12 volume % SO2 which is fixed as H2SO4. Written program was used to optimize the consumption of oxygen enriched air, fuel and lignite in this Flash Smelter by making material and heat balance of the plant.

In this study, by considering different mechanical properties such as wear resistance and toughness of two different metal alloys in design and production stages, bi-metal casting technique was used for producing composite material which will be a solution for the cracking and wear problem in coal crushing hammer heads. The failure analysis of the classical hammer heads which are made from Hadfield steels (austenitic steel) showed that there are crack formations through austenitic grains and also the phase transformation from austenite to martensite is not completed until the material consumed its life. Thermal analysis is the basic technique in this study to determine the solidification conditions. By using thermocouples with a suitable set-up, the cooling curves of the materials which were used in bi-metal casting had been taken and analysed. By using these cooling curve data with a written software program which is based on Newton Thermal Analysis, the solid fraction values by time and by temperate were obtained. According to these values, the interface was investigated by changing experimental conditions and solid fractions. At the last part of the study, a new approach was tried in white cast iron production.

Pure and palladium&amp / #8208 / covered 350 nm thick magnesium thin films were deposited on glass substrates via thermal evaporation. In the as&amp / #8208 / deposited state, films were highly textured with Mg (001) parallel to the substrate. Hydrogen loading experiments were carried out in two different conditions / namely isothermal and isochronal. Hydrogenation behaviors of the thin films were followed by twopoint probe electrical resistance and optical transmittance measurements, as well as x&amp / #8208 / ray diffraction studies. Isothermal hydrogenation experiments conducted on Pd&amp / #8208 / covered Mg thin films have revealed that these films can absorb hydrogen at temperatures starting from 333 K, producing MgH2 with a random texture. When the films were heated slowly starting from the room temperature, on the other hand, hydrogenation gives rise to a textured MgH2, where (110) parallel to the substrate with a minor (101) component. Formation of the textured hydride in isochronal loading was discussed within the context of lattice mismatch in Mg to MgH2 transformation. It was further shown that formation of such a textured hydride in Mg thin films minimizes in&amp / #8208 / plane lattice distortion.

The aim of this study was to investigate synthesis of lithium borides by mechanochemical synthesis from oxides. Lithium borides have promising properties in the area of high energy additives and hydrogen storage. Lithium oxide (Li2O), boron oxide (B2O3) and Mg were used to synthesize lithium borides. Experiments were conducted in a planetary ball mill under argon atmosphere. Analyses of the products were done by X-ray diffraction and scanning electron microscopy. Trilithium tetradecaboride (Li3B14) peaks were observed in the product powder. Removal of other phases that were formed during experiments was done by leaching in HCl/water solution. Leaching in 0.5 M HCl/water solution for 10 minutes was found to be sufficient to remove / iron (Fe) and magnesium oxide (MgO). Effects of ball milling parameters such as milling speed, ball to powder ratio, milling duration were investigated and milling for 20 hours with 300 rpm and 30:1 ball to powder ratio was found to be the optimum conditions. Syntheses of other lithium borides (LiB4, Li2B6, LiB13) were also experimented with the same milling parameters. Formation of LiB4, Li2B6 and LiB13 was not observed in the product powders. However, the results of LiB4 and LiB13 production experiments showed also Li3B14 peaks in the product. Li2B6 synthesis experiments resulted in Li2B9 peaks in the product powders.

High Pressure Torsion (HPT) is one of the most widely used severe plastic deformation methods which enable to obtain a crack free ultra-fine grained bulk material with improved mechanical properties like increased strength and toughness. In the process, a disc shaped sample is pressed between two anvils and deformed via surface friction forces by rotating one of the anvils. The aim of this study is to nondestructively characterize the variations in the deformation uniformity of the severely deformed steel disks. Two sets of low carbon steel samples were obtained by applying the unconstrained and constrained HPT process up to 6 turns. Magnetic Barkhausen Noise (MBN) method was used in order to evaluate the samples in a nondestructive manner via a commercial device. The results of the MBN measurements were verified with those of conventional methods such as / x-ray diffraction (XRD), metallographic examination and hardness measurements. The initial stages of HPT revealed the effects of conventional plastic deformation on MBN / however with further straining, grain size refinement prevailed and caused increase in MBN signals.

The aim of this study was to produce partially reinforced aluminum metal matrix composite components by insertion casting technique and to determine the effects of silicon content, fiber vol% and infiltration temperature on the mechanical properties of inserts, which were the local reinforcement parts of the components. Silicon content of alloys was selected as 7 wt% and 10 wt%. The reinforcement material, i.e. Saffil fiber preforms, had three different fiber vol% of 20, 25 and 30 vol% respectively. The infiltration temperatures of composite specimens were fixed as 750 &deg / C and 800 &deg / C. In the first part of the thesis, physical and mechanical properties of composite specimens were determined according to the parameters of silicon content of the matrix alloy, infiltration temperature and vol% of the reinforcement phase. X-ray diffraction examination of fibers resulted as the fibers mainly composed of deltaalumina fibers and scanning electron microscopy analyses showed that fibers had planar isotropic condition for infiltration. Microstructural examination of composite specimens showed that appropriate fiber/matrix interface was created together with small amount of micro-porosities. Bending tests of the composites showed that as fiber vol% increases flexural strength of the composite increases. The highest strength obtained was 880.52 MPa from AlSi10Mg0.8 matrix alloy reinforced with 30 vol% Saffil fibers and infiltrated at 750 &deg / C. Hardness values were also increased by addition of Saffil fibers and the highest value was obtained as 191 HB from vertical to the fiber orientation of AlSi10Mg0.8 matrix alloy reinforced with 30 vol% Saffil fibers. Density measurement revealed that microporosities existed in the microstructure and the highest difference between the theoretical values and experimental values were observed in the composites of 30 vol% Saffil fiber reinforced ones for both AlSi7Mg0.8 and AlSi10Mg0.8 matrix alloys. In the second part of the experiments, insertion casting operation was performed. At casting temperature of 750 &deg / C, a good interface/component interface was obtained. Image analyses were also showed that there had been no significant fiber damage between the insert and the component.

Increasing use of aluminum alloys in the automotive industry increases the importance of the production of sheet aluminum. To provide cost effective sheet aluminum to the industry, twin-roll casting (TRC) is becoming more important compared to DC casting. Demand for usage of different aluminum alloys in sheet form introduces some difficulties that should be considered during their applications. The main problem encountered during the welding of aluminum alloys is hot cracking. The aim of this study is to understand the difference in hot cracking susceptibility of two twin roll cast (TRC) aluminum-magnesium alloys (5754 and 5049 alloys) during welding. Varestraint test method was used to evaluate the effect of welding parameters, strain levels, filler alloys and mid-plane segregation on hot cracking susceptibilities. Hot cracking susceptibility of both 5049(Al-2wt%Mg) and 5754(Al-3wt%Mg) alloys increased with increasing strain level. Also, it was observed that hot cracking susceptibility was higher for the alloy having higher magnesium content. Thermal analysis results verified that hot cracking susceptibility indeed can be related to the v solidification range. As is suggested in the solidification range approach, the results of the present study confirm that the extent of solidification and liquation cracking depend on the magnitude of solidification range and the strain imposed during welding. Hot cracking susceptibility of 5754(Al-3wt%Mg) alloy has shown slightly decreasing behavior with addition of 5356 filler alloy. On the other hand, addition of 5183 filler alloy has increased solidification cracking susceptibility of two base alloys. The fracture surfaces of liquation and solidification cracks were investigated by scanning electron microscope with EDS. Liquation crack surfaces of the 5754(Al-3wt%Mg) alloy were found to have high Mg and Si content. For the 5754(Al-3wt%Mg) alloy, a quench test was designed to observe the effect of mid-plane segregation zone. It was observed that there was a eutectic reaction resulting in formation of liquid phase below solidus temperature of 5754(Al-3wt%Mg) alloy. Moreover, internal cracks have formed at the mid-plane segregation zone after Varestraint test. Results show that 5049(Al-2wt%Mg) alloy should be chosen compared to 5754(Al-3wt%Mg) alloy for welding. Moreover, low line energy should be applied and filler alloys with high magnesium content should be used during welding to decrease hot cracking tendency of welds.

In this study, residual stresses introduced via application of shot peening on the raceways of bearing rings and their effect on the fatigue life was investigated experimentally. For improvement of residual compressive stress state, shot peening operation with different parameters was utilized. Residual stress measurements were conducted via X-ray diffraction technique. Optimization of residual stress state during the production of ball bearings is the main target of this study. Process parameters for shot peening and super-finishing were studied for determination of the parameters that induce the most favorable residual stress state. The fatigue life of ball bearings were determined by life cycle tests and tabulated to show the results of the study. The results of the thesis are believed to help for optimization of residual stress distribution and improvement of service life of ball bearings.

Shot peening is a cold-working process by which residual compressive stresses are being induced in the surface region to increase the fatigue strength and the resistance to stress-corrosion cracking. This study covers non-destructive measurement of surface residual stresses in the shot-peened steel components by a micro-magnetic technique, named as Magnetic Barkhausen Noise (MBN) method. For this purpose, various low alloy steel specimens were prepared by a controlled shot peening process with different intensity, impact angle and coverage values. The measurements showed that a clear relationship exists between residual stresses and the MBN signals. Residual stress values determined by MBN technique were also verified by X-ray diffraction measurements.