In this study, the surfaces of titanium (grade 2) substrates were modified by different methods and then coated with a hydroxyapatite-graphene oxide (HA-GO) composite by electrophoretic deposition (EPD). The aim of the study is to improve the surface properties and increase the hydrophilicity of the surface of titanium by different surface treatments. The surface modification processes are as follows: sandblasting (S), acid etching (E), and finally anodic spark oxidation (ASO) on the etched surface. After the surface modification processes, the surface of titanium was coated with HA-GO suspensions (0, 2, 4, and 6 wt% GO) with a voltage value of 20 for 5 min by the EPD method. The surface morphology, elemental analysis, contact angle, phase composition, adhesion, biocompatibility, and bioactivity of the produced coatings were examined. Bioactivity analysis was performed in simulated body fluid (SBF) for 14 days. The MTT experiment was conducted with L929 (mouse fibroblast) cell cultures in accordance with the 70 % cell viability criterion. As a result of contact angle measurements, it was observed that all samples showed hydrophilic behavior due to the increased surface area after ASO treatment. The contact angle of the sanded surface was 71.03 degrees, whereas the contact angles of the ASO treatment and HA-GO coatings after the coating process were measured below 5 degrees. The bioactivity test results indicated that the surface modified with HA-GO (4 wt%) exhibited the best apatite nucleation outcome. As a result of the analysis with L929 cells, HA, HA-GO (2 wt%), HA-GO (4 wt%) composite coatings showed biocompatible behaviour with 102.17, 76.52, and 80.43 % cell viability, respectively. The best result in the adhesion test was reported for HAGO (4 wt%) coating with class 5B.

In this study, the laser weldability of Ti6Al4V materials produced by the selective laser melting (SLM) method, which is an additive manufacturing method, and the effects of heat treatment applied to the welded material on the welding performance were investigated experimentally. Stress relief and heat treatment were applied to the materials joined by laser welding at 800 °C (below the α phase transformation temperature), 950 °C (between α and β phase transformation temperature), and 1080 °C (above the β phase transformation temperature). In addition, transverse and longitudinal welded joining techniques were also investigated to determine anisotropy in the produced parts. The mechanical properties in the laser-welded region were examined by hardness and tensile tests, and an optical microscope, scanning electron microscope (SEM), and X-ray diffraction (XRD) examined the changes in the microstructure. Grain growth was observed in the microstructure due to the increase in heat treatment temperature, and the tensile strength increased from 631.2 to 754.2 MPa in transverse bonding, while it increased from 648.1 to 761.9 MPa in longitudinal bonding. High hardness values due to Widmanstatten morphology were determined in the hardness test, especially after heat treatments at 950 and 1080 °C. It has been observed that the heat treatment increases the welding performance of the laser-welded material, and the best welding performance is obtained with a welding efficiency of 83.5

In this study, AA2024 aluminum alloy was selected as the matrix material, while B4C was selected as the reinforcement material, and particle-reinforced Al-matrix composite materials were produced using the powder metallurgy method. B4C ceramic powders were added to the AA2024 matrix. Examinations were made to determine the effects of different reinforcement particle ratios and sintering temperatures on the mechanical properties of the composite materials that were produced. The powders were homogeneously mixed and compressed in a metal mold at room temperature and a pressure of 525 MPa under a uniaxial press. The raw specimens that were obtained were sintered for 45 minutes at different temperatures. The produced composite materials were subjected to three-point bending tests and hardness measurements. Optical microscopy analysis was carried out for characterization. The results allowed us to draw a conclusion on how the reinforcement material in the produced specimens affected composite properties.

Dental implantlarda en fazla kullanılan malzeme olan titanyumun yüzey morfolojisinin geliştirilmesi konusu birçok araştırmacının ve üretici firmaların üzerinde çalıştığı önemli konulardan biridir. Titanyumun biyouyumluluğu, üstün mekanik özellikleri, korozyon direnci ve osseointegrasyondaki başarısı biyomedikal uygulamalarda yoğun olarak kullanılmasının sebeplerindendir. Bu konuda yürütülen çalışmalar, implantın kemik ile olan etkileşiminde yüzey morfolijisinin doğrudan etkili olduğunu göstermiştir. Aynı zamanda implant malzemenin yüzey pürüzlülüğü, kimyasal bileşimi ve ıslanabilirliği de iyileşme aşamasında önemli rol oynar. Bu çalışma kapsamında saf titanyuma; kumlama, dağlama ve iki farklı çözelti ve voltajda anotlama olmak üzere toplamda dört farklı yüzey modifikasyon işlemi uygulanmıştır. Yüzeyi işleme tabi tutulan titanyum numunelerin, osseointegrasyonda önemli rol oynayan özelliklerden olan yüzey morfolojisi, faz yapısı ve yüzey pürüzlülük değerleri incelenmiştir. Dört farklı yüzey uygulamasının sonucunda yüzey morfolojileri başta olmak üzere farklı yüzey pürüzlülük sonuçları ve faz yapıları gözlemlenmiştir.

In this study, heat treatment was applied to Ti6Al4V materials produced by the selective laser melting (SLM) method at 550 ℃, 800 ℃, 950 ℃, and 1080 ℃ temperatures, and the effect of this process on microstructure and mechanical properties was also investigated. Moreover, the parts produced with the additive manufacturing technique can be exposed to many loads at the place of use. Therefore, to determine the resistance of the materials against bending, the V bending process was applied to the materials in 6-, 7.5-, and 9-degree dies. XRD and SEM investigated the microstructure and optical microscope changes, and the mechanical properties were examined by uniaxial tensile test and microhardness analysis. In the test samples, pore and unmelted powder particles due to production in the microstructure were observed, and it was observed that the grain sizes increased with the increase in the heat treatment temperature. It was observed that samples HT550, HT800, and HT950 were shaped without breaking in the bending process in the 6-degree die, and all the samples were broken in the experiments performed in the 7.5- and 9-degree die.

In this study, AA2024 aluminum alloy was selected as the matrix material, while B4C was selected as the reinforcement material, and particle-reinforced Al-matrix composite materials were produced using the powder metallurgy method. Examinations were made to determine the effects of different reinforcement particle ratios and sintering temperatures on the mechanical properties of the AA2024 matrix composite materials that were produced. The powders were compressed in a metal mold at room temperature and a pressure of 525 MPa under a uniaxial press. The raw specimens that were obtained were sintered for 45 minutes at different temperatures. The produced composite materials were subjected to three-point bending tests and hardness measurements. Optical microscopy analysis was carried out for characterization. The results allowed us to draw a conclusion on how the reinforcement material in the produced specimens affected Al-matrix composite properties. It was determined that the B4C reinforcement added to the matrix increased the hardness values of the composites at all sintering temperatures, the highest bending strength was obtained in the composite with 10% B4C particle reinforcement, and in general, the B4C reinforcement was homogeneously dispersed in the matrix. Increased B4C reinforcement ratios resulted in higher hardness values in the composite materials.

In this study, it was aimed to produce Al-matrix composite materials with B4C-SiC and B4C-Y2O3 particle reinforcement using the Powder Metallurgy (PM) method. In the composites in which the reinforcement materials were used at different particle sizes and ratios, AA2024 powders were selected as the matrix material. The powders were homogeneously mixed and compacted at room temperature under a pressure of 525 MPa. The raw specimens were sintered by keeping them at different temperatures for 45 minutes. The composite materials were subjected to wear tests, and their hardness and density values were investigated. In the study, the effects of reinforcement materials added to the matrix at different particle sizes and ratios on wear resistance, hardness, and density at different temperatures were examined.

The efficient use of a system is enabled with the life performance estimations. Thus, the effective use of underground resources is realized especially natural gas. Based on this, life performance models were generated to aim of improving the efficient use of energy for a combined cycle power plant (CCPP) of 243 MW installed in Izmir, Turkey by using fuzzy logic (FL) and artificial neural network (ANN) in this study. Therefore, output power estimations were carried out. Depending on the developed models, an estimation of the energy that the CCPP can produce and provide to the interconnected system in the following years has been made. According to the obtained results, the error prediction rates of FL and ANN models were determined. It was found that while the energy relative error estimation value that can be produced between the years calculated in modeling using FL varies between 0.59% and 3.54%, this value was found to vary between 0.001% and 0.84% in modeling using ANN. This result shows that the ANN model is more suitable for the life performance estimations of such a non-linear system.

In this study, for composite patch repairs, the impact degrees of patch configuration and patch sizes on repair performance were determined and compared with each other. First, stress intensity factor (SIF) values were calculated by using the Finite Element Method for tensile loading in an aluminum plate with center cracks, in unpatched situation. In this model, the repair was made by forming single and double sided patches and adhesive volumes too. The SIF values are recalculated for different patch thicknesses, widths, and crack lengths. The criterion that determines the impact degrees of the examined parameters was accepted to be the reduction rate in the SIF values. The results show that even the most disadvantageous patch application contributes significantly to the repair performance and that the application itself is the most effective factor. The second most effective parameter is patch configuration; the patch sizes have much less impact degree

Today, with the development of technology, different welding methods are applied for different alloys. In this work, changing of functional properties after using welding methods for NiTi alloy samples was targeted. However, two different welding methods were employed for the same alloy and results were compared to each other and commented on them. In the present study, samples were welded with TIG and Laser welding and their cross section was examined in the joint area. Then these samples were examined in optical microscope and SEM. The advantages and disadvantages of both welding methods were reported. The basic distinction of TIG and laser welded samples examined in microscope was the scale of HAZ area of TIG welded piece. Nevertheless, due to more thermal input is applied for materials in TIG welded parts, more molten materials are detected or heat effects are attained in this practice. In laser welding, heat input is less and this can be recognized from the observed micrographs. While HAZ area is obviously distinguished and welding border zone is detached from the base metal. The twin structures were not observed in optical microscope; for that reason they were investigated in SEM to see these twins in laser welded area.

Natural gas combined cycle power plants (CCPPs) are widely used to meet peak loads in electric energy production. Continuous monitoring of the output electrical power of CCPPs is a requirement for power performance. In this study, the role of ambient temperature change having the greatest effect on electric production is investigated for a natural gas CCPP. The plant has generated electricity for fourteen years and setup at 240 MW in Aliağa, İzmir, Turkey. Depending on the seasonal temperature changes, the study data were obtained from each gas turbine (GT), steam turbine (ST) and combined cycle blocks (CCBs) in the ambient temperature range of 8-23°C. It has been found that decreases of the electric energy in the GTs because of the temperature increase and indirectly diminishes of the electricity production in the STs. As a result, the efficiency of each GT, ST and CCB reduced, although the quantity of fuel consumed by the controllers in the plant was decreased. As a result of this data, it has been recommended and applied that additional precautions have been taken for the power plant to bring the air entering the combustion chamber to ideal conditions and necessary air cooling systems have been installed.