Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
Browse
3 results
Search Results
Master Thesis Synthesis of Titanium-Based Powders From Machining Waste by Using the Hydrogenation-Dehydrogenation Method(Izmir Institute of Technology, 2022) Genç, Aziz; Gökelma, Mertol; Gökelma, Mertol; Genç, Aziz; Gökelma, Mertol; 03.09. Department of Materials Science and Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologySustainability and recycling activities have gained importance in almost every field all over the world. Many studies are conducted to recycle titanium and titanium alloys owing to their outstanding properties like low density, biocompatibility, corrosion resistance, and high strength-to-weight ratio. Although they offer superior properties, their usage is limited due to their high production cost and potential to generate waste, and therefore, recycling activities in this area should be expanded using an appropriate method. Cold hearth melting, vacuum arc re-melting, and hydrogenation and dehydrogenation process are widely used for recycling titanium scraps in industry. Among them, the hydrogenation and dehydrogenation (HDH) process has a significant environmental and economic impact. In this thesis, titanium powders were synthesized from additive manufacturing turnings. Ti-6Al-2Sn-4Zr-6Mo turnings were used as starting materials on which HDH characteristics were not investigated in the literature. Both hydrogenation and dehydrogenation parameters were studied to reach optimum conditions. Our results revealed that hydrogenation was accomplished at 500 °C for 120 minutes with 5 °C/minute heating rate. The optimum dehydrogenation condition was found at 600 °C for 90 minutes. Ti-6Al-2Sn-4Zr-6Mo powder with average 56 μm particle size was synthesized; however, hydrogen and oxygen concentrations in the powder were not at the desired level and non-spherical shaped powders were produced end of the process.Master Thesis The Constitutive and Damage Models of Additively Manufactured Ti6al4v Alloy(01. Izmir Institute of Technology, 2021) Güden, Mustafa; Hızlı, Burak; Güden, Mustafa; 01. Izmir Institute of Technology; 03.10. Department of Mechanical Engineering; 03. Faculty of EngineeringElectron Beam Melting (EBM) is one of the metal additive manufacturing methods that enable the fabrication of Ti6Al4V alloy parts with intended shapes in where this alloy is of significant interest such as aerospace and biomedical industries due to its outstanding properties. In this study, the microstructural and mechanical properties of EBM-produced Ti64 were comprehensively investigated. Microstructural analysis was conducted on as-built specimens. Microstructural analysis showed that EBM-produced Ti64 possesses α+β duplex phase with directional microstructural alterations and high porosity fraction in the part volume. Mechanical properties were investigated under tension loadings at quasi-static rates (0.001-0.1 1/s) and compression loading at quasi-static and high strain rates (0.001-2154 1/s). Thereafter, Johnson-Cook (JC) strength and damage models were individually calibrated from the experimental results of tension and compression behaviors and experimental fracture strains in order to numerically predict the material flow behavior of EBM-produced Ti64 considering the strain, strain rate, and temperature effects in the case of various loadings combined with temperature changes. EBM-produced Ti64 exhibited proximate mechanical properties in terms of tension and compression behaviors, however extremely low ductile behavior under tension loadings resulting premature failure without necking. Eventual fracture of this material occurred via tearing of the scanned layers for tension loadings and shear crack following the shear band formation propagation on 45° to loading axis for compression loadings. Calibrated JC strength and damage models for EBM-produced Ti64 were able to predict flow behavior and fracture strains within strain rate range between 0.001 and 1000 1/s. However, the JC strength model could not predict the flow behavior at excessively high strain rates (2154 1/s) due to complex deformation mechanisms including adiabatic heating.Master Thesis Preparation and Characterization of Sintered Ti-6a1 Powder Compacts(Izmir Institute of Technology, 2004) Çelik, Emrah; Güden, Mustafa; Güden, Mustafa; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of TechnologySintered Ti6Al4V powder compacts were prepared using atomized spherical and angular powders in the porosity range of 29-63%. Cylindrical green powder compacts cold compacted at various compaction pressures and then sintered at 1200 C for 2 h. The final porosities and average pore sizes were determined as functions of the applied compaction pressure and powder type. The compression deformation behavior of Ti6Al4V powder compacts was also investigated at quasi-static (1.6x10-3-1.6x10-1s-1) and high strain rate (300 and 900 s-1) conditions using conventional mechanical testing and Split Hopkinson Pressure Bar techniques, respectively. The mean pore size of the compacts varied between 29 and 171 Um depending on the particle size range of the powders used and the compaction pressure applied. Microscopic studies of as-received powders and sintered powder compacts showed that sintering at high temperature (1200oC) and subsequent relatively slow-rate cooling in the furnace transformed the microstructure of spherical powder from the acicular alpha to the Widmanstatten microstructure and angular powder from bimodal to equiaxed+ Widmanstatten microstructure.In compression testing, at both quasi-static and high strain rate conditions, the compacts failed primarily by shear band formation along the diagonal axis 45 C to the loading direction. Increasing strain rate was found to increase both the flow stress and the compressive strength of spherical powder compacts while it did not affect the critical strain for shear localization. The mechanical properties of angular powder compacts were further shown to be a function of powder size; larger the particle size higher the percentage of equiaxed structure while in compacts of particles <100 um relatively large voids resulted in reduced strength and ductility. Microscopic analyses of deformed but not failed and failed spherical powder compact samples further showed that fracture occurred in a ductile (dimpled) mode consisting of void initiation and growth in alpha phase and/or at the alpha/beta interface and macrocraking by void coalescence in the interparticle bond region. In angular powder compacts, the failure was granular brittle type at the interparticle bond region while the compact samples of particles <100 um fractured transgranularly through the voids. The strength of the sintered compacts was further shown to satisfy the strength requirements for cancellous bone replacement. The strength of the compacts having porosity level of 40% and/or lower was comparable with that of human cortical bone.Compared to Ti powder compacts of previous studies, Ti6Al4V powder compacts provided higher strength and increased porosity level of the compacts suitable for cortical bone replacement.