Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Review Citation - WoS: 41Citation - Scopus: 42Review on the Parameters of Recycling Ndfeb Magnets Via a Hydrogenation Process(American Chemical Society, 2023) Habibzadeh, Alireza; Küçüker, Mehmet Ali; Gökelma, MertolRegarding the restrictions recently imposed by China on the export of rare-earth elements (REEs), the world may face a serious challenge in supplying some REEs such as neodymium and dysprosium soon. Recycling secondary sources is strongly recommended to mitigate the supply risk of REEs. Hydrogen processing of magnetic scrap (HPMS) as one of the best approaches for magnet-to-magnet recycling is thoroughly reviewed in this study in terms of parameters and properties. The processes of hydrogen decrepitation (HD) and hydrogenation-disproportio-nation-desorption-recombination (HDDR) are two common methods for HPMS. Employing a hydrogenation process can shorten the production route of new magnets from the discarded magnets compared to other recycling routes such as the hydrometallurgical route. However, determining the optimal pressure and temperature for the process is challenging due to the sensitivity to the initial chemical composition and the interaction of temperature and pressure. Pressure, temperature, initial chemical composition, gas flow rate, particle size distribution, grain size, and oxygen content are the effective parameters for the final magnetic properties. All these influencing parameters are discussed in detail in this review. The recovery rate of magnetic properties has been the concern of most research in this field and can be achieved up to 90% by employing a low hydrogenation temperature and pressure and using additives such as REE hydrides after hydrogenation and before sintering.Article Citation - WoS: 12Citation - Scopus: 16Misorientation and Grain Boundary Orientation Dependent Grain Boundary Response in Polycrystalline Plasticity(Springer, 2021) Yalçınkaya, Tuncay; Özdemir, İzzet; Tandoğan, İzzet TarıkThis paper studies the evolution of intergranular localization and stress concentration in three dimensional micron sized specimens through the Gurtin grain boundary model (J Mech Phys Solids 56:640-662, 2008) incorporated into a three dimensional higher-order strain gradient crystal plasticity framework (Yalcinkaya et al. in Int J Solids Struct 49:2625-2636, 2012). The study addresses continuum scale dislocation-grain boundary interactions where the effect of crystal orientation mismatch and grain boundary orientation are taken into account through the grain boundary model in polycrystalline metallic specimens. Due to the higher-order nature of the model, a mixed finite element formulation is used to discretize the problem in which both displacements and plastic slips are considered as primary variables. For the treatment of grain boundaries within the solution algorithm, an interface element is formulated and implemented together with the bulk plasticity model. The capabilities of the framework is demonstrated through 3D polycrystalline examples considering grain boundary conditions, grain boundary strength, the orientation distribution and the specimen size. A detailed grain boundary condition and stress concentration analysis is presented. The advantages and the disadvantages of the model is discussed in detail through numerical examples.Article Citation - WoS: 32Citation - Scopus: 37Void Growth Based Inter-Granular Ductile Fracture in Strain Gradient Polycrystalline Plasticity(Elsevier, 2021) Yalçınkaya, Tuncay; Tandoğan, İzzet Tarık; Özdemir, İzzetThe precipitation hardened, high strength aerospace alloys (e.g. Al 7000 alloy series) suffer from loss of fracture toughness due to the heat treatment leading to intergranular ductile fracture. Depending on the quenching and aging processes, large precipitates at the grain boundaries with wide precipitate free zones might develop. Therefore the grain boundaries constitute a potential location for micro void formation and evolution under the effect of external loads. This is a common problem of such materials where there is considerable ductile intergranular fracture, which is normally attributed to the embrittlement effects of the environment in other type of alloys. In this context, for the modeling of such a degradation process, the current paper develops a physics based intergranular cracking model of polycrystalline materials where a strain gradient crystal plasticity model is combined with cohesive zone elements whose traction separation relation is based on the evolution of micro-voids at the grain boundaries. The framework successfully predicts the intergranular crack formation and propagation, taking into account different microstructural features, such as porosity, pore shape, grain orientation distribution, and grain boundary conditions.Book Part Citation - Scopus: 4Strain gradient crystal plasticity: Intergranularmicrostructure formation(Springer, 2019) Özdemir, İzzet; Yalçınkaya, TuncayThis chapter addresses the formation and evolution of inhomogeneous plastic deformation field between grains in polycrystalline metals by focusing on continuum scale modeling of dislocation-grain boundary interactions within a strain gradient crystal plasticity (SGCP) framework. Thermodynamically consistent extension of a particular strain gradient plasticity model, addressed previously (see also, e.g., Yalcinkaya et al, J Mech Phys Solids 59:1-17, 2011), is presented which incorporates the effect of grain boundaries on plastic slip evolution explicitly. Among various choices, a potential-type non-dissipative grain boundary description in terms of grain boundary Burgers tensor (see, e.g., Gurtin, J Mech Phys Solids 56:640-662, 2008) is preferred since this is the essential descriptor to capture both the misorientation and grain boundary orientation effects. A mixed finite element formulation is used to discretize the problem in which both displacements and plastic slips are considered as primary variables. For the treatment of grain boundaries within the solution algorithm, an interface element is formulated. The capabilities of the framework is demonstrated through 3D bicrystal and polycrystal examples, and potential extensions and currently pursued multi-scale modeling efforts are briefly discussed in the closure. © Springer Nature Switzerland AG 2019. All rights reserved.Conference Object Citation - WoS: 1Citation - Scopus: 2Three Dimensional Grain Boundary Modeling in Polycrystalline Plasticity(American Institute of Physics, 2018) Yalçınkaya, Tuncay; Özdemir, İzzet; Fırat, Ali OsmanAt grain scale, polycrystalline materials develop heterogeneous plastic deformation fields, localizations and stress concentrations due to variation of grain orientations, geometries and defects. Development of inter-granular stresses due to misorientation are crucial for a range of grain boundary (GB) related failure mechanisms, such as stress corrosion cracking (SCC) and fatigue cracking. Local crystal plasticity finite element modelling of polycrystalline metals at micron scale results in stress jumps at the grain boundaries. Moreover, the concepts such as the transmission of dislocations between grains and strength of the grain boundaries are not included in the modelling. The higher order strain gradient crystal plasticity modelling approaches offer the possibility of defining grain boundary conditions. However, these conditions are mostly not dependent on misorientation of grains and can define only extreme cases. For a proper definition of grain boundary behavior in plasticity, a model for grain boundary behavior should be incorporated into the plasticity framework. In this context, a particular grain boundary model ([l]) is incorporated into a strain gradient crystal plasticity framework ([2]). In a 3-D setting, both bulk and grain boundary models are implemented as user-defined elements in Abaqus. The strain gradient crystal plasticity model works in the bulk elements and considers displacements and plastic slips as degree of freedoms. Interface elements model the plastic slip behavior, yet they do not possess any kind of mechanical cohesive behavior. The physical aspects of grain boundaries and the performance of the model are addressed through numerical examples.