Browsing by Author "Cetin, B."
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Conference Object Citation Count: 0Characterization of Thin Film Boron Nitride Coatings and Observation of Graphite-Like Boron Nitride(Polish Acad Sciences inst Physics, 2019) Durkaya, Göksel; Efeoglu, I.; Ersoy, K.; Cetin, B.; Kurtuldu, H.; Department of Metallurgical and Materials EngineeringCubic boron nitride is a coating solution to improve wear performances in demanding engineering applications. In order to achieve the best performance from this thin film system, the physical dynamics behind the phase compositions, phonon dynamics, surface quality, interfacial effects and stoichiometric relations should be understood. In this study, for this purpose, physical vapor deposition grown BN thin films were studied in detail using the Raman spectroscopy, atomic force microscopy, and scanning electron microscopy techniques.Conference Object Citation Count: 5Influence of Cu and Ni Alloying on the Microstructure and Mechanical Properties of Austempered Ductile Iron Castings(Polish Acad Sciences inst Physics, 2019) Davut, Kemal; Cetin, B.; Davut, K.; Department of Metallurgical and Materials EngineeringAustempered ductile cast iron (ADI) offers a good combination of high tensile and fatigue strength, good ductility, toughness, wear resistance and damping characteristics, lower density in an economical way. This excellent combination of properties is due to the specific microstructure of ADI; which is composed of spheroidal graphite particles on an ausferritic matrix. The ausferrite consists of acicular ferrite and high carbon retained austenite; which is produced via austempering heat treatment after casting. The alloying additions of Cu or Cu + Ni increases austemperability, which means completely ausferritic structures can be produced on larger cross-sections. In the present study the effect of the alloying additions of Cu and Cu + Ni on mechanical properties and microstructure of ADI was studied. For that purpose, Y-block specimens having a lean composition, 0.8% Cu and 0.8% Cu + 0.4% Ni alloying additions were cast. After austempering treatment, mechanical tests, fractographic and metallographic examinations were performed. The results show that the Cu + Ni alloyed specimen has higher strength and elongation. The lean alloy on the other hand, has the highest nodularity and matrix hardness but the lowest strength and ductility. Those differences in mechanical properties were attributed to the fraction and morphology of the retained austenite regions of the matrix.Conference Object Citation Count: 0Investigating the Effect of Auto-Focus and Auto-Threshold Algorithms in Advanced Nodularity Analysis of Austempered Ductile Iron Castings(Polish Acad Sciences inst Physics, 2019) Durkaya, Göksel; Davut, Kemal; Durkaya, G.; Davut, K.; Department of Metallurgical and Materials EngineeringAustempered ductile iron castings have a wide range of application fields including defense and heavy-duty industries due to their promising mechanical properties. Austempered ductile iron castings could provide excellent combination of high strength, toughness, and wear resistance at the same time. Unlike other spheroidal ductile cast irons, austempered ductile iron castings need to be processed by a special austempering heat treatment which enables the verification of the conformity of the nodularity level after the casting operations. Previous studies have shown that wide area mappings for determining nodularity are crucial to eliminate the representativeness problems. In this sense, some precautions should be taken for the accuracy of results in large scale nodularity examination. In this study, the effect of auto-thresholding and auto-focusing algorithms on the advanced nodularity analysis is investigated. The results suggest that auto-thresholding and auto-focusing methods have significant contributions for determining average nodularity levels and average graphite sizes.Conference Object Citation Count: 4A Material Perspective on Consequence of Deformation Heating During Stamping of DP Steels(Iop Publishing Ltd, 2017) Davut, Kemal; Cetin, B.; Şimşir, Caner; Davut, K.; Bayramin, B.; Department of Metallurgical and Materials Engineering; Manufacturing EngineeringRecent studies showed that, during stamping of high strength steels at industrially relevant production rates, local temperature in the blank may rise up to 200 degrees C - 300 degrees C due to deformation heating. Moreover, die temperature may also rise up to 100 degrees C - 150 degrees C for progressive stamping dies. Based on the common assumption that the blank softens as the temperature increases, thermal softening creates a margin in Forming Limit Diagram (FLD) and therefore the FLD determined at room temperature can safely be used for those cases. In this article, the validity of this assumption on DP590 steel is questioned by high temperature tensile tests (RT - 300 degrees C) at various strain rates (10(-3) s(-1) - 1 s(-1)). The results indicated a decrease both in uniform and total elongation in 200 degrees C - 300 degrees C range together with several other symptoms of Dynamic Strain Aging (DSA) at all strain rates. Concurrent with the DSA, the simulated FLD confirms the lower formability at high temperature and strain rates. Thus, it is concluded FLD determined at RT may not be valid for the investigated steels.Conference Object Citation Count: 0Non-Invasive 3D Optical Measurement of Round Surfaces(Polish Acad Sciences inst Physics, 2019) Durkaya, Göksel; Durkaya, G.; Cetin, B.; Department of Metallurgical and Materials EngineeringPrecise measurement of wear profiles in large areas of round surfaces such as shafts, suspension bars and high-deviation geometry surfaces is a challenge in manufacturing engineering. An optical measurement method is developed to overcome this challenge. This method, relying on angular reconstruction of scattered light profiles, is used for the measurement of irregular wear in quality testing of round surfaces which provides information on estimating the surface lifetime after prolonged use. This approach achieves a 3D depth accuracy better than 50 mu m in suspension bars with diameters up to 50 mm from an imaging distance of 250 mm.Article Citation Count: 15A Parallel Boundary Element Formulation for Tracking Multiple Particle Trajectories in Stoke's Flow for Microfluidic Applications(Tech Science Press, 2015) Karakaya, Z.; Baranoglu, B.; Cetin, B.; Yazici, A.A new formulation for tracking multiple particles in slow viscous flow for microfluidic applications is presented. The method employs the manipulation of the boundary element matrices so that finally a system of equations is obtained relating the rigid body velocities of the particle to the forces applied on the particle. The formulation is specially designed for particle trajectory tracking and involves successive matrix multiplications for which SMP (Symmetric multiprocessing) parallelisation is applied. It is observed that present formulation offers an efficient numerical model to be used for particle tracking and can easily be extended for multiphysics simulations in which several physics involved.Conference Object Citation Count: 3A Potential Solution to Mystical Materials in Indentation Test(Elsevier Science Bv, 2017) Billur, Eren; Davut, Kemal; Music, O.; Simsir, C.; Şimşir, Caner; Music, Ömer; Department of Metallurgical and Materials Engineering; Automotive Engineering; Manufacturing EngineeringVarious methods have been designed to determine the elasto-plastic properties of metals. Instrumented indentation test (IIT) is considered to be a good candidate to determine local properties after manufacturing operations. In order to acquire elastoplastic properties from IIT, either dimensional analysis or inverse analysis of the force-displacement curve is performed. However, the major drawback of those methods is the uniqueness of the solution. Some materials may exhibit almost identical force-depth curves, although they have different elastoplastic properties. Those materials are referred as "mystical materials". In this contribution, topological features of the indentation surfaces, i.e. indent size, pile-up and sink-in behaviour, are investigated to find a differentiating property. According to the results, indent size, pile-up and sink-in behaviour may help to find the unique solution to the inverse problem. (C) 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the International Conference on the Technology of Plasticity.