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Öğe Effects of cooling rate on the atomic structure and glass formation process of Co90Zr10 metallic glass investigated by molecular dynamics simulations(Tubitak Scientific & Technological Research Council Turkey, 2019) Celtek, Murat; Sengul, SedatIn this study, the atomic structure and the glass formation process of Co90Zr10 metallic glass alloy were studied by molecular dynamic simulation based on the embedded atom method using four different cooling rates. The average atomic volume and the potential energy of the system were observed to be strongly dependent on the cooling rate during rapid solidification, and the glass transition temperature decreased with decreasing cooling rate. The radial distribution functions and the structure factors derived from molecular dynamics simulations at 300 K agreed well with the experimental and other molecular dynamics results. The coordination numbers calculated at 300 K were consistent with the experimental results in the literature. The local structural atomic orders of the system have been characterized by Honeycutt-Andersen indices and the Voronoi tessellation method. We realized that the FCC and icosahedral short-range order increases with decreasing cooling rate, the icosahedral clusters are predominant in the Co90Zr10 metallic glass, and the fraction of the icosahedral polyhedra increases with decreasing cooling rate and temperature. We have seen that Co-centered Voronoi polyhedrals such as < 0,2,8,2 >, < 0,0,12,0 >, and < 0,1,10,2 > play a dominant role in the development of the icosahedral order of the Co90Zr10 alloy.Öğe Key factors of deformation mechanism of Cu-Ag alloy(Elsevier, 2022) Sengul, Sedat; Guder, VildanThis work focused on the effect of the structural order and dimensionality on the deformation mechanism of Cu-Ag alloy and the triggering factors of this mechanism. It is revealed that (i) the weakness of the system develops from bulk to nanoscale and crystalline to amorphous systems, (ii) Cu-Ag nanowires are more flexible than their bulk counterparts, (iii) crystalline Cu-Ag alloys are stiffer than amorphous systems. The reason for early yielding and less stiffness of amorphous Cu-Ag nanowire with respect to bulk material is the less fraction of ideal icosahedra. Cu atoms are a key factor to characterize the mechanical response of both amorphous Cu-Ag alloys. While there are two different deformation modes in crystalline systems, the only mode observed in the amorphous alloy is homogeneous deformation. The presence of (0,5,2,x) (x = 5,6) polyhedral is the reason for the transition of deformation from homogeneous to inhomogeneous in the crystalline Cu-Ag alloys.Öğe Molecular dynamics study of structure and glass forming ability of Zr70Pd30 alloy(Springer, 2016) Celtek, Murat; Sengul, Sedat; Domekeli, Unal; Canan, CemIn this study, the temperature effects on the structural evolution of the Zr70Pd30 binary alloy in the glassy and liquid states were studied using the molecular dynamics simulations based on the many-body type tight-binding potential. We considered the following properties in detail: the temperature dependence of the volume, the partial and total pair distribution functions and the simulated glass transition temperature. The effects of the cooling rates on the glass transition temperature were examined. The Wendt-Abraham parameter was calculated to determine the glass transition temperature of Zr70Pd30 glassy alloy. The pair analysis technique of Honeycutt-Andersen was applied to define local atomic arrangements produced from molecular dynamics simulations. The results show that the icosahedral ordering in glassy state has been composed during quenching period, and the simulated glass transition temperature and the total pair distribution functions are in good agreement with the experimental data.Öğe Moleküler Dinamik Benzetim Yöntemi ile Isıtma İşlemi Sırasında Platin Metalinin Yapısal Gelişimi ve Erime Noktası Üzerine Atomlar-arasıPotansiyel Etkisinin Araştırılması(2019) Celtek, Murat; Dömekeli, Ünal; Sengul, SedatBu çalışmada, farklı atomlar-arası potansiyeller ve klasik moleküler dinamik (MD) benzetimleri kullanılarak,yüzey merkezli kübik (fcc) yapıya sahip platin (Pt) elementinin taban durumdan başlayıp erime noktasının hemenüzerindeki bir sıcaklık aralığındaki fiziksel özellikleri ve atomik yapısının devinimi detaylı bir şekildeincelenmiştir. Artan sıcaklığa bağlı olarak katı sistemin yapısal gelişimini analiz etmek ve erime noktasınıbelirlemek için çiftler dağılım fonksiyonu (PDF), enerji-sıcaklık (E-T), örgü parametresi-sıcaklık (a-T), doğrusaltermal genleşme katsayı-sıcaklık (CLTE-T) eğrileri ve çift analiz yöntemi gibi analiz yöntemleri kullanıldı. Tümpotansiyeller için MD benzetiminin sonuçlarının analizinden elde edilen veriler daha önce rapor edilen deneyselveya teorik verilerle karşılaştırılmış ve tartışılmıştır. Farklı atomlar-arası potansiyellerle elde edilen sonuçlarçoğunlukla birbirleri ile tutarlı olmasına rağmen, farklılık gösterdikleri noktalar da bulunmaktadır. Özellikle,sistemin erime noktasının belirlenmesi konusunda, her bir potansiyelin farklı erime sıcaklıkları ürettiğigözlenmiştir. Tüm potansiyel enerji fonksiyonlarında ortak olarak, artan sıcaklıkla birlikte fcc yapıyı temsil eden1421 bağlı çiftlerinin sayısı azalmış ve bu çiftlerin büyük bir bölümünün özellikle kusurlu icosahedra (deficos) vekusurlu fcc yapıyı temsil eden 1541 ve 1431 bağlı çiftlerine dönüştüğü görülmüştür. Pt elementi için burada elealınan potansiyellerin bazıları düşük bazıları ise yüksek sıcaklık aralığındaki fiziksel özellikleri açıklamada başarılıolurken, Sheng ve arkadaşları tarafından öne sürülen gömülü atom metot potansiyeli (EAM1) ve sıkı-bağlı (TB)potansiyelinin saf Pt elementinin geniş sıcaklık ölçeğinde ele alınan tüm özelliklerini açıklamada diğerlerine göredaha başarılı olduğu görülmüştür.Öğe On the behavior of single-particle dynamic properties of liquid Hg and other metals(Amer Inst Physics, 2008) Gonzalez, Luis E.; Gonzalez, David J.; Calderin, Lÿzaro; Sengul, SedatRecent experiments and classical molecular dynamics simulations performed on liquid Hg near melting have suggested the existence of two processes with different time scales in its single-particle dynamics. We report a study of this system by using ab initio molecular dynamics simulations, which recover the same kind of behavior, and we analyze it in terms of a theoretical approach, which clarifies its origin. We show that the previous interpretation has been induced by the unphysical extension of the diffusive model to short times. Moreover, we also find that quite different liquid metals, such as Si and Mg, also exhibit a similar behavior as Hg, with the only difference being in the time scales involved due to the different masses and interactions.Öğe Surface effects on the mechanical properties of rhodium nanowires by molecular dynamics simulations(Elsevier, 2021) Sengul, Sedat; Guner, Alper Koray; Guder, VildanThis study comprehensively investigates the mechanical properties of rhodium (Rh) nanowires using molecular dynamics simulations in which the interactions were expressed by embedded atom method potentials and interprets their relation with the deformation process. We have observed that the stress-strain behavior of Rh nanowires is radically different from the bulk material. As the size increased, the Elastic Modulus of nanowires gradually decreases and saturates to reach bulk value. It is revealed that the mechanical response of thicker nanowires than the critical value of 2.8 nm size is characterized by the core atoms and the surface effects lose their dominance due to the stability of the core atoms. The high strain rates delay yielding and neck formation and can be used to design the strengthened thin Rh nanowires.Öğe Sıvı Pd25Ni75 Nanoparçacıklarının Katılaşma Süreci Üzerine Soğutma Oranının Etkisinin Moleküler Dinamik Benzetişim Yöntemiyle İncelenmesi(2019) Dömekeli, Ünal; Celtek, Murat; Sengul, SedatSıvı Pd25Ni75 nanoparçacığının katılaşma sıcaklığı ve atomik yapısının soğutma oranına bağlı değişimi molekülerdinamik benzetişimi kullanılarak incelendi. Soğutma oranının, sistemin atomik yapısı ve katılaşma noktasıüzerindeki etkilerini araştırabilmek için 0.05 K/ps ile 50.0 K/ps aralığında değişen soğutma oranları ile çalışıldı.Katılaşma sıcaklığı toplam enerjide gözlenen ani değişime karşılık gelen sıcaklıktan ve sistemin atomik yapısı iseçiftler dağılım fonksiyonu, Honeycutt-Andersen çiftler analizi ve atomik konfigürasyondan belirlendi. Pd25Ni75nanoparçacığı için elde edilen sonuçlar katılaşmanın soğutma oranına bağlı yapısal dönüşüm diyagramı üzerindeözetlendi. Bulgularımız, sistemin atomik yapısının ve katılaşma sıcaklığının soğutma oranı ile direkt ilişkiliolduğunu göstermektedir.Öğe Tensile strength and failure mechanism of hcp zirconium nanowires: Effect of diameter, temperature and strain rate(Elsevier, 2020) Guder, Vildan; Sengul, SedatThis study is a comprehensive analysis to demonstrate the deformation and failure mechanism of hexagonal Zr nanowires in [0 0 0 1] orientation. Molecular dynamics simulations in conjunction with embedded atom potentials are utilized to determine the effect of the temperature, diameter and strain rate on mechanical properties of nanowire. We have observed two basic scheme that these parameters have different impacts on elastic and plastic deformations of Zr nanowires. The elastic response of nanowire increases by high strain rate, low temperature and small diameter. Although Young's Modulus can be characterized by strain rate, the temperature and the diameter are more effective key variables in engineering of strength mechanism. On the other hand, high strain rate, low temperature and large diameter decrease the failure of Zr nanowires.
