Browsing by Author "Kalay, I."

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Citation Count: Sıkan, F...et al (2020). "Effect of Sm on Crystallization Kinetics of Cu-Zr-Al Metallic Glasses", Thermochimica Acta, Vol. 683.
Effect of Sm on Crystallization Kinetics of Cu-Zr-Al Metallic Glasses
(2020) Sıkan, F.; Polat, Gülkan; Kalay, I.; Kalay, Y. E.; 5743
The effect of Sm micro-alloying on non-isothermal and isothermal crystallization kinetics of (Zr50Cu40Al10)(100-x)Sm-x (x = 0, 2, 4 at. % Sm) alloys were investigated using differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Crystallization activation energies for each composition were calculated in non-isothermal conditions using Kissinger and Ozawa methods and in isothermal conditions using Johnson-Mehl-Avrami model. XRD analysis showed that crystallization product Cu10Zr7 changes to Cu2Sm with Sm presence in isothermal conditions. Both isothermal and isochronal calculations yield that the energy barrier for crystallization has increased with Sm addition. On the other hand, crystallization point drops to lower temperature at the expense of an increase in the pre-exponential factor. The Avrami exponents for all compositions were found to be below 2.5, indicating that crystallization was governed by a diffusion-controlled three-dimensional growth with a decreasing nucleation rate. The apparent increase in crystallization activation energies with increasing Sm content can be one of the affecting factors for commonly held idea of increased glass forming ability for rare-earth containing Zr-based metallic glasses.
Citation Count: Sikan, F...et al. (2019). "Effect of Sm on thermal and mechanical properties of Cu-Zr-Al bulk metallic glasses", Materials Science and Engineering A-Structural Materials Propertıes Mıcrostructure And Processıng, Vol. 743, pp. 168-174.
Effect of Sm on thermal and mechanical properties of Cu-Zr-Al bulk metallic glasses
(Elsevier Science SA, 2019) Sıkan, F.; Atabay, Sıla Ece; Motallebzadeh, A.; Özerinç, S.; Kalay, I.; Kalay, Y. E.; 101579
The effect of rare-earth (Sm) microalloying on the thermal stability and phase selection along with the effect of nanocrystallization on the mechanical properties of amorphous melt-spun ribbons of Zr50Cu40Al10, Zr49Cu39.2Al9.8Sm2 and Zr48Cu38.4Al9.6Sm4 alloys were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), Vickers and nanoindentation hardness tests and micropillar compression analysis. XRD and TEM analyses showed that all samples were fully amorphous in as-spun state; however, crystallization sequences for the Sm-free and the Sm micro-alloyed samples were different during devitrification. Combined study of XRD, DSC and TEM on melt-spun ribbons show that Zr48Cu38.4Al9.6Sm4 have nanocrystallization of Cu2Sm phase with an average diameter of 10 nm, which was absent in Zr50Cu40Al10, prior to crystallization of Cu10Zr7 phase. The nanoindentation and micropillar compression tests revealed Cu2Sm nanocrystals embedded in Zr48Cu38.4Al9.6Sm4 alloy improves strength and hardness. On the other hand, presence of these nanocrystals deteriorate shear band stability and thus result in a catastrophic brittle fracture through a single shear band burst.
Citation Count: Kalay, Y. E...et al. "Local chemical and topological order in Al-Tb and its role in controlling nanocrystal formation", Acta Materialia, Vol. 60, No. 3, pp. 994-1003, (2012)
Local Chemical and Topological Order in Al-Tb And its Role in Controlling Nanocrystal Formation
(Pergamon-Elsevier Science LTD, 2012) Kalay, Y. E.; Kalay, I.; Hwang, Jinwoo; Voyles, P. M.; Kramer, M. J.; 101579
How the chemical and topological short- to medium-range order develops in Al-Tb glass and its ultimate effect on the control of the high number density of face-centered-cubic-Al (fcc-Al) nuclei during devitrification are described. A combined study using high-energy X-ray diffraction (HEXRD), atom probe tomography (APT), transmission electron microscopy and fluctuation electron microscopy (FEM) was conducted in order to resolve the local structure in amorphous Al90Tb10. Reverse Monte Carlo simulations and Voronoi tessellation analysis based on HEXRD experiments revealed a high coordination of Al around Tb atoms in both liquid and amorphous states. APT results show Al-rich and Al-depleted regions within the as-quenched alloy. A network structure of Tb-rich clusters divides the matrix into nanoscale regions where Al-rich clusters are isolated. It is this finely divided network which allows the amorphous structure to form. Al-rich regions are the locus for fcc-Al crystallization, which occurs before the intermetallic crystallization. FEM reveals medium-range ordered regions similar to 2 nm in diameter, consistent with fcc-Al and trigonal-like Al3Tb crystal structures. We propose that the high coordination of Al around Tb limits diffusion in the intermetallic network, allowing for the isolated Al-rich regions to form at high density. These regions are responsible for the extremely high density of Al nanocrystal nuclei. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.