Mühendislik Fakültesi
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Article Citation Count: Kalay, Ilkay; Kramer, Matthew J.; Napolitano, RE., "Crystallization kinetics and phase transformation mechanisms incu56zr44 glassy alloy" Metallurgical And Materials Transactions A-Physical Metallurgy And Materials Science, Vol.46A, No.6, pp.3356-3364, (2015).Crystallization kinetics and phase transformation mechanisms incu56zr44 glassy alloy(Springer, 2015) Kalay, İlkay; Kramer, Matthew J.; Napolitano, R. E.; 101579The kinetics and phase selection mechanisms involved in the crystallization of an amorphous Cu-Zr alloy of eutectic composition (Cu56Zr44) were investigated using in situ high-energy X-ray diffraction (HEXRD), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC) under isothermal and constant heating rate conditions. In situ HEXRD results for 10 K/min (10 A degrees C/min) heating indicate that the amorphous alloy devitrifies into CuZr2 and mainly Cu10Zr7 at the crystallization temperature of 725 K (452 A degrees C). The sequence continues with the precipitation of CuZr (B2) at 1004 K (731 A degrees C), where these three phases coexist until the decomposition of CuZr2 is observed at 1030 K (757 A degrees C). The two equilibrium phases Cu10Zr7 and CuZr (B2) remain present on further heating until melting at the eutectic temperature for the Cu56Zr44 alloy. TEM investigation of the isothermal [705 K (432 A degrees C)] crystallization sequence reveals primary nucleation and growth of the Cu10Zr7 phase, where growth of the Cu10Zr7 crystals is initially planar with a transition to a cellular morphology, associated with partitioning of Zr at the growth front. Related cellular structures and composition profiles are quantified. (C) The Minerals, Metals & Materials Society and ASM International 2015Article 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.; 101579The 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.Article Citation Count: Genç, Ayşe Merve...et al. (2019). "Investigation of phase selection hierarchy in Mn-Al alloys", Intermetallics, Vol. 115.Investigation of phase selection hierarchy in Mn-Al alloys(2019) Genç, Ayşe Merve; Acar, Özgün; Turan, Servet; Kalay, İlkay; Savacı, Umut; Kalay, Yunus Eren; 101579Primarily attributed to the formation of the ferromagnetic tau-phase, near equiatomic composition of Mn-Al have recently received much attention in permanent magnet industry. Several mechanisms have been proposed in literature for the tau-phase formation but controversy still arises regarding the dominating mode. In the current work, MnAl-based alloys having different compositions in a range between Mn50.5Al49.5 and Mn57Al43 have been studied by means of in-situ high energy X-ray diffraction, differential scanning calorimetry (DSC) and magnetic measurements. Synchrotron and DSC experiments showed the dependence of the tau-MnAl on the intermediate disordered epsilon'-phase. Alloys having 53.4 at% or less Mn (S1, S2) followed a transformation route of epsilon+epsilon'-> tau ->beta+gamma(2) upon annealing. Alloys having more than 53.4 at% of Mn had only epsilon-phase. High energy X-ray diffraction patterns showed that epsilon-phase directly transformed into stable phases in the absence of epsilon'-phase. It is observed that epsilon' not only promoted the ferromagnetic tau-phase but also stabilized it by delaying the nucleation of stable phases.Article Citation Count: Cullinan, Tim...et al. (2015). "Kinetics and Mechanisms of Isothermal Devitrification in Amorphous Cu50Zr50", Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, Vol. 46, No. 2, pp. 600-613.Kinetics and Mechanisms of Isothermal Devitrification in Amorphous Cu50Zr50(2015) Cullinan, Tim; Kalay, İlkay; Kalay, Y. Eren; Kramer, Matt; Napolitano, Ralph; 101579The crystallization kinetics and microstructural dynamics associated with devitrifying a meltspun Cu50Zr50 metallic glass were investigated using isothermal treatments, in situ high-energy synchrotron X-ray diffraction, conventional and high-resolution transmission electron microscopy, and differential scanning calorimetry. The analysis of isothermal transformations allows us to more clearly unravel the complex interplay between nucleation and growth of competing stable and metastable phases. The isothermal devitrification response was found to involve the Cu10Zr7, CuZr2, and CuZr phases, consistent with previously reported constant heating rate experiments, but here we have resolved the phase evolution and structural characteristics of the transformation,including the very early stages of crystallization. At 671 K (398C),the isothermal transformation starts with the formation of the Cu10Zr7 phase, which grows in a generally equiaxed morphology. At a size of approximately 100 nm, the growth of the Cu10Zr7 particles is interrupted by the precipitation of a thin layer of the CuZr2 phase, upon which the metastable CuZr (B2) grows epitaxially. Crystallization kinetics are quantified here though in situ measurements (HEXRD, DSC) and ex situ microstructural analysis (TEM, HRTEM). Finally, the influences of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined. © 2014, The Minerals, Metals & Materials Society and ASM International.Article Citation Count: Cullinan, Tim...et.al., "Kinetics and mechanisms of isothermal devitrification inamorphous cu50zr50" Metallurgical And Materials Transactions A-Physical Metallurgy And Materials Science, Vol.46A, No.2, pp.600-613, (2015).Kinetics and mechanisms of isothermal devitrification inamorphous cu50zr50(Springer, 2015) Cullinan, Tim; Kalay, İlkay; Kalay, Y. Eren; Kramer, Matt; Napolitano, Ralph; 101579The crystallization kinetics and microstructural dynamics associated with devitrifying a melt-spun Cu50Zr50 metallic glass were investigated using isothermal treatments, in situ high-energy synchrotron X-ray diffraction, conventional and high-resolution transmission electron microscopy, and differential scanning calorimetry. The analysis of isothermal transformations allows us to more clearly unravel the complex interplay between nucleation and growth of competing stable and metastable phases. The isothermal devitrification response was found to involve the Cu10Zr7, CuZr2, and CuZr phases, consistent with previously reported constant heating rate experiments, but here we have resolved the phase evolution and structural characteristics of the transformation, including the very early stages of crystallization. At 671 K (398 A degrees C), the isothermal transformation starts with the formation of the Cu10Zr7 phase, which grows in a generally equiaxed morphology. At a size of approximately 100 nm, the growth of the Cu10Zr7 particles is interrupted by the precipitation of a thin layer of the CuZr2 phase, upon which the metastable CuZr (B2) grows epitaxially. Crystallization kinetics are quantified here though in situ measurements (HEXRD, DSC) and ex situ microstructural analysis (TEM, HRTEM). Finally, the influences of chemical partitioning, diffusion, and crystallographic orientation on this sequence are examined.Article 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.; 101579How 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.Article Citation Count: Kalay, İlkay (2020). "Microstructure and Mechanical Properties of CoCrFeNi(TiAl) High Entropy Alloys", Hittite Journal of Science and Engineering, Vol. 7, No. 2, pp. 157-162.Microstructure and Mechanical Properties of CoCrFeNi(TiAl) High Entropy Alloys(2020) Kalay, İlkay; 101579The structure and mechanical properties of CoCrFeNi and CoCrFeNiTi0.5Al0.5 (in molar ratio) high entropy alloys were investigated using X-ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM), hardness and compression tests. With the addition of Ti and Al, the crystal structure of CoCrFeNi changed from FCC to a mixture of FCC and double BCC structures. The lattice parameter of FCC increases upon addition of Al and Ti. The microstructure analysis shows the morphological transition of dendrites from non-equiaxed to equiaxed during the suction casting of CoCrFeNiTi 0.5Al 0.5 alloy. The Vickers microhardness testing of CoCr-FeNi alloy reveals significant increase in hardness with the addition of Al and Ti. The hardness values are improved in as-suction cast CoCrFeNi and CoCrFeNiTi0.5Al 0.5 alloys compared to their ascast alloys due to strengthening. The CoCrFeNiTi0.5Al 0.5 alloy yields at 1997 MPa and fails at 2344 MPa. The fracture mechanism of CoCrFeNiTi 0.5Al 0.5 alloy reveals a cleavage mode.Article Citation Count: Sikan, Fatih; Yasar, Bengisu; Kalay, Ilkay, "Nanocrystallization in Cu-Zr-Al-Sm Bulk Metallic Glasses", Metallurgical and Materials Transactions A-Physical Metallurgy and Materials Science, Vol. 49, No. 4, (2018)Nanocrystallization In Cu-Zr-Al-Sm Bulk Metallic Glasses(Springer, 2018) Sıkan, Fatih; Yaşar, Bengisu; Kalay, İlkay; 101579The effect of rare-earth element (Sm) microalloying on the thermal stability and crystallization kinetics of melt-spun ribbons and suction-cast rods of Zr48Cu38.4Al9.6Sm4 alloy were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), transmission electron microscopy (TEM), and atom probe tomography (APT). The XRD results of constant heating rate annealing indicated that amorphous Zr48Cu38.4Al9.6Sm4 melt-spun ribbons devitrifies into Cu2Sm at 673 K (400 A degrees C). The sequence continues with the precipitation of Cu10Zr7 and then these two phases coexist. XRD and TEM studies on 1 mm diameter as suction-cast rods indicated the precipitation of 30-nm-mean size Cu2Sm crystals during solidification. TEM investigation of the isothermal crystallization sequence of melt-spun ribbons and 1-mm-diameter suction-cast rods revealed the precipitation of Cu2Sm nanocrystals at the onset of crystallization and the restriction of the growth of these nanocrystals up to 10 nm diameter with further annealing. APT analysis of 1-mm-diameter suction-cast rods showed that the limited growth of Cu2Sm nanocrystals is due to sluggish diffusion of Sm and Al-Zr pile up at the interface.Article Citation Count: Hwang, Jinwoo...et al. (2012). "Nanoscale structure and structural relaxation in Zr 50Cu 45Al 5 bulk metallic glass", Physical Review Letters, Vol. 108, No. 19.Nanoscale structure and structural relaxation in Zr 50Cu 45Al 5 bulk metallic glass(2012) Hwang, Jinwoo; Melgarejo, Z.H.; Kalay, Y.E.; Kalay, İlkay; Kramer, M.J.; Stone, D.S.; Voyles, P.M.; 101579Hybrid reverse Monte Carlo simulations of the structure of Zr 50Cu 45Al 5 bulk metallic glass incorporating medium-range structure from fluctuation electron microscopy data and short-range structure from an embedded atom potential produce structures with significant fractions of icosahedral- and crystal-like atomic clusters. Similar clusters group together into nanometer-scale regions, and relaxation transforms crystal-like clusters into icosahedral clusters. A model refined against only the potential does not agree with the fluctuation microscopy data and contains few crystal-like clusters. © 2012 American Physical Society.
