Browsing by Author "Kalay, Ilkay"

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Citation - WoS: 25
Citation - Scopus: 27
Crystallization kinetics and phase transformation mechanisms incu56zr44 glassy alloy
(Springer, 2015) Kalay, Ilkay; Kalay, İlkay; Kramer, Matthew J.; Napolitano, Ralph E.; 101579; Mekatronik Mühendisliği
The 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 2015
Citation - WoS: 5
Citation - Scopus: 5
Investigation of phase selection hierarchy in Mn-Al alloys
(Elsevier Sci Ltd, 2019) Genc, Ayse Merve; Kalay, İlkay; Acar, Ozgun; Turan, Servet; Kalay, Ilkay; Savaci, Umut; Kalay, Yunus Eren; 101579; Mekatronik Mühendisliği
Primarily 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.
Citation - WoS: 22
Citation - Scopus: 23
Kinetics and Mechanisms of Isothermal Devitrification in Amorphous Cu50Zr50
(Springer, 2015) Cullinan, Tim; Kalay, İlkay; Kalay, Ilkay; Kalay, Y. Eren; Kramer, Matt; Napolitano, Ralph; 101579; Mekatronik Mühendisliği
The 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.
Microstructure and Mechanical Properties of CoCrFeNi(TiAl) High Entropy Alloys
(2020) Kalay, İlkay; Kalay, Ilkay; 101579; Mekatronik Mühendisliği
The 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 amixture of FCC and double BCC structures. The lattice parameter of FCC increasesupon addition of Al and Ti. The microstructure analysis shows the morphologicaltransition of dendrites from non-equiaxed to equiaxed during the suction casting ofCoCrFeNiTi0.5Al 0.5 alloy. The Vickers microhardness testing of CoCr-FeNi alloy revealssignificant increase in hardness with the addition of Al and Ti. The hardness values areimproved 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 failsat 2344 MPa. The fracture mechanism of CoCrFeNiTi0.5Al 0.5 alloy reveals a cleavage mode.
Citation - WoS: 11
Citation - Scopus: 13
Nanocrystallization In Cu-Zr-Al-Sm Bulk Metallic Glasses
(Springer, 2018) Sikan, Fatih; Kalay, İlkay; Yasar, Bengisu; Kalay, Ilkay; 101579; Mekatronik Mühendisliği
The 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.
Citation - WoS: 1
Citation - Scopus: 1
Nanomechanical Properties of Al-Tb Marginal Metallic Glass
(Elsevier Science Sa, 2023) Okuyucu, Can; Ulucan, Tolga Han; Abboud, Mohammad; Motallebzadeh, Amir; Ozerinc, Sezer; Kalay, Ilkay; Kalay, Yunus Eren
Al-Rare Earth (RE) metallic glasses provide an effective model system to study the effect of nanocrystallites in an amorphous matrix on nanomechanical behavior. In this work, we achieved a series of Al-Tb metallic glasscrystalline composites with systematically varying crystalline content through annealing. The nanomechanical properties were characterized using micropillar compression tests and nanoindentation for as-quenched amorphous and annealed amorphous/nanocrystalline composite specimens. The promising hardness increases after annealing from 3.0 GPa to 4.6 GPa and elastic modulus increment from 68 GPa to 92 GPa were discussed in detail, considering the structural features of Al-RE marginal metallic glass formers. The increase in elastic modulus is associated with the nucleated fcc-Al nanocrystals that divide the amorphous matrix, leading to the branching of the shear bands. The correlation between the fcc-Al nanocrystals and the behavior of shear bands was discussed in detail.