Browsing by Author "Kalay, İlkay"

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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.
Kinetics and mechanisms of isothermal devitrification inamorphous cu50zr50
(Springer, 2015) Kalay, İlkay; Kalay, İlkay; 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 - Scopus: 171
Nanoscale structure and structural relaxation in Zr 50Cu 45Al 5 bulk metallic glass
(2012) Hwang, J.; Kalay, İlkay; Melgarejo, Z.H.; Kalay, Y.E.; Kalay, I.; Kramer, M.J.; Stone, D.S.; Voyles, P.M.; 101579; Mekatronik Mühendisliği
Hybrid 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.
Samaryum Katkılı Bakır-Zirkonyum-Aluminyum Bazlı Metalik Cam ve Nanokompozitlerinin Üretilmesi ve Geliştirilmesi
(2020) Kalay, İlkay; Kalay, Yunus Eren
Bu proje, hem iyi cam yapabilme hem de birçok çok bileşenli metalik camın temelini oluşturması özellikleri ile dikkat çeken Cu-Zr sistemini temel almaktadır. Proje, Cu-Zr bazlı Cu-Zr-Al-Sm amorf ve amorf/kristal nanokompozit alaşım sistemlerinin üretilmesi, geliştirilmesi ve mikroyapı-mekanik özellik ilişkisinin tayin edilmesi ve kontrolü üzerine yoğunlaşmıştır. Bu bağlamda, cam oluşturma kabiliyeti (COK) en yüksek alaşım sistemleri, Cu-Zr-Al-Sm elementlerinin miktarları değiştirilerek tasarlanmıştır. Kompozisyonları tayin edilen metalik cam ve metalik cam nanokompozitleri, yüksek saflıktaki Cu, Zr, Al ve Sm elementlerinden, argon gazı altında ark ergitme tekniği kullanılarak üretilmiş ve yüksek soğutma hızına ulaşılarak amorf yapının oluşturulabilmesi için emme döküm tekniği ile farklı çaplardaki bakır kalıplara dökülmüştür. Alaşımların kinetik modellemesi de yapılarak çekirdeklenme ve büyüme kristallenme mekanizmaları incelenmiştir. Metalik cam nanokompozitleri, ayrıca kısmi kristallendirme yöntemi ile de üretilmişlerdir. Üretilen metalik cam ve metalik cam nanokompozitleri X-ışını kırınımı (XRD), diferansiyel taramalı kalorimetri (DSC), taramalı elektron mikroskobu (SEM), sertlik ve basma testleri kullanılarak incelenmiştir. Yapılan çalışmalar, Sm miktarının artması ile COK değerinin arttığını ve en yüksek COK değerinin Zr47.5Cu38Al9.5Sm5, Zr50Cu37Al10Sm3 ve Zr50Cu35Al10Sm5 alaşımlarında olduğunu göstermiştir. Kompozisyonları ve içerdikleri Sm miktarı değiştikçe metalik camların kristallenme eşik enerjilerinin ve izotermal koşullarda kristallenme mekanizmalarının değiştiği gözlemlenmiştir. Emme döküm sırasında çapı daha düşük olan çubukların soğuma hızının daha yüksek olması ve çap büyüdükçe soğuma hızının azalması nedeni ile 3 mm çaplı alaşımlarda kısmi amorf/kısmi kristal yapının oluştuğu gözlenmiştir. Basma testi sonuçları, alaşımların kırılma mekanizmalarında farklılık olduğunu göstermiştir. 3mm çapındaki Zr50Cu35Al10Sm5 çubuğu 45°’ye yaklaşan bir açı ile kırılmış ve kırılma yüzeyinde bulunan damarsı yapı ve nehir benzeri desenli bölgeler, sünek ve gevrek iki farklı kırılma tipinin varlığını göstermiştir. Zr50Cu37Al10Sm3 ve Zr47.5Cu38Al9.5Sm5 çubuklarında kırılma kayma bantları üzerinde hızlı bir şekilde gerçekleşmiş ve klivaj tipi ile gevrek kırılma meydana gelmiştir. Sünekliği en yüksek alaşım Zr50Cu35Al10Sm5 iken kırılma mukavemeti en yüksek olanlar Zr47.5Cu38Al9.5Sm5 ve Zr48.5Cu38.5Al10Sm1 metalik cam nanokompozitleridir.
Citation - WoS: 4
Citation - Scopus: 3
The Anomalous Nucleation in Al-Tb Metallic Glasses
(Springer, 2021) Ulucan, T. H.; Kalay, İlkay; Kalay, I.; Kalay, Y. E.; 101579; Mekatronik Mühendisliği
The effects of amorphous structure on the devitrification of Al90Tb10 marginal glass former system were investigated in detail by a combined study of high-energy X-ray diffraction (HEXRD), X-ray absorption fine structure (EXAFS), reverse Monte Carlo simulations (RMC), transmission electron microscopy (TEM) and thermal analyses. The atomic structures of melt-spun ribbons and magnetron sputtered amorphous samples with the same composition were simulated using RMC constrained by XRD, EXAFS, and ab-initio results. The fcc-Al nanocrystals nucleated and grown in thin-film specimens have a limited size with almost perfect spherical morphology. The population of these nanocrystals is three orders of magnitude higher as compared to ribbon specimens. The differences in the devitrified ribbon and thin-film metallic glasses were traced back to structural differences in the amorphous state. The amorphous melt-spun ribbons and magnetron sputtered thin- films were found to have different degrees of short-range order and clustering.