Malzeme Bilimi ve Mühendisliği Bölümü Yayın Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12416/396

Browse

Now showing 1 - 3 of 3

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.
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; 101579
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 Count: Esen, Ziya, "The effect of processing routes on the structure and properties of magnesium-TiNi composites", Vol. 558, pp. 632-640, (2012)
The Effect of Processing Routes On the Structure and Properties of Magnesium-Tini Composites
(Elsevier Science SA, 2012) Esen, Ziya; 52373
TiNi particulate-reinforced magnesium matrix composites were fabricated by rotary hot swaging and post-annealing heat treatment. The magnesium matrix of the processed composites was observed to contain elongated grains comprised of equiaxed recrystallised grains. Each elongated grain was surrounded by thin, non-continuous magnesium oxide layers composed of nanometric magnesium oxide particles. The TiNi reinforcement particles preserved their starting spherical shape during processing and testing. However, the hot deformation and annealing heat treatment changed the underlying room temperature microstructures and transformation behaviours of the reinforcements. In contrast to the majority of the ceramic reinforcements, the ductility of the composites was not significantly degraded by the addition of TiNi reinforcements; conversely, an approximately 25% enhancement was recorded in the elongation values for the Mg-5 vol% TiNi alloy. While the yield strengths of the composites changed linearly with increasing reinforcement content, the highest compression peak strength value was obtained with the addition of 5 vol% TiNi, beyond which the strength was slightly decreased. During mechanical testing, the TiNi particles debonded due to insufficient bonding between the matrix and reinforcement, and fracture resulted largely within the oxide layers present in the interfacial region and the magnesium oxide film in the magnesium grain boundaries. (C) 2012 Elsevier B.V. All rights reserved.

Browse

Browsing Malzeme Bilimi ve Mühendisliği Bölümü Yayın Koleksiyonu by Department "Çankaya Üniversitesi, Mühendislik Fakültesi, Malzeme Bilimi ve Mühendislik Bölümü"