Nano-scale phase separation and glass forming ability of iron-boron based metallic glasses

Aykol, Muratahan
This study is pertinent to setting a connection between glass forming ability (GFA) and topology of Fe-B based metallic glasses by combining intimate investigations on spatial atomic arrangements conducted via solid computer simulations with experimentations on high GFA bulk metallic glasses. In order to construct a theoretical framework, the nano-scale phase separation encountered in metallic glasses is investigated for amorphous Fe80B20 and Fe83B17 alloys via Monte Carlo equilibration and reverse Monte Carlo simulation. The phenomenon is identified regarding three topological aspects: 1) Pure Fe-clusters as large as ~0.9 nm and Fe-contours with ~0.72 nm thickness, 2) Fe-rich highly deformed body centered cubic regions, 3) B-centered prismatic units with polytetrahedral order forming distinct regions of high and low coordinations are found. All topological aspects are compiled into a new model called Two-Dimensional Projection Model for predicting contributions to short and medium range order (MRO) and corresponding spacing relations. The outcome geometrically involves proportions approximating golden ratio. After successfully producing soft magnetic Fe-Co-Nb-B-Si based bulk metallic glass and bulk nanocrystalline alloys with a totally conventional route, influences of alloying elements on structural units and crystallization modes are identified by the developed model and radial distributions. While Co atoms substitute for Fe atoms, Nb and Si atoms deform trigonal prismatic units to provide local compactions at the outset of MRO. Cu atoms alter the type of MRO which resembles crystalline counterparts and accompanying nanocrystals that precipitate. The GFA can be described by a new parameter quantifying the MRO compaction, cited as Φ.


Investigations on bulk glass forming ability of titanium based multicomponent alloys
Süer, Sıla; Mekhrabov, Amdulla O.; Department of Metallurgical and Materials Engineering (2008)
The aim of this study is to investigate the bulk glass forming ability (BGFA) of Ti-based alloy systems. These investigations were carried out in two main parts that are complementary to each other: theoretical and experimental. For theoretical studies, which are based on electronic theory of alloys in pseudopotential approximation, Ti-Zr, Ti-Co and Ti-Cu alloys were chosen as the binary systems. Alloying element additions were performed to each binary for the investigation of the BGFA of multicomponent Ti-...
Experimental investigation of residual stresses introduced via shot peening and their effect on fatigue life of ball bearings
Küçükyılmaz, Ali; Gür, Cemil Hakan; Department of Metallurgical and Materials Engineering (2010)
In this study, residual stresses introduced via application of shot peening on the raceways of bearing rings and their effect on the fatigue life was investigated experimentally. For improvement of residual compressive stress state, shot peening operation with different parameters was utilized. Residual stress measurements were conducted via X-ray diffraction technique. Optimization of residual stress state during the production of ball bearings is the main target of this study. Process parameters for shot ...
Isochronal hydrogenation of textured magnesium/palladium thin films
Özgit, Çağla; Öztürk, Tayfur; Department of Metallurgical and Materials Engineering (2009)
Pure and palladium‐covered 350 nm thick magnesium thin films were deposited on glass substrates via thermal evaporation. In the as‐deposited state, films were highly textured with Mg (001) parallel to the substrate. Hydrogen loading experiments were carried out in two different conditions; namely isothermal and isochronal. Hydrogenation behaviors of the thin films were followed by twopoint probe electrical resistance and optical transmittance measurements, as well as x‐ray diffraction studies. Isothermal hy...
Spectroscopic intensities as measures of order parameter close to order-disorder transitions
Yurtseven, Hasan Hamit (Springer Science and Business Media LLC, 1988-01-01)
The infrared and Raman intensities can be related to the order parameter close to order-disorder phase transitions in crystal systems. In the present study this relationship has been obtained and compared with our experimental results for ammonium halides. Our predictions give satisfactory agreement with the observations in these crystals. It is proposed that the FTIR techniques can be appropriately used to evaluating the order parameter in various crystal systems.
Investigation of photovoltaic properties of amorphous InSe thin film based Schottky devices
Yilmaz, K.; Parlak, Mehmet; Ercelebi, C. (IOP Publishing, 2007-12-01)
In this study, device behavior of amorphous InSe thin films was investigated through I-V, C-V and spectral response measurements onto SnO2/p-InSe/metal Schottky diode structures. Various metal contacts such as Ag, Au, Al, In and C were deposited onto amorphous p-InSe films by the thermal evaporation technique. The best rectifying contact was obtained in a SnO2/p-InSe/Ag Schottky structure from I-V measurements, while the Au contact had poor rectification. Other metal contacts (Al, In and C) showed almost oh...
Citation Formats
M. Aykol, “Nano-scale phase separation and glass forming ability of iron-boron based metallic glasses,” M.S. - Master of Science, Middle East Technical University, 2008.