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Amorphous and bulk amorphous metallic alloys are an intriguing class of structural materials and possess a range of interesting properties, including near theoretical strength, high hardness, extremely low damping characteristics, excellent wear properties, high corrosion resistance, low shrinkage during cooling and almost perfect as-cast surfaces with good potential for forming and shaping. In this study, new Ti-based bulk amorphous alloys are tried to be modeled and synthesized. For that purpose, electronic theory of alloys in the pseudo potential approximation was used as a tool for understanding the theory lying beneath the bulk glass forming ability (BGFA). The results from this approach were evaluated both separately and together with the other theories supposed by our colleagues. Glass forming parameters of ordering energy, &amp / #916 / HM, viscosity, mismatch entropy, Rc was calculated for various Ti-based binary and ternary and the change in these parameters in both cases was evaluated. The results of the theoretical calculations of glass forming parameters has shown good relation with the literature data that the predicted alloying elements, i.e. Mo, Hf, Zr, B, Fe, Sn, and Be, to increase GFA for Ti2Ni binary system were generally used in the production of Ti-based bulk amorphous alloys. In the second part of this thesis, new Ti-based compositions with high GFA were tried to be synthesized with light of these results and encouraging conclusions were drawn. The production of these alloys were made with centrifugal casting method which is relatively a new technique for producing such alloys and the characterization of these alloys were made with metallographic, X-ray and thermal means.

The aim of this study is to form a theoretical model for simulation of glass forming ability of Fe &amp / #65533 / Based bulk amorphous alloys, to synthesize Fe &amp / #65533 / based multicomponent glassy alloys by using the predictions of the theoretical study, and to analyze the influence of crystallization and solidification kinetics on the microstructural features of this amorphous alloys. For this purpose, first, glass forming ability of Fe &amp / #65533 / (Mo, B, Cr, Nb, C) &amp / #65533 / X ( X = various alloying elements, selected from the periodic table) ternary alloy systems were simulated for twenty different alloy compositions by using the electronic theory of alloys in pseudopotential approximation and regular solution theory. Then, by using the results of the theoretical study, systematic casting experiments were performed by using centrifugal casting method. The alloying elements were melted with induction under argon atmosphere in alumina crucibles and casted into copper molds of different shapes. Characterization of the cast specimens were performed by using DSC, XRD, SEM, and optical microscopy. Comparison of equilibrium and nonequilibrium solidification structures of cast specimens were also performed so as to verify the existence of the amorphous phase. Good agreement of the results of experimental work, with the predictions of the theoretical study, and the related literature was obtained.

The aim of this study is to synthesize and characterize new bulk amorphous alloys in the Ni- based systems. Theoretical studies on the basis of semi-empirical rules and the electronic theory of alloys in pseudopotential approximation has been provided in order to predict the impurity elements that will lead to an increase in the glass forming ability of Ni-based alloy systems. Glass forming ability of ten different compositions of alloys of Ni-Nb, Ni-Fe, Ni-B, Ni-Hf and Ni-Cr was simulated by using FORTRAN programs based on pseudopotential theory. In addition to the binary alloys, ternary alloys, which were formed by addition of 1 at% of third element to these systems, were also simulated. Since ordering energy is an indicator of glass forming ability, theoretical studies allowed to predict the effect of various third elements on the formation of amorphous phase. Furthermore, ordering energies were also used to calculate other parameters important for glass forming ability. In the second part of the study, on the basis of theoretical results, a series of casting experiments were done. Different compositions of Ni-Nb, Ni-Nb-Sn and Ni-Nb-Al alloys were cast in the centrifugal casting machine. Alloys were melted in alumina crucibles and cast into the copper moulds. Characterizations of cast alloys were done by the use of Metallography, SEM, XRD and DSC. Fully amorphous Ni52Nb41Al7 alloy was synthesized in bulk form with 0.8 mm thickness.