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Alloy design for the development and production of titanium based bulk metallic glasses

Demir, Iraz Begüm
The bulk metallic glasses (BMGs) are quite new type of metallic alloys exhibiting many superior features like high yield strength, improved elastic behavior, high corrosion resistance and superior abrasion resistance by virtue of its irregular atomic structures. Due to the importance of today’s reduced energy consumption, special attention is given to the light element-based bulk metallic glasses. Among these, Ti-based amorphous alloys have promising mechanical properties for use in engineering applications. Therefore, Ti-based bulk metallic glasses provides a hope as an advanced set of lightweight materials for use in medical applications, defense, automotive and aerospace industries. However, generally Ti-based bulk metallic glasses show poor bulk glass formation that restricts their potential application areas. Studies on this subject will provide an important involvement for the development of glass formation of the Ti based BMGs. In the literature, there are many studies on theoretical and semi-empirical criteria for evaluation of glass forming ability (GFA) of the alloy systems. However, these criteria do not work on every alloy system while providing positive results for some system. Therefore, it is essential to systematically examine the effects of alloying elements for the development of cast metallic glass alloy systems. In this thesis study, besides semi-empirical criteria, with the aim of improvement of the GFA, alloys were synthesized by alloying Ti-Cu binary system with potential candidate alloying elements derived from theoretical predictions by combining the electronic theory of alloys in the pseudopotential approximation which are the part of previous thesis study. As a starting point, Ni, Al and V were selected as alloying elements and correspondingly Ti48Cu30Ni10Al7V5 alloy was produced. After that gradual Si addition was provided on this alloy and Ti47Cu30Ni10Al7V5Si1 and (Ti48Cu30Ni10Al7V5)97Si3 alloys were fabricated to investigate effect of Si as a minor alloying element. Samples of alloys were fabricated by arc melting device equipped with suction casting unit under controlled atmosphere. The effect of the potential alloying elements on the ability to create Ti based BMG was presented by structural and thermal characterization techniques. Atomic 1% of Si addition favored the formation of approximately 40 µm in thickness amorphous structure at the outer zone of the alloy composition Ti47Cu30Ni10Al7V5Si1. Further addition of Si has detrimental effects on glass formation ability. Even at non-equilibrium cooling condition amorphous structure was not observed and the crystallization could not be prevented by copper mold suction casting.