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Synthesis and structural characterization of multifunctional Ti alloy: gum metal

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2020
Elçin, Orkun
Gum metal (Ti-23Nb-0.7Ta-2Zr-1.2O at%), a newly discovered titanium alloy, is considered as a suitable unique alloy for structural applications in aerospace, sports equipment, industrial, and especially in biomedical areas because of their outstanding properties such as high yield strength (up to 2000 MPa) with low elastic modulus (50 GPa), and biocompatibility. Furthermore, in the heavily deformed state, it still possesses an ultra-low elastic modulus, ultra-high-strength, large elasticity (up to 2.5%), Elinvar, and Invar properties. These exclusive mechanical and physical properties are mainly attributed to their extraordinary deformation mechanism. However, alloy design and production of gum metal are quite difficult since it consists of raw materials that are difficult to work with and tend to oxidize quite easily. In addition, these raw materials are quite challenging to forge an alloy with a homogeneous structure. Therefore, it is generally produced by powder metallurgy, a very laborious, sensitive, and troubled production. It is important to develop a new production process since this method is not suitable for mass production. This thesis focuses on three main subjects: (i) to develop the candidate alloys exhibit gum metal properties with the help of the theoretical calculations, (ii) to be able to produce alloys successfully by using the arc melting furnace which is suitable for mass production, easier and conventional production method rather than powder metallurgy, and (iii) to investigate the effects of alloying elements on deformation mechanism, structural and mechanical properties of Ti71.8+nNb25-nZr2O1.2 base alloy and approval of the validity of theoretical estimations proposed for single-phase gum metal alloy. According to theoretical calculations, three different forms, (S1) Ti-23.8Nb-2Zr-1.2O (at%), (S2) Ti-23Nb-0.93V-2Zr-1.2O (at%) and (S3) Ti-25Nb-0.7Ta-2Zr-2Al-1.2O (at%), were determined and casted successfully in an atmosphere-controlled arc melting furnace. The chemical characterization, mineralogical analyses, and mechanical properties of these alloys were investigated by using XRD, DSC, SEM, EDS, microhardness, and compression test instruments. It has been observed that these three alloys were prepared composing of only a single phase with homogeneous morphology and elemental composition. On account of the incorporation of various elements to the base composition, from alpha to beta phase transition temperature were reduced as much as 100 degrees C and mechanical properties were improved significantly. Around 85% reduction in thickness with the compression tests were obtained with no apparent crack formation. Also, no noticeable increase in hardness emerged with this deformation. In the end, these mechanical and structural investigations suggest that all the prepared compositions within the scope of this work could be in the gum metal family.