New Generation Titanium Alloys with Low Elastic Modulus for Orthopaedic Implants

Author: Magdalen Hui Ching Tan

Tan, Magdalen Hui Ching, 2018 New Generation Titanium Alloys with Low Elastic Modulus for Orthopaedic Implants, Flinders University, College of Science and Engineering

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Total hip replacement (THR) has progressively become a common treatment for patients with osteoarthritis or hip damage, which involves mostly the ageing population. The expectant rapid growth of the ageing population thus has necessitated a steady demand for the THR market. However, the current biomaterials used to fabricate the THR implants are found having much higher Young’s moduli compared to the bones and thus resulted in stress-shielding that causes failure and surgery revision. Owing to these circumstances, studies and research to develop biomaterials with Young’s moduli closer to that of cortical bones are gaining an extensive attention. This study therefore aims to investigate and develop titanium-based alloys (Ti-Nb-Zr) with new chemical composition which offer Young’s moduli lower than 50GPa. The alloys were designed after extensive research on the alloying effect, phase analysis, and the comparison of previously fabricated Ti-Nb-Zr alloys (of different compositions). Three alloys were therefore designed for investigation including Ti-23Nb-7Zr (sample 1), Ti-28Nb-7Zr (sample 2) and Ti-33Nb-7Zr (sample 3). Thermo Calc Software was utilised to predict the phases formed within the designated alloys prior to the fabrication process. The alloys were fabricated using a non-consumable vacuum arc melting furnace through the courtesy of Beihang University. Samples for microstructure examination and X-ray diffraction (XRD) analysis were prepared in accordance to the ASM standard (Volume 9: Metallography and Microstructures of Titanium and Its Alloys). Microstructures were observed under both optical microscope and scanning electron microscope (SEM). Hardness of the alloys were compared through microhardness and nanoindentation testing. The nanoindentation system was also employed to calculate the Young’s modulus of the alloys. The XRD analysis was carried out to identify the phases present in the alloys after the casting and solution treatment process. The microstructure results showed a platelike martensitic (α”) structure in the beta (β) matrix. The martensitic structure was most distinct and coarser in sample 1, with decreasing amount and coarseness towards sample 3. Basketweave and Widmanstätten patterns were also observed which resembles the α” distorted alpha structure. The XRD analysis exhibited the presence of two phases which are alpha (α”) and beta (β). As the most important finding, all the three fabricated alloys were measured to have a significantly reduced stiffness level as they offer a Young’s modulus of 40.0, 37.5 and 41.5GPa that are all less than the initial target of 50GPa.

Keywords: Ti-Nb-Zr, β-type titanium alloys, β-, α”-phase, acicular martensitic, Young’s modulus

Subject: Engineering thesis

Thesis type: Masters
Completed: 2018
School: College of Science and Engineering
Supervisor: Dr Reza Oskouei