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| Author(s): |
Camilo Augusto Fernandes Salvador
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica |
| Defense date: | 2019-04-02 |
| Examining board members: |
Rubens Caram Junior;
Claudemiro Bolfarini;
Andre Tschiptschin;
João Batista Fogagnolo;
Rodrigo José Contieri
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| Advisor: | Rubens Caram Junior |
| Abstract | |
An open challenge on structural biomaterials is to obtain low-cost Ti-alloys with a high elastic admissible strain (the ratio of yield strength to elastic modulus). In this study, we addressed the presented challenge via two working directions. Firstly, we explored the Ti-Nb-Fe system to find an optimal, cost-effective composition with a compromise between a low elastic modulus and low added Nb contents. Ti-(31-4x)Nb-(1+0.5x)Fe ingots were prepared, and Nb was substituted with Fe, starting at Ti-31Nb-1.0Fe and going down to Ti-11Nb-3.5Fe (wt%). The samples were solution-treated and tested under three conditions: water-quenched, furnace-cooled and step-quenched to different temperatures. Resultant microstructures were analyzed with the aid of X-ray diffraction, differential scanning calorimetry, scanning, and transmission electron microscopy. Among the ternary alloys, Ti-19Nb-2.5Fe (wt. %) presented the best combination of mechanical strength and elastic modulus. The heat-treated samples provided useful insights into how the alpha-phase formation starts and develops in this system during aging. In general, alpha-phase precipitation starts at the grain boundaries, even after very short-time isothermal heat-treatments (1 min). Overall, an optimized microstructure composed of beta-grains and fine and dispersed alpha-phase was obtained for most of the experimental alloys after aging at 450 ºC. The second part of this project comprises the exploration of Ti-Nb-Fe-Ze quaternary alloys, with additions of 4-13 wt.% of Zr. One additional alloy, based on Ti-19Nb-2.5Fe, was prepared with additions of 6 wt.% of Sn. Beyond all the characterization work, tensile tests performed at room-temperature confirmed that Ti-Nb-Fe-Zr alloys could reach an elastic admissible strain close to 1.5, with relatively good ductility. Regarding the Zr and Sn additions, they helped suppress omega formation after water-quenching. Also, Zr and Sn were equally distributed between matrix and precipitates during aging. While the diffusion of Nb and Fe were enhanced via grain-boundaries, they seemed to be inhibited by the presence of Zr and Sn. As a result, these elements allow higher yield-strengths and more refined secondary ?-phase. In the end, a materials selection chart is presented to help future researchers to compare materials for orthopedic implants considering the elastic admissible strain and cost as significant guidelines (AU) | |
| FAPESP's process: | 14/24449-0 - Phase transformations, microestructure and mechanical properties of new beta metastable Ti-Nb-Zr-Fe (TNZF) titanium alloys for biomedical applications |
| Grantee: | Camilo Augusto Fernandes Salvador |
| Support Opportunities: | Scholarships in Brazil - Doctorate |