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Soldadura Laser de Ti18Zr11Nb3Sn (at.%) liga com memória de forma para aplicações biomédicas
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Nos dias que correm, as ligas NiTi, devido às suas incomparáveis propriedades – efeito
de memória de forma, superelasticidade, alta resistência ao desgaste, excelente
trabalhabilidade na fase martensítica, resistência à fadiga e à corrosão – que as tornam
tão difíceis de substituir, têm inúmeras aplicações nas indústrias, como por exemplo, na
aeroespacial, automóvel, civil e biomédica.
A nível da indústria biomédica, começaram a surgir algumas questões quando foram
identificados problemas cardíacos e células cancerígenas devido à toxicidade e ao efeito
alergénico dos iões de níquel que são libertados no organismo humano pelas ligas NiTi,
a longo prazo. Desta forma, foi necessário investigar uma alternativa para estas e, assim,
surgiu a liga Ti18Zr11Nb3Sn (at.%).
Neste trabalho foi estudado o efeito da soldadura laser na liga Ti18Zr11Nb3Sn (at.%),
caracterizando microestrutural e mecanicamente a amostras soldadas. Esta caracterização
foi feita através das técnicas de Microscopia Eletrónica de Varrimento complementada
pela Difração de Eletrões Retroespalhados, Difração de Raio-X, Ensaio de tração à
fratura, Ensaios de ciclagem e avaliação de microdurezas. Deste estudo, a nível
microestrutural, conclui-se que a soldadura altera o tamanho do grão e a textura. A nível
mecânico, a soldadura afeta a ductilidade, a recuperação superelásticas e as tensões de
transformação, não tendo qualquer tipo de influência na capacidade do material absorver
energia e na microdureza. No entanto, a amostra soldada apresenta excelentes
propriedades mecânicas que possibilitam o seu uso em potenciais aplicações biomédicas.
Palavras-chave: Ligas com memória de forma, Superelasticidade, Soldadura laser
Nd:YAG,
Nowadays NiTi alloys have countless applications on the industry sector, such as aerospace, automotive, civil and biomedical, due to their unparalleled properties – shape memory effect, pseudoelasticity, high-wear resistance, excellent workability in the martensitic phase and fatigue and corrosion resistance – make them so difficult to replace. In the biomedical industry sector, some questions began to arise when cardiac problems and cancerous cells were identified due to the toxic and allergenic effect of nickel ions that are released into the human body by the long-term presence of NiTi alloys. Thus, to find an alternative to these alloys, the Ti18Zr11Nb3Sn (at.%) alloy appeared. In this thesis work, was studied the effect of laser welding on the Ti18Zr11Nb3Sn (at.%) alloy, for further characterization of the microstructure and mechanical behavior of the welded samples. This characterization was done using Scanning Electron Microscopy complemented by Electron Backscatter Diffraction, by X-Ray Diffraction and by uniaxial tensile test, mechanical cycling tests and microhardness assessment. Trough these experimental trials it is concluded that the welding changes the grain size and the texture of it at a microstructural level. At a mechanical level, the welding processes affects the ductility, the pseudoelasticity recovery and the stress strain having no influence on the material’s microhardness or ability to absorb energy. Nevertheless, the welded sample has excellent mechanical properties that make it feasible to use in biomedical applications.
Nowadays NiTi alloys have countless applications on the industry sector, such as aerospace, automotive, civil and biomedical, due to their unparalleled properties – shape memory effect, pseudoelasticity, high-wear resistance, excellent workability in the martensitic phase and fatigue and corrosion resistance – make them so difficult to replace. In the biomedical industry sector, some questions began to arise when cardiac problems and cancerous cells were identified due to the toxic and allergenic effect of nickel ions that are released into the human body by the long-term presence of NiTi alloys. Thus, to find an alternative to these alloys, the Ti18Zr11Nb3Sn (at.%) alloy appeared. In this thesis work, was studied the effect of laser welding on the Ti18Zr11Nb3Sn (at.%) alloy, for further characterization of the microstructure and mechanical behavior of the welded samples. This characterization was done using Scanning Electron Microscopy complemented by Electron Backscatter Diffraction, by X-Ray Diffraction and by uniaxial tensile test, mechanical cycling tests and microhardness assessment. Trough these experimental trials it is concluded that the welding changes the grain size and the texture of it at a microstructural level. At a mechanical level, the welding processes affects the ductility, the pseudoelasticity recovery and the stress strain having no influence on the material’s microhardness or ability to absorb energy. Nevertheless, the welded sample has excellent mechanical properties that make it feasible to use in biomedical applications.
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Palavras-chave
Ligas com memória de forma Superelasticidade Soldadura laser Nd:YAG Ligas de Titânio