Titre:	Caracterização microestrutural e fractofráfica da liga NI57TI43 com memória de forma tratada criogenicamente e submetida a ciclagem mecânica
Auteur(s):	Silva, Bernardo José Leite da
Orientador(es)::	Silva, Edson Paulo da
Assunto::	Ligas com memória de forma Pseudoelasticidade Fadiga estrutural Comportamento cíclico Caracterização microestrutural
Date de publication:	7-jui-2020
Data de defesa::	17-avr-2020
Référence bibliographique:	SILVA, Bernardo José Leite da . Caracterização microestrutural e fractofráfica da liga NI57TI43 com memória de forma tratada criogenicamente e submetida a ciclagem mecânica. 2020.,67f., il. Dissertação (Mestrado em Sistemas Mecatrônicos)—Universidade de Brasília, Brasília, 2020.
Abstract:	The Shape Memory Effect (SME) and Superelasticity (SE) are the two typical phenomena associated with Shape Memory Alloys (SMA), which are materials also known as smart materials. In both behaviors, SMA’s present the capacity of strain recovery up to 10%. In the SE, this recovery happens with the removal of the initial applied load, and in the case of the SME, the recovery takes place by heating the material above its transformation temperature, confirming that this kind of alloys have great potential in several areas. In applications in which the material is submitted to mechanical (SE) or thermomechanical (EMF) cyclicing, structural fatigue and functional fatigue are observed, where the functional fatigue is characterized by the change in the material’s properties throughout the cycling. The present work’s objective is to evaluate the influence of deep cryogenic treatment (DCT) from a microstructural point of view of the Ni57Ti43 alloy submitted to fatigue testing. Criogenically treated, at -196oC for 24 hours, and non treated test specimens were submitted to mechanical cyclicing until its rupture. In the superelastic behavior, it was observed that the cryogenically treated material showed an increase in residual and recoverable strain when compared to the as received material. In addition, it was observed a decrease at the transformation stress levels throughout the cycles for both treated and non treated samples. But when it comes to the structural fatigue, the cryogenically treated material showed a decrease in fatigue life when compared to the non treated test specimens. From these results and through microhardness, XRD and EDS tests, it was possible to identify eventual changes at the treated samples. It was observed that the cryogenic treatment did not cause changes in the material’s crystal structure, maintaining the B2 cubic structure with precipitates of same atomic composition. However, treated specimens presented the formation of oxides possibly associated with TiNiO3 and also an increase in microhardness of around 4%. In the treated samples and after its cycling, it was observed, from the microstructural morphology and XRD tests, the presence of residual martensite. In the failure analysis of the specimens, it was found that both treated and non treated test specimens had the same characteristics, which was the presence of fatigue striations and dimples, showing that the failure was ductile and occurred due to its overload. From the results analysis, it is concluded that the superelastic behavior of the Ni57Ti43 alloy was affected by the deep cryogenic treatment, at -196oC for 24 hours, and that the observed changes must be associated, mainly, with the formation of oxides, so that they can justify both the decrease at the fatigue life and the behaviors associated with residual strain and decrease of transformation stress levels.
metadata.dc.description.unidade:	Faculdade de Tecnologia (FT) Departamento de Engenharia Mecânica (FT ENM)
Description:	Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica,2020.
metadata.dc.description.ppg:	Programa de Pós-Graduação em Sistemas Mecatrônicos
Licença::	A concessão da licença deste item refere-se ao termo de autorização impresso assinado pelo autor com as seguintes condições: Na qualidade de titular dos direitos de autor da publicação, autorizo a Universidade de Brasília e o IBICT a disponibilizar por meio dos sites www.bce.unb.br, www.ibict.br, http://hercules.vtls.com/cgi-bin/ndltd/chameleon?lng=pt&skin=ndltd sem ressarcimento dos direitos autorais, de acordo com a Lei nº 9610/98, o texto integral da obra disponibilizada, conforme permissões assinaladas, para fins de leitura, impressão e/ou download, a título de divulgação da produção científica brasileira, a partir desta data.
Agência financiadora:	Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Collection(s) :	Teses, dissertações e produtos pós-doutorado

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