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Effects of aging heat treatments on phase precipitation and mechanical behavior of Ti-30Nb-xSn beta metastable titanium alloys

Grant number: 13/23532-8
Support type:Scholarships abroad - Research Internship - Master's degree
Effective date (Start): February 01, 2014
Effective date (End): July 31, 2014
Field of knowledge:Engineering - Materials and Metallurgical Engineering
Principal Investigator:Rubens Caram Junior
Grantee:Camilo Augusto Fernandes Salvador
Supervisor abroad: Hamish L. Fraser
Home Institution: Faculdade de Engenharia Mecânica (FEM). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
Local de pesquisa : Ohio State University, Columbus, United States  
Associated to the scholarship:12/10164-8 - Alpha phase nucleation during isothermal aging heat treatments in Ti-Nb and Ti-Nb-Sn alloys, BP.MS

Abstract

Ti-Nb-Sn biomedical alloys have been recently developed as promising biomaterials due to their excellent biocompatibility, low elastic modulus and even superelasticity. These desirable properties are highly influenced by the stability of metastable phases such as the orthorhombic martensite (alpha"), which has low elastic modulus, and the precipitation of omega and alpha phases during aging heat treatments. Previous studies reported a great divergence between the microstructure evolution on specimens submitted to QA (quench and aged) and DH (direct holding from beta field, step-quenched). It seems that in QA condition, the presence of omega modifies the alpha" stability and promotes an earlier and heterogeneous omega-assisted alpha precipitation. However, if there's a full suppression of omega, the mechanism of alpha precipitation must be different even in the QA condition. On the other hand, DH condition often leads to a non-classical mechanism of precipitation, different from the previous ones. The aim of this project is to study classical and non-classical mechanisms of solid-state precipitation in Ti-Nb-Sn alloys. In order to verify the conditions for the stability of alpha" and the precipitation of alpha during QA and DH aging heat treatments, the phase transformation sequence of three different alloys - Ti-30Nb, Ti-30Nb-2Sn and Ti-30Nb-4Sn (wt %) was evaluated. It is worth reminding there are no precedents in literature reporting DH (direct-holding, step quenching) heat treatments of Ti-30Nb-XSn alloys. (AU)