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 Opportunities: Scholarships abroad - Research Internship - Master's degree
• Start date: February 01, 2014
• End date: July 31, 2014
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Rubens Caram Junior
• Grantee: Camilo Augusto Fernandes Salvador
• Supervisor: Hamish L. Fraser
• Host Institution: Faculdade de Engenharia Mecânica (FEM). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Institution abroad: 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)