Alpha phase nucleation during isothermal aging heat treatments in Ti-Nb and Ti-Nb-Sn alloys

Author(s)

Camilo Augusto Fernandes Salvador

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica
• Defense date: 2015-01-29

Examining board members

Rubens Caram Junior; João Batista Fogagnolo; Andre Paulo Tschiptschin

• Advisor: Rubens Caram Junior

Abstract

Ti-Nb-Sn biomedical alloys have been recently developed as promising biomaterials due to their excellent biocompatibility, low elastic modulus and corrosion resistance. These desirable properties are highly influenced by the precipitation of ? and ? 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, Route 2) aging heat treatments. The aim of this project was to evaluate the microstructure evolution of three different alloys - Ti-30Nb, Ti-30Nb-2Sn and Ti-30Nb-4Sn (wt %) during QA and DH isothermal aging heat treatments. The alloys were arc melted, homogenized (1000°C, 12 hours), water quenched and then cold rolled to 2.5 mm thickness, resulting in a total reduction rate of 78%. The ingot was cut in samples of 10 x 10 x 2.5 mm. A recrystallization heat treatment (800°C for 30 min) was employed, followed by the isothermal heat treatments (QA or DH) - from 10 minutes to 48 hours - and water quenching. The samples were finally polished and analysed by FEG-SEM and also X-ray diffraction (XRD) using a spinner device. Furthermore, microhardness and elastic modulus measurements were performed. Conventional TEM sample preparation was used in order to obtain 3 mm disks suitable for BF/DF/SAD and CBED analysis. It was verified the addition of 4% Sn supresses the ? formation during DH aging heat treatments at 400°C, resulting in a low hardness and low elastic modulus microstructure. This Sn addition also allows ?" to be formed on water quenching even after 48 h of aging. For all compositions, despite of the aging heat treatment, the majority of ? precipitation was given on grain boundaries. Intragranular, triangular-shape ? precipitates were also observed in Ti-30Nb-2Sn and Ti-30Nb-4Sn alloys (AU)

• FAPESP's process: 12/10164-8 - Alpha phase nucleation during isothermal aging heat treatments in Ti-Nb and Ti-Nb-Sn alloys
• Grantee: Camilo Augusto Fernandes Salvador
• Support Opportunities: Scholarships in Brazil - Master