Study of chemical segregation through 3D APT technique during precipitation of omega and alpha phases in a metastable beta Ti-Nb-Fe-Sn alloy and correlation with intergranular and intragranular precipitation.

• Grant number: 24/16391-3
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: December 17, 2024
• End date: December 16, 2025
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Physical Metallurgy
• Principal Investigator: Rubens Caram Junior
• Grantee: Leticia Falcão Starck
• Supervisor: David Diercks
• Host Institution: Faculdade de Engenharia Mecânica (FEM). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Institution abroad: Colorado School of Mines, United States
• Associated to the scholarship: 21/06156-9 - Alfa phase nucleation in metastable beta Ti-Nb-Fe-Sn alloy: intergranular and intragranular precipitation mechanisms, BP.DR

Abstract

Aging heat treatments applied to metastable beta Ti alloys produce fine precipitation of the alpha phase in a beta phase matrix. When this phenomenon is based on heterogeneous nucleation assisted by the omega phase, precipitation is predominantly intragranular. However, aging can also produce intergranular precipitation when assisted by crystalline grain boundaries, although it is undesirable and deleterious to mechanical properties. In this context, this research aims to investigate the aging heat treatment conditions of the Ti-19Nb-2.5Fe-6Sn alloy (wt%) and explore the competition between intragranular and intergranular precipitation. The aging conditions for the Ti-19Nb-2.5Fe-6Sn alloy were investigated, and the competition between intragranular and intergranular precipitation was explored. Heating rates of 5, 10, and 20 °C/min were evaluated. It was found that, for the alloy under study, a rate of 5°C/min is sufficient to increase the intragranular fraction of precipitation to the aging temperature of 400 °C and 600 °C. For the 10 °C/min rate, low aging temperatures (350 °C - 450 °C) result in refined alpha with equiaxial morphology, while higher temperatures (550 °C - 700 °C) generate acicular alpha at grain boundaries. The precipitation of the omega and alpha phases was investigated through thermal analysis tests (DSC and dilatometry), X-ray diffraction, and microstructural analysis. The addition of a pre-aging treatment to the thermal route led to the precipitation of the isothermal omega phase, which acted as a nucleation site for the alpha phase in subsequent heat treatment, resulting in increased intragranular precipitation. To study the chemical segregation during phase precipitation in Ti192506, Atom Probe Tomography (APT) and Transmission Electron Microscopy (TEM) are needed. Therefore, the present project is been submitted to FAPESP to obtain an international scholarship for the development of these techniques abroad.