Thixoforming of titanium alloys: application to the Ti-Cu, Ti-Fe and Ti-Co systems

Author(s)

Kaio Niitsu Campo

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Mecânica
• Defense date: 2018-08-29

Examining board members

Rubens Caram Junior; Eugênio José Zoqui; Conrado Ramos Moreira Afonso; Maurizio Ferrante; Piter Gargarella

• Advisor: Rubens Caram Junior

Abstract

Thixoforming is a processing route that involves the use of metallic alloys with globular microstructures in the semisolid state. Due to its inherent properties, thixoforming exhibits several advantages over conventional manufacturing processes. However, it has not been extensively explored in industry, primarily because of the limited number of alloys amenable to the process, i.e., they do not present suitable thixoformability. In this regard, the present investigation aimed to develop Ti alloys specifically designed for thixoforming. Binary Ti-Cu, Ti-Fe, and Ti-Co alloys were selected based on certain thermodynamic criteria, such as length of the solidification interval and liquid fraction sensitivity. Afterwards, they were prepared in an arc furnace, hot worked, and then reheated to the semisolid state. Accordingly, the semisolid microstructural evolution, rheological behavior, and resulting mechanical properties after a forming step could be evaluated. The Ti-Fe alloys presented high mechanical strength, but they were quite brittle, impairing a proper deformation of their samples, thus a dendritic microstructure was observed in the semisolid state. On the other hand, the Ti-Cu and Ti-Co alloys presented favorable characteristics: they exhibited both excellent globularization behavior and low coarsening kinetic of the remaining solid phase. The rheological evaluation of these alloys highlighted their thixotropic behavior, in which the viscosity decreases with shear rate and time. In addition, the apparent viscosity values decreased with increasing Cu and Co contents (liquid fraction). Finally, the obtained mechanical properties revealed that the studied alloys present good mechanical strength, limited ductility under tensile loading, and suitable ductility under compressive loading. Therefore, it was concluded that Ti-Cu and Ti-Co alloys are excellent candidates for semisolid processing (AU)

• FAPESP's process: 13/24786-3 - Thixoforming of titanium alloys: application to Ti-Cu, Ti-Fe and Ti-Co systems
• Grantee: Kaio Niitsu Campo
• Support Opportunities: Scholarships in Brazil - Doctorate