Microstructure development and mechanical properties of rapidly solidified Ti-Fe and Ti-Fe-Bi alloys

Even though rapidly solidified Ti-Fe eutectic alloys may achieve good mechanical strength, increase in ductility is already a task to be accomplished. Addition of tin and arrangements of nano- and ultrafine-grain metallic materials have been shown as potential alternatives to overcome such drawback. Also, to address this problem, it seems that alternative alloy chemistries and processing routes must be adopted when manufacturing Ti-based alloys. In the present investigation, Ti-26 wt.%Fe (Ti-24.5 at%Fe) and Ti-20 wt.%Fe-3 wt.%Bi (Ti-18 at%Fe-0.7 at.%Bi) alloys have been prepared in a stepped copper mold using centrifugal casting. The as-cast Ti-Fe(-Bi) microstructures were formed by equiaxial arrangements of cells. Finer cell spacing (lambda(c)) was associated with the Ti-20 wt.%Fe-3 wt%Bi alloy. The results include cell spacing measurements, segregation profile by X-ray fluorescence (XRF), uniaxial compression tests, optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A wide variation on the scale of the microstructure was noted especially in the case of the Ti-26 wt.%Fe alloy with the lambda(c) varying from 11-30 mu m. This is due to the different cooling conditions of each diameter along the as-cast rod. Hall-Petch type equations are proposed relating sigma(max) to lambda(c) Bi was dissolved in the beta-Ti solid solution as well as TiFe compound formed in the cellular structure of the Ti-20 wt%Fe-3 vvaBi. (C) 2015 Elsevier Ltd. All rights reserved.