Microstructures analysis and quantitative strengthening evaluation of powder metallurgy Ti–Fe binary extruded alloys with (α+β)-dual-phase

In this study, Fe, one of the inexpensive β-phase stabilizers, was employed to fabricate Ti alloys by the powder metallurgy route. The formation mechanism of unique microstructures and texture of the extruded Ti–Fe alloy was elucidated through scanning electron microscopy-electron backscatter diffraction (SEM-EBSD) and transmission electron microscopy-energy-dispersive X-ray spectroscopy (TEM-EDS). For the Ti–Fe alloys consolidated from the pre-mixed pure Ti powder and Fe particles by spark plasma sintering and following hot extrusion, the additive Fe atoms existed as solid solution atoms in β-Ti phase. The increment in the Fe content was effective in increasing the β-Ti phase volume fraction and refining the α-Ti grains. The mean α-Ti grain size of Ti-4 wt.% Fe alloy was 1.27 μm, which was about ten times less than that of the pure Ti material (12.42 μm). The α and β phases of the extruded Ti-1–4 wt.% Fe material were aligned in parallel to the extrusion direction, and they suppressed the grain growth of each other. Although yield stress (YS) and tensile strength (TS) remarkably increased to 1093 MPa and 1183 MPa, respectively, with an increase in the Fe content, a large elongation of 28–38% was obtained in the extruded Ti–Fe alloys. These tensile properties were favorable compared to the commercial Ti-6 wt.% Al-4 wt.% V alloy. The dominant strengthening factors for the Ti–Fe alloys were α-Ti grain refinement and β-Ti hard phase dispersion. In the case of 4 wt% Fe addition, 50% of the YS increment was due to the latter strengthening mechanism.