Face-centered-cubic titanium - A new crystal structure of Ti in a Ti-8Mo-6Fe alloy

Highlights: • The microstructure of a Ti-8Mo-6Fe alloy prepared by powder sintering technology is ultrafine. • FCC (Fm-3m) Ti phase with a lattice constant of 0.431 nm was discovered. • The metallic properties and stability of FCC Ti were revealed by the first principle calculations. • Arc periodic strips formed by electron diffuse scattering were discovered on the SAED patterns of BCC TiMoFe phase. The microstructure of a Ti-8Mo-6Fe ternary alloy with ultrafine grains was systematically studied with Tecnai-G2 F20 field transmission electron microscope and JEMS 2010 transmission electron microscope. A new Ti phase with face-centered-cubic (Fm-3m) structure was discovered. The morphology of these FCC Ti phases was elliptical, and they were widely distributed at interfaces between the polygonal BCC TiMoFe phases. The size of the FCC Ti phases was concentrated in the range of 200–450 nm. The lattice constant of FCC Ti phase was 0.431 nm. Simulated high-resolution images of FCC Ti and compounds of FCC TiC, TiN and TiO with different thicknesses and different defocus amounts were carried out to prove that the FCC structure in Ti-8Mo-6Fe alloy was indeed FCC Ti but not FCC TiC, TiN and TiO. First principle calculations revealed the metallic properties and stability of FCC Ti. All alloy elements of Mo and Fe were in the polygonal BCC TiMoFe phases. The semicircular arc periodic strips formed by electron diffuse scattering were present on the selected area electron diffraction (SAED) patterns of the BCC TiMoFe phase, which may come from the ordered domain of Mo and Fe or local ordering by Mo, Fe and Ti.