Ultrahigh strength in Ti-Fe-Sn-Nb alloys through short-range chemical and topological ordering

Alloys with a stabilized β-titanium structure and high concentrations of late transition metals, especially Fe, exhibit exceptionally high mechanical strength exceeding 2 GPa and good biocompatibility but often suffer from insufficient ductility in tension. At the same time, the β-Ti phase in such alloys is sufficiently stabilized to prevent decomposition into ω-phase nanoparticles , which are typically responsible for mechanical embrittlement in Ti alloys. In this study, the atomic structure of a high-strength Ti 82 Fe 12 Sn 3 Nb 3 alloy is examined using high-resolution analytical transmission electron microscopy (TEM). We demonstrate that the high strength of these alloys is achieved primarily because dislocation glide in the supersaturated β-Ti solid solution is hindered by the nanoscale local ordering of iron atoms in the atomic lattice and the formation of solute-enriched clusters. These locally chemically ordered clusters, akin to Guinier-Preston zones and undetectable even by high-resolution TEM, precede the decomposition of β-Ti via ω-phase formation or eutectoid decomposition. This concept is proposed to be general in nature and may apply to other Ti alloys. • Exceptionally high mechanical strength. • Stabilized to prevent decomposition into ω-phase nanoparticles. • High-resolution analytical transmission electron microscopy. • Nanoscale local ordering of iron atoms in the atomic lattice. • Locally chemically ordered clusters.