Atomic structure of an amorphous Ti–Ta-based surface alloy synthesized on a TiNi substrate by an electron-beam method

The research presents the atomic (cluster) structure of an amorphous Ti–Ta-based surface alloy fabricated on a TiNi substrate by electron beam method. Transmission electron microscopy and "cluster-plus-glue-atom" model were utilized to resolve the atomic-level structure of amorphous phase by means of real-space radial distribution functions. It has been found that ~ 2 μm amorphous surface layer has gradient chemical composition and, relative to conventional metallic glasses, appears nonhomogeneous in structure depending on various atomic arrangements in the first and second neighboring shells. The amorphous Ti–Ta-based surface alloy is shown to have structure with the atomic medium-range order and can be described by principal cluster [Ti–Ti₁₀Ni₄]Ni₂Ta of Ti₂Ni intermetallic compound with icosahedral orientational ordering.