As the individual layer of Ti is reduced in thickness in a Ti/Nb multilayered thin film structure, the Ti layer can undergo a change in phase stability from hcp to bcc. Due to its high spatial resolution, atom probe tomography (APT) is ideally suited to characterize the compositional variations in such thin film structures. A series of hcp Ti / bcc Nb and bcc Ti / bcc Nb multilayers have been sputtered deposited and prepared as APT specimens using a Focus Ion Beam (FIB) milling procedure. The APT results have shown a substantial interdiffusion of Nb into the bcc Ti layers to a pseudo-equilibrium concentration of approximately Ti-20at%Nb while maintaining a compositionally modulated interface. In contrast, the hcp Ti layers indicated little Nb interdiffusion within the layers. Thermodynamic volumetric free energy modeling has indicated that this unexpected Nb interdiffusion facilitated the bcc phase stability. The coupling of APT results to the pseudomorphic bcc Ti phase demonstrates the capability APT has in quantifying the compositional characteristics in these types of multilayered nanocomposite systems.
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