title: Microstructure of surface and subsurface layers of a Ni-Ti shape memory microwire.
abstract: The microstructure of a 55 microm diameter, cold-worked Ni-Ti microwire is investigated by different transmission electron microscopy techniques. The surface consists of a few hundred nanometer thick oxide layer composed of TiO and TiO2 with a small fraction of inhomogeneously distributed Ni. The interior of the wire has a core-shell structure with primarily B2 grains in the 1 microm thick shell, and heavily twinned B19' martensite in the core. This core-shell structure can be explained by a concentration gradient of the alloying elements resulting in a structure separation due to the strong temperature dependence of the martensitic start temperature. Moreover, in between the B2 part of the metallic core-shell and the oxide layer, a Ni3Ti interfacial layer is detected.
authors.affiliation: EMAT, University of Antwerp, Groenenborgerlaan 171, B-2020 Antwerp, Belgium.
authors.forename: H
authors.initials: H
authors.lastname: Tian
authors.forename: D
authors.initials: D
authors.lastname: Schryvers
authors.forename: S
authors.initials: S
authors.lastname: Shabalovskaya
authors.forename: J
authors.initials: J
authors.lastname: Van Humbeeck