Reversible structural transition in monocrystalline Ni2FeGaNi_{2}FeGa microwires for shape-memory applications

We report on the production and characterization of Heusler-based Ni$_2$FeGa microwires exhibiting two – wayshape memory effect. The microwires are characterized by a monocrystalline structure with a strong preferredcrystallographic orientation that shows [1 1 1] axis parallel to the wire’s axis for high-temperature L2$_1$ austenitephase, while the [0 1 7] axis is preferred for low-temperature monoclinic phase. Variation of crystallographicaxis (and corresponding easy magnetization axis) leads to 1600% variation of magnetic permeability due to a 2%strain in axial direction. Such straining is reversible immediately after production without the necessity of furtherthermal treatment. These properties give the microwire function of very sensitive SMART actuators that can beeasily produced in a large amount

Structural characterisation of Cu-Zr thin film combinatorial libraries with synchrotron radiation at the limit of crystallinity

We report for the first-time combinatorial synthesis of thin film metallic glass libraries via magnetron co-sputtering at the limit of crystallinity. Special care was taken to prepare extremely pure CuZr films (1–2 µm thickness) with large compositional gradients (Cu18.2Zr81.8 to Cu74.8Zr25.2) on X-ray transparent polymer substrates in high-vacuum conditions. Combined mapping of atomic structure (synchrotron radiation) and chemical composition (X-ray fluorescence spectroscopy) revealed that over the entire composition range, covering multiple renowned glass formers, two phases are present in the film. Our high-resolution Synchrotron approach identified the two phases as: untextured amorphous Cu51Zr14 (cluster size 1.3 nm) and textured, nanocrystalline α-Zr (grain size 1–5 nm). Real space HR-STEM analyses of a representative composition substantiate our XRD results. Determined cluster and grain sizes are below the resolution limit of conventional laboratory-scale X-ray diffractometers. The presented phase mixture is not permitted in the Cu-Zr phase diagram and contrary to existing literature. The phase ratio follows a linear trend with amorphous films on the Cu-rich side and increasing amounts of α-Zr with increasing Zr content. While cluster size and composition of the amorphous phase remain constant thorough the compositional gradient, crystallite size and texture of the nanocrystalline α-Zr change as a function of Zr content