On the Impact of Texture and Grain Size on the Pseudoelastic Properties of Polycrystalline Fe–Ni–Co–Al–Ti Alloy

The effects of thermomechanical treatments on crystallographic texture and grain size evolution and their impact on the pseudoelastic properties in Fe41–Ni28–Co17–Al11.5–Ti2.5 (at.%) were studied in the present paper. The results show that cold rolling leads to brass-type texture in this alloy, which is typical for low stacking fault energy materials. Thermal treatments up to 1300 °C were conducted and it is shown that the presence of β-phase helps to control grain growth. After the dissolution of the secondary phase induced by heat treatment at higher temperatures, a strong {230}〈001〉 recrystallization texture evolves in cold rolled samples already upon imposing medium reduction ratios. Finally, good pseudoelastic properties are found in conditions being characterized by adequate texture and grain sizes spanning over the entire thickness of the samples tested.Fil: Sobrero, Cesar Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lauhoff, C.. University of Kassel; AlemaniaFil: Wegener, T.. University of Kassel; AlemaniaFil: Niendorf, T.. University of Kassel; AlemaniaFil: Krooß, P.. University of Kassel; Alemani

Additive Manufacturing of Binary Ni–Ti Shape Memory Alloys Using Electron Beam Powder Bed Fusion: Functional Reversibility Through Minor Alloy Modification and Carbide Formation

Shape memory alloys (SMAs), such as Ni–Ti, are promising candidates for actuation and damping applications. Although processing of Ni–Ti bulk materials is challenging, well-established processing routes (i.e. casting, forging, wire drawing, laser cutting) enabled application in several niche applications, e.g. in the medical sector. Additive manufacturing, also referred to as 4D-printing in this case, is known to be highly interesting for the fabrication of SMAs in order to produce near-net-shaped actuators and dampers. The present study investigated the impact of electron beam powder bed fusion (PBF-EB/M) on the functional properties of C-rich Ni50.9Ti49.1 alloy. The results revealed a significant loss of Ni during PBF-EB/M processing. Process microstructure property relationships are discussed in view of the applied master alloy and powder processing route, i.e. vacuum induction-melting inert gas atomization (VIGA). Relatively high amounts of TiC, being already present in the master alloy and powder feedstock, are finely dispersed in the matrix upon PBF-EB/M. This leads to a local change in the chemical composition (depletion of Ti) and a pronounced shift of the transformation temperatures. Despite the high TiC content, superelastic testing revealed a good shape recovery and, thus, a negligible degradation in both, the as-built and the heat-treated state

Spacer-layer–induced spin reorientation in Ni/Cu/Ni sandwiches

We report polar magneto-optical Kerr effect studies of Cu spacer layer on the perpendicular magnetic anisotropy in 70 Å  Ni/Cu wedged/70 Å  Ni structures. With increasing Cu thickness, the magnetic easy axis of the top Ni layer continuously changes to the direction perpendicular to the surface. This results from the gradual strain relaxation of the Cu spacer with increasing thickness followed by increasing strain in the top Ni layer. A crossover from coherent to incoherent strain in Cu spacer around 18 Å  results in a dramatic non-monotonic dependence of magnetic anisotropy on the Cu thickness

γ-phase evolution in aged Co–Ni–Ga shape memory alloy

A synchrotron X-ray diffraction study of high-temperature (HT) shape memory alloy 49Co–21Ni–30Ga (in at. pct.) was performed. The volume fraction, cell parameter and temperature evolution of the different secondary phases were analyzed. This study reports reliable experimental data on these parameters to be used as a future reference to adjust the composition of the material

Magnetic anisotropy and layer selective magnetometry of Cu/Co/Ni/Cu/Si (001)

Perpendicular magnetic anisotropy (PMA) up to 6.15±1.25 angstroms Co thickness is found for ferromagnetically coupled epitaxial Co/60 angstroms Ni/Cu/Si(0 0 1) structures. Polarized neutron reflection measurements on a Cu/9 angstroms Co/Ni/Cu(0 0 1) structure yield almost bulk like magnetic moments at room-temperature of 1.70±0.20 μB and 0.57±0.05 μB for Co and Ni, respectively. Magneto-optic Kerr effect measurements show that the uniaxial Co volume anisotropy is entirely attributed to the Co shape anisotropy due to an absence of strain in the Co film

Origin of the Co uniaxial volume anisotropy of the fcc Co/Ni/Cu(001) system

We studied layer selectively the magnetic moments on a Cu/9 Å Co/50 Å Ni/Cu/Si(001) and a Cu/50 Å Ni/Cu/Si(001) structure using polarized neutron reflection. The magnetic moments for the Cu/Co/Ni/Cu structure are 1.70±0.20 μB and 0.57±0.05μB for the Co and Ni, respectively, and within error the same as the relevant bulk magnetic moments at room temperature. For the Cu/Ni/Cu sample the magnetic moment per Ni atom of 0.53±0.03μB is only slightly lower than the bulk value. Within error the same magnetic moments are determined for a Cu/22 Å Co/11 Å Cu/53 Å Ni/Cu/Si(001) structure supporting the results on the Cu/Co/Ni/Cu(001) and Cu/Ni/Cu(001) structures. Using the magnetic moments values determined by polarized neutron reflection, we conclude that the uniaxial Co volume anisotropy for the Cu/Co/60 Å Ni/Cu(001) structures can be attributed to the Co shape anisotropy alone. ©1999 The American Physical Society

Strong anti-ferromagnetic coupling in τMnAl/Co perpendicular magnetic superlattices on GaAs

This paper reports on the structural and magnetic properties of tMnAl/Co superlattices epitaxially grown on AlAs/GaAs by Molecular Beam Epitaxy. In tMnAl/Co superlattices with Co layer thicknes

Cyclic Superelastic Behavior of Iron-Based Fe-Ni-Co-Al-Ti-Nb Shape Memory Alloy

Iron-based shape memory alloys came into focus as promising candidate materials for large-scale structural applications owing to their cost-efficiency. In the present work, the superelastic properties of a recently introduced Fe-Ni-Co-Al-Ti-Nb shape memory alloy are investigated. For 〈001〉-oriented single-crystalline material in aged condition (650 °C/6 h), an incremental strain test reveals excellent superelasticity at −130 °C with fully reversible strains up to about 6%. Under cycling loading at different test temperatures, however, the alloy system investigated suffers limited functional stability.Fil: Lauhoff, C.. University of Kassel; AlemaniaFil: Remich, V.. University of Kassel; AlemaniaFil: Giordana, María Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Sobrero, Cesar Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Niendorf, T.. University of Kassel; AlemaniaFil: Krooß, P.. University of Kassel; Alemani

Magnetic anisotropy, magnetic moments and coupling for Co/Cu/Ni/Cu(001) structures

Polar magneto-optic Kerr effect (MOKE) measurements on an epitaxial Cu/Co (23 angstroms)/Cu (0-49 angstroms)/Ni (53 angstroms)/Cu/Si(001) structure reveal that the Ni magnetization is aligned in plane for zero Cu spacer layer thickness and becomes increasingly aligned out of plane with increasing Cu spacer layer thickness, whereas an in-plane remanent magnetization for Co is always observed. Layer selective polarized neutron reflection (PNR) measurements yield almost bulk-like magnetic moments of 1.57±0.08 μ B for Co and 0.50±0.04 μ B for Ni for a Cu/Co (22 angstroms)/Cu (10 angstroms)/Ni (53 angstroms)/Cu/Si(001) structure at room temperature. A reduced remanence is observed for both the out-of plane magnetization by polar MOKE, and the in-plane magnetization for Co and Ni by PNR. This could suggest either a canted magnetization or multidomain state at remanence