Stimulus-responsive shape memory materials: A review

TiNi films were prepared by co-sputtering a Ti50Ni50 target and a Ti target under different process parameters. Stress in TiNi film on silicon substrate were evaluated using curvature method. A wide range of residual stress levels (either tensile or compressive) were found in the deposited films, depending significantly on Ti/Ni ratio, gas pressure, deposition temperature and/or annealing conditions. Stress evolution for as-deposited amorphous films during annealing process were systematically studied with the consideration of residual stress in as-deposited films; thermal stress; tensile stress due to densification crystallization; stress relaxation due to martensite transformation, etc. Upon heating, the crystallized TiNi films generated large tensile stresses when transforming from martensite to austenite, whereas during cooling, the stress relaxed significantly when austenite transformed back to the ductile martensite. The stress generation and relaxation behavior was significantly affected by film composition, deposition temperature and/or annealing temperature.

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Sputtering deposited TiNi films: relationship among processing, stress evolution and phase transformation behaviors

The phase transformation properties of Ti–Ni–Cu shape memory thin films prepared in the form of a continuous composition spread were investigated. The thin film materials library was fabricated from elemental targets using an ultra-high vacuum combinatorial magnetron sputter-deposition system. Alternating wedge-type layers of Ti, Ni, and Cu were deposited on a thermally oxidized Si wafer and subsequently annealed at 500 °C for 1 h in situ . Automated temperature-dependent resistance measurements ( R ( T )), energy dispersive X-ray analysis and X-ray diffraction measurements revealed the compositional region in the ternary phase diagram where thermoelastic transformations occur. The transformation temperatures and the thermal hysteresis were determined from R ( T ) measurements. Within the composition spread an extended transformation region was found. For Ni-rich compositions, a two-stage B2 → R → B19′ phase transformation was observed. Among others, compositions of Ti 51 Ni 49− x Cu x (at.%) show a single-stage transformation for a Cu-content 14 at.% (B2 → B19). In the intermediate composition range two-stage transformations (B2 → B19 → B19′) were found. The dependency of the thermal hysteresis on the Cu-content as described in the literature was confirmed.

Combinatorial fabrication and high-throughput characterization of a Ti–Ni–Cu shape memory thin film composition spread

https://iopscience.iop.org/article/10.1016/j.stam.2005.05.006/pdf

Fabrication and characterization of Ti–Ni shape memory thin film using Ti/Ni multilayer technique

Growth and characterization of TixNi1−x shape memory thin films using simultaneous sputter deposition from separate elemental targets

Characterization of shape-memory alloy thin films made up from sputter-deposited Ni/Ti multilayers

Spin valve multilayers consisting of magnetically hard and soft FeCoV layers separated by Ti spacer layers were investigated for their interface and magnetic properties. The chemical structure and interface roughness were characterized by measuring X-ray reflectivity. Polarized neutron reflectivity (PNR) was performed on selected samples at magnetic saturation, and the spin dependent reflectivities were analysed by modelling the magnetic states of the soft and hard FeCoV layers. PNR suggests the existence of two magnetic phases of FeCoV, i.e, in the bulk and at the interface. The extent of these two regions and their magnetic moments for various Ti thicknesses were estimated from PNR and are utilized to understand the magnetization reversal of these multilayers.

Polarized neutron reflectivity of FeCoV/Ti multilayers

For a polarized neutron beam in a neutron guide with a polarization parallel to the side walls of the guide, depolarization of the beam can occur at the top and bottom walls due to the in-plane magnetization of the Ni/Ti supermirrors. We alloyed the Ni-sublayers with Mo in order to suppress the magnetization of the layers. Magnetization measurements of the NiMo/Ti supermirrors indicate a Mo-dependency on the in-plane magnetization. For increasing Mo concentration the magnetization is decreased. Polarized neutron reflectivity measurements show no depolarizing for in-plane magnetization parallel to the neutron spin as normally is the case in the side walls of a neutron guide. A polarized neutron beam with polarization perpendicular to the magnetization of the layers is partially depolarized.

Influence of Mo in the Ni sublayers on the magnetization of Ni/Ti neutron supermirrors

Effect of Al doping on phase formation and thermal stability of iron nitride thin films

Monochromators used in neutron or X-ray experiments sometimes have unintended higher order contributions. In most cases filters are used to remove them. We sputtered multilayer monochromators with smooth interfaces to reduce the higher order contributions removing the need for a filter. Ni and Ti are selected as sublayer materials due to their high scattering length density contrast. We have strongly reduced the higher order contributions by annealing. This reduces the roughness and off-specular scattering, however the second and third-order Bragg peak intensities increase unexpectedly in neutron reflectivity experiments.

Smooth interfaces of multilayer monochromators

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