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Structure and morphology of whitlockite coating electrophoretically deposited on NiTi shape memory alloy

Dudek K., Goryczka T.

Engineering of Biomaterials

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2017

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Vol. 20, no. 140

2--6

EN

In order to improve the biocompatibility of NiTi shape memory alloy, the surface was modified by formation of multifunctional layer consisted of titanium oxides and whitlockite ceramic. Amorphous TiO2 interlayer was produced on NiTi substrate by autoclaving at 134°C for 30 minutes while the following whitlockite coatings were deposited using electrophoresis (EPD). Electrophoresis was performed under different voltage (from 20 to 80 V) at time periods (from 30 to 120 s). Applied deposition parameters 20 V and 60 s resulted in forming homogenous whitlockite coating, consisted of β-Ca3(PO4)2 and β-Ca2P2O7, on passivated NiTi alloy. In the next step, the material was heat-treated in vacuum condition at 1000°C for 2 h. As a result of sintering crystallization of titanium oxides was observed. The obtained layer was cracks-free. Applied deposition process increased the roughness of surface. Deposited whitlockite agglomerates had an average thickness ca. 5.6 μm. The structure of CaP coating material after applied heat-treatment remained unchanged in comparison to initial powder material. However, the partial decomposition of NiTi parent phase to equilibrium ones was observed. The whitlockite coating was also observed to have no impact on the martensitic transformation responsible for shape memory effect. Additionally, applied sintering condition changed the sequence of martensitic transformation from one to two-step.

2

Development of a shape memory alloy wire actuator to operate a morphing wing

Rim M., Kim E.-H., Kang W.-R., Lee I.

Journal of Theoretical and Applied Mechanics

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2014

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Vol. 52 nr 2

519--531

EN

DSC tests were performed on several types of SMAs to verify the phase-transformation temperatures, and then experiments to examine their characteristics were carried out. An electric-current was supplied to the SMA wire to measure the appropriate operational cur- rent range. The force generated by the SMA wire increased according to the supplied current, but it diminished when the over-current was supplied because thermo-mechanical properties of the wire started to degrade. The appropriate stress range for effective actuation charac- teristics was also investigated. The SMA wire actuator was designed to operate a morphing wing. Experiments for the wing were conducted to verify its characteristics and it was smo- othly deformed.

3

Actuation properties of adaptable hybrid composites with embedded shape memory alloy wires

Mezzanotti F., Salvia M.

Applied Mechanics and Engineering

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2000

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Vol. 5, no 1

195-206

EN

Adaptable hybrid composites are materials in which actuators are embedded into polymer matrix composites. Shape memory alloys (SMA) are among the potential candidates for actuators embedded in such composite smart structures. After plotting Clausius-Clapeyron diagrams for three structural states, thin wires ('fi'=120 micrometers) of Nickel-Titanium-Copper (nitinol) were incorporated parallel with the reinforcing fibres into a glass-epoxy unidirectional laminate during lay-up. Then the whole structure was subjected to different curing procedures. The interfacial shear strength between the matrix and the nitinol wires in various structural states was determined by micromechanical tests involving the interface directly: the pull-out and microdebond tests. The clamped-free (cantilever) beam method was used to evaluate the effect of actuation by heating the nitinol wires embedded into the composite. The comparison between the different composites points out to the leading role of the interfacial shear strength. The influence of the training conditions before embedding and the occurrence of a self-trained two way shape memory effect, can also be noted.