The surface of NiTi shape memory alloys applied as long-term implants has been modified by protective calcium phosphates (CaPs) coatings, with the objective of improving the biocompatibility of this material. The calcium phosphates such as hydroxyapatite Ca₅(PO₃)OH (HAP) and β-tricalcium phosphate β-Ca₃(PO₄)₂ (β-TCP) were deposited by electrophoretic deposition. In order to improve the adhesion, the deposited samples were vacuum-sintered at wide range of temperature from 500°C to 1000°C for 2 h. The studies revealed that applied sintering conditions did not change the structure of CaPs. The coatings consisted of HAP with hexagonal structure (P63/m) and β-TCP with rhombohedral structure (R-3c). Changes in lattice parameters for CaPs coatings after deposition and sintering were refined by the Rietveld method.
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The surface of NiTi shape memory was modified by deposition of chitosan-ZnO thin film. The electrodeposition process was carried out at room temperature at voltage-time conditions: 10 V/30 s, 10 V/300 s, 20 V/30 s, or 20 V/300 s. Structure of the obtained coatings was studied by means of grazing incidence beam X-ray diffraction. Distribution of the zinc oxide particles in the chitosan matrix was observed with use of scanning electron microscopy. It was found that depending on the electrodeposition parameters, the structure of the obtained chitosan-ZnO coatings varies from amorphous to coarse-grained.
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The Ni₂₅Ti₅₀Cu₂₅ shape memory alloy exhibits one-step martensitic transformation. Transformation occurs between the B2 parent phase and the B19 orthorhombic martensite. The course of the martensitic transformation was in situ studied in the alloy with use of electron backscatter diffraction. During heating, reverse martensitic transformation occurs from the B19 orthorhombic martensite to the B2 parent phase. On cooling, from the parent phase the B19 martensite is formed. Obtained results proved that the B19 martensitic plates forms the variants indexed as 1, 3, and 5. Thermal cycling does not change the crystallographic correlation between the parent phase and the martensite. However, after cycling, different rearrangement of the martensitic plates can be received. In consequence, characteristic temperatures of the martensitic transformation are shifted.
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