Study of Corrosion Behavior and In Vitro Bioactivity of Single NbSi2 and Duplex NbSi2/Nb5Si3 Coatings on Nb Substrates for Biomedical Applications

Protection of Metals and Physical Chemistry of Surfaces - Single NbSi2 and duplex NbSi2/Nb5Si3 coatings were successfully applied on Nb substrates using halide activated pack cementation (HAPC)...     

Investigation of three steps of hot corrosion process in Y_2O_3 stabilized ZrO_2 coatings including nano zones

Phase transformation of tetragonal ZrO2 to monoclinic phase and also increment of bond coat oxidation kinetic（TGO thickening） can substantially restrict the life time of thermal barrier coating systems（TBCs）. So, nanostructured and conventional Y2O3 stabilized ZrO2 coatings were evaluated in fused V2O5-Na2SO4 salts during thermal exposure in air. Microstructural characterization showed lower hot corrosion products（monoclinic zirconia, YVO4 crystals） formation and reduction of TGO thickness in thermal barrier coating system consisting of nanostructured Y2O3 stabilized ZrO2（YSZ） top coat. It was found that inhomogeneities, pores and micro-cracks played a principal role in the molten salts infiltration into the YSZ coating during three steps of hot corrosion process. In the nanostructured YSZ coating with tri-model structure, nano zones which surrounded by fully molten parts could fill the aforementioned defects and could act as barrier for the oxygen and corrosive molten salts penetration into the TBC.     

In-vitro corrosion inhibition mechanism of fluorine-doped hydroxyapatite and brushite coated Mg–Ca alloys for biomedical applications

Magnesium alloys have received great attention as a new kind of biodegradable metallic biomaterials. However, they suffer from poor corrosion resistance. In this study, Mg–Ca alloy was coated with nano-fluorine-doped hydroxyapatite (FHA), and brushite (DCPD); via electrochemical deposition (ED). Coatings were characterized by X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results revealed that nano-fluorine-doped hydroxyapatite coating produced more dense and uniform coating layer, compared to the brushite coating. The compression tests of the ED-coated Mg alloy samples immersed in simulated body fluid for different time periods showed higher yield strength (YS) and ultimate tensile strength (UTS), compared to those of the uncoated samples. The degradation behavior and corrosion properties of the ED-coated Mg alloy samples were examined via electrochemical measurements and immersion tests. The results showed that FHA coating could effectively induce the precipitation of more Ca²⁺ and PO₄³⁻ ions than DCPD coating, because the nanophase can provide higher specific surface area. It was also found that FHA and DCPD coatings can significantly decline the initial degradation rate of the alloy. A corrosion mechanism of the ED-coated alloy is proposed and discussed in this paper.     

Titania-carbon nanotubes nanocomposite coating on Mg alloy: microstructural characterisation and mechanical properties

Atmospheric plasma spraying was carried out to deposit a bilayered NiCrAlY/nTiO₂-CNT composite coating. Initially, NiCrAlY, as an under-layer with a thickness of around 100?µm, was deposited. Afterwards, nanostructured TiO₂ (nTiO₂), as an over-layer with a thickness of 135?μm, was deposited with and without the incorporation of carbon nanotubes (CNTs) on the Mg alloy surface. In contrast to NiCrAlY and NiCrAlY/nTiO₂, the NiCrAlY/nTiO₂-CNT nanocomposite coating displayed a higher bonding strength. The wear behaviour of the coatings was examined by the pin-on-disc test and the results revealed that the incorporation of CNTs into the nTiO₂ coating considerably enhanced the tribological behaviour of Mg alloy due to the CNT’s bridging mechanism.     

Effect of Y2O3 stabilized ZrO2 coating with tri-model structure on bi-layered thermally grown oxide evolution in nano thermal barrier coating systems at elevated temperatures

Bi-layered thermally grown oxide(TGO) layer plays a major role in the spallation of Y2 O3 stabilized ZrO2(YSZ) layer form the bond coat in the thermal barrier coating(TBC) systems during oxidation. On the other hand, bi-layered TGO formation and growth in the TBC systems with nanostructured YSZ have not been deeply investigated during cyclic oxidation. Hence, Inconel 738/NiCrAlY/normal YSZ and Inconel 738/NiCrAlY/nano YSZ systems were pre-oxidized at 1000 °C and then subjected to cyclic oxidation at 1150 °C. According to microstructural observations, nanostructured YSZ layer over the bond coat should have less micro-cracks and pinholes, due to the compactness of the nanostructure and the presence of nano zones that resulted in lower O infiltration into the nanothermal barrier coating system, formation of thinner and nearly continuous mono-layered thermally grown oxide on the bond coat during pre-oxidation, lower spinels formation at the Al2 O3 /YSZ interface and finally, reduction of bi-layered thermally grown oxide thickness during cyclic oxidation. It was found that pre-heat treatment and particularly coating microstructure could influence microstructural evolution(bi-layered TGO thickness) and durability of thermal barrier coating systems during cyclic oxidation.     

Fabrication and Corrosion Resistance Evaluation of Novel Epoxy/Oxide Layer (MgO) Coating on Mg Alloy

Protection of Metals and Physical Chemistry of Surfaces - A protective novel (MgO) oxide layer (with 91.92% corrosion protection efficiency) was successfully applied on Mg–0.4%Ca alloy using...     

氟化处理对植入材料Mg-Ca二元合金腐蚀行为的影响(英文)

在室温下,将Mg-0.5Ca合金在不同浓度的氢氧化钠和HF溶液浸渍不同的时间,研究HF处理对合金腐蚀行为的影响。采用原子力显微镜、X射线衍射、场发射扫描电子显微镜表征样品的微观组织变化。通过动电位极化和Kokubo溶液浸泡试验测试样品的耐腐蚀性。结果表明,与35%HF处理的样品相比,经40%HF溶液处理的Mg-0.5Ca合金具有更均匀、更致密、更薄的涂层(12.6μm)。电化学测试表明,在Kokubo溶液中,经氟化物处理的Mg-0.5Ca合金样品的耐腐蚀性比未处理样品的高35倍;前者的体外降解速率远远低于后者的。在40%HF溶液处理过的样品表面只出现了一些腐蚀点,而未经处理的样品完全被腐蚀产物覆盖且出现了分层现象。40%HF处理的Mg-0.5Ca合金,具有低的降解速率和良好的生物相容性,是一种有潜力的植入材料。