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)...     

Effect of Multi-Step Tempering on Retained Austenite and Mechanical Properties of Low Alloy Steel

 The effect of multi-step tempering on retained austenite content and mechanical properties of low alloy steel used in the forged cold back-up roll was investigated. Microstructural evolutions were characterized by optical microscope, X-ray diffraction, scanning electron microscope and Feritscope, while the mechanical properties were determined by hardness and tensile tests. The results revealed that the content of retained austenite decreased by about 2% after multi-step tempering. However, the content of retained austenite increased from 36% to 51% by increasing multi-step tempering temperature. The hardness and tensile strength increased as the austenitization temperature changed from 800 to 920 ℃, while above 920 ℃, hardness and tensile strength decreased. In addition, the maximum values of hardness, ultimate and yield strength were obtained via triple tempering at 520 ℃, while beyond 520 ℃, the hardness, ultimate and yield strength decreased sharply.     

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.     

Corrosion Inhibitive Property of Self-Assembled Films Formed by Schiff base Molecules on Carbon Steel Surface

Protection of Metals and Physical Chemistry of Surfaces - N,N'-bis (salicylaldehyde)-1,3-diaminopropane (Salpn) has been evaluated as corrosion inhibition for iron in 0.1 M HCl when the films...     

Recent advances on akermanite calcium-silicate ceramic for biomedical applications

Owing to great biocompatibility and high capacity of apatite formation, bioceramics, especially calcium silicate-based compounds, were extensively employed in orthopedic and dental uses concerning biomedical applications. Lately, akermanite (AK; Ca₂MgSi₂O₇), as a bioceramic containing Ca-, Mg- and Si, has gained an increased level of attention because of its more tunable mechanical characteristics and degradation rate. All studies indicate that this magnesium incorporating Ca-silicate ceramic has a great capacity to use as a bone graft material to fulfill the necessity of bone reconstruction. Despite the rising interest in using these materials in biomedical fields, there has not yet been an extensive overview of this bioceramic property and its potential benefits. Thus, it has been speculated that this concept and the emergence of akermanite bioactive ceramics might lead to significant upcoming advancements in the field of bone tissue engineering (BTE). Definitely, the approach still requires additional advances to considerably better respond to the vital concerns regarding the clinical application. The review tackles the present research trends on akermanite ceramics for biomedical purposes such as bone scaffold, coating materials, bone cement, and treatment of osteoporotic bone defects, commencing with recent status and shifting to upcoming developments.     

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.     

Effects of Mn Additions on the Structure,Mechanical Properties,and Corrosion Behavior of Cu-Al-Ni Shape Memory Alloys

The influences of different amount (0.4, 0.7, and 1 wt.%) of Mn addition on the structure, mechanical properties, and corrosion behavior of Cu-Al-Ni shape memory alloys have been studied using differential scanning calorimetry, field emission scanning electron microscopy, transmission electron microscopy, x-ray diffraction, tensile test, shape memory effect test, hardness test, and electrochemical test. It was observed that the transformation temperatures, microstructural characteristics, and mechanical properties are highly sensitive to the composition variations. The obtained results show that the transformation temperatures and mechanical properties of Cu-Al-Ni SMAs exhibited the best results with 0.7 wt.% of Mn addition. These kinds of enhancements are mainly due to the type, amount, and morphology of the martensite phase, including the grain refinement. The result of electrochemical test showed that an increment in Mn content up to 0.7 wt.% improved the corrosion resistance of Cu-Al-Ni SMA. However, further increase of Mn content decreases the corrosion resistance of the alloy.     

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.     

Investigation of Corrosion Protection Performance of Multiphase PEO (Mg<Subscript>2</Subscript>SiO<Subscript>4</Subscript>, MgO,MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript>) Coatings on Mg Alloy Formed in Aluminate-Silicate- based Mixture Electrolyte

Plasma electrolytic oxidation (PEO) coatings in the aluminate-silicate-based mixture electrolyte solution with different duty cycles were successfully applied on Mg alloy. The corrosion behavior of the samples was evaluated by water contact angle test, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and immersion tests. Hydrophobic PEO coating could be obtained by adjusting the duty cycle of the applied electric signal. This coating considerably diminished the Mg dissolution and could enhance the impedance values of Mg alloy in 3.5 wt % NaCl solution. However, the surface of other PEO coated samples showed more hydrophilic properties compared to that of the uncoated sample. Dense structure of the modified PEO multiphase (including Mg₂SiO₄, MgO and MgAl₂O₄ phases) coating and also its appropriate thickness provided an effective barrier to remarkably delay corrosive solution penetration into the PEO coating. This phenomenon led to major decrease in anodic current density of alloy in chloride solution.