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Microarc oxidation (MAO) coated magnesium (Mg) with improved corrosion resistance appeal increasing interests as a revolutionary biodegradable metal for fractured bone fixing implants application. However, the in vivo corrosion degradation of the implants and bone healing response are not well understood, which is highly required in clinic. In the present work, 10 μm and 20 μm thick biocompatible MAO coatings mainly composed of MgO, Mg 2 SiO 4 , CaSiO 3 and Mg 3 (PO 4 ) 2 phases were fabricated on AZ31 magnesium alloy. The electrochemical tests indicated an improved corrosion resistance of magnesium by the MAO coatings. The 10 μm and 20 μm coated and uncoated magnesium plates were separately implanted into the radius bone fracture site of adult New Zealand white rabbits using a 3 mm width bone fracture defect model to investigate the magnesium implants degradation and uninhibited bone healing. Taking advantage of the good biocompatibility of the MAO coatings, no adverse effects were detected through the blood test and histological examination. The implantation groups of coated and uncoated magnesium plates were both observed the promoting effect of bone fracture healing compared with the simple fracture group without implant. The releasing Mg 2+ by the degradation of implants into the fracture site improved the bone fracture healing, which is attributed to the magnesium promoting CGRP-mediated osteogenic differentiation. Mg degradation and bone fracture healing promoting must be tailored by microarc oxidation coating with different thickness for potential clinic application. [ABSTRACT FROM AUTHOR]

Abstract: Amorphous AlPO4 based ceramic coatings with 13μm thick were prepared on Ti–6Al–2Zr–1Mo–1V titanium alloy surface using amorphous aluminum phosphate as a binder and Al2O3/Cr2O3 based mixing particles as the fillers. The phase composition and microstructure of the coated samples before and after exposing oxidation test were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). After exposing oxidation at 600°C for 100h, no oxide scales were found either at coating/substrate interface or on coating surface, exhibiting a significantly lower weight gain (0.07mg/cm2) compared with the bare titanium (0.54mg/cm2). After exposing oxidation at 800°C, the TiO2 dominated oxide scales began to form on coating surface after oxidation for 5h and at coating/substrate interface after oxidation for 60h, finally got weight gain of 1.4mg/cm2 after oxidation for 100h. The coating had a higher infrared emissivity value (>0.8) than titanium substrate (0.15–0.3) in the wide wavelength range of 3–20μm, which was attributed to the uniform dispersion of high emissivity Al2O3 and Cr2O3 particles in the amorphous AlPO4 binder matrix. [Copyright &y& Elsevier]

Abstract: An infrared emissivity coating material containing γ-Al2O3 was prepared on 2024 aluminium alloy surface by the microarc oxidation (MAO) method. The microstructure of the coatings was analysed by SEM, XRD and EDS techniques. The infrared emissivity properties tested at 500°C were investigated by an infrared radiometer based on a Fourier transform infrared spectrometer. The results show that the infrared emissivity values of coated Al samples depend on the phase composition and surface roughness of the coatings. Corresponding to increasing coatings thickness, the gradually increasing γ-Al2O3 content and some oxide compounds containing Si and P contribute to the higher infrared emissivity value (about 0.85) in the wavelength range of 8–20μm. The increasing surface roughness leads to an obvious increase in emissivity from 0.2 to 0.4 at wavelength 3–5μm. [Copyright &y& Elsevier]

Abstract: We report a strategy to prepare biocompatible metasilicate-based ceramic coatings by microarc oxidation (MAO) on AZ91D magnesium alloy in sodium silicate solution with Ca(H2PO4)2 additive. X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to assess the phase composition and microstructure of the coatings. The corrosion behavior of the coated samples was evaluated by electrochemical and immersion tests in simulated body fluid (SBF). The results show that the corrosion resistance of AZ91D alloy is significantly improved due to the formation of dense coatings with biocompatible CaSiO3, CaMgSiO4 and Mg2SiO4 phases. Increasing Ca(H2PO4)2 content in the based sodium silicate leads to better corrosion resistance of AZ91D alloy. The results suggested a promising method for surface modification of degradable magnesium alloy as biomedical applications. [Copyright &y& Elsevier]

Abstract: Ceramic coatings containing TiO2 were formed on Ti6Al2Zr1Mo1V alloy surface by microarc oxidation (MAO) method. The microstructure, phase and chemical composition of the coatings were analyzed by SEM, XRD and EDS techniques. The coating mainly consists of rutile TiO2 and a small amount of anatase TiO2. The infrared emissivity values of coated and uncoated titanium samples when exposed to 700 °C were tested. It was found that the coating exhibits a higher infrared emissivity value (about 0.9) in the wavelength range of 8–14 μm than that of the uncoated titanium alloy, although which shows a slight increase from 0.1 to 0.3 with increasing exposure time at 700 °C. The relatively high infrared emissivity value of the MAO coating is possibly attributed to the photon emission from the as formed TiO2 phase. [Copyright &y& Elsevier]

Abstract: Magnesium and its alloy currently are considered as the potential biodegradable implant materials, while the accelerated corrosion rate in intro environment leads to implant failure by losing the mechanical integrity before complete restoration. Dense oxide coatings formed in alkaline silicate electrolyte with and without titania sol addition were fabricated on magnesium alloy using microarc oxidation process. The microstructure, composition and degradation behavior in simulated body fluid (SBF) of the coated specimens were evaluated. It reveals that a small amount of TiO2 is introduced into the as-deposited coating mainly composed of MgO and Mg2SiO4 by the addition of titania sol into based alkaline silicate electrolytic bath. With increasing concentration of titania sol from 0 to 10vol.%, the coating thickness decreases from 22 to 18μm. Electrochemical tests show that the E corr of Mg substrate positively shifted about 300∼500mV and i corr lowers more than 100 times after microarc oxidation. However, the TiO2 modified coatings formed in electrolyte containing 5 and 10vol.% titania sol indicate an increasing worse corrosion resistance compared with that of the unmodified coating, which is possibly attributed to the increasing amorphous components caused by TiO2 involvement. The long term immersing test in SBF is consistent with the electrochemical test, with the coated Mg alloy obviously slowing down the biodegradation rate, meanwhile accompanied by the increasing damage trends in the coatings modified by 5 and 10vol.% titania sol. [Copyright &y& Elsevier]

Abstract: Three functional coatings (namely Al-C, Si-P-Al and P-F-Al coating) were fabricated by microarc oxidation method on Ti6Al4V alloy in different aqueous solutions. The microstructure, phase and chemical composition of coatings were investigated using scanning electron microscope, X-ray diffraction and energy dispersive spectroscopy. The interface adhesion failure mode of the coating is revealed by shear, tensile and thermal shock methods. The coatings exhibit high adhesion strength by the quantitative shearing test, registering as 110, 70, and 40MPa for Al-C, Si-P-Al and P-F-Al coating, respectively. The tensile test of the coated samples shows that microarc oxidation treatment does not significantly deteriorate mechanical properties of substrate titanium alloy. The observations of the coating failure after subjected to the identical tensile elongation of 3.0% are well in agreement with those results of the shear test. The thermal cycle test indicates that all the coatings have good anti-thermal shocking properties. [Copyright &y& Elsevier]

Abstract: Microarc oxidation coatings were fabricated on Ti6Al4V alloy in NaAlO2 containing solution. Microstructure and adhesion properties of the coatings were evaluated. For antifriction purpose, a novel duplex coating of microarc oxidation combined with spraying graphite process was developed. The results show that the microarc oxidation coating with 20μm thickness is compact and uniform in the inner layer, while porous in the surface layer. The coating has high adhesion strength of about 110MPa to the substrate. The novel duplex coating exhibits good antifriction property, registering friction coefficient of ≈0.12, which is 5 times lower than that of the microarc oxidation coating sliding in the similar condition. The good tribological property is attributed to the specially designed duplex structure, the coating adhering strongly to the substrate and serving as the underlying loading layer and the graphite layer on top of it working as solid lubricant. [Copyright &y& Elsevier]

Bioactive composite coatings with a microarc oxidation (MAO) bottom layer and a biomimetic top hydrothermal layer were developed on an AZ31B magnesium alloy by combined MAO and hydrothermal treatment. The composition and microstructure of the coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Potentiodynamic polarization and soaking test in simulated body fluid (SBF) were used to evaluate the biodegradation and bioactivity of coated magnesium. The results show that the bioactive top hydrothermal layer containing CaHPO 4 , HA and Ca 3 (PO 4 ) 2 grows on a 10 μm thick MAO bottom layer. The corrosion current of samples with MAO-hydrothermal duplex layers is reduced to 4.780 × 10 − 6 A cm − 2 , the corrosion potential is increased to − 0.92 V. The sealing pore effect of the top hydrothermal layer enabled the MAO bottom layer to obtain a significantly improved corrosion resistance property. The MAO-hydrothermal sample had a weight increase of 14.52 mg cm − 2 compared to 24.7 mg cm − 2 weight loss for the MAO bottom layer after 28 days, due to the CaP compound deposition induced by the top hydrothermal surface. [ABSTRACT FROM AUTHOR]

The aluminide coating was prepared on Ti-6Al-2Zr-1Mo-1 V titanium alloy by pack cementation to enhance the high temperature oxidation resistance for aircraft and aerospace applications. High temperature oxidation behaviors of packing cementation coated and uncoated titanium alloy samples were comparatively investigated by isothermal oxidation at 800 °C and 900 °C in air. The results show that the compact coating with about 60 μm thick was composed of TiAl 3. With isothermal oxidation for 100 h at 800 and 900 °C, the weight gains of the coated samples are 1.29 mg·cm−2 and 4.06 mg·cm−2 respectively, which are about 2/5 and 1/5 of that of titanium alloy substrates (3.20 mg·cm−2 and 20.33 mg·cm−2). The excellent oxidation resistance performance is attributed to the formation of a continuous and dense Al 2 O 3 layer on the TiAl 3 coating surface, which was effective to prevent the O element diffusing into the coating and then reduce the oxidation rate. • Aluminide coating was prepared on Ti-6Al-2Zr-1Mo-1 V alloy by pack cementation. • The coating used NH 4 Cl as activator and CeO 2 as accelerant. • The coating improved oxidation resistance of titanium alloy at 800 and 900 °C. [ABSTRACT FROM AUTHOR]

Novel morphologies of chromium sesquioxide (Cr 2 O 3 ) were successfully formed on AISI 304 stainless steel surface by Nd: YAG pulsed laser oxidation in air. The obtained Cr 2 O 3 presented mainly dendritic, gear-like, flower-like and regular hexagonal morphologies with sizes from hundred nanometers to several micrometers. These various morphologies chiefly originated from two groups of diverse growth directions within (0 0 0 1) basal plane, i.e., 〈 2 1 ¯ 1 ¯ 0 〉 and 〈 0 1 1 ¯ 0 〉 directions. The preferential growth along different directions determined the final Cr 2 O 3 morphologies. And the crystallographic analyses basically accorded with the experimental results. Moreover, the growth mechanism of the hexagonal Cr 2 O 3 was analyzed in detail from its morphology evolution, and a corresponding growth model was reasonably proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Oxidation phenomenon in one laser spot on stainless steel surface is studied. [•] Compositions and morphologies vary from center to edge in one laser spot. [•] Hexagonal Cr2O3 distributes in the edge, while spherical Fe2O3 in the center. [•] Oxidation mechanism is proposed based on thermodynamics and kinetics. [Copyright &y& Elsevier]

Abstract: Different surface morphologies on AISI 304 stainless steel have been obtained after millisecond Nd:YAG pulsed laser oxidation. The effects of laser processing parameters, especially pulse width and laser energy density on the surface morphologies of the stainless steel were emphatically investigated. The results showed that surface morphologies were significantly changed with increasing laser pulse widths and laser energy densities. When the pulse width was 0.2–1.0ms and laser energy density was 4.30×106–7.00×106 J/m2, the surface was obviously damaged and the morphologies varied gradually from craters to ripple structures. However, when the pulse width was longer than 1ms and the laser energy density was increased from 1.90×107 to 3.16×107 J/m2, the sizes of craters got smaller until disappeared and the surface became flatter and smoother. Nevertheless, the smooth surface was not obtained under overhigh laser energy densities. In addition, the schematic relationship was used to describe the formation process and mechanism of different surface morphologies. [Copyright &y& Elsevier]

Abstract: NiTi shape memory alloy thin films are deposited on pure Cu substrate at substrate ambient temperatures of 300°C and 450°C. The surface and interface oxidation of NiTi thin films are characterized by X-ray photoelectron spectroscopy (XPS). After a subsequent annealing treatment the crystallization behavior of the films deposited on substrate at different temperatures is studied by X-ray diffraction (XRD). The effects of substrate temperature on the surface and interface oxidation of NiTi thin films are investigated. In the film surface this is an oxide layer composed of TiO2. The Ni atom has not been detected on surface. In the film/substrate interface there is an oxide layer with a mixture Ti2O3 and NiO in the films deposited at substrate temperatures 300°C and 450°C. In the films deposited at ambient temperature, the interface layer contains Ti suboxides (TiO) and metallic Ni. [Copyright &y& Elsevier]