This work aims to modify the surface of the Ti-25Ta-xZr (x = 0, 25, and 50wt.%) system alloys through micro-arc oxidation (MAO) to incorporate calcium, phosphorus, and magnesium ions in the oxidized layer deposited. The MAO surface modification was performed by changing the limited voltage applied to the system (200, 250, and 300V). Structural characterizations by X-ray diffraction and X-ray photoelectron spectroscopy showed that the formed MAO films comprise TiO2, Ta2O5, ZrO2, and CaCO3 oxides. Voltage inhibits the formation of Ta2O5 and CaCO3 phases and decreases the incorporation capacity of Ca, P and Mg ions. The MAO layers' topography, thickness, and roughness, analyzed by scanning electron microscopy and confocal microscopy techniques, showed that increasing the voltage tends to increase pore sizes and reduces film thickness; conversely, it decreases the number of pores per μm2. Regarding hardness and elastic modulus, adding Zr increases the MAO layer's hardness due to the formation of ZrO₂. However, increasing the voltage decreases the MAO films' hardness due to the formation of the compound CaCO3. The MAO process increased the elastic modulus of the Ti-25Ta-xZr bulk alloys. Finally, the adhesion of the films was analyzed by the Rockwell-C adhesion test. The results showed a good adhesion of MAO films to Ti-25Ta-xZr substrates. 

Assessment of applied voltage on the structure, pore size, hardness, elastic modulus, and adhesion of anodic coatings in Ca-, P-, and Mg-rich produced by MAO in Ti-25Ta-Zr alloys

Titanium (Ti) and its alloys have good biocompatibility, mechanical properties and corrosion resistance, making them attractive for biomedical applications. However, their biological inertness and lack of antimicrobial properties may compromise the success of implants. In this review, the potential of micro-arc oxidation (MAO) technology to create bioactive coatings on Ti implants is discussed. The review covers the following aspects: 1) different factors, such as electrolyte, voltage and current, affect the properties of MAO coatings; 2) MAO coatings affect biocompatibility, including cytocompatibility, hemocompatibility, angiogenic activity, corrosion resistance, osteogenic activity and osseointegration; 3) antibacterial properties can be achieved by adding copper (Cu), silver (Ag), zinc (Zn) and other elements to achieve antimicrobial properties; and 4) MAO can be combined with other physical and chemical techniques to enhance the performance of MAO coatings. It is concluded that MAO coatings offer new opportunities for improving the use of Ti and its alloys in biomedical applications, and some suggestions for future research are provided.

Micro-arc oxidation (MAO) and its potential for improving the performance of titanium implants in biomedical applications

A review on recent progress of refractory high entropy alloys: from fundamental research to engineering applications

This work discussed the influences of voltage on the microstructure and corrosion resistance of micro-arc oxidation (MAO) coating developed on Mg-2Zn-0.3Ca (ZX20) alloys. The MAO coatings on ZX20 alloy surface consist of MgO and Mg2SiO4 compounds. They feature two layers, namely a porous outer layer and a dense inner layer. Higher voltage forms a thicker MAO coating on ZX20 alloy, meanwhile, larger diameter micropores and more thermal micro-cracks are generated in the coating. The MAO coating on ZX20 alloy obtained at 400V has the largest thickness (5.98±0.23 μm), the largest diameter of the micropores (1.02±0.64 μm), the most thermal cracks and the most amount of Mg2SiO4. The MAO coating on ZX20 alloy obtained at 300V has the largest contact angle value and the highest bonding strength. During the immersion corrosion, the corrosive ions such as Cl- can enter the outer layer of the coating and react with MgO to generate Mg(OH)2, resulting in the dissolution of the coating. With the prolong of the immersion time, local corrosion and cracks form at the weak site of the coating, speeding up the corrosion. While, the dense inner layer containing chemically stable Mg2SiO4 has less defect, providing an effective physical barrier for the substrate and enhancing the corrosion resistance of ZX20 alloy. The ZX20 alloy coated at 300V exhibits the lowest degradation rate (PH=0.13 mm·y-1) due to its dense inner layer, as well as having the largest contact angle value and the highest bonding strength. 

Effect of voltage on microstructure and corrosion resistance of micro-arc oxidation coating on Mg-Zn-Ca biodegradable alloy

The technology of the TiB2/TiB cladding layer addresses the issue of the insufficient wear resistance of cup-shaped parts composed of titanium alloy materials. In order to eliminate the cracking problem of laser cladding TiB2/Ti-based alloy, 30%TiB2/Ti-based alloy gradient coating was prepared on the surface of titanium alloy by laser cladding in this study. The results revealed that the microstructure of the matrix and the cladding layer is metallurgically bonded. The microstructures of the cladding layer appear as rod-like and coarse-grained features on the surface, and fine needle-like and small-grained morphologies inside. The fine needle-like TiB precipitated in situ from the melt has a flat interface with Ti and exhibits a low degree of interfacial mismatch, while the interface between small particle-like TiB and Ti is wavy and has a high degree of interfacial mismatch. The gradual increase in the amount of TiB is present from the surface to the bottom of the cladding layer, while the amount of unmelted TiB2 particles decreases. The chemical structure of the cladding layer is mainly presented as TiB2, TiB and α-Ti phases. The maximum hardness of the cladding layer is 725 HV0.2, where it is more than twice the hardness of the substrate. The fretting wear resistance of the cladding layer is better than that of the titanium alloy substrate under low loads (50 N–100 N), while a high load (more than 150 N) triggers a reverse outcome.

/pdf/gradient-coating-of-laser-cladding-tib2-ti-based-alloy-on-3egnm7ai.pdf

Gradient Coating of Laser Cladding TiB2/Ti-Based Alloy on Titanium Alloy Surface

In order to improve the high-temperature oxidation resistance of refractory high-entropy alloys (RHEAs), we used micro-arc oxidation (MAO) technology to prepare ceramic coatings on AlTiCrVZr alloy, and the effects of voltage on the microstructure and high-temperature oxidation resistance of the coatings were studied. In this paper, the MAO voltage was adjusted to 360 V, 390 V, 420 V, and 450 V. The microstructure, elements distribution, chemical composition, and surface roughness of the coatings were studied by scanning electron microscopy (SEM), energy dispersive (EDS), X-ray photoelectron spectroscopy (XPS), and white-light interferometry. The matrix alloy and MAO-coated samples were oxidized at 800 °C for 5 h and 20 h to study their high-temperature oxidation resistance. The results showed that as the voltage increased, the MAO coating gradually became smooth and dense, the surface roughness decreased, and the coating thickness increased. The substrate elements and solute ions in the electrolyte participated in the coating formation reaction, and the coating composition was dominated by Al2O3, TiO2, Cr2O3, V2O5, ZrO2, and SiO2. Compared with the substrate alloy, the high-temperature oxidation resistance of the MAO-coated samples prepared at different voltages was improved after oxidation at 800 °C, and the coating prepared at 420 V showed the best high-temperature oxidation resistance after oxidation for 20 h. In short, MAO coatings can prevent the diffusion of O elements into the substrate and the volatilization of V2O5, which improves the high-temperature oxidation resistance of AlTiCrVZr RHEAs.

/pdf/effect-of-voltage-on-the-microstructure-and-high-temperature-3b3ntuz8.pdf

Effect of Voltage on the Microstructure and High-Temperature Oxidation Resistance of Micro-Arc Oxidation Coatings on AlTiCrVZr Refractory High-Entropy Alloy

In this paper, MAO-Cu/Cu-(HEA)N composite coatings on TC4 titanium alloy were prepared by combining micro arc oxidation (MAO) with magnetron sputtering (MS) to enhance the wear resistance and antibacterial ability of the substrate in simulated seawater. The number of micropores on the surface of the composite coatings decreased with increasing CuSO4 concentration in the electrolyte, causing the surfaces to be flat and smooth. XPS and EDS analyses revealed that the MAO-Cu/Cu-(HEA)N composite coatings predominately contained TiO2, Cu2O, and (HEA)N. Moreover, the addition of CuSO4 increased the growth rate of the MAO coatings. Comparatively, the MAO-Cu/Cu-(HEA)N composite coating with 5 g/L CuSO4 showed superior wear resistance, reduced friction coefficient (approximately 0.2), and shallow and narrow grinding cracks were observed compared to the other coatings. Antibacterial experiments showed that the MAO-Cu/Cu-(HEA)N composite coatings had better bacterial killing effects than the TC4 substrate, which is of great significance to the antifouling abilities of titanium alloys in marine applications.

/pdf/microstructure-and-properties-of-mao-cu-cu-hea-n-composite-1xkti9ox.pdf

Microstructure and Properties of MAO-Cu/Cu-(HEA)N Composite Coatings on Titanium Alloy

This paper analyzes the influence of the adhesive layer material type, interface roughening treatment technology and temperature on the bond performance between the cement concrete pavement and the overlay layer of the highway tunnel through direct shear test and shear test. The results showed that the interlayer shear strength and drawing strength increase and decrease after reaching a limit value with the increase in the amount of sticky layer oil spread when the sticky layer oil is within a certain range. The effect of roughening treatment is obvious. The effect of vibrating cut and milling is increased by 2 to 3 times and more obvious than the effect of groove and napping. The interlayer shear strength and drawing strength of the three adhesive layer materials decrease with the increase of temperature. The shear strength and drawing strength of SBS modified asphalt are higher than SBR modified emulsified asphalt and rubber asphalt with the increase of temperature.

Study on influencing factors of bond performance between cement concrete pavement and overlay layer in highway tunnel

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Papers

Effect of Voltage on the Microstructure and High-Temperature Oxidation Resistance of Micro-Arc Oxidation Coatings on AlTiCrVZr Refractory High-Entropy Alloy

Microstructure and Properties of MAO-Cu/Cu-(HEA)N Composite Coatings on Titanium Alloy

Study on influencing factors of bond performance between cement concrete pavement and overlay layer in highway tunnel