Micro-arc Oxidation Surface Research Articles

Corrosion and wear resistance of AZ91D magnesium alloy with and without microarc oxidation coating in Hank’s solution

Immersion test, electrochemistry test and block-on-cylinder type wear test have been applied to study the corrosion and wear resistance of AZ91D Mg alloy with and without microarc oxidation (MAO) treatment in Hank’s solution. Through MAO, a ceramic coating is directly formed on the surface of AZ91D Mg alloy, by which its corrosion and wear resistances are greatly improved. The immersion test results show the mass loss of untreated AZ91D Mg is 15 times of that of MAO ones after 21 days immersion test. The electrochemical corrosion experiments show that the corrosion potential of Mg alloy is improved from −1.5786 V to −0.43019 V through MAO surface treatment, the corrosion current is reduced from 0.028703 A/cm2 to 2.0456 × 10−7 A/cm2, and the polarization resistance is improved from 1.2753 × 10−5 Ω/cm2 to 0.90886 Ω/cm2. The lubricate sliding wear test results show the mass loss of untreated AZ91D Mg is 1.5 times of that of MAO ones.

Characteristic and in vitro bioactivity of a microarc-oxidized TiO 2-based coating after chemical treatment

Microarc oxidation (MAO) was used to prepare a TiO 2-based coating containing Ca and P on titanium alloy. An alkali treatment was developed to modify the surface of the MAO coating to improve the apatite-forming ability of the coating. The chemically treated MAO coating exhibits a modified layer, with the main constituents being O, Ti, Ca and Na, showing anatase. The modified MAO coating shows a rough and porous morphology containing numerous nanoflakes of ∼100 nm thickness. During the alkali treatment process, P on the surface of the MAO coating shows a main dynamic process of dissolution; however, Ca exhibits a re-deposition process as well as dissolution. The formation of the modified layer could be explained by this mechanism: negatively charged HTiO 3 - ions are formed on the MAO coating due to the attack of OH − ions on the TiO 2 phase. The HTiO 3 - ions could incorporate sodium from the alkali solution and calcium from the alkali solution and MAO coating. The apatite-forming ability of the MAO coating is improved remarkably by the simple chemical treatment, since the surface of the alkali-treated MAO coating could provide abundant Ti–OH groups probably formed by ionic exchanges between (Ca 2+, Na +) ions of the alkali-treated MAO coating and H 3O + ions of a simulated body fluid (SBF). Moreover, Ca released from the alkali-treated MAO coating increases the degree of supersaturation of SBF, promoting the formation of apatite. The apatite induced by the alkali-treated MAO coating possesses carbonated structure and pore networks on the nanometer scale.

Effects of surface morphology on human osteosarcoma cell response

It is known that surface roughness enhances the anchorage of implants to bone and opens up the possibilities of the incorporation and release of antibiotics around titanium implants. In this study, titanium oxide was formed by the micro-arc oxidation (MAO) method. Commercially available pure titanium disks with diameter of 10 mm and 2 mm in thickness were used as substrates. MAO of the specimen was carried out in an aqueous electrolyte by applying a pulsed DC wave to the specimen. The surface characteristics of the MAO implants, including surface morphology and surface roughness, were analyzed by SEM and surface profilometer, respectively. The purpose of this study is to evaluate the effect produced by MAO of the titanium surface on cell cultures by cell proliferation assay, cell morphology and alkaline phosphatase activity. The results showed the formation of an oxide layer with micropores and roughness by MAO. No significant difference in the proliferation and spreading morphology of machined, blasted and MAO surfaces was observed. However, the ALP activity of osteoblast cells on MAO surface was higher than on machined and blasted surfaces in 4 day and 7 day cultures, respectively. From this study, it was concluded that the MAO-treated titanium exhibited an effect on early osteoblast differentiation.

Effects of microarc oxidation surface treatment on the mechanical properties of Mg alloy and Mg matrix composites

Mechanical properties of coated AZ91 Mg alloy, Al 18B 4O 33w/AZ91 and SiCw/AZ91 composites by microarc oxidation (MAO) surface treatment technique were measured and effects of MAO treatment on the mechanical properties were investigated. Tensile test shows that MAO treatment just slightly decreases ultimate tensile strength (UTS) and elongation of the Mg-based materials, while enhances their elastic modulus to some extent. But the effects of MAO treatment on the mechanical properties will be influenced by the energy parameters applied during surface treatment. The three materials coated under the same process conditions have exhibited differential surface morphology and fracture after tensile test, which indirectly indicates that the qualities of MAO coatings are also related with the substrate materials.

ANTIFRICTION PROPERTY OF MICROARC OXIDATION COATING ON TITANIUM ALLOY UNDER SOLID LUBRICATING SLIDING CONDITION

Ceramic coatings were fabricated on Ti6Al4V alloy surface by microarc oxidation (MAO) in Na 2 SiO 3–( NaPO 3)6– NaAlO 2 solution using an AC power supply. Microstructure and phase composition of coating were characterized by SEM and XRD, respectively. The antifriction property of the coating with and without solid lubricant sliding against SAE 52100 steel ball was investigated on a pin-on-disk friction and wear tester. The results show that the microarc oxidation coating is relatively dense and uniform, mainly composed of rutile and anatase. The coating sliding against the steel has friction coefficient as low as 0.2–0.3 at an applied load of 0.5 N and sliding cycle below 2500, which is much smaller than that of uncoated Ti6Al4V against the same counterpart. The transferring of materials from the softer steel ball onto the coating surface is the main wear event, while the microarc oxidation coating is characterized by slight abrasive wear and adhesive wear. Introducing solid graphite lubricant into the porous surface of microarc oxidation coating significantly improves the long-term antifriction property (registering friction efficient of 0.15 in the long-term sliding) under a similar sliding condition. This improvement is attributed to the reduction of materials that are transferred from the softer steel ball onto the coating surface.

Rolling and recrystallization textures in dispersion strengthened molybdenum

Micro-arc oxidation (MAO) ceramic coatings on the surface of aluminum alloy substrates with and without micro-groove have been successfully fabricated in the Na2SiO3-NaOH-EDTA-2Na solution. Microstructure characterization indicated that the micro-grooves on substrate surface could increase the content of α-Al2O3, γ-Al2O3 and 3Al2O3·2SiO2 phases and reduce the content of Al phase in the ceramic coating due to the sharp corner effect. EDS and XPS analysis showed that the content of Al and Si on the near outer surface of MAO coating on grooved substrate was more than that on non-grooved substrate. Meanwhile, MAO ceramic coating on micro-grooved substrate exhibited the faster growth rate in the initial stage of oxidation and the lower growth rate in the later oxidation. The final MAO coating showed the bigger micro pores and thicker oxidation film compared with that on the non-grooved substrate. Furthermore, the surface micro grooving pretreatment could dramatically improve the wear resistance and hardness of MAO coating, and the highest hardness of ceramic coatings of grooved substrate was around 1715 HV, which could be attributed to their special trapezoidal micro-groove structure.

Influence of microarc oxidation surface treatment of D16 and V96 alloys on their fatigue strength

Influence of microarc oxidation surface treatment of D16 and V96 alloys on their fatigue strength