Corrosion behavior of microarc oxidized CeO2-Al2O3 composite coatings on 2A12 Al alloy

Research on cavitation erosion and wear resistance performance of coatings

Laser surface melting (LSM) of Manganese Nickel Aluminium Bronze (Cu-Mn-Al-Ni-Fe) to improve cavitation erosion and corrosion resistance was performed using a 2-kW continuous wave (CW) Nd-YAG laser. A modified layer with a single β-phase structure and with highly refined and homogenized grains was obtained. Under favorable laser processing conditions (Power = 1 kW; Scanning velocity = 35 mm/s; Spot diameter = 2 mm) the microhardness was increased by 2 times and the cavitation erosion resistance in 3.5 wt% NaCl solution was increased by 5.8 times. This was even higher than that of Nickel Aluminium Bronze (NAB). For as-received MAB, the SEM micrographs of the surface taken at an early stage of the cavitation erosion and general corrosion tests revealed that the iron/manganese-rich κI phase and the α/κI interface were initiation sites of damage. On the other hand, attack was much milder in the laser melted samples and started at the triple junctions of the grain boundaries. The corrosion current density in 3.5 wt% NaCl was also improved after laser surface melting, with a reduction from 9.54 µA/cm2 to 4.26 µA/cm2. The corrosion potential also shifted in the noble direction by about 80 mV. It could be concluded that the improvement in both cavitation erosion and corrosion resistance was in particular attributable to homogenization and refinement of the microstructure.Laser surface melting (LSM) of Manganese Nickel Aluminium Bronze (Cu-Mn-Al-Ni-Fe) to improve cavitation erosion and corrosion resistance was performed using a 2-kW continuous wave (CW) Nd-YAG laser. A modified layer with a single β-phase structure and with highly refined and homogenized grains was obtained. Under favorable laser processing conditions (Power = 1 kW; Scanning velocity = 35 mm/s; Spot diameter = 2 mm) the microhardness was increased by 2 times and the cavitation erosion resistance in 3.5 wt% NaCl solution was increased by 5.8 times. This was even higher than that of Nickel Aluminium Bronze (NAB). For as-received MAB, the SEM micrographs of the surface taken at an early stage of the cavitation erosion and general corrosion tests revealed that the iron/manganese-rich κI phase and the α/κI interface were initiation sites of damage. On the other hand, attack was much milder in the laser melted samples and started at the triple junctions of the grain boundaries. The corrosion current density in 3...

The correlation between the Na2SiO3·9H2O concentrations and the characteristics of plasma electrolytic oxidation ceramic coatings

AA2024-T3 are widely used in various applications because of their exceptional physical properties. However, they are susceptible to corrosion and cavitation erosion in aggressive environments due to high concentration of copper. Sol-gel coatings in the field of corrosion prevention are emerging. Improved thickness of coatings significantly improves the barrier effect of the coatings, thereby improving their operational-life in industrial applications. To date, a limited amount of work has been carried out in determining the effect of hybrid sol-gel coatings on abrasion and cavitation erosion of AA2024-T3. The present study investigates the effect of thickness of the coatings on morphology, corrosion, abrasion and cavitation erosion properties of the prepared hybrid sol-gel coatings deposited on AA2024-T3 surfaces. The hybrid sol-gels have been synthesized from 3-trimethoxysilylpropylmethacrylate (MAPTMS), and a zirconium complex prepared from the chelation of zirconium n-propoxide (ZPO), and methacrylic acid (MAAH). AA-2024 T3 were coated using single-dip, double-dip and triple-dip. Abrasion and cavitation erosion tests were performed according to the relevant standards. Structural damage caused by corrosion, abrasion and cavitation erosion was studied by Optical Microscope and Scanning Electron Microscope (SEM). Corrosion protection performance of the coatings was tested using Open Circuit Potential (OCP) and Potentiodynamic polarization (PDS). Results indicated that the multilayer coated samples improved the corrosion, cavitation erosion and abrasion resistance of AA2024-T3. Hence, the prepared silica-based coatings can be proposed as a potential choice for marine renewable energy applications.

Cavitation erosion resistance of microarc oxidation coating on aluminium alloy

A relatively new process called microarc oxidation (MAO), also called plasma electrolytic oxidation (PEO), has emerged as a unique technique to produce hard, thick ceramic oxide coatings on different Mg or Al alloys. The magnesium offers various possibilities of application in industry, but its poor property in corrosion resistance, wear resistance, hardness and so on, limited its application. Through microarc oxidation, ceramic coating is directly formed on the surface of pure magnesium, by which its surface property is greatly improved. In this paper, a dense ceramic oxide ceramic coating was prepared on the magnesium by microarc oxidation in a Na2SiO3-Na2WO4-KOH-Na2EDTA electrolytic solution. The surface morphology of the coating was observed by the Scanning Electron Microscope (SEM). Using the X-ray diffraction (XRD), the phase structure of the coating was analyzed. The friction and wear behavior of the micro-arc oxidation ceramic coating under dry sliding against GCr15 steel was evaluated on a ball-on-disc test rig. The results showed that the magnesium was characterized by adhesion wear and scuffing under dry sliding against the steel, while the surface micro-arc oxidation ceramic coating experienced much abated adhesion wear and scuffing under the same testing condition. The micro-arc oxidation ceramic coating showed good friction-reducing and fair antiwear ability in dry sliding against the steel.

Microstructure and Properties of Ceramic Coatings on 7N01 Aluminum Alloy by Micro-Arc Oxidation

Effect of MAO coatings on cavitation erosion and tribological properties of 5056 and 7075 aluminum alloys

Micro arc oxidation (MAO) technology known as a newly surface treatment technology has got a widely application in the field of aviation, aerospace, automotive, electronics, and medical industry. Strength, toughness, hardness and corrosion of valve metal such as aluminum, magnesium, copper, zinc, zirconium and their alloys can be greatly improved by MAO technology. This paper tries to probe into the feasibility of using MAO technology in nuclear power industry. Aluminum and its alloys are used as structural materials such as the cladding of reactor fuel and all kinds of pipes in the low nuclear reactor. Zirconium alloys are widely used for the fuel cladding, cannula, catheter and other components of the fuel assemblies. Titanium and its alloys offer a unique combination of desirable mechanical properties which makes them to be the candidate materials for structural application in the field of nuclear energy. The surface of all these materials may be destroyed which increasing the risk of the nuclear accident due to the severe serving conditions. As a result, it is necessary to improve the corrosion and wear resistance behavior. With the urgent requirements of safety and durability of nuclear reactor, MAO technology must have a broad prospect in nuclear industry.

Influence of chemical composition, grain size, and spray condition on cavitation erosion resistance of high-velocity oxygen fuel thermal-sprayed WC cermet coatings

Aluminium oxide ceramic composite coatings containing hexagonal BN (h-BN) powder were produced successfully by a two-step microarc oxidation process. The incorporation of h-BN powder was achieved by means of wiping an emulsion into the pretreated coatings between these two steps. The thermal shock resistance of the fabricated samples was tested via quenching method. The morphological characteristics and the distribution of elements were analysed by SEM, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The microhardness of samples was determined by employing a Vickers indenter. The phase composition of composite ceramic coatings was investigated by X-ray diffraction. The results showed that the inclusion of h-BN powder has no influence on the growth and microhardness of alumina ceramic coatings. However, the modified coatings exhibit lower area and number of pores than conventional coatings. More significantly, the incorporation of a certain amount of h-BN powder improves the thermal shock resistance of aluminium oxide ceramic composite coatings even in a thick coating.

The hardness and wear resistance of micro arc oxidation (MAO) ceramic coatings were influenced by phase compositions, surface thickness, porosity and microcracks. In this work, ceramic coatings with enhanced microhardness and friction resistance were fabricated on 6061 Al-alloy by increasing thickness and decreasing porosity through adding sodium hexametaphosphate ((NaPO3)6) as additive in silicate-based electrolyte. Surface morphologies and microhardness of the as-fabricated MAO coatings were evaluated using scanning electron microscope (SEM) and thickness meter. As a binary additive, the addition of (NaPO3)6 in electrolytes can obviously change the surface morphologies, thickness and microhardness of the resultant MAO coatings.

An iron-cobalt alloy ceramic coating grows on the surface of Q235 carton steel in situ by the micro-arc oxidation technology; and the phase composition, elementary composition, surface morphology, surface roughness and thickness of the ceramic coating are analyzed by X-ray diffractometer, energy disperse spectroscopy, scanning electron microscopes, handheld roughness meter and coating thickness gauge. The results show that the morphology of ceramic coating is irregular porous structures at the surface and the elements of electrolyte and Q235 carbon steel matrix exist in the ceramic coating as amorphous phase. And then, the degradation of the rhodamine B (RhB) by the ceramic coating in a H2O2 Fenton system was investigated. The degradation rate of the rhodamine B solution can reach 99%; and meanwhile, the degradation rate is not reduced along the increased using times.

The interaction effect of micro arc oxidation (MAO) parameters on the microstructure and wear properties was investigated. The results showed that the electric current and oxidation time significantly influenced the thickness and grinding crack width of the ceramic coatings within the range of the selected parameters, and the interaction effect of the electrical parameters was not obvious. The surface morphology, cross-section morphology, and element distribution of the coatings were observed using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that ceramic coatings with γ-Al2O3 and α-Al2O3 formed, which enhanced the coating performance. After that, the microhardness and wear resistance were tested. Under the optimal process, the microhardness of a coating section was up to 1200 HV0.1, and the friction coefficient was just 0.3. When wear occurred, the volcanic microstructures experienced extrusion and deformation, and then peeled off under shear stress, which led to the formation of a grinding crack. The main failure modes of the micro arc oxidation coatings were abrasive wear and spalling failure.

Cavitation erosion is one of the major problems to be solved in hydraulic machinery. Propellers of high speed boats require a light weight metallic material for their improved high performance. This example tells us that solutions are the developments of way for the improvement of cavitation erosion resistance of light weight metallic material. Coatings on aluminum alloy can enhance the cavitation erosion resistance. This study discussed the cavitation erosion behavior of 6061 aluminum alloy coated with TiAlN thin film. TiAlN coatings were deposited by DC magnetron sputtering method at various nitrogen partial pressures of the coating process using Ti based alloy cathode. The composition of target material was 90wt%Ti, 6wt%Al and 4wt%V. Using the TiAlN coated 6061 aluminum alloy specimen, cavitation erosion tests were carried out to investigate its resistance to the ultrasonic cavitation erosion. Prior to and after the tests, the specimen surfaces were analyzed by using the surface analysis techniques such as micro-hardness test, AFM, SEM, GXRD and scratch test to measure the microstructure of thin film and bonding properties of the applied TiAlN coatings to the substrate material. An improvement in cavitation erosion resistance could be seen with TiAlN coating on 6061 aluminum alloy. Especially, the coating at a nitrogen flow rate of 0.85 sccm or more were very effective in reducing the surface cavitation erosion from the ultrasonic cavitation. In the observation of surface damages during the cavitation erosion tests, the surface cracks in TiAlN were created by the bending of TiAlN coating which were resulted from the plastic deformation of the soft substrate material of aluminum alloy. Once the cracks initiate, drastic delaminations of TiAlN from the substrate material occured. The mean depth erosion rate (MDER) could be evaluated by critical and delamination loads measured by scratch test.