Preparation of Al_2O_3/Au nano-laminated composite coatings and their oxidation resistance on stainless steel

Al2O3/Au nano-laminated composite coatings were prepared by means of magnetron sputtering. The coating was compact and comprised of nano-laminated Al2O3 and Au layers. High temperature cyclic oxidation test was employed to investigate the oxidation resistance of the composite coatings. The results revealed that the applied Al2O3/Au nano-laminated composite coatings improved the oxidation and spallation resistance of the stainless steel substrate significantly. The mechanism accounting for oxidation resistance was related with the suppression of inward oxygen diffusion and selective oxidation of Cr in the substrate. The mechanism accounting for spallation resistance was attributed to the relaxation of thermal stress by the nano-laminated structure.

Wetting of molten Sn-3.5Ag-0.5Cu on Ni-P(-SiC) coatings deposited on high volume faction SiC/Al composite

The wetting of molten Sn-3.5Ag-0.5Cu alloy on the Ni-P(-SiC)coated SiCp/Al substrates was investigated by electroless Ni plating process,and the microstructures of the coating and the interfacial behavior of wetting systems were analyzed.The SiC particles are evenly distributed in the coating and enveloped with Ni.No reaction layer is observed at the coating/SiCp/Al composite interfaces.The contact angle increases from^19°with the Ni-P coating to 29°,43°and 113°with the corresponding Ni-P-3SiC,Ni-P-6SiC and Ni-P-9SiC coatings,respectively.An interaction layer containing Cu,Ni,Sn and P forms at the Sn-Ag-Cu/Ni-P-(0,3,6)SiC coated SiCp/Al interfaces,and the Cu-Ni-Sn and Ni-Sn-P phases are detected in the interaction layer.Moreover,the molten Sn-Ag-Cu can penetrate into the Ni-P(-SiC)coatings through the Ni-P/SiC interface and dissolve them to contact the SiCp/Al substrate.

Effect of MoSi_2 content on dielectric and mechanical properties of MoSi_2/Al_2O_3 composite coatings

Molybdenum disilicide （MoSi2） sheath and aluminum oxide （Al2O3） core blended powders were fabricated by spray drying. A derived coating material was produced for the application as microwave absorbers using the as prepared powders by atmospheric plasma spray （APS） technology. The effects of MoSi2/Al2O3 mass ratio on the dielectric and physical mechanical properties of the composite coatings were investigated. When the MoSi2 content of the composites increases from 0 to 45%, the flexure strength and fracture toughness improve from 198 to 324 MPa and 3.05 to 4.82 MPa-m1/2 then decline to 310 MPa and 4.67 MPa-m1/2, respectively. The dielectric loss tangent increases with increasing MoSi2 content, and the real part of permittivity decreases conversely over the frequency range of 8.2-12.4 GHz. These effects are due to the agglomeration of early molten MoSi2 particles and the increase of the electrical conductivity with increasing MoSi2 content.

Parameter optimization for plasma-sprayed Al2O3p/Al composite coatings on AZ31 magnesium alloy

Al2O3p/Al composite coatings were prepared on the surface of AZ31 magnesium alloy by plasma spraying technology with mixed powders of Al and Al2O3. An orthogonal test containing six factors and five levels was carried out to acquire the optimum technical parameters. Mierostruetures and properties of the composite coatings were studied. The results show that the coatings consist of Al2O3 particulates distributed uniformly and Al matrix, and the interface between the particulate and matrix is continuous, compact and clean. With increasing the mass fraction of Al2O3 in the mixed powders, the volume fraction of Al2O3 in the coatings iacreases. The Al2O3p/Al composite coating with 14% Al2O3 volume fraction has more compact microstrueture and more satisfactory properties.

Laser Cladding Al-Si/Al_2O_3-TiO_2 Composite Coatings on AZ31B Magnesium Alloy

To improve the wear resistance and corrosion resistance of magnesium alloys, a 5 kW continuous wave CO2 laser was used to investigate the laser surface cladding on AZ31 B magnesium alloys with Al-Si/Al2O3-TiO2 composite powders. A detailed microstructure, chemical composition, and phase analysis of the composite coatings were studied by scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS）, and X-ray diffraction （XRD）. The laser cladding shows good metallurgical bonding with the substrate. The composite coatings are composed of Mgl7Al12, Al3Mg2, Mg2Si, Al2O3, and TiO2 phases. Compared to the average microhardness （50HV0.05） of the AZ3 1 B substrate, that of the composite coatings （230HV0.05） is improved significantly. The wear resistances of the surface layers were evaluated in detail. The results demonstrate that the wear resistances of the laser surface-modified samples are considerably improved compared to the substrate. It also show that the composite coatings exhibit better corrosion resistance than that of the substrate in 3.5wt% NaCI solution.

Effect of Al_2O_3on Structure and Wearability of Composite Coating

The composite coating was prepared by thermal spray welding after making composite powder,which is composed of Ni-based self-melted alloy and AlOceramic powder including nano,sub-micron and micron powders.The influences of contents and sizes of AlOon the structure and wearability were investigated.The results show that the wear resistance of the coating would be increased greatly by adding AlO,but the spray weldability decreases with increasing AlOcontent.So there is an optimal content of AlOpowder.The composite coating with AlOnano or sub-micron powder of 0.5% has the best abrasive resistance,while the optimal content of AlOmicron powder is 1 %.

Si-Al-Ir Oxidation Resistant Coating for Carbon/Carbon Composites by Slurry Dipping

A Si-Al-lr oxidation resistant coating was prepared for SiC coated carbon/carbon composites by slurry dipping. The phase composition, microstructure and oxidation resistance of the as-prepared Si-Al-lr coating were studied by XRD （X-ray diffraction）, SEM （scanning electron microscopy）, and isothermal oxidation test at 1773 K in air, respectively. The surface of the as-prepared Si-Al-lr coating was dense and the thickness was approximately 100 um. Its anti-oxidation property was superior to that of the inner SiC coating. The weight loss of SiC/Si- Al-lr coated carbon/carbon composites was less than 5 wt. pct after oxidation at 1773 K in air for 79 h. The local oxidation defects in the coating may result in the failure of the SiC/Si-Al-Ir coating.

MICROSTRUCTURAL STUDY OF Fe-Cr-Al/Al COMPOSITE COATINGS DURING OXIDATION AND SULFIDATION AT 900℃

The microstructure of a composite coating system, which was composed of an inner layer of Fe-Cr-Al and an outer layer of aluminum, was studied after it was respectively oxidized and sulfurdized at elevated temperatures. Apart from the Al2O3 scale formed on the surface, the microstructure of the composite coatings exposed at 900℃ in air for 4h was a three-layer structure. The first layer consisted of a solid solution of Cr and Fe in α aluminum and an intermetallic compound FeAl3 while the second layer was a single phase of the aluminide and the third layer still remained the same appearance as the original Fe-Cr-Al coating. The microstructural observation of the specimen tested at 850-900℃ at low oxygen pressure and high sulfur pressure for 576h revealed that the surface coatings of the specimen had transformed into a duplex structure containing an outer layer and a thicker aluminide layer beneath. X-ray diffraction results showed that the out layer was composed of Al2S3 and Al2O3 and that AlCrFee was the main phase composition of the aluminide layer, with a few of Al2S3 and Al2O3 accompanied.

Preparation of TiAl_3-Al composite coating by cold spraying

TiAl3-Al coating was deposited on orthorhombic Ti2AlNb alloy substrate by cold spraying with the mixture of pure Al and Ti as the feedstock powder at a fixed molar ratio of 3-1 when the spraying distance,gas temperature and gas pressure for the process were 10 mm,250 ℃ and 1.8 MPa,respectively.The as-sprayed coating was then subjected to heat treatment at 630 ℃ in argon atmosphere for 5 h at a heating rate of 3 ℃/min and an argon gas flow rate of 40 mL/min.The obtained TiAl3-Al composite coating is about 212 μm with a density of 3.16 g/cm3 and a porosity of 14.69% in general.The microhardness and bonding strength for the composite coating are HV525 and 27.12 MPa.

Oxidation Performance of Fe-Al/WC Composite Coatings Produced by High Velocity Arc Sprayed at 650 ℃

The Fe-Al/WC intermetallic composite coatings have been prepared by high velocity arc spraying(HVAS) technology on 20G steel and the oxidation performance of Fe-Al/WC composite coatings has been studied by means of thermogrativmetic analyzer. The results demonstrate that the kinetics curve of oxidation approximately follows the logarithmic law. The composition of the oxidized coating surface mainly is composed of A12O3, Fe2O3, Fe3O4 and FeO which distribute unevenly. The protective A12O3 film firstly forms and preserves the coatings from further oxidation.

Corrosion Behavior of Electrodepositing Ni/Al_2O_3 Composite Coatings under the Presence of NaCl Deposit

The morphology and corrosion behavior of Ni/Al2O3 composite coatings prepared using double-pulsed electrodepositing technique after oxidized under 800 ℃ NaCl deposit in air environment were analyzed by scanning electrical microscope (SEM), X-ray diffraction(XRD) and energy dispersive spectrum(EDS). The results showed that the corrosion of all composite coatings was accelerated under NaCl deposits, and the corrosion products were rather porous with poor adherence to the matrix. Al2O3 particles in the coatings can refine the grain size and improve the high temperature corrosion resistance of the coatings. Within the test scope, the more Al2O3 particles in the coatings, the lower corrosion rates could be obtained, and the corrosion mechanism was also discussed.

Mixed rare earth metal conversion coatings on 2024 alloy and Al6061/SiC_p metal matrix composites

The processes of mixed rare earth metal (REM) conversion coatings on 2024 alloy and Al6061/SiC p metal matrix composites (MMC) were introduced. The coatings were examined to be honeycomb like feature by scanning electron microscope. X ray diffraction analysis revealed that the coatings are amorphous structure. The results of X ray photoelectron spectroscopy indicated that the mixed REM conversion coatings consist predominantly of Ce and O, the contents of other rare earth elements (such as La, Pr) are relatively low, the coatings are about 2～4 μm thickness with excellent adhesion and wearability. The results of mass loss test showed that the mixed REM conversion coatings produce corrosion resistant surface of 2024 alloy and Al6061/SiC p. [

Oxidation performance of Fe-Al/WC composite coatings produced by high velocity arc spraying

Fe-Al intermetallics with remarkable high-temperature intensity and excellent erosion, high-temperature oxidation and sulfuration resistance are potential low cost high-temperature structural materials. But the room temperature brittleness induces shape difficult and limits its industrial application. The Fe-Al intermetallic coatings were prepared by high velocity arc spraying technology with cored wire on 20G steel, which will not only obviate the problems faced in fabrication of these alloys into useful shapes, but also allow the effective use of their outstanding high-temperature performance. The Fe-Al/WC intermetallic composite coatings were prepared by high velocity arc spraying technology on 20G steel and the oxidation performance of Fe-Al/WC composite coatings was studied by means of thermogrativmetic analyzer at 450, 650 and 800℃. The results demonstrate that the kinetics curve of oxidation at three temperatures approximately follows the logarithmic law. The composition of the oxidized coating is mainly composed of Al2O3, Fe2O3, Fe3O4 and FeO. These phases distribute unevenly. The protective Al2O3 film firstly forms and preserves the coatings from further oxidation.

Improved wettability and mechanical properties of metal coated carbon fiber-reinforced aluminum matrix composites by squeeze melt infiltration technique

In order to improve the wettability and bonding performance of the interface between carbon fiber and aluminum matrix,nickel-and copper-coated carbon fiber-reinforced aluminum matrix composites were fabricated by the squeeze melt infiltration technique.The interface wettability,microstructure and mechanical properties of the composites were compared and investigated.Compared with the uncoated fiber-reinforced aluminum matrix composite,the microstructure analysis indicated that the coatings significantly improved the wettability and effectively inhibited the interface reaction between carbon fiber and aluminum matrix during the process.Under the same processing condition,aluminum melt was easy to infiltrate into the copper-coated fiber bundles.Furthermore,the inhibited interface reaction was more conducive to maintain the original strength of fiber and improve the fiber−matrix interface bonding performance.The mechanical properties were evaluated by uniaxial tensile test.The yield strength,ultimate tensile strength and elastic modulus of the copper-coated carbon fiber-reinforced aluminum matrix composite were about 124 MPa,140 MPa and 82 GPa,respectively.In the case of nickel-coated carbon fiber-reinforced aluminum matrix composite,the yield strength,ultimate tensile strength and elastic modulus were about 60 MPa,70 MPa and 79 GPa,respectively.The excellent mechanical properties for copper-coated fiber-reinforced composites are attributed to better compactness of the matrix and better fiber−matrix interface bonding,which favor the load transfer ability from aluminam matrix to carbon fiber under the loading state,giving full play to the bearing role of carbon fiber.

Study on Anticorrosive Cerium Conversion Coating of C_f/6061A1 Composite Surface

The optimum chemical passivation process of the rare earth metal (REM) conversion coating on the Cf/6061Al composite surface was introduced in this paper and its polarization curves properties were investigated. Ridge-like coatings were found by scanning electro microscope (SEM) observations, and the Al matrix and carbon fibre reinforcement were both coated with Ce conversion coatings, with some minor cracks. The energy dispersive spectroscopy (EDS) plane scan analysis indicates that the major elements in the coating are Ce, O, Si, Al and the Ce content reaches 47.48% (mass fraction). The Ce conversion coatings increase the corrosion resisting properties of Cf/6061A1 composite, with a higher free corrosion potential (Ecorr) and a lower free corrosion current density (icorr) for the coated composite than those of the bare composite. And the Boehmite-treatment would enhance the corrosion resistance of the REM conversion coating. The ca-thodic polarization and anodic polarization were retarded by REM conversion coating, resulting in an improved corrosion resistance.

TENSILE PROPERTIES AND INTERFACIAL FEATURE OF SiC COATED C/Al COMPOSITE WIRES UNDER ISOTHERMAL HEAT TREATMENT

The effect of different regimes of heat treatment on the tensile strength of SiC coated composite of C fibers reinforced Al wires has been investigated.Their tensile strength may increase under treatment either at 500℃ for 2h or 550℃ for 1h,but decrease over 600℃.After the strength tests of extracted fibers from composite wires,the SiC coating is an excellent protection to C fibers.EPMA and EDAX showed that the C/Al interface of the composite wires is stable under treatment below 600℃,but unstable at 650℃

Compositing Soft Coated Ti-Fiber Reinforced Ti-Al Matrix Composites

It is showed that there are Ti 3Al, Ti 2Cu and β phase in the interface of Ti/Ti Al composites reinforced with Y 2O 3 Cr composite soft coated Ti fiber, and that interface bonding is intact. Bending strength of the composites can be increased by 26%, to 709 MPa, and bending deflection increased slightly compared with the Ti/Ti Al composites reinforced by Ti fibers coated with Y 2O 3.

低压冷喷涂制备Al-Ni-xCr复合涂层及其磨损特性研究

防腐性能较好的铝基涂层存在耐磨性不足的问题。本文设计了Ni粉和Cr粉复合沉积的方法来改善涂层的耐磨性。采用低压冷喷涂技术,制备了一系列Cr含量不同的Al-Ni-xCr复合涂层。通过金相、扫描电镜及X射线衍射等方法分析了复合涂层的微观形貌和成分。采用显微硬度计和磨损仪测试了涂层的显微硬度和磨损曲线,结合磨痕形貌分析了复合涂层的磨损机理。研究得出:低压冷喷涂可实现Al、Cr、Ni三种金属粉的共沉积,并获得致密、均匀的Al-Ni-xCr复合涂层。枝晶状Ni粉沉积率较高,Cr粉沉积率较低。含70 wt.%Cr的混粉涂层中,Cr含量约为31 wt.%。硬质颗粒Cr同时起到夯实涂层的作用,随着Cr含量增加,Al-Ni-xCr复合涂层的致密性提高。Al-Ni-xCr复合涂层的耐磨性能主要来自于Cr而非Ni,且与Cr含量有关。Al-Ni-70Cr复合涂层耐磨性最佳,磨损率仅为Al涂层的1/2。其优异的耐磨性归因于摩擦界面形成了稳定的、较硬的、含Cr量较高的复合氧化膜,抑制了磨损过程。

Reactive Processing and Mechanical Properties of Al/SiC_P Composite

The reactive process for Al/SiC P composite was studied. SiC particles were in situ coated by the exothermal reaction of SiC Ti powder compact in Al melt bath, and easily incorporated into Al melt. The detailed study was carried out to understand the microstructures of the reacted SiC particles. During the reaction and consequent mixing, the successive processes include in situ coating on the reacted SiC particles, coat dissolution and SiC P splitting. The tensile mechanical properties of 6013Al/SiC P composite processed by the present technology showed that the reacted SiC P considerably reinforced the 6013 matrix.

Using EIS to evaluate anti-corrosion properties of the SiC_p/5A06 aluminium MMC treated by cerium conversion coatings

This paper evaluated the protection effect of the cerium conversion coatings on the SiCp/5A06 Al composite and the 5A06 Al alloy.Electrochemical impedance spectroscopy(EIS) was employed to examine the variation of the electrochemical variables of the samples treated and immersed in 3.5% NaCl solution at 35 °C for 1 h,which showed the enhancement of charge transfer resistance(Rt) and coating film resistance(Rc),i.e.,the corrosion resistance of the conversion coated samples was improved.The best protection ef...