Infrared emissivity and corrosion-resistant property of maleic anhydride grafted ethylene-propylene-diene terpolymer (EPDM-g-MAH)/Cu coatings

Maleic anhydride grafted ethylene-propylene-diene terpolymer (EPDM-g-MAH) was prepared by grafting copolymerization method. Composite coatings with varied infrared emissivity were obtained by using copper (Cu) powder as inorganic pigments, either EPDM or EPDM-g-MAH as organic adhesive. The influences of the content of Cu powder and adhesive kinds on the infrared emissivity of the composite coatings were investigated. The as-prepared coatings were characterized by FTIR spectroscopy, infrared emissometer and SEM. The corrosion-resistant property of the coatings in aqueous 3.5 wt.% NaCl was assessed by the potentiodynamic polarization technique and electrochemical impedance spectroscopy (EIS). The results have shown that the interfacial interaction between EPDM and Cu is improved due to the MAH grafting on EPDM, benefiting from the compatibility of EPDM with Cu and the low porosity of EPDM/Cu coatings, which leads to the lower infrared emissivity and better corrosion-resistant property of the coatings.     

炭/炭复合材料表面SiC/ZrSiO4-SiO2复合涂层的抗氧化性能与红外发射特性研究

为提高炭/炭(C/C)复合材料的高温抗氧化性能并降低其红外发射率,采用包埋–刷涂法在其表面制备了SiC/ZrSiO_4-SiO_2复合涂层。借助XRD、SEM等表征分析了涂层的成分与微观结构,并研究了SiC/ZrSiO_4-SiO_2复合涂层包覆C/C复合材料在1500℃动态空气条件下的抗氧化性能,以及在90和500℃下的红外发射率。结果表明:由疏松结构SiC内涂层和镶嵌结构ZrSiO_4-SiO_2外涂层组成的SiC/ZrSiO_4-SiO_2复合涂层具有优异的抗氧化性能,在1500℃流动空气(0.6 L/min)等温氧化条件下氧化50 h后试样的氧化失重率仅为0.03%。在C/C复合材料表面制备SiC/ZrSiO_4-SiO_2复合涂层后其红外发射率明显降低,并随温度升高而越低。复合涂层包覆试样在90℃时3~5μm和8~14μm波段的平均红外发射率分别为0.55和0.66;在500℃时3~5μm和8~14μm波段的平均红外发射率分别为0.48和0.62。SiC/ZrSiO_4-SiO_2复合涂层包覆C/C复合材料可作为优良的低红外发射率高温热结构材料应用于航空航天领域。     

Preparation and characteristics of thermal resistance polysiloxane/Al composite coatings with low infrared emissivity

The electrochemical hydrogen permeation tests were applied to determine permeability and the effective diffusivity of hydrogen in a plastically deformed FeAl-based alloy. The experimental results reveal that both the hydrogen permeation rate and effective diffusion coefficient are reduced with the increase in plastic working degree. Structural defects induced by preliminary deformation are the main retardation factor for hydrogen transport in iron aluminides.     

Hierarchical nanoporous metal/BMG composite rods with excellent mechanical properties

Hierarchical nanoporous structured NPC/BMG composite rods (NPC/BMG: nanoporous copper/bulk metallic glass) were facilely fabricated by one-pot chemical dealloying the Cu₅₀Zr₄₅Al₅ BMG rods in 0.05 M HF solution for 24 h. The cross-sectional SEM images illustrate that the NPC/BMG composite rods exhibit the perfect combination of inner rod-shaped Cu-Zr-Al amorphous phase core and outer tube-shaped NPC layer with a thickness of 85 μm. As compared to the reported NPC composites, the new composite rods demonstrate remarkable enhanced mechanical properties with an ultrahigh strength of 1500 MPa and a large compression strain of 2.9%. Additionally, the increase in the compression strain is attributed to the formation of the buffer deformation zone resulting from the existence of the outer nanoporous copper tube.     

Electrodeposition and characterization of Ni-Co/SiC nanocomposite coatings

Ni-Co/SiC nanocomposite coatings were electrodeposited in a modified watt type of Ni-Co bath containing 20 nm SiC particles to be codeposited. Potentiodynamic polarization tests were conducted to study the effect of the SiC particulates on the electrodeposition of Ni and Co. Scanning electron microscopy was used to assess the morphology of the Ni-Co alloy and Ni-Co/SiC nanocomposite coatings. The distribution of the particulates in the matrix was considered by means of transmission electron microscopy. Applying nanomechanical testing instruments coupled to atomic force microscopy, mechanical properties of the alloy and composite coatings were studied and compared. The presence of 11 vol.% SiC in the Ni-Co matrix increased hardness more than 60%. The average depth of scratch in the mentioned composite coating was about 15% less than that of the Ni-Co alloy coating. The corrosion penetration rate (CPR) of the Ni-Co alloy coating in a 3.5 wt.% NaCl solution was more than 17 times greater than that of the Ni-Co/SiC coating with 30.5 vol.% SiC.     

Corrosion resistance and mechanical properties of pulse electrodeposited Ni–TiO2 composite coating for sintered NdFeB magnet

Ni–TiO₂ composite coating which was prepared under pulse current conditions was successfully performed on sintered NdFeB magnet. As a comparison, pure nickel coating was also prepared. The phase structure, the surface morphology, the chemical composition, the anti-corrosion performance of the coatings for magnets, the microhardness and the wearing resistance performance of the coatings were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), electrochemical technique, Vickers hardness tester and ball-on-disc tribometer, respectively. The results revealed that Ni–TiO₂ composite coating provided excellent anti-corrosion performance for the magnets, and showed higher microhardness and better anti-wear performance.     

Corrosion behaviour of Mg/Al alloys with composite coatings

The corrosion behaviour of aluminium/silicon carbide (Al/SiC) composite coatings deposited by thermal spray on AZ31, AZ80 and AZ91D magnesium-aluminium alloys was investigated by electrochemical and gravimetric measurements in 3.5 wt.% NaCl solution at 22 °C. Corrosion products were examined by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and low-angle X-ray diffraction (XRD). Al/SiC composite coatings in the as-sprayed state revealed high level of porosity with poor bonding at the Al/SiC and coating/substrate interfaces, which facilitated degradation of the magnesium substrates by a mechanism of galvanic corrosion. Cold-pressing post-treatment produced more compact coatings with improved corrosion performance in 3.5 wt.% NaCl compared with as-sprayed coatings.     

高发射率金属氧化物涂料的制备与性能

以改性粘结剂、Cr2O3、MnO2为主要原料,辅以ZrSiO4、Fe2O3、MgO等多种氧化物,分别在950、1100和1250℃下保温2 h,水淬急冷出料,然后采用高温熔烧法在不锈钢表面制备高发射率涂层。采用X射线衍射仪、扫描电镜、红外辐射测量仪对涂料样品物相、形貌和辐射性能进行了测试表征,并测试了涂层抗热震性能。结果表明:不同温度下煅烧生成不同的尖晶石结构,1250℃煅烧后生成多种复杂尖晶石及其固溶体结构,表现出最佳的红外辐射性能,在1～22μm波段法向发射率可达0.90;涂层试样的抗热震次数可达25次(室温至800℃),表明涂层结合强度较高。     

Electrodeposition and properties of Zn–Ni–CNT composite coatings

Zn–Ni–CNT composite coatings were prepared by electrodeposition from a sulphate bath. The effect of CNTs on the corrosion behavior, wear resistance and hardness of the composite coatings was investigated. Their corrosion properties were evaluated by polarization, impedance, weight loss and salt spray tests. The CNT particles inclusion improved the corrosion resistance, hardness and wear resistance of the coating. The grain size of the composite coating was smaller than that of a pure Zn–Ni coating with the same Zn/Ni ratio. Scanning electron microscope images and X-ray diffraction patterns of coating revealed its fine-grain nature.     

The effects of parameters on the mechanical properties of Ni-based coatings prepared by automatic brush plating technology

The pure nickel coatings were prepared by using a newly developed automatic brush plating system. The microstructure of the coatings was characterized using SEM and the crystalline size of the coatings was determined by XRD based on Scherrer's formula. The hardness, elastic modulus and wear performance of the coatings were also investigated. The results showed that the microstructure and performance of the coatings were greatly affected by the processing parameters such as current density, relative motion and contact pressure. Pure nickel coatings prepared at lower current density possessed smoother, denser and more uniform microstructure, and exhibited higher microhardness, elastic modulus and better wear resistance. Pinholes were eliminated from the coatings when the relative speed exceeded a critical value. Coatings prepared at higher contact pressure were smoother and denser. However, high internal stress was generated and resulted in crack somewhere in the coating. The results presented here revealed that we can adjust the electrodepositon parameters properly to improve the mechanical and tribological properties of the coatings.     

Preparation,characterization and infrared emissivity properties of polymer derived coating formed on 304 steel

High infrared emissivity coatings were prepared on 304 steel by pyrolyzing reactions with poly(hydridomethylsiloxane) (PHMS) and Al/HW powders. The microstructure, phase and chemical composition of the coatings were determined by SEM, XRD and EDS techniques. The infrared emissive properties at wavelength 3–20 μm of the coatings pyrolyzed at 600 and 800 °C on the steels were investigated. It was found that the 800 °C pyrolyzed coating exhibited a slightly higher infrared emissivity value than that of the 600 °C pyrolyzed coating, which was attributed to the complete conversion of Al to Al₂O₃ and pyrolysis of PHMS into SiO₂, as well as the enhancement of photon emission by HW. Comparatively, the uncoated steel indicated a much lower infrared emissivity value about 0.2 in 8–14 μm.     

Co-electrodeposition and characterization of Cu-Si3N4 composite coatings

Smooth copper coatings containing well-distributed silicon nitride particles were obtained by co-electrodeposition in acidic sulfate bath. The cathodic current density did not show significant influence on incorporated particle volume fraction, whereas the increase of particle concentration in the bath led to its decrease. The increase of stirring rate increased the amount of embedded particles. The microhardness of the composite layers was higher than that of pure copper deposits obtained under the same conditions due to dispersion-strengthening and copper matrix grain refinement and increased with the increase of incorporated particle volume fraction. The microhardness of composites also increased with the increase of current density due to copper matrix grain refining. The composite coatings presented higher strength but lower ductility than pure copper layers. Pure copper and composite coatings showed the same corrosion resistance in 0.5 wt.% H₂SO₄ solution at room temperature.     

TEM study of TiN coatings fabricated by mechanical milling using vibration technique

A mechanical milling method was used for the deposition of TiN coatings. The principle of this method is that a substrate and powder were placed along with balls into the vibration chamber that was vibrated by a mechano-reactor. During mechanical milling process, the substrate surface was impacted by a large number of flying balls. The TiN particles trapped in between the balls and the substrate became cold welded to the surface. The repeated substrate-to-ball collisions forged TiN particles into a coating on the substrate surface. The process allowed the thick TiN coatings to be produced at room temperature in an ambient atmosphere. TEM study of the as-fabricated coatings was carried out. The coating formation depended on the size of the initial TiN particles. The 50-nm TiN nanoparticles were more easily cold welded than 1.5-μm microparticles. The nanoparticles had a tendency to consolidate and densify into the bulk material under the applied compressive loading. The TiN particles better consolidated and densified on the hard Ti surface than on the soft Al one.     

Corrosion properties of in situ laser remelted NiCrBSi coatings comparison with hard chromium coatings

This study aims at evaluating the effect of an in situ laser remelting treatment of NiCrBSi coatings, deposited by plasma spraying. Life Cycle Assessment (LCA) method was used to estimate the environmental impacts of coating processes. It was demonstrated with this LCA that the in situ remelting process was clean. Microstructural results were also evaluated. A good metallurgical bond was formed at the remelted coating interface. Scanning electron microscopy observation revealed also that laser treatment induces a change of the microstructure from lamellar to columnar dendritic. The dependence between the microstructure of NiCrBSi coatings, which was modified by laser treatment, and corrosion resistance has been evaluated by potentiodynamic polarization curves. Results show that, the corrosion resistance was increased because of a finer structure and higher densities of the coatings, but corrosion mechanisms occurring in all cases were different. From the electrochemical experiments in NaCl solution it can be deduced that laser remelting of as-sprayed coatings does not affect their corrosion rate. Corrosion evolves due to a progressive penetration of the electrolyte through the disturbed structure of the as-sprayed samples, whereas the substrate surface of remelted coating is not reached, because of a higher density. But ClMO intermediate species were formed on the surface, because Cl⁻ can destroy the protective film on the coating. The hybrid plasma/laser process was cleaner than hard chromium plating and its corrosion behavior is superior too.     

Preparation and characterization of Ni-P-nanoTiN electroless composite coatings

Ni-P-nanoTiN composite coatings were prepared successfully by electroless plating technique on AZ31 magnesium alloys. The composition, morphology, structure and phase transformation behaviour of the composite coatings were characterized respectively by using of scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD). The micro-hardness and wear resistance of the nano composite coatings, both in as-deposited and heat treated states, were investigated. The results demonstrated that the composite coatings, which contained nano TiN particles, exhibited much better properties in hardness and wear resistance than the conventional Ni-P coatings and original AZ31 magnesium alloys. These enhancements of properties are attributed to the nano TiN particles uniformly distributed in the Ni-P matrix.     

Structural evolution of the Ti–Al coatings produced by mechanical alloying technique

By means of the mechanical alloying (MA) method, the Ti + Al coatings were deposited on Ti alloy substrates. The structural formation of the Ti–Al coatings as a function of the milling time was studied. The thickness of coatings and their structure depended on the milling duration. At initial stage Al covered the Ti substrate. Then Ti particles were embedded in the Al matrix. Gradually the composite coating was formed. Greater plastic deformation led to the formation of the layered coating structure. Prolonged milling resulted in refinement of the particles into the nanometer scale near surface region of the Ti–Al coating.     

Effect of microstructure on the mechanical and corrosion behaviors of a hot-extruded nickel aluminum bronze

In this paper,the influence of microstructure on the corrosion behavior of a hotextruded nickel aluminum bronze was studied.Three kinds of samples subjected to the hot-extrusion,annealing and quenching conditions were prepared and immersion tests in 3.5% NaCl solution were carried out.Microstructures and corrosion surface morphologies of the samples were observed by SEM.It was found that the retained β martensite and(α+κⅢ) lamella eutectoid in the as hot-extruded material were eliminated after annealing,and...     

石英光纤表面Cu-石墨烯复合镀层的性能研究

为制备耐高温、寿命长的金属镀层光纤,利用化学镀技术在石英光纤表面制备Cu基镀层.同时将石墨烯片层材料引入镀液,制备了Cu-石墨烯复合镀层.采用扫描电镜(SEM)、能谱仪(EDS)、X射线光电子能谱仪(XPS)、Raman光谱仪等,对石墨烯片层和Cu基镀层的微观形貌进行表征.利用电化学工作站、纳米压痕仪等对金属镀层的性能...     

Structural and mechanical properties of AlTiN/CrN coatings synthesized by a cathodic-arc deposition process

Monolayered AlTiN and Multilayered AlTiN/CrN coatings were synthesized by a cathodic-arc deposition process, using TiAl (with 50/50 and 33/67 at.%) and Cr elemental cathodes. The atomic ratio of Al/(Ti + Al) in the AlTiN coatings was reduced to 0.44 and 0.61, respectively, compared with the corresponding Ti₅₀Al₅₀ and Ti₃₃Al₆₇ cathode materials. The multilayered AlTiN/CrN films showed smaller crystallite size, larger lattice strain, higher hardness, higher residual stress, and better adhesion strength as well than the monolayered AlTi films. The multilayered Al_0.35Ti_0.22N_0.43/CrN coating exhibited the highest hardness of about 38 GPa and the highest H³/E*² ratio value of 0.188 GPa, indicating the best resistance to plastic deformation, among all the coatings studied.     

Corrosion and mechanical properties of duplex-treated 301 stainless steel

Plasma nitriding is a widely used technique for increasing the surface hardness of stainless steels, and consequently, for improving their tribological properties. It is also used to create an interface between soft stainless steel substrates and hard coatings to improve adhesion. This paper reports on the mechanical and corrosion properties of AISI301 stainless steel (SS) after a duplex treatment consisting of plasma nitriding followed by deposition of Cr bond coat and CrSiN top layer by magnetron sputtering. Mechanical properties of the deposited films, such as hardness (H) and reduced Young's modulus (E_r), were measured using depth-sensing indentation. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were carried out to evaluate resistance to localized and to general corrosion, respectively. The corrosion behavior has been correlated with the microstructure and composition of the surface layers, determined by complementary characterization techniques, including XRD, SEM, and EDS. The CrSiN layers exhibited an H value of 24 GPa, whereas the nitrided layer was shown to present a gradual increase of H from 5 GPa (in the nitrogen-free SS matrix) to almost 14 GPa at the surface. The electrochemical measurements showed that the nitriding temperature is a critical parameter for defining the corrosion properties of the duplex-treated SS. At a relatively high temperature (723 K), the nitrided layer exhibited poor corrosion resistance due to the precipitation of chromium nitride compounds and the depletion of Cr in the iron matrix. This, in turn, leads to poor corrosion performance of the duplex-treated SS since pores and defects in the CrSiN film were potential sites for pitting. At relatively low nitriding temperature (573 K), the nitrided interface exhibited excellent corrosion resistance due to the formation of a compound-free diffusion layer. This is found to favor passivation of the material at the electrode/electrolyte interface of the duplex-treated SS.