Effect of SiC/nano‐CeO2 on wear resistance and microstructures of Ti3Al/γ‐Ni matrix laser‐cladded composite coating on Ti–6Al–4V alloy

The Ti–6Al–4V alloy is an important aviation material, but has a poor resistance to slide wear. Laser cladding of the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ + SiC/nano‐CeO₂ preplaced powders on the Ti–6Al–4V alloy can form the Ti₃Al/γ‐Ni matrix composite coating, which improves the wear resistance of the substrate. In this study, the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ + SiC/nano‐CeO₂ laser‐cladded coating was researched by means of X‐ray diffraction, scanning electron microscopy, and energy dispersive spectrometry. The experimental results indicate that under the action of SiC/nano‐CeO₂, this composite coating exhibited a fine microstructure. Furthermore, the proper content of nano‐CeO₂ decreased the crack tendency. The results above indicated that, it is feasible to improve the tribological property of the Al₃Ti + Ni/Cr/C + TiB₂/Al₂O₃ laser‐cladded coating by adding of SiC/nano‐CeO₂. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface modification of titanium alloy with the Ti3Al + TiB2/TiN composite coatings

Laser cladding of the Ti₃Al + TiB₂ pre‐placed alloy powder on the Ti–6Al–4 V alloy in nitrogen protective atmosphere can form the Ti₃Al + TiB₂/TiN composite coating, which can dramatically improve the wear resistance of the Ti–6Al–4 V alloy surface. In this study, the Ti₃Al + TiB₂/TiN composite coatings on the Ti–6Al–4 V alloy have been researched by means of X‐ray diffraction, SEM and energy dispersive spectrometry. It was found that there is a metallurgical combination between the Ti₃Al + TiB₂/TiN composite coating and the substrate. The microhardness of the Ti₃Al + TiB₂/TiN composite coatings were 3 ~ 4 times higher than that of the Ti–6Al–4 V alloy because of the actions of the Ti₃Al + TiB₂/TiN hard phases and the grain refinement strengthening. Moreover, the wear mass losses of the Ti₃Al + TiB₂/TiN composite coatings were much lower than that of the substrate. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and properties of Ni–Co–P/nano‐sized Si3N4 electroless composite coatings

Ni–Co–P/nano‐sized Si₃N₄ composite coating was successfully fabricated on aluminum alloys by electroless plating in this work. The surface and cross‐sectional morphologies, composition, microstructure, microhardness, friction and wear behavior of deposits were investigated with SEM, EDS, XRD, Vickers hardness and high‐speed reciprocating friction, respectively. It was found that a Ni–Co–P/nano‐sized Si₃N₄ composite coating on aluminum alloy substrate is uniform and compact. The existence of nano‐sized Si₃N₄ particles in the Ni–Co–P alloy matrix causes a rougher surface with a granular appearance, and increases the microhardness but decreases the friction coefficients and wear rate of electroless coatings. Meanwhile, the effects of heat treatment at 200, 300, 400 and 500 °C for 1 h on the hardness and tribological properties were researched. It is revealed that both of the microhardness and tribological properties of Ni–Co–P coatings and Ni–Co–P/Si₃N₄ composite coatings increase with the increase of heating temperature in the range of 200–400 °C, but show different behavior for the two coatings after annealing at 500 °C. Copyright © 2011 John Wiley & Sons, Ltd.     

Grey relational analysis for optimization of wear parameters and surface roughness on nano composite coating

The higher wear resistance of Ni based nano composite coatings makes them potential replacement in protecting the substrate materials. The role of surface roughness of the coating along with wear parameters on the specific wear rate, pin temperature, and COF are addressed in the present study. The use of hard nano Al₂O₃ particles found significant role in increasing the resistance to wear for Ni matrix coatings on Al6061 material. The resistance to dislocation offered by these nano Al₂O₃ particles and smear out of debris with plastic deformation indicated abrasive and adhesive nature of wear mechanism in combination. The optimization of wear parameters are carried out by surface response method based grey relation analysis. The normal load applied onto the pin has significant influence on the specific wear rate and temperature rise in the pin. The surface roughness of the coating has also found instrumental in the higher pin temperature and friction coefficient.     

Protective yttria coatings of melting crucible for metallic fuel slugs

As one of the candidate coating materials for a melting crucible, yttrium oxides were deposited on graphite and niobium substrates using slurry and plasma spraying methods. Thermal cycling tests and interaction studies between U–Zr/U–Zr–RE fuel melt and the Y₂O₃ coatings were carried out to evaluate the performance as reusable coatings for a melting crucible. A multi‐layer coating method was also applied to overcome the issue of a thermal expansion mismatch between the coating and substrate. The results showed that the plasma‐sprayed coatings showed a good consolidation after deposition compared to slurry coating. The plasma‐sprayed Y₂O₃ coating on the niobium substrate showed better thermal cycling resistance than those coated on a graphite substrate. The proposed TaC/Y₂O₃ double‐layer coating which was plasma‐sprayed on the niobium substrate showed improved characteristics with no reaction layer formation and no separation from the substrate after the interaction with the U–Zr–RE melt. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and properties of iron oxide coated carbon nanotubes hybrid materials and their use in epoxy coatings

Multi‐walled carbon nanotubes (MWCNTs) were acidified with nitration mixture, and the Fe₂O₃‐MWCNTs (iron oxide coated multi‐walled carbon nanotubes) hybrid material via sol‐gel method then verified the results through scanning electron microscope, X‐ray diffraction, and thermal gravimetric analysis. We modified the hybrid material with silane coupling agent (KH560), Fe₂O₃‐MWCNTs/epoxy, MWCNTs/epoxy composites coating, and the pure epoxy coatings were respectively prepared. The properties of the composite coatings were tested through the electrochemical workstation (electrochemical impedance spectroscopy), shock experiments, and thermal gravimetric analysis. Finally, we used scanning electron microscope to observe the surface conditions of the coatings. The results show that Fe₂O₃‐MWCNTs have good dispersion in the epoxy resin, and the Fe₂O₃‐MWCNTs/epoxy composite coatings have enhanced mechanical properties and corrosion resistance. Copyright © 2015 John Wiley & Sons, Ltd.     

Zn–HA–TiO2 nanocomposite coatings electrodeposited on a NiTi shape memory alloy

In this work, zinc–hydroxyapatite (Zn–HA) and zinc–hydroxyapatite–titania (Zn–HA–TiO₂) nanocomposite coatings were electrodeposited onto a NiTi shape memory alloy, using a chloride zinc plating bath. The structure of the composite coatings was characterized by X‐ray diffraction, scanning electron microscopy and high‐resolution transmission electron microscopy. According to the results, the Zn–HA–TiO₂ coating exhibited a plate‐like surface morphology, where the addition of the nanoparticles caused to an increase in roughness. It was also found that due to applying a proper stirring procedure during co‐deposition, a homogenous dispersion of the nanoparticles in the coatings was achieved. Also, the addition of the TiO₂ nanoparticles to the Zn–HA–TiO₂ coating enhanced the microhardness and wear resistance. Copyright © 2014 John Wiley & Sons, Ltd.     

Nano-crystalline zirconia: a viable adsorbent for the column chromatographic separation of 58Co from neutron irradiated nickel targets

Owing to the high chemical reactivity of molten uranium alloys, the use of traditional graphite crucibles for casting fuel slugs for a sodium-cooled fast reactor (SFR) is problematic. Moreover, rare earth (RE) elements retained in the fuel slugs for an SFR, which are extracted from the spent fuel by pyro-processing, are more reactive than uranium melt. Therefore, in this study, Y₂O₃ single-layer coatings with thicknesses of approximately 50, 70, and 120 μm and double-layer coatings of TaC/Y₂O₃ and Y₂O₃/TaC were plasma-sprayed onto niobium substrates and tested for thermal shock resistance and compatibility against U–10 wt% Zr and U–10 wt% Zr–5 wt% RE melt. The Y₂O₃ single-layer coating, regardless of coating thickness, and the TaC/Y₂O₃ double-layer coating showed good contact at the interface between the coating and the niobium substrate, with no deterioration after the thermal cycling test. In the interaction studies, the single- and double-layer coatings showed good compatibility with the U–Zr melt. However, the Y₂O₃ coatings with thicknesses of approximately 50 and 70 μm showed severe penetration of the U–Zr–RE melt and reacted with the niobium substrate. The single-layer Y₂O₃ coating with a thickness of 120 μm and the double-layer TaC/Y₂O₃ coating exhibited the most promising performance among the candidate coatings.     

Impact of Al nanoparticles upon the microstructure and wear properties of Ni-Cr-Al nanocomposite coatings

Ni–7Cr and Ni–7Cr–2Al (wt.%) nanocomposite coatings were fabricated by co-electrodeposition of Ni with Cr (40 nm) or and Al (75 nm) nanoparticles from a nickel sulfate bath, their microstructure, friction and wear performance were comparably evaluated in order to elucidate the effect of Al nanoparticles on the properties of nanocomposite coatings. The results indicated that the co-deposition of minor Al nanoparticles significantly increases the microhardness and wear resistance because Al nanoparticles with surface amorphous oxides layers exert the dispersion-strengthening effect like Al₂O₃ nanoparticles.     

Conversion‐coating treatment applied to in situ TiB2p reinforced Al?Si‐alloy composite for corrosion protection

In this work, continuous conversion coatings on the surface of in situ TiB₂ particulate reinforced A356 composite were formed successfully by cerium surface treatment for the first time. Scanning electron microscope (SEM) analysis showed that the conversion coatings were inhomogeneous and could be divided into two types of regions, namely, fine crack region and noncrack region. Many cerium‐rich nano‐nodules were uniformly distributed in the whole coatings. Energy dispersive spectroscopy (EDS) analysis testified that the crack coatings mainly covered the interdendritic sites occupied by TiB₂ particulates and Si phases. X‐ray photoelectron spectroscopy (XPS) analysis indicated that the conversion coatings were composed of CeO₂, Ce₂O₃, Ce(OH)₄, Ce(OH)₃, and a little amount of Al₂O₃. The electrochemical polarization tests showed that the cerium‐conversion treatment markedly improved the corrosion resistance of in situ TiB_2p/A356 composite in chloride environment, and the protection degree of the coatings was superior to that of conventional chromate‐conversion coating. According to these results, the formation mechanism of cerium‐conversion coatings was discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrodeposition and characterization of Cu-TiO2 nanocomposite coatings

Cu-TiO₂ nanocomposites were prepared by electrodeposition method onto copper substrate using an acid copper plating bath containing dispersed nanosized TiO₂. The composition of codeposited TiO₂ nanoparticles in the composite coatings was controlled by the addition of different concentrations of TiO₂ nanoparticles in the bath solution. The average crystallite size was calculated by using X-ray diffraction analysis and it was ~32 nm for electrodeposited copper and ~33 nm for Cu-TiO₂ composite coatings. The crystallite structure was fcc for electrodeposited copper and Cu-TiO₂ nanocomposite coatings. The surface morphology and composition of the nanocomposites were examined by scanning electron microscopy and energy dispersive X-ray spectroscopy analysis. The effect of TiO₂ content on the corrosion and wear resistance properties of the nanocomposite coatings was also presented. The codeposited TiO₂ nanoparticles in the deposit increased the corrosion and wear resistance, which were closely related with TiO₂ content in the nanocomposites. The wear resistance and microhardness of the Cu-TiO₂ nanocomposite coatings were higher than electrodeposited copper. The corrosion resistance property of the electrodeposited copper and Cu-TiO₂ nanocomposite coatings was evaluated by electrochemical impedance and Tafel polarization studies. Cu-TiO₂ composite coatings were more corrosion resistant than electrodeposited copper.     

Formation and Mechanical Properties of CoNiCuFeCr High-Entropy Alloys Coatings Prepared by Plasma Transferred Arc Cladding Process

Plasma transferred arc cladding process was used to fabricate CoNiCuFeCr multi-element alloys coatings. The experimental results show that the coating forms a face-centered-cubic solid solution phase. The microstructure of the coating is mainly composed of dendrite and discontinuous interdendritic segregation. The average hardness of the coating reaches 194.8 HV₁₀₀. The nano-indentation testing indicates that the micro-hardness and elastic modulus of the coating are 3.64 GPa and 211 GPa, respectively. The CoNiCuFeCr high-entropy alloy coating has excellent wear and corrosion resistance. The wear resistance of the coating is about 1.7 times higher than that of Q235 steel substrate under the same wet sand rubber wheel abrasion testing conditions. In 1N hydrochloric acid solution, the coating presents lower i _corr values in polarization curves and higher fitted R _f values in EIS plots than that of as-cast 304 stainless steel.     

A novel spinel coating on cobalt‐based Superalloy GH605 via an in‐situ oxidation approach

Cr‐Mn‐O spinel coating was prepared on the surface of cobalt‐based superalloy GH605 via an in‐situ oxidation method in H₂O‐H₂ environment. The composition, morphology, and chemical value state of the oxide spinel coatings were investigated by SEM, EDS, XRD, Raman spectra, and XPS. It indicated that the morphology of coating varied with oxidation temperature, and granular surface appeared when oxidation temperature increased to 1100°C. The formed Cr‐Mn‐O spinel coating was composed of Cr₂O₃ and MnCr₂O₄, and the thickness increased significantly with oxidation temperature. In the coating, Cr element existed in the state of Cr³⁺ ions and Cr⁶⁺ ions, while Mn element only existed in the form of Mn²⁺ ions.     

Fabrication,morphology and mechanical properties of Al2O3–Al graded coatings on China low activation martensitic steel substrates

Al₂O₃, Al₂O₃/Al and Al₂O₃–Al graded coatings were fabricated on China low activation martensitic steel and silicon substrates by RF magnetron sputtering. The coating composition and cross‐section morphologies were investigated using X‐ray photoelectron spectroscopy, Auger electron spectroscopy and field‐emission scanning electron microscopy. The mechanical properties of the coatings were studied using nanoindentation, wafer‐curvature measurements and microscratch tests. The results show that usable Al₂O₃–Al graded coatings could be fabricated. With a more continuous compositional gradient, the interface zone was more compact. The hardness and elastic modulus of Al₂O₃–Al graded coatings were less than those of Al₂O₃ coatings, but greater than those of Al₂O₃/Al coatings. After annealing at 773 K for 3 h, the hardness of Al₂O₃–Al graded coating showed a small increase. The residual stresses in Al₂O₃–Al graded coatings declined to about 0.3 GPa, compared with the 6.6 GPa for Al₂O₃ coating. The adhesion of Al₂O₃ was improved by deposition of Al or Al compositional gradient oxide layers. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrophysical properties of Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>2 − δ</Subscript> + <Emphasis Type="Italic">x</Emphasis> mol % Al<Subscript>2</Subscript>O<Subscript>3</Subscript> solid composite electrolytes

The influence of aluminum and cobalt oxides on the microstructure and the mechanical, electrical, and optical properties of the Ce_0.8Gd_0.2O_2−δ solid electrolyte was studied. Using nanosized Al₂O₃ in the synthesis allowed it to be uniformly distributed in the composite electrolyte and improved the microhardness of the resulting ceramics. The introduction of cobalt oxide made it possible to lower the synthesis temperature during the preparation of gasproof ceramics and hindered, to a certain extent, the formation of the GdAlO₃ phase during synthesis. Using the standard set of investigation methods allowed us to find solutions to several problems in using this electrolyte for solid-oxide fuel cells (SOFCs).     

Deposition and characterization of TiAlSiN coatings prepared by hybrid PVD coating system

TiAlSiN coatings with different Si contents were deposited on silicon and high‐temperature alloy by using a hybrid physical vapor deposition coating system, where the cathodic arc ion plating was combined with a twin target mid‐frequency magnetron sputtering. The chemical composition, microstructure, cross‐sectional structure and morphology were carried out by X‐ray photoelectron spectroscope (XPS), X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM), respectively. NanoTest 600 nanomechanical system and ball‐on‐disc friction tester were used to investigate the mechanical and friction properties of TiAlSiN coatings. The worn surface of the TiAlSiN coatings and counterballs were investigated by means of surface profilometer and optical microscope. The wear rates were also measured by surface profilometer. The results showed that the Si addition did not change the coatings growth orientation, and the coating transfered into amorphous phase when the Si content reached about 13.9 at.%. The tribological properties and the hardness were improved by solid solution of Si atoms and grain boundary strengthening of SiN_x amorphous phase with moderate Si content addition. In addition, the SiNx amorphous phase improved oxidation resistance of TiAlN coating, but with a high Si content (more than 8.3 at.% in this work) the agglomeration of SiN_x amorphous phase would reduce the mechanical properties and oxidation resistance of the coating. Copyright © 2014 John Wiley & Sons, Ltd.     

Fabrication of Fe3O4@SiO2 nanocomposites to enhance anticorrosion performance of epoxy coatings

SiO₂‐coated Fe₃O₄ (Fe₃O₄@SiO₂) nanocomposites were prepared by sol–gel method, and the anticorrosion performance of composite coatings was discussed. The structure of the Fe₃O₄@SiO₂ nanocomposites was verified through Fourier transform infrared, X‐ray diffraction, and scanning electron microscopy. Composite epoxy coatings with same concentrations of Fe₃O₄ and Fe₃O₄@SiO₂ were measured by scanning electron microscopy contact angle meter. More importantly, the Fe₃O₄@SiO₂ nanocomposites not only obtained a homogeneous dispersion and compatibility in epoxy resin but also exhibited an obvious superiority in enhancing the anticorrosion performance of epoxy coatings. Furthermore, the anticorrosion mechanism of Fe₃O₄@SiO₂/epoxy composite coating was tentatively discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

The formation mechanism and biocorrosion property of CaSiO3/CaHPO4 · 2H2O composite conversion coating on the extruded Mg‐Zn‐Ca alloy for bone implant application·

In this work, a calcium silicate and calcium phosphate (CaSiO₃/CaHPO₄ · 2H₂O) composite coating was applied by a chemical reaction to an extruded Mg‐Zn‐Ca magnesium alloy. SEM observation showed that a flat and sand‐like conversion coating was formed. X‐ray diffractometer (XRD) analysis indicated that the conversion coating was composed of CaHPO₄ · 2H₂O and a little amount of CaSiO₃. The formation mechanism of CaSiO₃/CaHPO₄ · 2H₂O composite conversion coatings was discussed. The electrochemical polarization tests showed that the conversion coating markedly improved the biocorrosion resistance of Mg‐Zn‐Ca alloy in Hank's solution. Copyright © 2010 John Wiley & Sons, Ltd.     

Composite Copper-Based Coatings with Ultradispersed Phase

The electrolytic deposition of composite copper-based coatings with an ultradispersed phase(TiN or Al₂O₃) was studied. Conditions for obtaining coatings with the maximum microhardness were determined.     

Anchoring calcium carbonate on graphene oxide reinforced with anticorrosive properties of composite epoxy coatings

Calcium carbonate nanoparticles (nano‐CaCO₃) anchored graphene oxide (GO) sheet nanohybrids (GO‐CaCO₃) are fabricated, and their structure can be measured by scanning electron microscope, transmission electron microscopy, X‐ray photoelectron spectroscopy, X‐ray diffraction and Fourier‐transform infrared spectroscopy analysis. Afterwards, composite epoxy coatings, filled with GO and GO‐CaCO₃ nanohybrids, are prepared via a curing process. The dispersion and anticorrosive properties of composite epoxy coatings are investigated. The results reveal that GO‐CaCO₃ nanohybrids achieve a homogeneous dispersion as well as reinforce corrosion resistance of epoxy coatings. Furthermore, the anticorrosive mechanisms are tentatively proposed for the GO‐CaCO₃/epoxy coatings. Copyright © 2016 John Wiley & Sons, Ltd.