Electroless plating was employed for making copper (Cu)-high density polyethylene (HDPE) core-shell particles for following coating deposition by flame spraying. Our previous works already reported large-scale fabrication of HDPE/Cu composite coatings against corrosion, biofouling and ageing for marine applications. In this work, we further investigated tribological behaviours of the HDPE and the HDPE/Cu composite coatings. The structure of the composite coatings was designed via controlling the thickness of the copper shell coated on the composite powder. The result shows that the addition of copper slightly decreased the anti-wear property of the composite coating. The tribology mechanisms of the composite coating and the HDPE coating were discussed.

There have been increasing demands for adequate gas sensors to monitor O 3 , a respiratory irritant gas associated with a spectrum of adverse health events. Here we report film construction by liquid flame spray route and characterization of nanostructured WO 3 -reduced graphene oxide (rGO) composites and their gas-sensing activities to O 3 . The starting feedstock was prepared from WCl 6 and rGO for pyrolysis synthesis by flame spray. Nanosized WO 3 grains exhibited oriented nucleation on rGO flakes and rGO retained intact nano-structural features after the spraying. Constrained grain growth of WO 3 was realized in the rGO-containing films with 60-70 nm size as compared to ~220 nm in the pure WO 3 film. The WO 3 -rGO film sensors showed quicker response to O 3 and faster recovery than the rGO-free WO 3 film sensors. Addition of rGO in 1.0wt.% or 3.0wt.% in the films caused significantly reduced effective working temperature of the film sensors from ~250°C to ~150°C. These results might shed some light on liquid flame spray fabrication of novel functional nanocomposites for gas-sensing applications.

Polyimide-copper layers consisting of individual capsule-like splats were one-step fabricated by solution precursor flame spray through controlling the reaction between dianhydride and diamine dissolved in copper nanoparticles containing dimethylformamide solvent. The polyimide splat exhibited hollow structure with an inner pore of 10-15 µm and a tiny hole of 1-5 µm on its top surface. Transversal cut by focused ion beam milling of the individual splats and scanning electron microscopy characterization further revealed unique dispersion of the copper nanoparticles inside the polyimide shell. After 1000 h exposure to the testing synthetic seawater, continuous release of copper from the coatings containing up to 30wt.%Cu kept remarkable. Antifouling performances of the constructed layers were assessed by examining colonization behaviors of typical bacteria Bacillus sp. and marine algae Phaeodactylum tricornutum and Chlorella on their surfaces. Distribution of the inorganic nanoparticles endows the polyimide coatings with special capsule structure and exciting hydrophobicity and antifouling performances. The liquid flame spray route and the encapsulated structure of the polyimide-Cu coatings would open a new window for designing and constructing environment-friendly marine antifouling layers for long-term applications.

Sub-micro-structured titanium nitrides (TiN) coatings on Al 2 O 3 substrates were fabricated by vacuum cold spray (VCS) process using ceramic powders, which were ball-milled at room temperature. The microstructure features and crystal structures of the VCS TiN coatings were analyzed by scanning electron microscopy and X-ray diffraction. The adhesion between the coating and the substrate was evaluated with a scratch tester. The sheet resistance of the VCS TiN coatings was measured by using a four-point probe method. The effects of nozzle traverse speed on the microstructure, adhesion to substrate and electrical properties of the coatings were investigated. It was found that the adhesion improves greatly with the nozzle traverse speed increasing from 5 to 15mm/s, and the electrical resistivity levels of the coatings is decreased significantly. The resistivity of sub-micron-structured TiN coatings is substantially lower than those of nano-structured ones fabricated by the same VCS process. And a minimum resistivity of 1.16×10 -4 Ω·m is achieved.

A Fe48Cr15Mo14C15B6Y2 alloy with high glass forming ability (GFA) was selected to prepare amorphous metallic coatings by atmospheric plasma spraying (APS) process. The as-deposited coatings present a dense layered structure and low porosity. Microstructural studies show that some nanocrystals and a fraction of yttrium oxides formed during spraying process, which induced the amorphous fraction of the coatings decreasing to 69% compared with fully amorphous alloy ribbons of the same component. High thermal stability employs the amorphous coatings to work below 910K temperature without crystallization. Corrosion behavior of the amorphous coating was investigated by electrochemical measurement. The results show that the coatings exhibit extremely wide passive region and low passive current density in 3.5% NaCl and 1mol/L HCl solutions, which illustrate their superior ability to resist localized corrosion. Moreover, the corrosion behavior of the amorphous coatings in 1mol/L H 2 SO 4 solution is similar to their performance in chlorine ions contained conditions, which manifests their flexible and extensive ability to withstand aggressive environments.

In this investigation, bioactive ceramic materials, including dicalcium silicate, titania, and zirconia, were deposited on titanium substrates by plasma spraying in order to determine their effect on the bioactivity of metal implants. Cell-seeding tests show that MG63 osteoblast-like cells grow and proliferate well on each of the coating materials. In the case of Ca 2 SiO 4 , the presence of silicon ions is thought to be the key to this behavior. In regard to TiO 2 and ZrO 2 , the bioactivity is thought to result from the nanostructured surfaces and special surface compositions.

Yttria stabilized zirconia coatings (YSZ) have received great attention as a good candidate for thermal barrier coatings (TBCs). However, the grain growth and phase transformation, within applied coatings particularly under temperatures higher than 1473 K limit its further applications to great extent. In our present study, in order to develop better understanding of aforementioned phenomena and explore effective methods to conquer this challenge, TBCs using traditional and La 2 O 3 modified YSZ powders were deposited by atmospheric plasma spraying and their microstructures were investigated. Results show that the La 2 O 3 addition can effectively alleviate the grain growth of coatings under high temperature.

The microstructure of thermally sprayed ceramic coatings is characterized by the existence of various pores and microcracks. The porous microstructure makes coating desirable for thermal insulation, but this unique microstructural feature also gives rise to anelastic response under tension and compression loads. Detail investigations of curvature measurements of ceramic coated substrate indicate the coatings to exhibit anelastic behavior composed of nonlinear and hysteresis characteristics. In this paper, the mechanisms of such behaviors were studied from curvature-temperature measurements and finite element analysis through modeling the microstructure of yttria stabilized zirconia (YSZ) coating. Computational models contain numerous randomly distributed pores and microcracks with various sizes, aspect ratios, locations and orientations. The effects of such attributes of pores and microcracks on coating anelastic behavior were studied by simulations of curvature change during thermal cycles.

Over the last decade there has been an explosion in terms of available tools for sensing the particle spray stream during thermal spray processes. This has led to considerable enhancement in our understanding of process reproducibility and process reliability. However, in spite of these advances, the linkage to coating properties has continued to be an enigma. This is partially due to the complex nature of the build-up process and the associated issues with measuring properties of these complex coatings. In this paper, we present an integrated strategy, one that combines process sensing, with process modeling and extracting coating properties in situ through the development of robust and advanced curvature based techniques. These techniques allow estimation of coating modulus, residual stress and non-linear response of thermal sprayed ceramic coatings all within minutes of the deposition process. Finally, the integrated strategy examines the role of process maps for control of the spray stream as well as design of thermal spray coatings. Examples of such studies for both MCrAlY and YSZ coatings will be presented.

The delamination wear mechanism of the thermally sprayed coatings was studied by analyzing coatings structural feature and stress distribution on the warm surface, and the influencing factors on the delamination wear were discussed. And the delamination wear mode of coating was developed. The results show that, the thermally sprayed coatings have typical aspect of lamellar structure. There are oxide layers between splats, and there also exist porosity and micro-crack in the coatings. The coating surface was subjected to alternately tensile stress and compression stress caused by normal load and friction force during sliding. In a certain depth below the surface, there exists maximum shear stress. Therefore fatigue damage will take place at subsurface of the coating under alternate stress. The adhesion strength between splats of coating prepared by HVAS is by far lower than casting material because of lamellar structure. And the adhesion strength between splats is further weakened due to the defects (such as porosity and micro-crack) appearing mostly on the boundaries between thin oxide sheets and splats. When the fatigue damage accumulates to a certain value, micro-cracks initiate at the defects between splats. Then these micro-cracks grow, connect, and propagate along the defects between splats. Finally, these cracks shear to the coating surface leading to spallation of the splats, and thus wear debris is generated. By repeating the above process delamination of the coatings will occur. Reducing friction coefficient, increasing coatings hardness and adhesion strength between inter-splats are the basic methods to improve the wear resistance of thermally sprayed coatings. Abstract only; no full-text paper available.

Cored wires and high velocity arc spraying technique (HVAS) were applied to produce Zn-Al-Mg and Zn-Al-Mg-Re alloy coatings on low carbon steel substrates. And the effects of rare-earth metal on microstructure and corrosion resistance of the Zn-Al-Mg coating were investigated. The microstructures and mechanical properties were studied by SEM, EDS and XRD. The coatings show a typical aspect of layered thermal sprayed material structure. SEM results revealed that the addition of small amount of REM to the cored wires would result in a fine grained structure in the coating layer together with a dense microstructure, which is the reason for the adhesion strength enhancement and the porosity reducing of the coating. And the electrochemical corrosion mechanisms of the coatings were discussed. Chemical analysis of the coating indicated the composition to be Zn-16.5Al-5.9Mg-4.6O-RE (wt%). The phases of the coatings are Zn, Al 5 Mg 11 Zn 4 , MgZn 2 and Al 3 Mg 2 mainly, together with oxide ZnO, ZnAl 2 O 4 , and MgAl 2 O 4 . The electrochemical corrosion behaviors of Zn-Al-Mg-RE coating were investigated in 5%NaCl solution comparing with Zn-Al-Mg coating. Electrochemical measurements in the forms of potential-time and potentiodynamic polarization tests showed that such two coatings behaved excellent electrochemical corrosion resistance in salt solution, and the Zn-Al-Mg-RE coating was much more stable. Electrochemical impedance spectroscopy (EIS) results revealed that small amount of rare-earth metal can not promote to form the passive film but it could enhance the surface property of the coating extraordinarily, which will has a great effect on the corrosion behaviors of the coating. Keywords: Zn-Al-Mg-RE coating; high velocity arc spraying; cored wires; potentiodynamic polarization; electrochemical impedance spectroscopy

The effects from thermal shock loading on pre-existing microcracks within thermal barrier coatings (TBCs) have been investigated through a finite element based fracture mechanical analysis. The TBC system consists of a metallic bond coat and a ceramic top coat. The rough interface between the top and bond coats holds an alumina oxide layer. Stress concentrations at the interface due to the interface roughness as well as the effect of residual stresses were accounted for. At eventual closure between the crack surfaces, Coulomb friction was assumed. To judge the risk of fracture from edge cracks and centrally placed cracks, the stress intensity factors were continuously monitored during simulation of thermal shock loading of the TBC. It was found that fracture from edge cracks is more likely than from centrally placed cracks. It was also concluded that propagation of an edge crack is initiated already during the first load cycle whereas the crack tip position of a central crack determines whether or not propagation will occur.

Microcracks in thermal barrier coatings are inherent from the plasma spraying process. Such cracks might constitute a threat to the coating. The influence of pre-existing cracks in the global direction of the interface between the bond coat and the top coat on the risk of delamination is addressed through finite element simulations. Stress concentrations at the interface due to the roughness of the plasma sprayed bond coat are accounted for by a sinusoidal interface. The effect of oxidation of the bond coat is modelled by including a thin oxide layer between the ceramic coat and the bond coat. It was found that the crack tip position of pre-existing cracks, as well as the presence of an oxide layer, significantly influences the risk of delamination. As the oxide thickness increases, the risk of crack propagation increases. It is also found that not all pre-existing cracks can propagate. For some crack tip locations, the crack remains closed during the entire loading sequence.

To determine the effect of bond coat oxidation on the coating life, thermal shock testing were performed, using three different thermal cycles. The failure mode and crack paths were investigated in scanning electron microscope. A finite element model was developed to simulate the thermal shock tests. First, transient temperature fields during the thermal cycling were calculated. Second, stresses and strains evolving in the coatings due to thermal expansion mismatches and temperature gradients during the cycling were computed. The stress concentration at the interface due to the roughness of the bond coat was accounted for by using an ideal sinusoidal interface in the model. By adding an oxide layer with and without residual stresses to the model, the influence of the bond coat oxidation was determined. Both the experimental and numerical results revealed that the TBC failed by crack initiating in the ceramic top coat very close to the grown oxide layer at the interface followed by coating fatigue failure. Numerical simulation indicated that bond coat oxidation led to stress concentration at the peak of the asperity of the interface proceeding crack growth. It also showed that bond coat inelasticity and ceramic creep might further enhance the crack growth. There was little effect on coating behavior due to the residual stresses in the oxide layer.