In this work, liquid plasma spraying is used to deposit composite coatings for potential use as cathodes in intermediate-temperature solid oxide fuel cells. A suspension containing well-distributed Gd-doped ceria (GDC) nanoparticles in a lanthanum strontium cobalt ferrite precursor solution was used as the feedstock, and GDC concentration was varied to study its effect on phase composition, microstructure, surface morphology, and electrochemical performance. The results are presented and discussed.

This study investigates the relationship between in-flight particle characteristics, splat formation, and microstructure of CrMoBW-Fe base nanocomposite coatings produced by wire arc spraying. Focused ion beam milling was used to prepare transversal cross-sections of in-flight particles and splats for SE-SEM, EDS, and XRD analysis. The results show that particle size and splat morphology greatly influence the microstructure and properties of the coatings. In-flight particles were found to have a spherical shape with a broad size distribution ranging from 0.8 to 115 μm. The particles were well flattened on impact, resulting in flower-shaped splats with an average diameter of 100 μm. Splats were very thin with fine lamella structure, implying that the particles were fully melted at the time of impact.

Protective coatings with high wear, erosion and corrosion resistance are of great importance in many fields of application and in particular, in the electric power generation sector. In this paper, the HP-HVOF (high-pressure high velocity oxy-fuel) technique is used to produce dense rapidly quenched metal-ceramic nanocomposite protective coatings. The powders for the thermal spray process are produced by high energy ball milling using mechanochemical displacement reactions to synthesize ceramic components in-situ at the nanometric scale. Boron nitride solid lubricant is used as a source of nitrogen and boron to precipitate nitride and boride phases in a corrosion resistant iron aluminide metal matrix. The formation of the hard phases during milling and/or thermal treatments is investigated using various analytical methods. The tribological properties of the coatings with and without ceramic additives are reported.

This study assesses the viability of producing electrically conductive carbon nanofiber (CNF) reinforced mullite coatings by thermal spraying. Mullite-CNF agglomerated powder was prepared by spray drying and was deposited on steel by atmospheric plasma spraying. The coatings obtained are characterized based on composition, structure, shape, thickness, and electrical conductivity and are compared with coatings produced from commercial mullite powder.

This study evaluates candidate coatings for potential use in the manufacture of metal-seated ball valves for hydrometallurgy service. All coatings were deposited on grit-blasted titanium coupons by air plasma spraying to a nominal layer thickness of 500 µm. The feedstock powders used were selected based on literature review and field experience and include Cr 2 O 3 , TiO 2 -Cr 2 O 3 , nano TiO 2 , and a novel mixture of nano TiO 2 and conventional Cr 2 O 3 . The resulting coatings are compared based on microhardness, shear strength, friction properties, and wear resistance. Specimen preparation procedures and test methods are described in the paper along with the findings and potential implications of the study.

cBN/NiCrAl nanocomposite coating was deposited by cold spraying using mechanically alloyed composite powders. To examine the thermal stability of coating microstructure, the nanocomposite coating was annealed at different temperatures from 750 to 1000°C. The microstructure of composite coatings was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the nanostructure was retained in the coating when the annealing temperature was lower than 825°C which is 0.7 times of the melting point of NiCrAl matrix. The dislocation density significantly reduced when annealing temperature was higher than 750°C. The cBN particle growth became significant when the annealing temperature was higher than 825°C. The effects of crystal grain refinement and work-hardening strengthening mechanisms were quantitatively estimated as the function of annealing temperature. The effect of annealing temperature on the contribution of different strengthening mechanisms to coating hardness was discussed.

Homogenous mixtures of Ce 0.8 Gd 0.2 O 1.9 (GDC) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF6428) nanopowders were successfully synthesized using radio frequency (RF) induction plasma by axial injection of a solution. Two kinds of powders with different mass ratio of GDC/LSCF, such as 3/7 and 6/4, were obtained. The crystallinity and morphological features of the powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The particles are almost globular in shape with a diameter lower than 100nm and the BET specific areas around 20m 2 /g. In addition, suspensions, made with the composite nanopowders and ethanol, were used to deposit some cathode coatings using suspension plasma spray method. Several initial results of the coatings are also presented. The coatings are homogeneous and porous with cauliflower structures.

Nanocomposite epoxies are novel sealants developed especially for sealing metalized coatings. In order to test the corrosion protection performance of arc-sprayed aluminum coatings plus this sealer, steel panels were coated and placed in a corrosion test site on the East China Sea. Test panels were mounted in a marine atmosphere zone, seawater splash zone, tidal zone, and full-immersion zone. Several tests were conducted including corrosion and coating adhesion tests. This paper presents the results obtained from composite-coated steel panels after three years of seawater exposure.

Due to their enhanced mechanical properties and high range applications in severe environments use, there is ongoing research in the area of amorphous metallic glasses and nanostructured materials. The science and mechanisms leading to these exceptional properties are discussed herein. The arc sprayed coatings produced for study in this paper show remarkable performance and are analyzed in-depth using advanced characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Additional analysis of the mechanical properties of the coatings show enhanced strength and hardness, good wear and corrosion properties, along with high temperature corrosion and oxidation resistance.

Alumina-zirconia nano-composite coating were fabricated by plasma spraying using agglomerated feedstock from alumina and yttria partially stabilized zirconia fine powders of about 100 nm in diameter. The coating was very dense and showed the striped contrast in the splats. XRD analysis and TEM observation revealed that the splats contained gamma-alumina and tetragonal-zirconia crystals, which sizes were under 10 nm. The striped contrast in the splats corresponded to the inhomogeneous distributions of these crystals. To investigate the mechanical properties of this nano-composite coating, micro-hardness and fracture toughness were measured. The critical strain energy release rate of nano-composite coating was 106.4 J/m 2 , which was two times larger than YSZ coating.

Mechanical properties of micro/nanoscale structures are necessary to design reliable ceramic coatings. Micro/nanomechanical characterizations of novel nanocomposite coatings (NCCs) and micron composite coatings (MCCs) have been studied. Hardness, elastic modulus and creep resistance of these materials were measured by means of nanoindentation. It is found that the nanocomposite coatings exhibit higher hardness, elastic modulus and creep resistance as compared to the micron composite coatings. The nanoindentation tests used in this study can be satisfied to evaluate the mechanical properties of micro/nanoscale structures of ceramic coatings

In the materials world, there are two distinct usages of the term nanotechnology; Particulate Materials Nanotechnology (PMN) and Bulk Materials Nanotechnology (BMN). Both approaches have been used in attempts to produce nanoscale coatings with characteristic length scales from 10 to 100 nm. While particulate strategies are widespread, a different approach is presented which focuses on producing coatings through a solid / solid state transformation which results in the refinement of the microstructural scale (i.e. phase / grain size) down to the nanoscale regime. The essential features of BMN are the 2-d grain and phase boundary defects and achieving this nanoscale regime is key to enhancing bulk properties. This paper will attempt to clarify the terminology, definitions, and usages of the term nanoscale to clear up misconceptions and clearly show the salient features allowing for the production of nanoscale microstructures on an industrial scale. A clear demonstration of this achievement will be presented with a case study on the formation of amorphous / nanocomposite coatings while processing in air using off the shelf thermal spray technology using conventionally sized feedstock. Examples of nanostructured HVOF and wire-arc as-sprayed and heat treated coatings with average phase sizes of 50 nm and 80 nm respectively will be presented using detailed TEM micrographs.

Neutron absorbers are expected to play an important role in the long-term storage of spent nuclear fuels and nuclear wastes. High neutron absorbing capability, long-term stability, and the capacity to stay with the fuel are important criteria in preventing critical conditions during possible waste package degradation in geological time frames. Existing available neutron absorbing materials are based on boron or boron-10 isotope modifications of austenitic stainless steels or to aluminum based metal matrix composites. Specific rare earths such as gadolinium, samarium, or europium are found to have much higher thermal neutron cross section than boron or boron-10 but have high reactivity which limit their stability and ultimate applicability. In this paper, it is described how it is possible through a nanotechnology approach, to overcome the solubility and stability limitations of conventional materials to allow incorporation of high amounts of boron and rare earths into advanced HVOF coatings. During the development of the NeutraShieldTM Coatings, it was found that high fractions of rare earth elements such as gadolinium along with high concentrations of boron could be dissolved in the liquid melt and then remain soluble in the metallic glass structure. During the transformation of the glass to the nanocomposite structure, the rare earths are found to come out of supersaturated solid solution to form stable nanoscale ternary intermetallic R2Fe14B phases which form in a commensurate fashion and is protected by the highly noble matrix. Abstract only; no full-text paper available.

A typical high-pressure fuel pump for direct injection (DI) engines operates with fuels such as petroleum-based hydrocarbons that have inherent lubricating properties. However, environmental requirements put the thrush to use cleaner fuels that don’t contain lubricants and consequently an increasing abrasion problem presents with the surface of high-pressure fuel pump for direct injection engines. To alleviate this problem, the alternative solution is to promote wear and corrosion resistance of DI engines by applying high-lubricity coatings onto surfaces of engine components such as pump plungers. In this work, self-lubricating nanocomposites with nano-Al 2 O 3 /TiO 2 matrix and Fe 3 O 4 additive as solid lubricant was the first applied. The nanocomposites had been fabricated into lubricant coatings with a single layer or a functionally graded structure in plasma spray process. Tribological test results for the nanocomposite coatings demonstrated 4 times increase in sliding wear resistance and 3-5 times increase in abrasive wear resistance in under the tested conditions. The lowest coefficient of friction about 0.18 was measured on the nanocomposite coating with an optimal Fe 3 O 4 content in pin-on-disk test in ethanol. Based on morphologies and wear behavior analyses, the wear mechanism was proposed for the nanocomposites. The nanocomposite coatings have exhibited the advantages of cleavability, chemical stability, low friction and high wear resistance, and will have a potential for various applications that require high lubricity at ambient and elevated temperature.

Alumina-zirconia composite coatings were fabricated by plasma spraying using both of mixture of commercial feedstocks and agglomerated feedstock from fine powders of about 100 nm. The coating from mixture had an ordinary lamella structure which consisted of alumina splats and zirconia splats, whereas that from fine powders showed the striped contrast in the splat. X-ray deflection profiles revealed that the latter contained gamma-alumina, monoclinic-zirconia and tetragonal-zirconia crystals, which sizes were under 10 nm. These facts mean the fine crystals dispersed inhomogeneously. The nano-composite coating had a higher Vickers hardness and lower thermal diffusivity than the coating from mixture. Moreover, it showed good thermal stability and its crystallite size kept under 50 nm even after the heat treatment at 1500°C for 100h.

Nanostructured materials and nanocomposites have the potential to have a dramatic impact on technological progress in the 21st century. Of great interest, is the outstanding deformation behavior of nanostructured materials and nanocomposites. In this study, the fatigue and mechanical properties of HVOF sprayed nanostructured and conventional WC-Co coatings were investigated. High velocity oxy-fuel process was used to spray the WC-12Co from a feedstock in which the WC phase was mainly in the micron size range (conventional) or contains a significant fraction of nanosized grains (multimodal).The fatigue strength of coatings deposited onto Aluminum alloy showed that the nanostructured WC-Co coated specimens exhibited higher fatigue strength compared to the conventional WC-Co coatings. Microhardness test was performed. Relationships between the microstructures and mechanical properties were discussed.

The high velocity oxy-fuel (HVOF) combustion spray technique previously has been shown to be an excellent solution for depositing nano-reinforced thermoplastic polymer coatings. Dense polymer coatings can be produced regardless of ceramic particle size with little change in the spray parameters. Composite powders with multiple scales of silica reinforcement, ranging from 12 nm to 100 µm, have been created. Preliminary testing was begun using melt processing. The multiple scales have shown improved scratch resistance relative to single-scale reinforcements.

The present work describes abrasion wear tests that were carried out on low carbon steel test wheels coated with a series of plasma sprayed and HVOF sprayed Al 2 O 3 -SiC coatings with varying SiC contents. These were compared to a pure Al 2 O 3 coating applied by HVOF and to uncoated steel. The HVOF sprayed coatings exhibited consistently superior abrasion wear resistance compared to plasma sprayed coatings of equivalent composition and uncoated steel. Overall, the HVOF Al 2 O 3 -10%SiC nanocomposite coating showed the best abrasion resistance of all the coatings tested. They were worn very slowly by a micro-abrasion process. The poor performance of the plasma sprayed coatings was attributed to a low cohesive strength which made them particularly vulnerable to grain pull-out.

The high velocity oxy-fuel [HVOF] combustion spray technique has previously been shown to be an excellent solution for depositing crystalline matrix nano-reinforced polymer coatings. Dense polymer coatings can be produced by controlling both the particle dwell time in the HVOF jet and through substrate thermal management. Use of an amorphous matrix material, polycarbonate, will enable the role of matrix crystallinity on the structure and properties of thermally sprayed polymer matrix nanocomposite coatings to be separated from effects resulting from the reinforcing phase. An amorphous, commercial polycarbonate powder with a broad particle size distribution and irregular particle morphology has been successfully deposited by HVOF spraying using hydrogen as fuel gas. Polycarbonate matrix coatings up to 18 mils thick with zero to 10 vol. % loadings of nano-sized hydrophobic and hydrophilic silica, and carbon-black have been sprayed onto Al substrates. Results from optical microscopy. X-ray diffraction, scratch, density, microhardness and dilute-solution viscometry measurements will be presented. These indicate that incorporation of the nanosized filers improved the scratch resistance and microhardness of the coatings by 50 % and 23 %, respectively, relative to sprayed pure polymer. Some degradation of the polymer matrix was also detected, with molecular weight being reduced from 17,000 in the feedstock to ~5,000 in the sprayed deposits. The influence of variations in process parameters such as fuel:oxygen ratio, total gas flow, spray distance, nozzle length, total travel distance, and spray distance/nozzle length ratio on coating structure will also be addressed. The threshold loading of silica in the polycarbonate matrix for which dense coatings can be obtained has also been determined.

The high velocity oxy-fuel (HVOF) combustion spray technique has previously been shown to be an excellent solution for depositing crystalline matrix nano-reinforced polymer coatings. The use of multiple scales of reinforcement is expected to improve the load transfer from the larger reinforcing particles to the matrix through the mediation of the smaller particles. The initial step in developing multi-scale coatings is studying the effects of reinforcement size on distribution and properties. Nylon 11 coatings filled with silica particulates of 7 nm, 20 nm, 10µm and 100µm have been produced using the high velocity oxy-fuel (HVOF) combustion spray process. The physical properties and microstructure have been evaluated as a function of the reinforcement size. Nylon 11 was co-milled with the fillers to a 10% volume fraction. The filler was agglomerated at the splat boundaries in the final coating microstructures. All filled coatings had significant changes in x-ray pattern relative to pure nylon 11 coatings, indicative of both increased crystallinity and changes in crystal structure. Coatings containing the smallest reinforcements exhibited improvements of 40 % in scratch and 84 % in wear resistance above those containing the largest reinforcement particles in coatings with nominal 10 vol. % of hydrophobic silica. This increase appeared to be primarily due to filler addition and increased matrix crystallinity.