The High Velocity Oxy-Fuel (HVOF) combustion spray process has been used successfully for spraying polymers and polymer-matrix composite coatings. Spraying of polymer ceramic composite powders produced by ball-milling nominal 60 ..m Nylon-11 with different size scale (7 nm to 15 µm) ceramic reinforcements is an effective method of producing semi-crystalline micron and nano-scale reinforced composite coatings. Polymer matrix composite coatings with nominal 10 vol. % of different size scale silica and alumina reinforcements have been produced. The levels of filler loading in both the feedstock powders and HVOF-sprayed coatings were determined by thermo-gravimetric analysis (TGA) and compared using ashing. Particle size analysis, microstructural characterization and the elemental compositions of the feedstock powders and as-sprayed coatings were determined by optical and scanning electron microscopy and energy dispersive spectroscopy. The influence of dispersion, distribution and size of the reinforcing phase was studied and correlated to coating microstructure and process parameter variations. The scratch resistance of the coatings was measured as a function of reinforcement size and compared with those of the pure HVOF-sprayed Nylon-11 coatings.

The high velocity oxy-fuel (HVOF) combustion spraying of ball-milled Nylon-11/ceramic composite powders is an effective, economical and environmentally sound method for producing semi-crystalline nano- and micron-scale reinforced polymer composite coatings. Polymer matrix composite coatings reinforced with multiple scales of ceramic particulate materials are expected to exhibit improved load transfer between the reinforcing phase and the matrix due to interactions between large and small ceramic particles. An important step in developing multi-scale polymer matrix composite coatings and associated load transfer theory is determining the effect of reinforcement size on the distribution of the reinforcement and the properties of the composite coating. Composite feedstock powders were produced by dry ball milling Nylon-11 with fumed silica particles of 7, 20 and 40 nm, with fumed alumina particles of 50 and 150 nm, and with white calcined alumina 350 nm, 1, 2, 5, 10, 20, 25 and 50 µm at 10 % by volume overall ceramic phase loadings. The effectiveness of the ball-milling process as a function of reinforcement size was evaluated by SEM, EDS microanalysis and by characterizing the behavior of the powders during HVOF spraying. The microstructures of the as-sprayed coatings were characterized by optical microscopy, SEM, EDS and XRD. The reinforcement particles were found to be concentrated at the splat boundaries within the coatings, forming a series of interconnected lamellar sheets with good 3-dimensional distribution. The scratch resistance of the coatings improved consistently and logarithmically as a function of decreasing reinforcement size and compared to those of HVOF sprayed pure Nylon-11.

A three-dimensional model of particle impact and deformation on rough surfaces has been developed for HVOF sprayed polymer particles. Fluid flow and particle deformation was predicted by the Volume of Fluid (VoF) method using Flow-3D® software. The effect of roughness on the mechanics of splatting and final splat shapes was explored through the use of several prototypical rough surfaces, e.g. steps and grooves. In addition, a numerical representation of a more realistic rough surface, generated by optical interferometry of an actual grit blasted steel surface, was also incorporated into the model. Predicted splat shapes were compared with SEM images of Nylon 11 splats deposited onto grit blasted steel substrates. Rough substrates led to the generation of fingers and other asymmetric three-dimensional instabilities that are seldom observed in simulations of splatting on smooth substrates.

The high velocity oxy-fuel (HVOF) combustion spray process has been demonstrated to be a suitable technique for the deposition of nano-reinforced polymer matrix composite coatings by controlling both the particle dwell time and the substrate temperature. HVOF-sprayed polymer matrix composites incorporating reinforcements with size scales ranging from 7 nm to 100 µm are being studied to bridge between the nano and conventional scale regimes. Microstructural characterization has been used to characterize the dispersion and distribution of the ceramic reinforcements within the polymer matrix. The effect of particle size distribution on reinforcement dispersion and distribution has been studied, and the influence of substrate temperature on coating adhesion has also been investigated. Changes in crystallinity, as determined by Differential Scanning Calorimetry (DSC), are being correlated to coating microstructure, reinforcement loading and process parameter variations. Results of optical and scanning electron microscopy, scratch testing and DSC characterization of the feedstock materials and sprayed coatings are presented. Coatings of nominal 60 µm Nylon 11 with 10 vol. % of nano and micron size hydrophilic silica reinforcements exhibited a ~22 % improvements in scratch resistance compared to pure Nylon 11 coatings. An ~15 % improvement in scratch resistance was obtained for coatings containing 10 vol. % nano scale hydrophilic silica reinforcement.

In this paper, WC-Co reinforced polymer matrix coatings are sprayed on preheated steel and carbon-fiber reinforced substrates, producing relatively dense, adherent coatings. The particle morphology of the feedstock materials and the microstructure of the HVOF sprayed coatings are characterized and the thermal properties of the polymer powder and coatings are compared. It was found that the deposition and build-up of the polymer coating was only successful when substrates were preheated to the curing temperature of the thermosetting polyimide powder used. Layered coatings of varying polyimide and WC-Co content have been successfully deposited, showing that it is possible to produce graded composite coatings consisting of pure polymer at the substrate and pure WC-Co on the surface. Paper includes a German-language abstract.

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.

The high velocity oxy-fuel (HVOF) combustion spray technique has been shown previously to be an excellent solution for depositing crystalline matrix nano-reinforced polymer coatings [1]. Dense polymer coatings can be produced by HVOF combustion spraying by controlling particle dwell time in the 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 composite coatings to be separated from effects resulting from the reinforcing phase. An amorphous, commercial polycarbonate resin with a broad particle size distribution of irregular particle morphology has been successfully deposited. Results from optical microscopy, X-ray diffraction, scratch and density measurements are presented. The influence of variations in process parameters such as spray distance, nozzle length, chiller temperature, fuel: oxygen ratio, and total gas flow rate on coating microstructure are presented.

This paper evaluates the physical properties of nano-reinforced nylon 11/silicon oxide composite coatings produced using high-speed flame spraying as a function of the process technology and the composition. The coatings were created from nylon 11 powders with starting particle sizes of 30 and 60 micrometer and with 5 to 20% by volume of 9 nm reinforcing silicon oxide particles. Corrosion tests on aluminum and steel substrates showed that the metallic substrate is effectively protected and that the corrosion resistance does not change even if the coating is exposed to salt water for 100 hours. Paper includes a German-language abstract.