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Thermal spraying of polymer-ceramic composite coatings with multiple size scales of reinforcements
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|Title: ||Thermal spraying of polymer-ceramic composite coatings with multiple size scales of reinforcements|
|Authors: ||Gupta, Varun|
|Keywords: ||Materials science|
|Issue Date: ||20-Jul-2006 |
|Abstract: ||Thermal spraying is a solvent-less and low-VOC technique for producing polymer and polymer composite protective coatings. The high velocity oxy-fuel (HVOF) combustion spray process, a part of the thermal spray family tree, has been demonstrated as a viable approach for producing nano-scale and multi-scale reinforced semi-crystalline polymer composite coatings by controlling both the particle dwell time and substrate temperature. HVOF sprayed polymer matrix composites incorporating nominal 10 Vol. % of multiple size ceramic reinforcements ranging from 7 nm to 15 μm were studied to bridge the nano and conventional micron size scale regimes. The goal of this research project was to improve the scratch and wear resistance of thermally-sprayed polymer coatings by incorporating multiple scales of ceramic reinforcements.
The polymer and ceramic powders were dry ball-milled to produce the composite powders. Dry ball-milling polymer and ceramic particles together resulted in a core-shell powder morphology with ceramic-rich shells around polymer-rich cores. The morphology of the composite powders, particle size distribution and elemental phases present were characterized by scanning electron microscopy (SEM), particle size analysis and energy dispersive spectroscopy (EDS). Ashing & thermo gravimetric analysis (TGA) was used to confirm the ~10 Vol. % loading of ceramic reinforcement in the composite feedstock powders.
The microstructure of the HVOF sprayed composite coatings was a cellular lamellar structure with ceramic reinforcements agglomerated at splat boundaries. EDS
analysis confirmed the concentration of ceramic reinforcements at splat boundaries in sprayed coatings. The effect of particle size on dispersion and distribution, and the influence of substrate temperature on coating adhesion, were investigated. Microstructural characterization was used to analyze the dispersion and distribution of the ceramic reinforcements within the polymer matrix. Changes in crystallinity, as determined by TGA and differential scanning calorimetry (DSC), were correlated to nano/multi scale coating microstructures, reinforcement loadings and processing parameter variations. The amount of ceramic reinforcement incorporated within the sprayed coatings was studied by ashing and TGA, which indicated a ~50% loss of reinforcement during spraying.
The HVOF sprayed coatings were characterized for mechanical properties such as scratch resistance. Multi-scale composite coatings exhibited improved scratch resistance over HVOF sprayed pure Nylon-11 and single scale (nano-scale) reinforced composite coatings. Multi-scale ceramic reinforcements reduced scratch depths by as much as 50% relative to pure polymer coatings, and by up to 20% compared to single-scale reinforcements. Improvement in the mechanical properties was likely due to mechanical reinforcement/load transfer provided by the ceramic particles.|
|Appears in Collections:||Drexel Theses and Dissertations|
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