In this investigation, flame spraying is used to deposit polyether ether ketone (PEEK) layers on stainless steel substrates and CO 2 and Nd:YAG laser remelting treatments are performed to densify the deposited material. Microstructural analysis of the as-sprayed and remelted coatings shows that both lasers are suitable for densifying PEEK polymer layers on stainless steel and that the resulting crystalline structure depends on laser processing parameters. Hardness measurements and tribological and scratch tests are also carried out and the results are correlated with microstructure.

Release or nonstick properties are not typically achieved through thermal spraying because of the high surface energy of the resulting deposit. Polymer coatings can provide release properties but are low in durability. However, by adding a nonstick low-friction polymer or release topcoat to a hard metal matrix deposit, a variety of properties can be incorporated in the coating solution. This paper explains how such coatings are produced and examines the tradeoffs involved in the selection of materials. It presents numerous examples of successful industrial applications and introduces an accelerated test that has been developed to predict release performance over the life of the coating which correlates well to field conditions.

In this study, single splats of polyether ether ketone were plasma sprayed onto aluminum substrates that had been boiled, etched, or polished and then thermally treated, except for one etched substrate, to remove water from the surface. Splat morphology was viewed in a scanning electron microscope and splat-substrate interfaces were examined using TEM and focused ion beam imaging. The results show that PEEK splats have a poor level of contact on aluminum substrates that were boiled and those that were etched but not thermally treated. In contrast, specimens that had undergone thermal treatment to minimize the presence of water on the substrate surface exhibited high levels of contact at the splat-substrate interface with significantly less porosity.

In this paper, submicron α-Fe/nylon-12 microwave absorbing composite coatings were deposited by a Low Temperature High Velocity Air Fuel (LTHVAF) spraying technique. The microstructure and the electromagnetic parameters of coatings and powders were tested. The coatings are dense and have low porosity. The microwave reflectivity coefficient of the coatings was calculated with permeability and permittivity of the powders. It shows that there is a relationship between the mass fraction of composite powders and microwave absorption ability of coatings. At the threshold value, the composite coatings can absorb microwave strongly. When the coatings thickness increases, the minimal reflectivity coefficient moves to the low microwave frequency. There exists an appropriate coatings thickness in order to optimize the absorption of the microwave energy. The mass fraction and the thickness can affect the performance of composite absorber coatings.

The high velocity oxy-fuel (HVOF) combustion spray process has previously been shown to be a successful method for depositing pure polymer and polymer/ceramic composite coatings. Polymer and polymer-ceramic composite particles have high melt viscosities and require the high kinetic energy of HVOF in order to generate sufficient particle flow and deformation on impact. One of the goals of reinforcing polymer coatings with particulate ceramics is to improve their durability and wear performance. Composite coatings were produced by ball-milling 60 µm Nylon-11 together with nominal 10 vol.% of nano and multi-scale ceramic reinforcements and HVOF spraying these composite feedstocks onto steel substrates to produce semi-crystalline micron and nano-scale reinforced coatings of polymer matrix composites. The room temperature dry sliding wear performance of pure Nylon-11, Nylon-11 reinforced with 7 nm silica, and multi-scale Nylon-11/silica composite coatings incorporating 7 to 40 nm and 10 µm ceramic particles was determined and compared. Coatings were sprayed onto steel substrates, and their sliding wear performance determined using a pin-on-disk tribometer. Coefficient of friction was recorded and wear rate determined as a function of applied load and coating composition. Surface profilometry and scanning electron microscopy were used to characterize and analyze the coatings and wear scars.

Numerical predictions and experimental observations have been correlated to improve the qualitative understanding of the degree of thermal degradation occurring during the HVOF spray deposition of Nylon-11. Particle residence time (<1 ms) in the HVOF jet was insufficient for significant decomposition of the Nylon-11 but was sufficient for noticeable discoloration (yellowing) of the particles of a powder with a mean particle size of 30 µm. Experimental observations showed this to be the case even though numerical predictions indicated that the temperature of a 30 µm diameter particle should be considerably higher than the upper degradation limit of Nylon-11. Initial thermal oxidation of Nylon-11 promotes the formation of carbon-carbon double bonds that strongly absorb in the visible spectrum even at concentrations of parts per million, resulting in discoloration of the Nylon.

Thermoplastic Polyamide-11 powder coatings serve many industries – such as water handling, automotive, and appliances. This utility is based on the ability to simultaneously provide exceptional resistance to: corrosion, impact/abrasion, and numerous chemicals. Typically application is by traditional methods – electrostatic spray or fluidized bed dipping. The present work demonstrates for the first time that the flame spray method can produce Polyamide- 11 powder coatings very close in performance to those produced by traditional methods. The keys are proper substrate pre-heating, and flame conditions that minimize polymer degradation. Coatings performance, impact resistance, and molecular weight data are presented.

Flame sprayed PEEK (poly-ether-ether-ketone) coatings, with an amorphous structure, were subjected to isothermal treatments with annealing temperatures from 180 to 300 °C and holding time from 1 to 30 min. The coating structures were studied by means of DSC (Differential Scanning Calorimetry) and XRD (X-Ray Diffraction) analyses. All annealed coatings exhibit semi-crystalline structures. Coexistence of thick and thin lamellae in the spherulites of annealed coatings can be deduced from the analysis results. The Knoop hardness and the interfacial adhesion of the coatings were examined. The annealed coatings exhibit higher hardness than the amorphous ones. The formation of the thick lamellae is the determinant factor for improving the coating hardness. However, the annealed coatings exhibit a weak adherence to the substrate. Some fissures or spherical porosities could be observed, in certain zones, on the coating/substrate interface. The formation of these fissures and porosities could be ascribed to the coating residual stress and the big volume contraction during the crystallisation that occurred under the annealing condition.

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.

PEEK was sprayed with a Browning Aerospray HVAF thermal spray gun to enable the study of the wetting and interaction of single splats with an aluminium 5005 substrate. Single splats were obtained by exposing the substrate to the spray flame for 0.02 s by dropping a steel shutter with a 25 mm aperture milled in the centre. The single splats were then analysed through SEM (scanning electron microscopy) and FIB microscopy (focussed ion beam). Splat shape was found to be dependant on nozzle length, with a 100 mm nozzle resulting in more splashing, and a 450 mm spray distance providing more disc splats. PEEK splats do not wet the aluminium oxide surface well. Porosity occurs independently of nozzle length, in the form of cracks and pores in the splats, some cracks completely segmenting a splat.

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 fracture behavior of polymer coatings fabricated by low temperature high velocity air fuel (LTHVAF) spray was investigated. It was shown that the coatings were dense and had a mean bonding strength of 13.5 MPa. During the tensile stress process, the fracture occurred in the interior of the coatings, which indicates that the cohesive strength within coatings is less than the bonding strength between the coatings and substrate. A significant amount of crazing and honeycombed holes existed in the fracture surface. Under a tensile stress, cracks initiated at porous defects in the coatings. Dispersed particles interrupted the crack expansion, and caused a change in direction of crack propagation.

This article gives an overview of thermal spraying of polymers with respect to the different spraying processes, the polymer materials in use for thermal spraying and new trends of using polymers as separate spraying material and in combination with plastic and non-plastic materials. Flame spraying is by far the most common process used for thermal spraying of plastic materials. In addition in the past years two other processes have been used to produce thermal sprayed plastic coatings: plasma spraying and high-velocity oxy fuel spraying (HVOF). The areas where the different processes are used as well as the modifications to conventional plasma and HVOF devices and the advantages and disadvantages using these two processes to produce plastic coatings will be described. In addition to the common materials used for flame spraying (e.g., PA 11, PA 12 or EVAL), other materials giving new opportunities of application of thermal sprayed coatings have been used like PEEK and LCPs. The areas where these materials are used are described as well as the special features of these materials. Furthermore there are new trends in using plastic materials for thermal spraying. Thermal sprayed polymer materials are for example combined with plastic as well as non-plastic materials or pigments giving special effects to the coatings, e.g, reflective or anti-skidding coatings. It is described how coatings with the mentioned effects can be produced.

Ultra-high molecular weight polyethylene (UHMWPE) has remarkable properties in the bulk state and has substantial potential for use as a protective coating on metals. However, the molecular architecture responsible for these exceptional properties also causes difficulties in the formation of coatings by flame spraying. This paper studies two UHMWPE materials with molecular weights of 2 million and 6 million. The flow of splats for each UHMWPE and blends of selected polyethylenes were characterized and a model developed for the flow of these polymers with respect to polymer composition, viscosity and thermal spray parameters. The model was applied to the polyethylene system and the experimental results show that controlling the composition and the process parameters is essential for the deposition of high-quality coatings.

Ceramic / plastic composite powder (ceraplas powder) has been produced by Fluidized-bed granulation process (FG process) by varying the binder. Alumina (Al 2 O 3 ) has been used as ceramics and Polyphenylene-sulfide (PPS) has been used as plastics. PPS has high heat and corrosion-resistant performance. Moreover, sprayed composite coatings have been evaluated by the observation of the coating microstructure, the thermal analysis, the corrosion test and the abrasive wear test. It has been recognized that sprayed composite coatings produced by FG powder have high corrosion-resistance and good wear resistance

An important factor in the process of formation of a metal-polymer coating is the effect of a high-temperature gas jet on the "coating-substrate" system, as the jet favours penetration and spread of a polymeric material over the surface of the substrate. It is this factor that makes this form of thermal spraying radically different from spraying metallic coatings. On the other hand, excessive heating of the surface can lead to oxidation and degradation of the polymeric component. Therefore, thermal phenomena taking place during the formation of thermal sprayed metal-polymeric coatings, i.e. the level and distribution of temperatures through the thickness of a coating were analysed. Based on the results of mathematical modeling, recommendations for the thermal spraying of metal-polymeric coatings (heat source speed, spraying distance, flow rate of working gases, etc.) were developed.

In recent years, polymers have grown successfully in industrial applications such as protection against corrosion, chemical or wear resistance. However, the use of these materials is often limited because of their poor abrasion resistance. For example, PTFE is certainly a polymer that has the most attractive properties such as low coefficient of friction but it is characterized by a very low scratch resistance. These restrictions can be overcome by use of composite structure. This way, mechanical resistance can be then provided by ceramic materials. As a result, this study is devoted to feasibility of ceramic – fluoropolymer composite coatings by plasma spraying. Two types of organic powder (PTFE and PFA) and that of alumina powder were chosen. Blends of these compounds were then sprayed. Owing to thermal properties of both materials, specific spray parameters must be optimized. Two varied parameters were picked up (spraying distance and plasma gas mixture) and their effects on the coating quality were estimated by several types of characterization (morphology, polymer rate, roughness…).

The use of polymer matrix composites (PMC's) in the gas flow path of advanced turbine engines offers significant benefits for aircraft engine performance but their useful lifetime is limited by their poor erosion resistance. High velocity oxy-fuel (HVOF) sprayed polymer/cermet functionally graded (FGM) coatings are being investigated as a method to address this technology gap by providing erosion and oxidation protection to polymer matrix composites. The FGM coating structures are based on a polyimide matrix filled with varying volume fractions of WC-Co. The graded coating architecture was produced using a combination of internal and external feedstock injection, via two computer-controlled powder feeders and controlled substrate preheating. Porosity, coating thickness and volume fraction of the WC-Co filler retained in the coatings were determined using standard metallographic techniques and computer image analysis. The pull-off strength (often refered to as the adhesive strength) of the coatings was evaluated according to the ASTM D 4541 standard test method, which measured the greatest normal tensile force that the coating could withstand. Adhesive/cohesive strengths were determined for three different types of coating structures and compared based on the maximum indicated load and the surface area loaded. The nature and locus of the fractures were characterized according to the percent of adhesive and/or cohesive failure, and the tested interfaces and layers involved were analyzed by Scanning Electron Microscopy.

It is well known that residual stresses in plasma-sprayed coatings play a prominent role on coating-substrate adhesion in particular. This is all the more prominent because the coating is thick and adhesion intricate. The control and measurements of residual stresses in plasma-sprayed coatings onto organic-based substrates result in an issue of very high concern, even though very little (not to say nil) was published in this specific area. In this work, thick coating of a polyurethane resin with Inconel 625 was achieved by plasma spraying coupled with Atmosphere and Temperature Control (ATC), i.e. using cryogenic cooling to limit thermal degradation of the substrate when spraying. Residual stresses were determined by X-ray diffraction at the coating surface due to low X-ray penetration in nickel. In addition, residual stress in-depth profiles were obtained using the incremental hole drilling method. The investigation mainly focused on the measurement of residual stresses. In this paper, residual stresses were studied as a function of plasma spraying conditions. Results are discussed in the light of the coating microstructure. Residual stress measurements resulted in optimizing and controlling coating deformation and adhesion which are crucial for applications.