The polymer cold spray (CS) process has been demonstrated as a promising coating and repair technique for fiber-reinforced polymer composites (FRPs). However, a noticeable variation in coating thickness (herein referred to as checkerboard pattern) often occurs in the initial (bond) layer of low-pressure CS deposition. The checkerboard pattern occurs due to essentially periodic variations in matrix thickness above the subsurface fiber weave pattern. When the bond layer exhibits the so-called checkerboard pattern, the CS deposition for subsequent layers may be negatively affected in terms of deposition efficiency, porosity, adhesion, surface roughness, and surface thickness consistency. The present work compares results of both numerical simulations and experimental studies performed to reveal the governing mechanisms for and elimination of checker-boarding. Numerical single particle impact simulations are conducted to observe various thermomechanical domains for CS impact on the FRP surface in different regions of the composite material. Complementary experimental CS studies of exemplar powders onto FRPs with various surface interlayer thicknesses are also presented. Experimental analyzes of deposits include microstructural observations to compare against the simulations while also providing practical strategies for the elimination of checkerboarding effects.

In this study, microstructural characterization is conducted on WC-17Co coatings produced via High Velocity Oxygen Fuel (HVOF), High Velocity Air Fuel (HVAF), and Cold Spraying (CS). All coatings prepared were observed to be of good quality and with relatively low porosity content. SEM study showed important microstructural features and grain morphologies of each coating. While composition of feedstock material was approximately similar, elemental composition using EDS showed higher Co content and lower WC in the CS deposited coating. XRD experiment identified formation of more complex oxides and tungsten phases in coatings deposited technologies involving melting of powders such as HVOF and HVAF. These phases consisted mainly of cobalt oxides and brittle phases such as W 3 Co 3 C or W 2 C caused by decarburization of the tungsten carbide particles. Hardness of all coating samples were examined and CS deposited coating exhibited considerably lower hardness compared to the other two coating samples instead of having significantly lower porosity content. It could be contributed to dissociation and physical loss of hard carbide phase during high velocity impact of particles in CS process. It is in good agreement with detection of higher amount of cobalt in CS deposited coating material. It is strongly believed that results obtained from this study can be used for future investigation in thermo-mechanical properties of WC-Co coatings.

The promising structural properties of fiber-reinforced polymer composites make them widely popular in the energy, automotive, defense, and aerospace industries. One of the most challenging limitations associated with the use of composites in the above applications is the maintenance and repair protocols. In this study, a novel cold spray approach is introduced as an efficient alternative for the structural repair of fiber composites. Damages in the form of circular tapered holes are created in glass fiber-reinforced polymer (GFRP) composite substrates using a conventional drilling process. The in-lab created damages are repaired by cold spray with thermoplastic (nylon 6) and thermoset (polyester epoxy resin, PER) materials. The fundamental adhesion mechanisms are investigated through microstructural observations, which point to adiabatic shear instability due to the occurrence of severe plastic deformation as a governing factor. Microstructural examinations also suggest that no significant fiber damage or surface degradation occurs after the repair by cold spray. Mechanical tests performed on neat, damaged, and repaired composites reveal the partial recovery of structural performance and load-bearing capacity after cold spray repair. Results obtained in this work highlight cold spray as a promising alternative technique for onsite structural repair of composite structures with minimal pre/post-processing requirements.

Anisotropy of stress-strain behavior, fracture toughness, and fatigue crack growth rate of Ti6Al4V deposited by cold spray using nitrogen was studied. For that, flat deposits were tested with stress acting in the in-plane directions and tubular deposits were tested in the out-of-plane stress directions. In all tests, unified small-size specimens were used. It was shown that for the in-plane stress, the deposits can be considered isotropic, whereas the out-of-plane stress led to significantly lower values of the measured properties. The obtained results were related to fractography and microstructural analysis. While a combination of trans-particle and inter-particle fracture determined the fatigue properties in the near-threshold regime, at higher loads, inter-particle fracture was dominant. It was also shown that the different particle-to-stress orientations influenced the resulting fatigue and static properties.

A solid oxide fuel cell is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. It involves ionic transport and electrochemical reactions where the electrolyte and electrode properties play a major role in performance, along with a range of complementary materials that need to ensure equally relevant functions across the cell. The lifetime of such functional materials is expected to reach many thousands of hours with minimal degradation. This article is centred around the process development, optimization and scale up of a thin plasma sprayed ceramic barrier layer to mitigate long-term performance degradation of metal-supported solid oxide fuel cells. The evolution from the proof of concept in a laboratory environment to the scale up toward large scale manufacturing production is discussed. The challenges associated with minimizing application time and lowering cost while maintaining high coating performance at high yield are discussed. Empirical observations such as microstructural analysis and in-flight particle monitoring are used to gain understanding of the plasma spray process and guide its development for high-volume production. Results show how this effort has led to the reduction of the coating deposition time by 94% to enable large-scale manufacturing at high yield.

In general, similar MAX-Phase coatings are considered as oxidation protection layer for preventing disastrous reactions of the Zircaloy fuel rods during a cooling water failure in a nuclear power plant. For the present study on Aerosol Deposition, Ti3SiC2 was selected as MAX-phase model system due to the availability of property data and commercial powder. The as-received powder was milled to different nominal sizes. For revealing details on coating formation and possible bonding mechanisms, Aerosol Deposition experiments were performed for different particle size batches and process gas pressures. Microstructural analyses reveal that coating formation preferably occurs for particle sizes smaller than two microns. Using such small particle sizes, crack-free, dense layers can be obtained. The individual deposition efficiencies for the different particle sizes, particularly the critical size below which deposition gets prominent, vary with process gas flows and associated pressures. Detailed microstructural analyses of coatings by high resolution scanning electron microscopy reveal plastic deformation and fracture, both attributing to shape adaption to previous spray layers and probably bonding. In correlation to coating thickness or deposition efficiencies, respective results give indications for possible bonding mechanisms and a tentative window of Aerosol Deposition for Ti3SiC2 MAX-phases as spray material.

The porous architecture of coatings has a significant influence on the coating performances and thus should be properly designed for the intended applications. For simulating the coating properties, it is necessary to determine the numerical representation of the coating microstructure. In this study, YSZ coatings were manufactured by suspension plasma spray (SPS). Afterwards, the porous architecture of as-prepared coatings was investigated by the combination of three techniques, imaging analysis, Ultra Small Angle X-ray Scattering (USAXS), and X-ray transmission. A microstructural model for reconstructing the porous architecture of the SPS coating was subsequently computed according to the collected experimental results. Finally, the coating thermal properties were simulated based on the model and were compared with the experimental results.

Hybrid plasma spraying is emerging as the next potential technology leap in thermal spraying. The combination of high throughput and deposition rates of coatings sprayed from powders with the tailored functionality of liquid-feedstock sprayed coatings appears highly promising for a wide range of applications. Moreover, possible refined mixtures of different materials come readily with the utilization of multiple feedstocks with varying particle sizes. However, the practical aspects of hybrid coatings production are accompanied with several peculiarities not encountered when using distinct feedstocks. To deepen the understanding of this novel route, this paper presents fundamental hybrid coating formation principles and the effect of selected deposition parameters using multiple case-study material systems, such as Al2O3-YSZ, Al2O3-Cr2O3, and Al2O3-TiO2.

In this work, CeO 2 -G d2 O 3 co-stabilized ZrO 2 (CGZ) thermal barrier coatings are deposited by solution precursor plasma spraying and the microstructure, phase stability, thermophysical properties, and thermal cycling behaviors of the resulting coatings are investigated and discussed in comparison to conventional 8YSZ coatings.

This study assesses the plasma erosion resistance of Y 2 O 3 and YF 3 films deposited on aluminum 6061 substrates by vacuum kinetic spraying, a low-temperature deposition process. Y 2 O 3 and YF 3 powders with different particle sizes were selected as feedstock materials and characterized in their as-delivered and heat-treated states. Dense films several micrometers in thickness were sprayed using helium as the process gas and surface component analysis confirmed the successful formation of the yttrium-based layers. Plasma etch rates were measured in nanometers per minute and the results show that there is no significant difference between the two films.

In this paper, the principles of computational fluid dynamics are used to simulate the complex gas flows in the cylinder bore of an automotive engine during internal-diameter twin-wire arc spraying. A number of experiments are conducted as well and the results are presented and analyzed in order to optimize the properties of the coating. The combination of simulation and experiments led to the development of a process that achieves uniform layer adhesion strength over the length of the cylinder bore.

While depositing Fe-Al intermetallic powders applying a gas detonation spraying a certain coating structures containing oxide ceramics are created. These structures exhibit both extreme mechanical resistance and unusual thermophysical properties (TP) also. One of such property is relatively low thermal conductivity. A possible application as thermal barrier coatings needs precise determination of TP dependence on temperature and resistance of the coating structure to temperature exposition. At present study TPs were investigated for a coating produced from Fe-Al intermetallic powder in a course of complex measurements including DSC analyses, laser flash thermal diffusivity measurements, dilatometric studies complemented with microstructural analyses. The study resulted in full characterization of the investigated structure TPs: density, thermal expansivity, heat capacity and thermal conductivity. During thermal analyses interesting phenomena concerning thermal resistance to the temperature exposition of the investigated coating were revealed. The obtained results complement rather sparse literature data on TPs in that subject and contribute to better understanding of gas detonation spraying (GDS) process technology and intermetallic/oxide structures property understanding.

In this study, ball-milled Al 2 O 3 powder was used as a feedstock material for vacuum kinetic spray to deposit hard ceramic Al 2 O 3 coating on a relatively soft polycarbonate substrate. Microstructural and X-ray diffraction analysis of powders and coatings were performed. The results shows that the ball-milled powder has more unstable state than the primary powder. Compared to primary Al 2 O 3 coating the crystallite size and coating thickness of ball-milled Al 2 O 3 coating are smaller and thicker, respectively. Since the ball-milled Al 2 O 3 particles are more easily fragmented during the VKS coating process, it is possible to deposit hard Al 2 O 3 coating on the soft polycarbonate substrate.

This paper presents the results of mechanical and tribological property measurements obtained from NiCrBSi alloy coatings and evaluates the effect of different heat treatments. Coating specimens were deposited by means of flame spraying and heat treated using an acetylene torch. HVOF samples were also prepared as a reference for comparison. The microstructure of as-sprayed and heat-treated coating samples were compared, hardness and surface roughness were measured, and erosion resistance tests were performed. The processes and procedures used are described and the results obtained presented and discussed.

This study investigates the influence of powder feed rate on the deposition efficiency of HVOF sprayed materials, including NiCr, FeNiCrMoCSi, 316L stainless, Cr 3 C 2 /NiCr, WC-Co/Cr, and WC-Cr 3 C 2 /Ni. A liquid-fuel HVOF spray gun is used in combination with a modified injector block that increases the number of powder injection ports from two to four. In the experiments, powder feed rates were incremented from a baseline of 100 g/min to 400 g/min for the metal powders and up to 500 g/min for the cermets, while measuring deposition efficiency for each run. Coating samples were also produced for metallographic analysis, hardness testing, and the evaluation of porosity and roughness. All results are presented and discussed along with potential implications on coating costs.

In this investigation, an air plasma sprayed TBC system consisting of a CoNiCrAlY bond coat (BC) and a YSZ topcoat (TC) is produced with a PVD AlOx interlayer in order to study its effect on thermally grown oxides. For comparative purposes, a reference TBC without the AlOx interlayer was also prepared and studied. A cyclic thermal load was applied to both systems and the coatings were examined after 6, 12, 24, 40, and 80 cycles. Crack lengths were measured in the YSZ layer and TGO thicknesses were assessed at the BC-TC interface. An examination of coating microstructures revealed the expected mixed-mode failure in both TBCs. In comparison to the reference TBC, the system with the AlOx interlayer showed reduced crack formation in the TC and slowed TGO formation at the BC-TC interface both during and after thermal treatment.

This study investigates arc behavior associated with twin-wire arc spraying and the effect of pulsed current power on arc formation and coating properties. It is shown through false color images and by calculations that arc length is directly related to voltage and that a “natural” frequency can be obtained from voltage fluctuations. By applying current pulses at this frequency, arc movement along the wire tips is effectively controlled because the arc reignites with each current pulse. This results in coatings with lower oxide content and a microstructure nearly free of the lamellae typically found in dc arc spray deposits. Further improvements are likely to be achieved by optimizing the configuration of the wire guides relative to the gas nozzle.

In this study, the current industry standard topcoat for thermal barrier coatings, 8YSZ, is deposited by suspension plasma spraying and its room-temperature erosion resistance is compared with that of SPS sprayed gadolinium zirconate/YSZ and triple-layered GZ dense /GZ/YSZ. A columnar microstructure was observed in both the single- and multi-layered TBCs. Single-layer 8YSZ had a higher erosion resistance than multi-layered GZ/YSZ despite of its higher porosity among the as-sprayed coatings. In the case of the triple-layer coating, the denser top layer helped to slightly improve erosion resistance over that of the GZ/YSZ double-layer TBC.

Water droplet erosion (WDE) is a well-known phenomenon. This type of erosion is due to the impingement of water droplets of several hundred microns to a few millimeters size at velocities of hundreds of meters per second on the edges and surfaces of components. The solution to this problem is in high demand especially for the moving blades of gas turbines’ compressors and those operating at the low-pressure (LP) end of steam turbines. Thermal sprayed tungsten carbide based coatings have been the focus of many studies and are industrially accepted for a multitude of wear and erosion resistance applications. The present work studies the microstructural, phase analysis and mechanical properties and their effects on water droplet erosion resistance of such coatings deposited with high velocity oxygen fuel (HVOF) and high velocity air fuel (HVAF) processes. The feed nano-agglomerated tungsten carbide-cobalt powders are in either sintered or non-sintered conditions. The WDE tests were performed using 0.4 mm water droplets at 300 m/s impact velocity. The study shows promising results for this cermet (better than the Ti6Al4V bulk material) as WDE resistant coatings when deposited using HVOF or HVAF processes under optimum conditions.

The Cold spray method of material deposition is widely used for surface enhancement, to improve properties such as corrosion and wear. A detailed microstructural analysis of cold sprayed Ni based coatings (IN625 (Inconel 625 is a Trademark of Huntington alloys corporation) using the transmission electron microscope, revealed the occurrence of three distinct types of microstructures in the as sprayed condition, adjacent to each other. These include the occurrence of large (> 1 μm) grains having a high dislocation density, along with regions comprising shear bands (20-30 nm wide) and twins with a large aspect ratio (> 1000), along with locations having a very fine grained structure (20-30 nm). The crystallite size, using a Hall-Williamson plot measures an average 50 nm. The substrate deformation indicates a bilayer dynamic recrystallization, as a means to accommodate the strain. The microscopy studies will serve to correlate the bonding mechanism of cold sprayed IN625 on 4130 steel.