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.

The use of process-microstructure-property relationships for cold spray can significantly reduce application development cost and time compared to legacy trial and error strategies. However, due to the heterogeneous microstructure of a cold spray deposit, with (prior) particle boundaries outlining consolidated splats (deformed particles) in the as-spray condition, the use of automated analysis methods is challenging. In this work, we demonstrate the utility of quantitative data developed from a convolutional neural network (CNN) for feature extraction of cold spray microstructures. Specifically, the power of CNN is harnessed to automatically segment the deformed particles, which is hardly accessible at scale with traditional image processing techniques. Deposits produced with various processing conditions are evaluated with metallography. Parameters related to particle morphology such as compactness are also quantified and correlated to strength.

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.

The aim of this study is to characterize the mechanical behavior of wire-arc sprayed Zn-Al coatings and correlate the results with microstructure via computational techniques. High-resolution microstructural images obtained by SEM were imported into NIST-developed FEA software, which calculates macroscale properties based on user-selected features such as voids, pores, cracks, and splat boundaries. To assess the validity of the approach, elastic modulus was measured various ways and the results compared to the simulated value. Resonant frequency analysis provided the most accurate measurement, which was found to be closest to the simulated value.

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.

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.

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.

Aluminum titanate (Al 2 TiO 5 ) is a congruently melting compound in the binary Al 2 O 3 -TiO 2 system, which decomposes below 1200 °C. Its properties (e.g. thermal conductivity, CTE) differ significantly from those of Al 2 O 3 and TiO 2 . Thus it is of special interest to study the stability of Al 2 TiO 5 in the spray process and its influence on the coating properties. A commercial fused and crushed Al 2 O 3 -40%TiO 2 powder, which was found to be substoichiometric, was selected as the feedstock material for the experimental work, as the composition is close to stoichiometric Al 2 TiO 5 . Part of that powder was heat-treated in air at 1150° and 1500°C in order to vary the phase composition, while not influencing the particle size distribution and processability. The powders were analyzed by thermal analysis, XRD and FESEM including metallographically prepared cross sections. A powder having Al 2 TiO 5 as the main phase was not possible to be prepared due to inhomogeneous distribution of Al and Ti in the original powder. Plasma spraying was performed with a TriplexPro-210 (Oerlikon Metco) using Ar-H 2 and Ar-He plasma gas mixtures with 41 and 48 kW plasma power. Coatings were studied by XRD, SEM of metallographically prepared cross sections, and microhardness HV1. Moreover, the results show a clear influence of the Al 2 TiO 5 content in the feedstock powder on the phase composition of the coatings.

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.

Different types of tungsten carbide materials (fused tungsten carbide, nickel clad fused tungsten carbide, macrocrystalline WC and sintered and crushed WC/Co) are used for laser dispersing of construction steel surfaces. Surface roughness analyses and metallographic evaluation of cross sections concerning efficiency of carbide embedding as well as crack formation tendency are carried out. Generally, all types of tested carbides permit production of rough surfaces with metallurgical bonding to the metallic matrix, but only use of nickel clad fused tungsten carbide permits to prevent crack formation. The effectiveness of silicon and silicon carbide for production of durable rough surfaces on aluminium alloys is investigated. Both silicon and silicon carbide qualify for production of rough surfaces by laser dispersing. While silicon carbide particles show higher hardness, use of silicon does not include danger of embrittlement due to formation of aluminium carbide.

In this study abrasive wear resistance of NiCrBSi self-fluxing alloys claddings reinforced by tungsten carbide (up to 80 vol.%) and pure tungsten (up to 50 vol.%) was compared. For this purpose, metal matrix composite samples were cladded by diode laser then metallography studies and hardness measurements were provided. Finally, all specimens passed ASTM G65 abrasion test and their wear resistance was compared to alternatives claddings.

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.