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 the thermal spray process, particle state at impact is among the key factors influencing the quality, characteristics and properties of the deposit formed. Measuring and eventually controlling in-flight particle jet characteristics can help ensure the repeatability of desired coating properties. Moreover, monitoring particle jet can lead to cost savings by allowing replacement of consumable parts on a need-basis rather than on a preventive-basis. However, successful use of in-flight particle sensors in a production environment requires developing an implementation strategy that minimizes impact on coating cycle time, limits operator intervention and reduces analysis time, while still generating useful data. The usefulness of in-flight particle sensor in a high yield production environment is investigated. A preliminary study was first conducted to define a strategy to implement the data acquisition process using an ensemble in-flight particle monitoring system that allows real-time measurements of average particle temperature and velocity and overall particle jet profile. Data was collected to capture representative torch and particle jet behaviors over the life of several consumable hardware sets. Evolution of the particle jet parameters over time is compared to that of some of the process parameters, as well as to the deposition efficiency and one selected characteristic of the coating deposited. Some trends are identified, and potential benefits and drawbacks of using in-flight particle monitoring in a high yield production environment are highlighted.

In order to characterize the performance of nanostructured coatings during wear, nanostructured and conventional titania (TiO 2 ) coatings were sprayed via three different thermal spray processes: APS, VPS and HVOF. Three distinct types of wear resistance were evaluated: dry-abrasion and slurry-erosion at 30° and 90°. The ranking of the wear performance of the different coatings varied for the three wear tests, except for the HVOF-sprayed nanostructured titania. The HVOF-sprayed nanostructured coating exhibited the highest wear resistance in all three types of wear. The different angles of erosion (30° and 90°) did not cause a change in the wear performance (ranking) of the HVOF-sprayed nanostructured coating, as was observed for the other coatings tested. The superior mechanical performance of the HVOF-sprayed nanostructured titania can be explained by observing the microstructure of the coating via high magnification SEM. These observations show that the nanostructured zones in the coating microstructure act as crack arresters, thereby increasing the coating toughness. The wear scars for the different coatings were also analyzed via SEM and used to help understand the wear performance of the different materials.

Nanostructured and conventional titania feedstocks were thermally sprayed using APS, VPS and HVOF techniques to study the effects of processing, microstructure and properties on the abrasion behavior. The in-flight characteristics (temperature and velocity) of the APS and HVOF-sprayed particles were also investigated. For the nanostructured coatings, a process map was developed relating the in-flight particle characteristics during coating deposition to the abrasion resistance. This map showed that the particle velocity and particle temperature had an important influence on the volume loss in abrasion tests. Coatings were characterized using SEM to investigate the microstructural features, image analysis to measure coating porosity and Vickers indentation to determine hardness. The abrasion behavior of the coatings was evaluated using the ASTM standard dry sand/rubber wheel test. The abrasion results indicated that the VPS and HVOF-sprayed nanostructured titania coatings exhibited the highest abrasion resistance among the 14 coatings studied.

Boron carbide has been successfully deposited on Ti alloy by vacuum plasma spraying (VPS). Mechanical properties of the deposited structure were assessed by micro-hardness and nano-hardness indentation. Chemical and phase compositions of the starting powder and the as-sprayed structure were characterized using hot gas extraction (LECO), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and Raman spectroscopy. The microstructure consisted of equiaxed boron carbide grains, microcrystalline boron carbide particles, and amorphous carbon regions at the grain boundaries. The amount of boron oxide and amorphous carbon increased during spraying. Carbon segregation to grain boundaries in the as-deposited B 4 C was observed. The measured micro-hardness was slightly higher than values previously reported (1033 ± 2009 HV). There was significant variation of nano-hardness from point to point in the material due to the existence of multiple phases, splat boundaries, and porosity in the deposited structure.

PyroGenesis Inc. has been conducting a program on the development of coatings prepared from nanostructured ceramic and cermet materials using atmospheric (APS), vacuum plasma spraying (VPS), and high velocity oxy-fuel spraying (HVOF). In the work presented in this paper, APS and VPS coatings from nanostructured or sub-micron Al 2 O 3 - 13TiO 2 , Cr 2 O 3 -5SiO 2 -3TiO 2 , and TiO 2 feedstock materials were developed and optimized for abrasion wear resistance. They were subsequently tested for sliding wear resistance. The resulting wear properties are discussed in terms of coating microstructure, and compared to those obtained from conventional microstructured feed materials. It is found that the starting powder and the spraying conditions play a major role in the resulting coating characteristics. VPS applied coatings from nanostructured powder were found to generally offer the best performance, most notably under sliding wear conditions.

The growing need for new materials and material combinations with superior properties for severe service applications has led to the development of near net-shape forming techniques for certain materials, such as superalloys, refractory metals and highly reactive metals, including Titanium and its alloys. In this work, the vacuum plasma spraying process (VPS) was optimized to prepare dense spray-formed components from high purity plasma atomized Ti-6Al-4V powder. VPS offers a unique environment for spraying reactive materials such as Ti- 6Al-4V as a controlled inert atmosphere is used during deposition of the material. Three particle size distributions of the powder were used to investigate the influence of the starting powder characteristics (size, chemical composition) on the resulting spray-formed material. Post-deposition heat-treatments were subsequently applied to modify the deposit structure in order to improve their mechanical properties. The as-deposited and post-treated specimens were characterized for their internal microstructure and mechanical properties. Results indicate that a combination of high purity starting powder, controlled environment, and tailored deposition and post-processing conditions can be used to produce dense spray-formed Ti-6Al-4V structures with properties comparable to those of cast and wrought materials. Yield strength in the order of 800 MPa, with ultimate tensile strength close to 900 MPa and elongation near 10% were measured for spray-formed and heat-treated Ti-6Al-4V specimens. The results of this investigation on vacuum plasma spray forming of Ti-6Al-4V are presented in a series of two papers. The first one (this one) focuses on the preparation of the spray-form components, and on the resulting mechanical characteristics. The second paper is dedicated to the detailed characterization of the internal microstructure of the as-sprayed and heat-treated deposits, and the correlation with the measured mechanical properties.

Titanium alloys are extremely reactive in the molten state, therefore near-net shape and complex shape components cannot be produced by many techniques used for steel, aluminum and other less reactive metals. The vacuum plasma spray (VPS) process is a well-known method for coating and forming reactive metals and alloys such as titanium alloys. In this study the internal microstructure of individual splats, porosity, and mechanical properties of Ti-6Al-4V deposited by vacuum plasma spray forming (VPSF) were studied using SEM, XRD, mercury porosimetry, image analysis and mechanical testing. Results described in a companion paper show that while tensile and yield strength rise with increasing initial powders size, elongation still remains as low as 1%. The as-sprayed structure consists of α’ martensite with a small amount of residual β between the martensite colonies as well as pores between the splats. The fracture surface within the splats is indicative of ductile failure. The low cohesion between the splats results in damage accumulation at the boundaries and failure at small elongations. Post deposition heat treatments were conducted to improve the coating structure and were successful in improving the ductility to levels approaching that of traditionally processed material.

This paper investigates the mechanical properties of plasma-sprayed Al 2 O 3 -TiO 2 coatings. Micro and nano powders were deposited on hot and cold substrates under different conditions using atmospheric and vacuum plasma spraying. The coatings were then characterized based on microstructure, hardness, phase composition, abrasive wear rate, and adhesion strength. It is observed that Al 2 O 3 -TiO 2 layers are very dependent on the coating system, powder form, and spray parameters used. The layers sprayed with nanopowder in a vacuum were found to have the best combination of properties. Paper includes a German-language abstract.

The damaging of the electrodes during spraying can affect the reproducibility of the plasma spray process. Indeed, this may influence the plasma characteristics and the energy transfer to the sprayed particles resulting in significant changes in the coating attributes. In this paper, results from a detailed investigation on the stability of plasma spraying are presented. Specifically designed diagnosis tools were used to study the evolution of key parameters of a plasma spray process during a long-term experiment. A comprehensive analysis is carried out on the collected set of data, with an emphasis on the correlation that may exist among them. Results show significant variations in the particle state and gun characteristics with the spraying time. These variations are reflected in the microstructure of the sprayed coatings. The investigation also gives some indication on how the spray process could be controlled.

Pressure acid leaching (PAL) of lateritic nickel ores requires the use of extremely severe processing conditions (250 °C, > 4000 kPa, 98 % H2SO4). In addition to the severe corrosive nature of the acid solution, up to 30% of abrasive solids are present in the slurry. PyroGenesis Inc. has applied its expertise in materials science and thermal spray technologies into developing and commercially applying coatings for the protection of ball valve components used in PAL autoclaves. Vacuum plasma spray (VPS) and atmospheric plasma spray (APS) processes are used to apply coatings of metals and ceramics for corrosion and wear resistance, respectively. A comparative study on the microstructure and mechanical properties of different coatings, applied with the two processes, will be presented. Although APS coatings provide enhanced abrasive resistance, VPS coatings have shown the potential for superior properties. The extreme temperatures and pressures associated with the actual PAL conditions are too severe to simulate in laboratory conditions, hence, corrosion testing was not possible. Microstructural analysis, microhardness, adhesion, and abrasion testing were determined for each coating/processing combination.

Four high velocity thermal spray guns were evaluated in the production of 10%Co-4%Cr tungsten carbide cermets. Three HVOF guns (the JP-5000, JP-5000ST and DJ-2700) and one plasma gun, (the Mettech Axial III) were used to spray the same angular, agglomerated and crushed WC-10Co-4Cr powder. The DPV-2000 was used to monitor the in-flight velocity and temperature of the WC cermet sprayed particles. From those values, spray conditions were selected to produce coatings that were evaluated in terms of porosity, hardness and deposition efficiency. Results show that the plasma Axial III provides the highest particle temperature, between 2000°C and 2600°C, depending on the spray conditions. The JP-5000 imparts the highest velocity to the particles, between 550 m/s and 700 m/s, depending on the spray conditions. The ST version of the JP-5000 provides the same velocity as the standard version but with lower particle temperature. The DJ-2700 sprays particles with temperature and velocity between those of the JP5000 and the Mettech Axial III. Minimum porosity values of 2.1%, 3.7% and 5.3%) were obtained for the JP-5000, the DJ-2700 and the Axial III guns respectively. The porosity and carbide degradation are found to mostly depend on the particle velocity and temperature respectively. The values for the Vickers microhardness number (200g) ranged from 950 to 1250. Measurements of the deposition efficiency indicated a variation between 10 and 80%o, depending on the spray conditions and the gun used.

In this paper, two long-term experiments are conducted in order to investigate the evolution of the arc root fluctuations and the evolution of the in-flight particle state during plasma spraying. Voltage as well as the acoustic fluctuations measured at three different angles are characterized while particle state was monitored using an optical integrated system, the DPV2000. A detailed study of the evolution of the gun power, in-flight particle state (temperature, velocity, diameter, particle flux) and coating microstructure is was carried out. Results showed that the microstructure of the deposited coating significantly changed during the forty-hour spraying period. Paper includes a German-language abstract.

Novel thermal spray technologies must be thoroughly tested before they can replace the existing processes. In order to reproduce the properties of the accepted coatings, numerous test pieces must be sprayed and characterized by many different combinations of the available spray parameters. The method is time-consuming and often not very efficient. In this paper, a different approach is considered, whereby the state of the sprayed particles is characterized during the flight. The main objective is to examine the possibility to spray particles with similar in-flight characteristics with two different plasma guns in order to spray similar coatings with both guns. It is observed that the SM-F100 plasma gun can produce similar yttria stabilized zirconia particle jets as those sprayed with the F4-MB gun with 50% less electric power. Paper includes a German-language abstract.

The microstructure of plasma-sprayed deposits (PSD) is dominated by two void systems - interlamellar pores and intralamellar cracks - each with a different anisotropy. Varying anisotropics and crack-to-pore ratios within PSDs are responsible for the anisotropic properties observed in the deposits. While it is difficult to apply standard porosity measurement techniques to the assessment of anisotropic microstructures, novel techniques utilizing different approaches have recently emerged. Image analysis (IA) of impregnated PSD samples is the most direct technique. The structure is stabilized by impregnation and then polished and imaged. The limitations of IA lie in the impregnation process and in the subsequent polishing. Also, the images produced from anisotropic materials can be difficult to interpret quantitatively. The technique of small-angle neutron scattering (SANS) has recently been successfully applied to the study of PSDs. The major advantages of SANS are that it does not require sample preparation and that quantitative information can be gotten about the separate crack and pore systems, including their distinctive anisotropics. However, the relationship between the SANS results and the underlying structure is more complex and less intuitive than for IA, and the availability of the SANS technique is limited by the need to have access to a powerful neutron source, such as a reactor. Also, the two techniques present different views of the microstructure because of the different sensitivities in different parts of the size range. This paper compares results from IA and SANS from a set of thick plasma-sprayed ceramic deposits possessing a range of crack/pore microstructures, and discusses how the two techniques might complement one another.

The influence of input spray parameters on the state of plasma-sprayed zirconia powder is studied. The particle temperature, velocity and diameter are measured using an integrated optical monitoring system. The monitoring system allows the investigation of the particles behavior in the spray jet. The collected information is correlated to coating characteristics such as deposition efficiency, microstructure and thermal diffusivity. Results show that, by monitoring the state of sprayed particles, a better understanding of the coating microstructure and properties can be achieved.

In plasma spraying temperature and velocity of the sprayed particles are among the most important parameters influencing the microstructure and properties of the deposited coatings. However, the sprayed particle state is influenced by uncontrollable parameters such as the wear state of the electrodes. In order to investigate the influence of the electrode wear state on sprayed particles, a long-term experiment was conducted during which on-line measurements of plasma sprayed yttria-zirconia powder were performed. Results show that even though input parameters were kept constant during the experiment the state of the sprayed particle changed significantly and coatings prepared at different spraying times have different microstructures and can have different properties. However, by changing some input spray parameters it was possible to retrieve the initial sprayed particle state and coating microstructure.