This work deals with ZrB 2 -based coatings prepared by inert plasma spraying and their behavior under high heat flux in moist atmospheres. ZrB 2 coatings with different compositions and microstructures were produced and subjected to high-temperature oxidation testing in order to identify the most oxidation-resistant sample. It is shown that coating microstructure can significantly influence oxidation kinetics and that uniformly dispersed nanoscale additives are particularly effective for slowing oxidation.

The aim of this study is to evaluate the thermal lifetime properties of yttria-stabilized zirconia (YSZ) coatings with a columnar microstructure. YSZ suspensions were sprayed under different conditions in order to obtain a sample lot with columnar microstructures varying from well-separated to closely spaced. Thermo-cyclic fatigue (TCF) tests were performed at 1100 °C and the results are presented. Coatings with well-separated columns reached 2150 cycles prior to failure compared to 1300 cycles in the case of coatings with compact columns. The apparent lower TCF resistance is attributed to a loss of thermal compliance inducing the development of sharp intercolumnar cracks. Failures seem to be linked to debonding at the TGO-substrate interface. The bond coat and substrate surface roughness also play a role in such failures and their impact is discussed.

Normal hemispherical spectral reflectances of plasma sprayed Al 2 O 3 /Al cermets were measured from visible to infrared wavelengths for several metal concentrations ranging from pure alumina to aluminum. Microstructure and composition of the samples were carefully characterized to explain their optical response, highly dependent on volume and/or surface scattering. Besides their contribution to the knowledge of microstructure, 2D scanning electron microscopy and 3D micro-tomography images were exploited to get statistical data in order to generate simplified numerical samples. A Monte Carlo ray-tracing model was then intended to reproduce experimental trends of the optical spectra. A good agreement with the experimental data was obtained.

Very low pressure plasma spraying (VLPPS) is an emerging process allowing manufacturing oxide and metallic coatings by condensation of vapors generated by feedstock powder vaporization. This process operates at unusually low pressures, typically between 100 and 1000 Pa. This paper aims at presenting recent developments for manufacturing Ti,Al,N coatings via a reactive mode. At first, nitrogen was used as the primary plasma forming gas to enrich spraying surrounding with nitriding species. Plasma jet mass enthalpy and substrate surface temperature were varied to evidence nitride phase formation during spraying. Then, a secondary nitrogen injection was implemented and located close to the surface to be covered in view of creating a continuous nitrogen supply to promote the nitriding mechanisms on the surface. SEM, XRD, GDOES and NHT were implemented to characterize coatings structure. This study highlights the nitrides formation versus spray operating conditions. The microstructural and mechanical features as well as the chemical composition are presented.

In this work, a numerical model of the cold spray process was developed to reproduce microstructures obtained in coatings by simulating the deformation of impinging particles and resulting coating build-up. The model employs a library of particle images generated by x-ray microtomography. To each image, a velocity is assigned and the deformation that would be produced by particle impact is estimated by means of finite element analysis and stored for later use. Based on the results, the ing approach has good potential for simulating coating microstructures that can be achieved through cold spraying.

This work evaluates the potential of using a plasma spray process to introduce SiC into zirconia diboride ceramic coatings. Controlling the spraying of the ultra-refractory compound ZrB 2 is the first challenge as it represents the matrix in which SiC particles will reside. To that end, the experiments focus on spraying parameters that influence the plasma jet and the nature of the precursor feedstock. The results show that ZrB 2 coatings containing controlled amounts of SiC can be obtained through high-energy suspension plasma spraying. The ZrB 2 -SiC coatings will be evaluated in a high-temperature oxidative environment in future work.

In the present study, X-ray microtomography is used to examine cold-sprayed tantalum splats on copper substrates. To resolve tantalum splats intermeshed with other splats of the same chemical composition, a contrasting medium of some sort is required. For this purpose, the feedstock powder is coated with an iron layer by means of fluidized-bed chemical vapor deposition. Experimental tests were coupled with finite element simulations to determine how stresses generated during the impact of a spherical iron-coated particle affect the integrity of the added contrasting layer.

Very low pressure plasma spraying (VLPPS) has been used to manufacture thin, dense, finely-structured ceramic coatings for various applications. This paper presents the results of work in which VLPPS is used to deposit metal. Aluminum was chosen as a demonstrative material, due to its moderate vaporization enthalpy (38.23 KJ·cm -3 ), with the objectives of better understanding the behavior of a solid precursor injected into the plasma jet, leading to the formation of vapors, and controlling the factors affecting coating structure. Nearly dense aluminum coatings were successfully deposited by VLPPS at 100 Pa with an intermediate power (45 kW) plasma torch. Optical emission spectroscopy (OES) was used to observe the behavior of the metal powder injected into the plasma jet, and simplified CFD modeling provided a better understanding of thermophysical mechanisms. The effect of powder size distribution, substrate temperature, and spray distance were studied. Coatings were characterized by SEM observations and Vickers microhardness measurements.

In this study, ceramic-matrix composites consisting of elongated metal (CoNbZr) particles in a cordierite (MgAlSiO) matrix were produced by plasma spraying. The metal powder was injected into the plasma jet downstream of the ceramic powder to minimize metal decomposition and oxidation. The microstructure and composition of cermet coatings containing 5, 10, and 20 vol% metal were analyzed by SEM and XRD and their electromagnetic properties were evaluated via saturation magnetization, permittivity, and permeability measurements. As expected, flake-shaped metallic particles were obtained and all coatings exhibited soft ferromagnetic behavior.

The residual stress level in coatings is a main issue in controlling in-service deformation, spallation or cracking. Residual stress generation has been widely studied for plasma and HVOF sprayed coatings, but only scare data are available for cold sprayed coatings. This paper describes the measurement and analysis of residual stresses in tantalum cold sprayed coatings. Residual stress measurements were performed by the hole-drilling and curvature methods. The former provided a through-thickness residual stress profile in the coating while the latter was used to investigate the in-situ residual stress evolution during the deposition process. The results from both methods were consistent and showed compressive stress of 350 MPa for a tantalum coating deposited on a 3 mm thick copper substrate at 80°C.

To answer current issues adequately considering technical, economic, as well as environmental requirements, material transformation and especially surface treatment industries must be source of innovations to be proactive. As a result, developing new alternative solutions to existing ones had become a top priority. Considering surface treatment processes, conventional ones (thermal spraying, plasma transferred arc) do not allow to consider this approach since the processes themselves (co-treatment of different powders) do not permit to guarantee the initial composition nor do they ensure a sufficient homogeneity to the coating structure. If indeed the dry surface treatment processes have already shown large potential, several limits remain such as an inefficient adhesion, an environmental impact over the life cycle or almost no materials on the market. To overcome these issues hybrid coating technologies (combining several processes) are likely to be developed. From all of them, laser technology seems to be very promising due to its high flexibility considering all the potential parameters (varying power, continuous or pulsed beam, etc.) and the localised treated area. For instance, combining simultaneously a laser with a thermal spray process enables the elaboration of a thick coating showing a good adherence. The ablation laser applied on the substrate surface just before the impacting particles as promoted in the PROTAL process permit to insure a suitable surface state favourable to the particles adhesion. The control of the coating microstructure was not so much studied. That is why, to complete the knowledge in this area, this work aims at studying the influence of laser technology in association with plasma spraying on the coating microstructure and more precisely on the coating mechanical properties. Coatings were characterized by SEM and void content was evaluated through image analysis and Archimedean porosimetry. Mechanical properties were assessed by the four points bending test for evaluating the coating apparent Young modulus.

Yttrium silicates are among the candidates for protection of silicon-based ceramics in high temperature and moist environments due to chemical and mechanical compatibility with substrate, low volatility and moisture resistance. Here we reported on the development of yttrium silicate coatings by sol precursor plasma spraying. The use of a sol feedstock allowed easy composition flexibility. The microstructure and the structure of as-sprayed and heat-treated coatings were investigated. Finer microstructure was obtained compared to micrometric powder plasma spraying traditionally used to produce environmental barrier coatings (EBC). XRD analyses on as-sprayed coatings revealed amorphous or crystalline layers depending on plasma parameters. In EBC application, a volume change from crystallization or phase transformation was envisaged to be damaging due to induced stresses and fully crystalline phases are a key durability requirement for EBC from conventional plasma spraying. Yttrium silicates are characterized by an important polymorphism and the ability to form amorphous coatings. Therefore, special attention was so paid to the amorphous degree of the coatings.

The adhesion mechanisms involved in the cold spray coatings are not still well elucidated. The quality of the deposit does depend mainly on particles and dynamic characteristics (which result from nozzle type, nozzle-substrate distance, etc.). The present work is based on the study of particle-substrate and particle-particle interfaces in the tantalum-copper coating-substrate system. The content focuses on the influence of the oxygen content in the starting powder on interface features, consequently on coating properties. Tantalum powders with different oxygen levels were studied using SEM (Scanning Electron Microscopy) and EPMA (Electron Probe Microanalysis). Laser shock spallation of cold-sprayed Ta coatings was developed as a reliable and flexible process to achieve Ta spalls to be deposited at a high-velocity onto Cu targets. The velocity due to the laser shock could be controlled to be similar to that of particles in conventional cold spray. This results in Ta-Cu interfaces, the study of which was carried out to go into interface phenomena involved in cold spray, using TEM (Transmission Electron Microscopy) in particular. Results were compared to those obtained from laser shock spallation of Ta bulk specimens (i.e. made of a conventional Ta sheet). The role of powder oxidation on interface soundness was exhibited. Adhesion was shown to be all the lower as powder oxygen content was higher, using LASAT (“ Laser Shock Adhesion Test”) in addition to direct observation of interfaces. Results were exploited to discuss properties of the corresponding Ta coatings onto Cu, i.e. which were cold sprayed using powders with different oxygen contents.

Tungsten-based cermets are well-known engineering materials finding applications in aerospace, nuclear equipment, and many other fields. Plasma spraying is an interesting industrial process to manufacture those refractory materials. Original plasma sprayed hard coatings for wear protection composed of a stainless steel matrix and inclusions of tungsten carbide (WC) nanoparticles were developed. To built-up the coatings, two precursors were injected separately in the plasma jet : a stainless steel micrometric powder was classically injected into the plasma jet using a carrier gas whereas WC nanoparticles were injected with a liquid carrier, like in the so-called process suspension plasma spraying. One of the challenges is to maintain the WC phase stoichiometry in the deposit, without decomposing the carbide into brittle W 2 C, W 3 C, and metallic tungsten, phenomenon usually occurring with thermal spraying techniques. Another issue is to succeed in including homogeneously the carbide nanoparticles in a sufficiently dense stainless steel matrix. Coatings with different WC contents were deposited on stainless steel substrates and investigated with respect to their microstructure by optical and scanning electron microscopy, porosity level using the Archimedean method, phase composition by X-ray diffraction and Vickers micro-hardness. Results have shown that coatings consisting of a stainless steel matrix containing inclusions of carbide nanoparticles can be produced by plasma spraying. The phase composition analysis indicated that nanoparticles are largely composed of the WC phase and contain a small amount of WC1-x phases. A slight increase of the porosity level was measured for coatings containing nanoparticles, compared to the pure matrix, probably due to the cooling effect of the WC carrier liquid on the in-flight characteristics of the stainless steel particles. Micro-hardness measurements gave similar values for with or without nano-sized particles, showing that the amount of WC included in the samples was insufficient to improve the hardness property.

Solid oxide fuel cell are being widely considered as the promising answer to the fossil energy decrease. To achieve high efficiency and longevity for SOFC stack it is essential to maintain stable hermetic sealing. In order to obtain an efficient airtightness between two SOFC layers, the authors had developed a solid seal composed with a ceramic matrix charged with glass particles. The seal is plasma-sprayed using low-cost manufacturing methods such as atmospheric plasma spraying. This technical deposit can be plasma-sprayed on a wide range of substrates: whatever its nature and shape. It is solid, distortable and adhesive to its support at ambient temperature. The sealing properties are acquired when the SOFC is put into service: the glassy phase migrates into the peculiar plasma-sprayed microstructure of the ceramic matrix towards the interface involving the airtightness. The performance of this seal are pretty good: the leak rate observed at 70 mbar is 0.0042 mbar.l/s whereas the preconisation of the US Department of Energy is 0.005 mbar.l/s.

This paper is devoted to the study of coatings elaborated by a process permitting Air Plasma Spraying (A.P.S.) of finely structured ceramic coatings. This process mainly consists in injecting in a d.c. plasma jet, a ceramic suspension containing sub-micron ceramic particles. Coating characteristics are close to those observed in P.E.C.V.D., but with a faster elaboration rate (. 15 µm/m2.h) and, the possibility to produce a wide range of thicknesses (1 < e < 100 µm). This paper is aimed at producing the Yttria Stabilized Zirconia electrolyte (Y.S.Z.) of Solid Oxide Fuel Cells with a thickness of 5 to 30 µm. Previous studies of this process have been devoted to the influence of the spray parameters on the structure of Y.S.Z. splats collected and have allowed determining some well adapted working conditions. The new stage described in this paper, is related to the study of the growth of Yttria Stabilized Zirconia coatings and the influence of different parameters such as the ceramic particle size distributions contained in the suspension and the heat flux imposed to the surface of the substrate and successive passes during the coating elaboration.

Plasma coating performances and lifetimes may be ruined during service conditions because of uncontrolled residual stress development within the coating. This study presents the results of a CAST3M thermomechanical numerical model which purpose is to simulate the different residual stresses development within the duplex coating-substrate during the coating built up and its comparison with the experimental results. To achieve the thermal spray process understanding all the thermal fluxes transferred to a metallic beam and surrounding temperatures were measured so as to provide the CAST3M model with precise boundary conditions, corresponding to a specific geometry. The residual stresses were experimentally determined by the in situ curvature measurement and, afterwards, by the hole drilling method. The plasma torch stand-off distance, the relative torch/substrate velocity and the substrate material were considered as the parameters of this study. The main results concern the substrate temperature and deflection during the preheating stage, the thermal energy transferred by the molten splats to the substrate together with the quenching stress and the development of thermal stress during the final cooling.

The aim of this paper is to compare the impact of plasma deposition processes onto Yttria Stabilized Zirconia (YSZ) electrolytes’ properties. Indeed, physical properties and microstructure of plasma sprayed coatings depend on the in-flight treatment of the particles in the plasma jet. Investigations of the relationships between spraying conditions and the in-flight properties of the particles upon impact for Air Plasma Spraying (APS) and Vacuum Plasma Spraying (VPS) were carried out using a MacLean & Anderson design of experiment. The In-flight particle properties were determined using the DPV 2000. For each type of plasma spraying process, coatings were elaborated with optimized plasma spraying conditions that allowed reaching the highest particle velocity upon impact keeping the highest temperature as possible. Coatings properties were then, evaluated by SEM and impedance spectroscopy.

This paper describes a study of a plasma spray process to deposit ceramic coatings with finer structures than those that can be produced by conventional DC plasma spraying. The structures are similar to those produced by plasma-enhanced chemical vapor deposition (PECVD), but with a very fast coating rate and the ability to produce a wide range of thicknesses (1 < e < 100 µm). The process involves injecting a ceramic suspension containing submicronic ceramic particles into a DC plasma jet. The goal is to develop the process so that it can be used for the production of such coatings as yttria stabilized zirconia (YSZ), Ni-YSZ, or perovskite (for solid oxide fuel cells) or YSZ, Al 2 O 3 -YSZ, or Pyrochlore (for thermal barrier applications). The research stage described in this paper is related to the study of the growth of YSZ coatings, to calculations of the dynamic and thermal plasma-particle transfers, linked to the effect on particle flattening of the various spray parameters (arc current intensity, particle collection distance, substrate temperature, plasma gas composition, and so on). It also describes the achievement of a multi layered coating of YSZ and alumina.

The aim of this paper is the optimization of Yttria Stabilized Zirconia (YSZ) particle injection in a supersonic induction plasma torch to improve the reproducibility of this plasma deposition process. Indeed, the optimization is necessary to eradicate clogging in the supersonic nozzle due to the constriction of the nozzle. Investigations of the relationships between the parameters of particle’injection and the in-flight properties of the particles are carried out using an ANOVA experiment design. The in-flight particle properties were determined using two commercial systems, the DPV 2000 associated with the CPS 2000 (temperature, velocity and diameter of in-flight cold particles) and the Control Vision system (divergence of plasma jet imagery). First results have shown the necessity of a new design of the injection probe; development that allowed to reach a good reproducibility in terms of particle velocity and molten state.