An innovative hybrid process which combines the two very effective solid-state techniques of cold spraying (CS) and friction stir processing (FSP), was proposed to fabricate a high-strength ultrafine-grained Cu-Zn coating. Results show that the CS coating had an elongated microstructure with 78.42% of low-angle grain boundaries. Following FSP, there appear ultrafine grains with 90.47% of high-angle grain boundaries and a composition of α, β' and γ phases while the CS coatings was mainly α. Significant mechanical properties enhancement is achieved, i.e. with the ultimate tensile strength increasing from 87.2 MPa to 257.5 MPa and fracture elongation increasing from 0.17% to 0.81%. The precipitates have a significant effect on the fracture behavior of FSP coatings.

The objective of this research is to investigate the changes of the microstructure and mechanical property of aluminum based coatings manufactured by VLPPS along the radial directions of the plasma plume. Aluminum powders were sprayed with a F4-VB low-power plasma gun under a working pressure of 150 Pa. Coatings deposition is studied at different distances from the plasma plume impact. Front of the plasma plume, in-situ reactions between aluminum and substrate elements (such as Fe, Cr, Ni) present in the base metal take places. It mainly forms aluminum based intermetallic Al 3 Fe coating according to the XRD. Based on the SEM observation, the packed columnar microstructure mixed with nanometer particles is formed with a majority of pure vapor condensation due to evaporated particles from the plasma jet and/or aluminum coating already made. For different distances relative to the center of plasma plume (i.e. from 10 mm to 110 mm along the radial directions), the deposited coatings exhibit a lamellar binary structure which was formed by the mixed deposition of vapor and molten droplets. The coatings morphologies vary from nearly dense to loose and highly porous. Finally, the hardness of typical coating is investigated. The Al based intermetallic Al x Fe y coating, on the center of the plasma plume, reached 448HV 0.025 , which is much higher than those obtained at other positions.

In this study, YSZ coatings were deposited on different substrate materials (stainless steel and aluminum) using suspension plasma spray (SPS) technique. The effects of substrate properties (material, surface topology, temperature, and thickness) on the formation of coatings were investigated. The results showed that, with the identical spray parameters, the porosity is higher for the coatings deposited on aluminum than that on stainless steel due to the high thermal transfer ability of the former substrate material. The SEM results revealed that the microstructure of as-prepared coatings could be tailored from the vertical cracked structure to the columnar structure by increasing the substrate surface roughness and their formation mechanisms were discussed. The substrate preheating temperature has an influence on the microstructure of the coatings, especially in the interfacial region and increasing the substrate temperature is an effective means for reducing the interface defects in the coatings. With the increase of the substrate thickness, the quantity of the vertical cracks in the coatings is reduced and their width becomes narrower.

The presence of defects such as voids, inter-lamellar porosities or cracks, provides a decrease of the effective thermal conductivity of plasma sprayed coatings as well as a decrease of the corresponding mechanical properties such as the Young’s modulus. In general, effective properties of thermal spray coatings are thus strongly different from that of the bulk material and have thus to be quantified to validate their in service performances. A complementary approach allowing understanding the relationships between the microstructure of a coating and its macro-properties is the use of Finite Element Modeling. The case of composite coatings is still more complicated due to the presence of different materials. In the present study, thermo-mechanical properties of a plasma sprayed composite coating were estimated by numerical modeling based on FEM. The applied method uses directly cross-sectional micrographs without simplification using a one-cell per pixel approach. Characteristics such as the thermal conductivity, the Young’s modulus, the Poisson ratio and the dilatation coefficient were considered. The selected example was an AlSi/polyester coating used as abradable seal in the aerospace industry.

Abradable seals are used in aircraft engine compressor and turbine to decrease fuel consumption. Their role is to minimize the clearance between the rotating blades of an engine rotor and the casing to reduce air leakages (compressor) or air-fuel combustion product leakages (turbine). Operating temperatures in turbines (up to 1800°C) can induce a thermal expansion of the blades and give rise to contacts providing damages to the blades or casing. Thus, in case of contact, the blade should remove the abradable seals applied to the casing without being damaged. Besides, the seal must be resistant to the turbine environment. Direct relationships have been observed between plasma spray operating parameters and abradable coating performances. The aim of this study is to determine those relationships for YSZ-Polyester abradable composite coatings. This study is conducted within the frame work of the 7FP European project E-BREAK to reach the environmental objectives of the European Advisory Council for Aviation Research and innovation.

Alumina and yttria coatings, manufactured by suspension plasma spraying, were investigated to understand the “material effect” in the coating building. Some particle image velocimetry measurements were carried out to evaluate the particle velocities into the plasma. Some particle collections were performed to get information on their molten state. Splats were observed by scanning electron microscopy (SEM) and their dimensions were measured with an interferometric profilometer. Coating cross sections were finally observed by SEM and porosity rates were evaluated by image analysis and ultra-small angle X-scattering. This study revealed no real difference between the two materials concerning particle velocity. However, splat analyses highlighted a better flattening ratio for yttria particles, due to a lower difficulty to melt of this material. This property seems to enhance particle vaporization whose condensates are found on coating surface. These observations explain the difference of pore size distributions observed for both coatings.

Atmospheric Plasma Spray is widely used for tens of years to elaborate protective coatings on parts for several applications. However, our understanding of the APS process can still be improved, requiring a fine modeling of the process in parallel with some corresponding experiments. In the present work, a complete series of models was applied to reinforce our knowledge of the process: the case of an alumina coating was considered. A 3D CFD model was first used to study the internal arc within the torch. Interactions between the external plasma jet and the injected particles were then computed in a second step. At this level, the predicted in-flight particle characteristics were compared with some corresponding measurements recorded with the DPV 2000 diagnostic tool. A third model was then applied to investigate the particle flattening on the substrate/coating material. SEM pictures of coating cross-sections were then captured and a last model was finally applied to estimate the coating effective thermos-mechanical properties based on calculations performed directly on the SEM micrographs. This set of models allows investigating the APS process from the DC arc within the torch to the coating properties.

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.

The primary aim of this work is to develop an emulator to accurately simulate the dynamic behavior of a plasma torch. To that end, a nonlinear autoregressive model with exogenous inputs was designed around a mono-cathode torch used for atmospheric plasma spraying. Operating parameters such as current and gas flow rate were used as input variables and in-flight particle characteristics were used as output variables. In order to compensate for unstable and random process phenomena, data smoothing is used to decrease signal noise and improve data relevance. This is a key step as it allows most of the in-flight particle properties to be processed. Prior to implementation in the emulator, the smoothed data are optimized to get the best possible match with actual measured values. With the refined data, the difference between simulated and measured particle temperature and velocity is less than 3%.

In the present work, a mechanical alloying (ball milling) method was developed to synthesize NiCrBSi-WC composite powders for HVOF spraying. Coating properties and microstructure are shown to vary with composition and initial powder size prior to ball-milling. With nanometric particles, metallic and carbide powders appear to be intimately linked with WC, forming a highly protective layer. Conversely, with micrometric powders, ball-milled particles appear more fractured and regularly dispersed inside the matrix.

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.

The aim of this work is to develop a model that predicts coating thickness based on thermal spray robot trajectories and the thermal history of the workpiece. To test the model, an alumina layer is deposited on a steel substrate by air plasma spraying. Robot path coordinates are stored in a text file and used to compute substrate temperature fields by solving the transient heat conservation equation during torch displacement. The contributions of the impinging plasma jet and molten particle stream are accounted for in the model. The distribution of matter in the particle spray is used to simulate coating formation and determine coating thickness.

This paper describes the development and testing of an emulator representing a single-cathode atmospheric plasma torch. The emulator consists of three subsystems: input, simulator, and output. Arc current intensity, the hydrogen ratio of the forming gas, and its total mass flow rate are taken as input parameters, while in-flight particle temperature and velocity are the designated output. The simulator was developed in a two-stage process. By collecting and analyzing experimental data, a mathematic model expressing plasma torch operation was defined. The model was then tested and compared with experimental data. It is shown to be relatively accurate with an average error of about 2.2% in particle temperature and 1.1% in velocity.

During plasma spray process, many intrinsic operating parameters allow tailoring the in-flight particle characteristics (temperature and velocity), thus affecting the final coating characteristics. Among them, plasma enthalpy, thermal conductivity, momentum, density, etc. result from the selection of extrinsic operating parameters such as the plasma torch nozzle geometry, composition and flow rate of plasma forming gases, the arc current intensity, etc. The complex relationships among those operating parameters make it difficult to fully predict their effects. Moreover, temporal fluctuations (anode wear for example) require "real time" corrections to maintain particle characteristics to targeted values. In addition, substrate temperature has to be maintained to targeted values depending upon the feedstock to be sprayed, the geometry of the part to be coated, its thermal capacity, etc. An expert system was built to optimize and control some of the main extrinsic operating parameters. This expert system includes two parts: 1) an artificial neural network (ANN), which predicts an extrinsic operating window and 2) a fuzzy logic controller (FLC) to control it. The paper details the general architecture of the system, discusses its limits and typical characteristics. An example is finally presented.

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.

The field of materials processing experiences many applications and developments in multiple industrial sectors where the used materials have to operate in most cases under extreme conditions (of temperature, pressure, reactivity of the environment, etc.). Under such conditions, he implementation of a system dedicated to the knowledge capitalization and ability concerning the use of technologies of the manufacturing processes remains today very important for the promotion of collective progresses in these fields. This is the main objective of this project which aims at promoting distance learning (e-learning) and at developing new knowledge-based systems to undergo scientific and technological skills. Currently, the research and education world is experiencing many urges of change, partly enabled and stimulated by the new possibilities offered by the Web. There is clear evidence that e-learning offers increased opportunities for training assessment leading to real benefits in terms of learner retention and achievement. This paper outlines the steps of the development of thermal spraying training supports using appropriate technologies in the thermal spraying field.

Suspension plasma spraying (SPS) is able to process a stabilized suspension of nanometer-sized feedstock particles to form thin (from 20 to 100 µm) coatings with unique microstructures. The void network architecture of these ceramic coatings is a challenge to be characterized and quantified using commonly used techniques due to small sizes involved. Nevertheless, the discrimination of these pore architectures in terms of size and shape distribution, anisotropy, specific surface area, etc., is critical for the understanding of processing, microstructure, and properties relationships. USAXS (Ultra-Small Angle X-Rays Scattering) appeared as a suitable measurement technique allowing discriminating the void size distribution over a large range (up to four orders of magnitude). Results indicate that as-sprayed SPS coatings exhibit unusual porous architecture: 1) average void size is about the same than the feedstock one; i.e., nanometer sizes with multimodal void size distribution; 2) about 80% of the voids exhibit characteristic dimensions smaller than 30 nm; 3) the total void content varies between 13 to 20% depending upon considered operating parameters. In-situ annealing measurements were performed as they proved to deliver more relevant results compared to ex-situ measurements: even at temperatures as low as 800°C, the microstructure transforms - while the total void content does not change significantly. Indeed, it has been demonstrated that the smallest voids (equivalent diameters smaller than 50 nm) coalescence was the predominant mechanism and that it was more sensitive to temperature than time.

Alumina-titania plasma spray coatings are widely used for their tribological performances. The combination of these two ceramics in a particular mix percentage permits to manufacture coatings with better wear resistance in comparison to those made of pure alumina. Suspension plasma spraying permit to manufacture sub-micrometer structure coatings very fine structure thanks to precursors which have an initial size of 10 to 300 nm. The use of a liquid feedstock, aqueous or alcoholic, allows the use of nanometer particles directly without the need to agglomerate them to obtain conventional nanostructured micrometer-sized powders. This study aims at studying Al 2 O 3 and Al 2 O 3 -TiO 2 coatings made from aqueous and alcoholic suspensions produced by suspension plasma spraying. Microstructures and phase evolutions are considered. Manufactured coatings present different architectures depending of operating parameters and feedstock particle sizes; the lower the particle diameter, the thinner the microstructure. Phases composition are discussed and compared to conventional micrometer-sized structure Al 2 O 3 and Al 2 O 3 -TiO 2 coatings.

Large (3 x 3 x 0.05 m 3 ) refractory pieces (as the ones used for examples in smelters or incinerators) do not sustain regular glazing in a kiln, mostly due to high associated costs. Still, glass coatings could find use on such pieces due to their physical properties (durability, chemical inertia, tightness, etc.). Thermal spraying, using oxyacetylenic flame in particular, appears as a cost-effective solution permitting to circumvent the aforementioned disadvantages. This study aims at evaluating the quality of two types of coatings in terms of permeability. The first type considered coatings (resulting from a previous optimization of the spray operating parameters) sprayed directly on the substrates whereas the second one considered an additional brass underlayer manufactured by twin-wire electric arc spraying. The wettability of the glaze on the refractory substrate and on the brass underlayer was studied to comprehend the coating structural attributes (thickness, porosity, crazing, etc.) as well as their effects on the permeability. A specific measuring device was developed to assess permeability.

Intermediate temperature solid oxide fuel cells include in their design a solid electrolyte layer, usually made of yttria-stabilized zirconia, that acts as an ionic conductor through which oxygen ions diffuse. This layer must be as thin as possible to limit ohmic losses yet have a low leakage rate corresponding to a low level of connected stacking defects such as microcracks. Suspension plasma spraying (SPS) appears to be a viable method for manufacturing such layers and is used in this study to produce gastight coatings that with further improvements may meet the requirements of SOFCs. The paper describes the setup and optimization of the SPS process and the methods used to evaluate the solid electrolyte layers.