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.

Commercial available Ni and Ti powder were blended together and deposited on stainless steel by atmospheric plasma spray(APS). Subsequently the as-sprayed coatings were laser remelted with a Nd -YAG pulsed laser source. Cross-sections of as-sprayed and laser-remelted coatings were characterized by scanning electron microscopy (SEM). Prior to SEM observations, the laser remelted coatings were polished and etched by Kroll etchant. Meanwhile, the energy dispersive spectrometer (EDS) was employed to analyze the chemical distribution of the coating both as-sprayed and laser remelted. The results indicated that APS sprayed NiTi coatings presented a dense microstructure with Ni splats and Ti splats distributing uniformly. Oxygen partial pressure in the argon leads to the burning of Ti splats during the laser remelting process. And Ti oxides located at the bottom of the laser molten pool because of the laser stiffness and molten flow. Moreover, the top part of the molten pool mainly involved in Ni columnar grains.

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.

In this study, laser glazing is used to densify plasma-sprayed YSZ coatings on carbon steel substrates. Melt pool characteristics are assessed for different laser settings and treatment conditions, including substrate preheating. SEM examination of coating surfaces and cross-sections before and after laser treatment shows how microstructure responds to process parameters. It also shows how preheating widens the melt pool, deepens the laser-glazed layer, and reduces the surface density of cracks, thus improving coating quality.

In this study, cold sprayed Ni is deposited on Al substrates using different gas pressures. Spherical Ni powder was sprayed on cylindrical substrates using argon as the powder carrier and compressed air as the propellant. Coating and splat surfaces and cross-sections were examined, adhesion strength was measured, and particle velocity and temperature were determined through CFD simulations. The results show that denser, more well adhered coatings were obtained under higher propellant pressure. Higher gas pressure increases particle velocity, which intensifies material deformation and the disruption of surface oxides in the impact area, resulting in greater metallurgical bonding between the splats and the substrate. The formation of Ni-Al intermetallic phase at the interface region due to heat treatment was confirmed and its effect on bonding strength is discussed.

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.

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 this work, numerical modeling is used to simulate the effects of laser remelting as a post treatment and as an in-situ component of a hybrid plasma spraying process. Initially, a single-pass 2D model is used to simulate the laser post-treatment process in order to obtain relationships between melting pool depth, relative scanning velocity, and laser power. A 3D finite-element model is then used to study temperature variations during multi-layer deposition of a NiCr alloy by plasma spraying with in-situ laser melting. The effects of phase change are taken into account by defining the enthalpy of the material as a function of temperature. Predicted melting pool depth corresponded well with experimental values.

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.

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.

Magnesium alloy AZ91D-SiC composite coatings were fabricated by cold spraying to study the effects of SiC particle size and volume fraction on microstructure and mechanical properties. The results show that coatings with large SiC particles have higher microhardness and bonding strength. Mechanically blended powders with fine SiC particles, on the other hand, are difficult to deposit. SiC volume fractions in the starting powders were 15, 30, 45, and 60 vol%, resulting in coatings with SiC volume fractions of 19, 27, 37, and 51 vol%. Based on test results, coating hardness and bonding strength increase with increasing volume fraction of SiC particles.

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.

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.

Very low pressure plasma spraying has been intensively studied in recent years especially the properties of plasma jet. These properties are affected by plasma generating and working conditions. These operating parameters such as arc power, plasma gas flow rate and chamber pressure have influences on specific enthalpy and temperature of plasma jet. In this work, the measurements under very low pressure were performed using enthalpy probe which was previously modified (increase of the internal diameter and depositing TBC coating (Ni/Al and ZrO 2 + Y 2 O 3 ) on the head). Different parameters, for instance, current intensity, hydrogen gas flow rate and detecting distance were changed in order to point out their effect on the characteristics of plasma jet. The specific enthalpy, temperature and quantity of heat in this situation were obtained.

Magnesium coatings were deposited upon aluminum and stainless steel substrates by cold spraying. Three Mg powders with different particle size distributions were used as feedstock. The microstructures of as-sprayed coatings were evaluated by optical microscopy, and scanning electron microscopy. The coating observations show that a main gas temperature has an important effect on the deposition behaviour of particles. Changing the gas temperature from 350°C to 630°C involves an increase of the deposition efficiency from 1.57% to 19.57%. The effects of the particle size distribution and substrate material on the deposition efficiency of particles were also investigated. The results show that the particle size distribution has a significant effect on the deposition efficiency of particles which increases from 19.57% to 59% when the mean particle size decreases from 63 µm to 38 µm under gas temperature of 630°C. However, the deposition efficiency of particles was slightly influenced by the substrate material. In addition to these experimental results, the in-flight particle velocities were simulated by FLUENT software to point out the effects of the gas temperature and particle size distribution.

In this paper, a commercial AZ91D magnesium alloy powder and its mixture with 30 vol.% SiC powder were used to deposit coatings by cold spraying. Two types of converging-diverging nozzles with different cross-sectional shapes were employed. The velocity and temperature of in-flight particles under different operating conditions were simulated using the FLUENT software. The simulated results show that the particle velocity through the rectangular cross-section nozzle is the same with that through the circular one. However, the coating observation shows that the AZ91D coating and its composite could only be deposited using the rectangular cross-section nozzle. The increase of gas temperature has little effect on the coating microstructure, porosity and microhardness. Furthermore, the observation of the composite coating produced under the gas temperature of 600°C shows that the SiC content in the composite is about 23 vol.%. The microhardness of the composite is improved to about 140 HV 0.3 due to the enhancement of SiC particles, compared to that of about 100 HV 0.3 for the AZ91D coating.

As a promising thermal spray technology, the very low pressure plasma spray (VLPPS) process has been significantly used to deposit thin, dense and homogenous ceramic coating materials for special application needs in recent years. In this study, a home-made transferred arc nozzle was mounted on a low power F100 plasma torch for enhancing the plasma jet energy under very low pressure conditions. Thin and dense alumina (Al 2 O 3 ) and yttria-stabilized zirconia (YSZ) ceramic coatings with an average thickness of 30-40 µm were successfully elaborated by VLPPS process below 1 mbar. Optical emission spectroscopy (OES) was used to analyze the properties of the plasma jet with or without powder injection. The microstructures of the coatings were observed by means of scanning electron microscopy (SEM). It was found that the YSZ coatings displayed a bimodal microstructure that was composed of splats formed by melted particles and a little amount of vapor condensation from evaporated particles. However, vapor condensation could not be observed in the Al 2 O 3 coatings formed by lamellar splats only. The Vickers microhardnesses of both coatings were also evaluated.

Cu coatings were obtained by the VLPPS (Very Low Pressure Plasma Spray) process using a torch F4-VB. The tank pressure was varied from 1 mbar to 5 mbar: these specific conditions can allow obtaining a higher vapor condensation fraction in the coating. Different sizes of powders are used to compare the vaporization level. The other possible influencing factors for obtaining compact film-like coating are also considered such as the distance between the torch and substrate, the orientation of the vapors and also the substrate temperatures. Microstructures of coatings are analyzed and combined with the results of plasma diagnostics. Jobin-Yvon spectrometer (type TRIAX190, UK) and Plasus Specline Spectroscopy software are both used for detecting and analyzing plasma spectrum data. The value of plasma electronic excited temperature Te was calculated through choosing Hα and Hβ two atom spectra. The results showed that the plasma belongs to cold plasma in the local thermodynamic equilibrium situation in VLPPS.

This study shows that surface preheating is required to avoid delamination of flame sprayed coating glazes. In the experiments, preheating parameters are determined from heat flux measurements and potential substrate degradation is characterized and controlled by optimizing spray parameters. Coating adhesion is determined by pull-out tests and remains constant even after freeze-thaw cycling. Although gas tightness was not characterized, aging tests show that no water percolates through pore networks in the coatings.