An optimized powder/suspension based atmospheric Plasma Spray (PS) process, using a Triplex Pro 210 TM torch, was implemented to elaborate Cu:TiO2 surface coatings on stainless steel. Nanometric Degussa P25 TM powder was prepared in a water-based suspension and co-sprayed with a Cu spheroidal powder. The bacterial reduction, evaluated with 1h-exposure to Escherichia Coli (E. Coli), was two times higher for the Cu:TiO2 coating compared to the bare stainless steel substrate. Since the coatings obtained by plasma spray are relatively porous, their antibacterial efficacy was compared to smooth Ag and Cu doped titanium nitride (TiN) films obtained by physical vapor deposition technique (PVD). For the same exposure time, the PVD smooth coatings showed a much lower antibacterial efficacy proving the topography effect on bacterial adhesion.

In this study, two coatings, one produced by HVOF spraying, the other by physical vapor deposition (PVD), were applied on a nickel superalloy substrate in order to compare their hot corrosion behavior. The coating samples were initially characterized by OM and SEM-EDS analysis, then a mixture of V 2 O 5 , Na 2 SO 4 , and NaCl was deposited on the surface and the samples were to 900 °C for 35 h. The results show that the PVD CrN coating provided better corrosion protection than HVOF-sprayed CrC-NiCrAlY.

Molten calcium-magnesium-aluminum-silicate (CMAS) particles cause significant degradation of thermal barrier coatings (TBCs) in aero-engines. One way to protect TBCs against CMAS attack is through the application of a sacrificial topcoat. In this work, Al 2 O 3 coatings were deposited on top of EB-PVD 7wt% YSZ layers via suspension thermal spraying using an aqueous Al 2 O 3 suspension. Spray parameters were varied in order to obtain Al 2 O 3 layers with two different microstructures and porosity levels. The coating systems were evaluated by means of CMAS infiltration testing at 1250 °C. It was found that the porosity and morphology of Al 2 O 3 strongly influence CMAS infiltration and the formation of reaction products and that CMAS mitigation is a function of coating morphology and the speed at which Al 2 O 3 reacts with CMAS deposits.

Thermal barrier coatings are generally produced one of two ways, depending on the thermomechanical loading expected. This study assesses an alternative approach in which the output of an air plasma torch is directed through two chambers connected by an expansion nozzle. In the first chamber, the particles evaporate under high pressure and temperature conditions. The vapor then passes through a supersonic nozzle into a low-pressure chamber where it condenses on the target substrate. A number of models are developed and used in order to assess the effects of process geometry and operating conditions on gas flows, powder vaporization efficiency, and nucleation and growth kinetics. Numerical simulations also informed various design decisions such as the length of the high-pressure chamber and the diameter of the expansion nozzle.

Fabrication of Thermal Barrier Coatings (TBCs) with higher lifetime and relatively cheaper processes is of particular interest for gas turbine applications. Suspension Plasma Spray (SPS) is capable of producing coatings with porous columnar structure, and it is also a much cheaper process compared to the conventionally used Electron Beam Physical Vapor Deposition (EB-PVD). Although TBCs fabricated using SPS have lower thermal conductivity as compared to other commonly used processes, they are still not commercialized due to their poor lifetime expectancy. Lifetime of TBCs is highly influenced by the top coat microstructure. The objective of this work was to study the TBCs produced using axial SPS with different process parameters. The bond coat was deposited using High Velocity Air Fuel (HVAF) spray. Influence of the microstructure on lifetime of the coatings was of particular interest and it was determined by thermal cyclic fatigue testing. Thermal conductivity of the coatings was determined by laser flash analysis. The results show that axial SPS could be a promising method of producing TBCs for high temperature gas turbine applications.

The erosion behaviour at room temperature (RT) of as-deposited SPS, EB-PVD and APS YSZ-based TBCs was investigated. All coatings were deposited on Inconel 625 alloy coupons. The same APS CoNiCrAlY bond coat was employed for all SPS and APS TBCs. The erodent material was 50 μm alumina and the impact angles were 15° and 90°. A total of 4 different types of SPS YSZ-based TBCs were tested, which consisted of two distinct columnar-segmented and two distinct columnar-grown microstructures. The EB-PVD and APS YSZ TBCs were employed as benchmarks. The erosion performance of the different TBCs in this study was ranked based on the coating volume loss after wear testing. The TBC microstructures and phase compositions were evaluated via SEM and XRD. The erosion mechanisms of the different TBCs were compared by analyzing the cross-sectional and top surface microstructures of the as-sprayed and eroded TBCs. These are released results from the Surftec Industrial R&D Group of the National Research Council of Canada (NRC).

In the Plasma Spray-Physical Vapor Deposition (PS-PVD) process, the vapor atom of feedstock material is one deposition unit of the columnar structure coating. It is reported that the gas phase may be transformed into cluster when the powder feeding rate increases from small to large or the sedimentation distance increases from a certain distance to another distance. In order to understanding the variation of vaporized coating material in free plasma jet, the gaseous material capacity of plasma jet must be fundamentally understood. In this work, the thermal characteristics of plasma were firstly measured by optical emission spectrometry (OES). The results show that the free plasma jet is in the local thermal equilibrium due to a typical electron number density from 2.1×1015 to 3.1×1015 cm -3 . In this condition, the temperature of gaseous zirconia can be equal to the plasma temperature. A model was developed to obtain the vapor pressure of gaseous ZrO 2 molecules as a two dimensional map of jet axis and radial position corresponding to different average plasma temperatures. The overall gaseous material capacity of free plasma jet was further established. At a position of plasma jet, clusters may form when the gaseous material exceeds local maximum gaseous material capacity.

In surface science of functional oxides, Titanium dioxide (TiO 2 ) is one of the most investigated crystalline systems either in rutile or anatase phases. Rutile phase is widely used in microelectronic, tribological applications and in the conversion of solar energy. Anatase phase is used in self-cleaning, antifogging, photo-catalytic and biomedical technologies. This work focuses on studying the required process conditions to obtain TiO 2 targets by APS onto metallic substrates using commercial TiO 2 powders (Oerlikon Metco in Switzerland) with suitable physical and chemical properties for technological and medical applications as PAPVD coatings. APS targets were compared to sintered ones. The raw powders were characterized by laser diffraction, SEM, XRF and XRD while the characteristics of the APS-deposited targets as well as the sintered ones were determined by SEM and XRD to identify the constituent phases. This work allowed confirming the advantages and limitations of both processes in terms of grain size, chemical composition, microstructural homogeneity and density in order to choose the best option to manufacture targets for PAPVD coatings for technological and medical applications.

Environmental barrier coatings (EBC) are currently being investigated to protect ceramic matrix composite (CMC) turbine engine components in water-vapor rich combustion environments. Dense, crack-free, uniform and well-adhered coatings are demanded for this purpose. This paper represents an assessment of different thermal spray techniques for deposition of Yb 2 Si 2 O 7 and silicon (Si) EBC layers. Plasma spraying of refractory silicates is known to be complicated by undesired glass transition due to rapid solidification as well as evaporation of Si-bearing species during spraying. Plasma spraying of low-density Si also requires careful optimizations as it tends to oxidize during spraying, particularly at atmospheric conditions. Bearing these problems in mind, the Yb 2 Si 2 O 7 coatings were deposited by atmospheric plasma spraying (APS), high-velocity oxygen-fuel spraying (HVOF), and plasma-spray physical vapor deposition (PS-PVD) techniques. As-sprayed microstructure, amorphous content and phase composition of the coatings were analyzed. Based on the findings, the advantages and disadvantages of each method over other techniques are discussed with respect to process parameters and material properties.

Cr 3+ Photoluminescence piezo-spectroscopy (CPLPS) has been developed as a non-destructive inspection technique for the measurement of residual stresses within the thermally grown oxide (TGO) in thermal barrier coatings (TBCs). In this study, plasma spray - physical vapor deposition (PS-PVD) process was used to deposit yttria stabilized zirconia (YSZ) topcoat with quasi-columnar structures. Evolution of the microstructures and residual stress distribution in such kind structured TBCs before and after thermal cycle test on burner rigs were investigated. The accumulated tensile stress in the as-sprayed ceramic topcoat changed to compressive state after 100 cycles, and then gradually increased. In addition, the mapping compressive stresses in the TGO measured through the ceramic topcoat surface decreased rapidly firstly and then essentially maintain at a relatively stable value with further testing. Moreover, the pre-oxidation of the bondcoat could significantly affect the stress distribution in the TGO, in contrast, no obviously influence on the stresses in the YSZ topcoat.

As a new processing technology, plasma spray physical vapor deposition (PS-PVD) is capable to deposit coatings out of the vapor phase with high deposition rate. Moreover, the resulting quasi-columnar coatings were unique, hardly deposited by other process. Due to its low thermal conductivity and excellent superior strain tolerance, quasi-columnar coatings attract much attention in the thermal barrier coatings (TBCs) field. In this paper, the morphology variation of the quasi-columnar yttria stabilized zirconia (YSZ) coatings deposited under different conditions was investigated. Combined the morphology of the initial deposits during short time spraying, the deposition mechanism of quasi-column microstructure was concluded. It can be found that the quasi-column coating was formed by co-deposition of vapor phases and solid particles. The vapor phase can develop into column, while the solid particles not only intensified the shadowing effect but also destroyed the nucleus during vapor deposition.

Plasma Spray Physical Vapor Deposition aims to substantially evaporate a powder in order to produce coatings with microstructures ranging from lamellar to columnar. This is achieved by the deposition of fine melted powder particles and nanoclusters and/or vapor condensation. The deposition process typically operates at pressure ranging between 10 and 200 Pa. In addition to experimental works, numerical works help to better understand the process and optimize the experimental conditions. However, the combination of high temperature and low pressure with the appearance of shock waves resulting from the supersonic expansion of the hot gas in the low pressure medium, makes questionable the suitability of the continuum approach for modelling such a process. This work deals with the study of (i) the effect of the pressure dependence of the thermodynamic and transport properties on the CFD predictions and (ii) the validity of the continuum approach for thermal plasma flow simulation under very low pressure conditions. It compares the flow fields predicted with a continuum approach (ANSYS Fluent CFD code) and a kinetic-based approach using a Direct Simulation Monte Carlo method (DSMC, SPARTA code). It also shows how presence of flow gradients can contribute to the errors in the results for typical PS-PVD conditions.

Due to the superposed thermal and mechanical stress profile, thermo-mechanically coupled forming processes require tools and machine components which meet high demands. High forming forces and process temperatures in the contact zone between the tool and the workpiece limit the life span of these tools. A promising approach for protecting such tools is a combination of thermally sprayed coatings and physical vapor deposited layers. This coating system combines the characteristics of the individual layers and leads to superior mechanical, tribological as well as thermal properties under the mentioned coupled stresses. In this study thermally sprayed alumina (Al 2 O 3 ) and yttria-stabilized zirconia (ZrO 2 ) coatings were produced by atmospheric plasma spraying. Therefor different coating porosities were adjusted in order to varied the effect of thermal insulation for the substrate made of AISI H11 (1.2343). After the coating process the surface roughness of the thermal barrier coatings (TBC) were reduced by polishing process in preparation for the PVD top layer. Subsequently, wear and heat resistant hard TiAlSiN and CrAlSiN coatings were deposited on top of the polished TBCs by using magnetron sputtering process. As a reference the PVD coatings were also applied on a nitrided steel samples. Titanium and chromium interlayers were applied by PVD technique in different coating thicknesses (50 – 150 µm) between PVD and thermally sprayed coatings. Afterwards the influence of these metallic interlayers on coating adhesion of PVD coatings were analyzed by performing scratch tests. Hardness and young’s modulus of PV coatings were investigated by means of nanoindentation. The morphology and topography of the coatings were analyzed by scanning electron microscopy, light microscopy and optical three-dimensional surface analyzer. EDX analyses and X-ray diffraction were used to determine the chemical composition of the PVD coatings. Finally the wear resistant of the PVD top layers were determined at different temperatures (20°C, 500°) by using a high temperature tribometer.

A numerical model of a supersonic compressible plasma flow has been developed with the aid of CFD software to describe the thermodynamic and transport properties of a plasma jet in order to investigate the PS-PVD process and how to optimize it for thermal barrier coatings and, in particular, the formation of columnar microstructures. The required properties of the plasma gas mixtures were obtained as a function of temperature and pressure from thermodynamic calculations in chemical equilibrium with the effect of ionization. Two-dimensional Monte Carlo simulations were conducted to provide insight on the evolution of columnar microstructure, accounting for self-shadowing and vapor incidence angle but ignoring the effect of diffusion. Simulated structures and predicted values are presented and compared with actual images and measurements.

In this work, computational fluid dynamics (CFD) results confirm earlier calculations indicating that significant evaporation occurs in plasma torch nozzles. In addition, experimental work is performed, investigating the nature of ceramic deposits produced by plasma spray-physical vapor deposition (PS-PVD), particularly coatings composed of nanosized clusters. It was found that as the hot plasma jet comes close to the relatively cool substrate, a boundary layer is formed due to the rapid drop in temperature and velocity. In summary, coatings produced by PS-PVD are a mixture of nanocluster and vapor deposition.

One way to reduce plasma jet velocity and prolong the dwell time of spray particles in the jet is to enlarge the orifice of the torch nozzle. In this study, normal and modified nozzles are used to deposit YSZ particles on ceramic and superalloy substrates by plasma spray-physical vapor deposition (PS-PVD). The modified nozzle is shown to increase the evaporation of YSZ particles and thus the quantity of Zr atoms and Zr 1+ ions in the plasma jet, which allows columnar structured coatings to be realized at higher deposition rates using a conventional 80 kW plasma spray system. The columnar ceramic coatings are also shown to have good conformity on cold-sprayed MCrAlY bond coats with high surface roughness.

In this study, dense multicomponent NiCoCrAlTaY bond coats and feather-structured YSZ topcoats are deposited on DZ40M alloy vane surfaces by the PS-PVD method. Based on thickness measurements and microstructure examination, it is shown that the double vane surface was completely covered by both layers. The thickest portion of the coating was found close to the leading and trailing edges of the vane. The results show that it is possible to manufacture TBCs, including the bond coat and topcoat, on first-stage turbine blades by a single PS-PVD process.

In the present work, YSZ coatings were deposited on graphite substrates by plasma spray-physical vapor deposition (PS-PVD) in order to study the influence of spray distance on microstructure and durability. Four coating samples were examined in detail via SEM and XRD analysis. The results show that the as-sprayed YSZ has a dense lamellar-columnar microstructure with low porosity. Both monoclinic and tetragonal zirconia were detected in the coatings along with ZrO 2 -x, the latter indicating that oxygen loss occurred at short spraying distances. Coating hardness and Young’s modulus were also measured and were found to vary with spraying distance as well.

A thermal cycling test was carried out in an EB-PVD MCrAlY – superalloy system, the result of which showed that a continuous β-NiAl layer formed in the MCrAlY coating near the coating–superalloy interface. Since β phase can be as a reservoir of Al, the formation of the β layer, in which much Al is reserved, is probably beneficial to the coating’s life. An oxidation-diffusion model was adapted to simulate the development of the microstructures in the coating-superalloy system. The simulation results indicate that the formation of the β layer was strongly related to the high Al activity in the substrate; if the Al activity of the substrate was high enough, a β layer could be built up in the coating near the coating-substrate interface.

For many years, the aeronautics industry has been actively engaged in the development of thermal barrier coatings (TBCs) to enhance the performance of hot section components in aerospace engines, such as turbine blades or nozzle guide vanes. The electron beam physical vapor deposition (EB-PVD) process has been widely utilized for high-performance TBCs on metallic substrates, primarily due to its extended lifespan. However, the drawbacks of EB-PVD TBCs, including their cost, relatively high thermal conductivity, and susceptibility to chemical attack, pose challenges for the next generation of turbine engines. To address these issues, suspension plasma spraying (SPS) has been investigated in this study as an alternative for TBC application. It has been demonstrated that the SPS process enables the production of a columnar microstructure that can be easily adjusted in terms of size, distribution, and morphology.