Abradable seal coatings are widely employed in the gas turbine of aero-engine, which not only strength enough to resist the impact of external particles and airflow, but also excellent wear resistance. In the current study, we concentrate on APS sprayed Aluminum Bronze Polyester abradable coating that can be used in turbo engines both for seals and clearance control. A composite thermal spray powder, substantially in the form of clad particles each of which has coarse polyester powders and sub-particles of Cu-Al alloy powders, was prepared using mechanically clad process. Abradable seal coating was prepared by atmospheric plasma spraying. The microstructure, hardness, bonding strength, thermal shock resistance and corrosion resistance of coatings were researched. Properties of the coating were able to meet the application requirements. The coating microstructures and phase compositions were evaluated via SEM. The corrosion mechanisms of the coating were compared by analyzing the cross-sectional and top surface microstructures of the as-sprayed and eroded coatings.

Multi-electrode APS has proven significant advantages with regard to spray rates, deposit efficiency and component life time. So far, three-cathode and three-anode spray guns have been established successfully in several industrial sectors where high spray rates are mandatory. Based on the successful three-anode plasma spray gun DELTA, the five-anode APS gun PENTA was developed to further increase productivity. With its gross power of up to 125 kW it allows very high spray rates and thus significantly reduced coating times. This paper focusses on the development of high spray rate parameter settings for producing oxide ceramic coatings. All coatings will be investigated with regard to their microstructures. Furthermore, economical benefits of the five anode technology will be highlighted.

In the present work, three different APS alumina coatings were fabricated using three fused and crushed alumina powders of different particle size fine, medium and coarse. The influence of the particle size on thermal properties and micro-structural features of the produced coating were investigated by thermal insulation test and detailed image analysis technique, respectively. The analyzed micro-structural features include the total porosity, pore size (fine, medium, and large) and cracks. All types of cracks were considered in calculations as voids and were evaluated according to their sizes as pores. All spray parameters except the particle size were fixed throughout the spraying process. The results revealed that the fine starting powder has produced the densest coating with the lowest total porosity and that the total porosity increases with an increasing particle size. This was expected as powders of smaller particle size will reach a higher in-flight temperature and velocity than powders of bigger particle sizes as long as the same spray parameters are applied. However, a detailed image analysis investigation on the three produced coatings showed that the fraction of fine pores and cracks versus the total porosity is substantially higher in coatings produced by using fine starting powders than those produced using medium and coarse powders. In this work, a connection between the thermal insulation and the porosity fraction, which includes fine pores and cracks, was revealed.

Plasma generators are frequently used in a wide field of applications. These applications include thermal coating, plasma-welding, preprocessing of surfaces, sterilization and propulsion systems. The industrial use of plasma generators demands a high level of accuracy and reproducibility which has to be monitored throughout the process. Rather than analyzing results of e.g. a coating process (by electron microscopic) one prefers to have an online assessment of the plasma generator. The plasma generated is defined by various parameters (e.g., temperature, conductivity) which can be measured with suitable measuring systems. Determining all plasma parameters in one setup is very costly and requires a big setup. In industrial facilities it is often suitable to measure one or two physical quantities and derive the plasma parameters from these measurements. This paper focuses on the evaluation of the electric current consumed by the plasma generator and the sound emitted by the whole system. A quick analyzation of these signals - that may result in an online assessment -was accomplished by using the wavelet transform. Multiple experiments were performed to gain reliable and significant data (behavior of the arc/plasma).

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.

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.

It has been well accepted that thermal sprayings present a typical lamellar structure with limited lamellar interface bonding. It has been a great challenge to deposit a fully dense coating with fully bonded lamellae. In this report, three different novel approaches are introduced to deposit fully dense ceramic coatings and metal alloy coatings. With the deposition of a specific ceramic coating, it was found that there exists an intrinsic bonding temperature corresponding to the glass transient temperature of spray material. A chemical bonding is formed at the interface upon splatting of a molten ceramic droplet, as far as the maximum interface temperature between the spreading splat and the solid splat reaches over the intrinsic bonding temperature. Moreover, it will be presented that a simple critical bonding temperature in a linear relation with the melting point of coating materials can be utilized to deposit fully dense ceramic coatings by controlling the deposition temperature. Furthermore, with metal alloy coatings, a self-bonding mechanism is proposed utilizing the ultrahigh temperature molten droplet for dense coating with fully bonded lamellae. Using specially designed core-shell structured powders, the investigators demonstrated that a bulk-like metal coating is deposited by creating ultra-high temperature molten droplet. It will be found that such coatings present excellent properties and performance comparable to bulk materials. Moreover, it will be shown that, for ductile metal alloys, the solution-impermeable dense metal coatings can be deposited by using the novel in-situ shot-peening assisted cold spraying.

In this study, titanium carbonitride (TiCN) coatings are obtained by atmospheric plasma spray synthesis, or reactive plasma spraying. In order to promote reactions between Ti particles and reactive gases, an extended gas tunnel was mounted at the end of a conventional plasma gun. The oxidation behavior of the TiCN coatings was investigated over a wide temperature range, showing that the coatings suffered severe oxidation at temperatures above 700 °C and were entirely oxidized to the TiO 2 phase at 1100 °C. The principal oxidation mechanism was revealed, indicating that oxygen can penetrate into the TiCN coatings at high temperatures. Changes in microhardness were also investigated as a function of temperature, showing a precipitous drop over the range of 700-1100 °C.

In this study, a hybrid plasma spraying process is used to produce particle-reinforced metal-matrix composite coatings on 316 stainless steel. Two injectors are mounted at the output of the plasma gun, one feeding a nickel-base alloy powder, the other feeding a suspension of alumina nanoparticles. Different feed rates, suspension compositions, and alumina particle contents are used and their effects on microstructure, microhardness, porosity, adhesion, and wear behavior are assessed.

In this investigation, commercial Al 2 O 3 and Y 2 O 3 nanopowders were used to produce a composite powder feedstock that was plasma sprayed on graphite substrates. An Al 2 O 3 /Y 3 Al 5 O 12 (YAG) eutectic crystalline structure was expected in the coating due to the high enthalpy, large temperature gradient, and rapid solidification of the plasma spraying process, but microstructure and phase analysis of as-sprayed deposits revealed only a small amount of crystalline grains in an amorphous coating matrix. After heat treating, the expected structure was obtained and found to have excellent microstructure and microhardness stability at high temperatures.

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 work, ZrB 2 -MoSi 2 (ZM) composite coatings are fabricated using two plasma spraying techniques: VPS and APS. Phase composition and coating microstructure were assessed and microstructural changes at 1500 °C were investigated along with corresponding oxidation behaviors. The results show that the VPS composite coatings have lower oxide content, surface roughness, and porosity and much higher oxidation resistance than coatings produced by atmospheric plasma spraying. Possible reasons for the differences observed 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 study, a wide range of suspension plasma spraying conditions are used to produce YSZ coatings for intended use in liquid gas engines. To meet specifications, the coatings must exhibit a homogeneous microstructure with no vertical cracks or columns, low surface roughness, and low thermal conductivity. The properties of the plasma jet (velocity, enthalpy, stability), droplets (trajectory, number, size), and particles (velocity) were measured during spray trials and are correlated with coating microstructure. Suspension plasma spraying conditions necessary for depositing disk-shaped splats and achieving finely structured coatings with no stacking defects are described along with substrate cooling requirements.

Three YSZ powders with different particle size distributions and an ethanol-based YSZ suspension were deposited on steel substrates using a cascaded plasma torch with a 9 mm nozzle. Coatings with dense, porous, segmented, and columnar microstructures were achieved by varying process parameters such as gun current, argon flow rate, spray distance, and suspension injection pressure. Linear relationships between in-flight particle state and process variables were observed and are shown to correlate well with coating structure and porosity.

The purpose of this study is to determine if a GTAW (TIG) repair weld under an APS ceramic coating would cause a reduction in adhesion strength. Two stainless steels and a titanium alloy were selected for the study. For each material, 300 buttons were machined and further processed in groups of 50 through the application of one-pass, three-pass, or full pad welds. Welded buttons were lapped parallel to within 0.0002 in. and their lengths were compared with measurements obtained from buttons that had not been welded. NiCrMo bond coats were applied by HVOF spraying to both welded and unwelded samples, which were then top-coated with a ceramic layer (Cr 2 O 3 , Cr 2 O 3 -Al 2 O 3 , or TiO 2 ) deposited by air plasma spraying. A ten-cycle heat treatment was conducted on half of the samples to determine if the weld would amplify thermal expansion stresses. Based on adhesion test results, the welding had no measurable effect on adhesion strength nor did the heat treatment. Heat input from the HVOF flame and the plasma jet was sufficient to reduce weld-related solidification stresses.

This study deals with the deposition of coating materials that can be difficult to process by plasma spraying, including lanthanum and gadolinium zirconate, two pyrochlores of interest for thermal barrier applications, and lanthanum strontium cobalt ferrite (LSCF), a perovskite of interest for gas separation membranes. In addition to conventional atmospheric plasma spraying (APS), the feedstock powders were applied by suspension plasma spraying (SPS) and plasma spray-physical vapor deposition (PS-PVD). The spraying processes are described in detail along with the characteristics of the powders and coatings and the effects of various spray parameters on splat behavior and coating composition and structure.

This study evaluates the effects of heat treating on the microstructure, phase composition, and friction and wear behavior of plasma sprayed FeAl coatings. Fe-40Al feedstock powder was deposited on mild steel substrates by atmospheric plasma spraying and the coatings were vacuum annealed at 500, 650, 900, and 1000 °C. An examination of coating cross-sections revealed the presence of diffusion layers in the samples treated at 900 and 1000 °C. XRD analysis indicates that annealing at 650°C facilitates the transformation of Fe(Al) solid solution into FeAl intermetallic phase, resulting in an increase in coating hardness. At higher temperatures, however, Al depletion occurs along with a reduction in hardness. Tribological testing showed that both the friction coefficient and the effects of wear increased after heat treatment.

This study investigates a new zirconia-based ceramic for potential use in thermal barrier coatings. In the experiments, Sc 2 O 3 -Gd 2 O 3 -Yb 2 O 3 -ZrO 2 (SGYZ) powder was synthesized by coprecipitation and calcination, then agglomerated and sintered to facilitate spraying. The structure, morphology, and phase stability of the powder and plasma-sprayed SGYZ coatings were analyzed and thermal conductivity was measured. Test results show that the powders and coatings have good phase stability even after 500 h at 1400 °C and do not undergo tetragonal-to-monoclinic phase transition upon cooling. Plasma-sprayed SGYZ also has a lower thermal conductivity than YSZ, which is currently used in gas turbine engines.

The aim of this study is to better understand the formation of nonbonded splat-to-splat interfaces in thermally sprayed ceramic coatings. To that end, the surfaces between splats in plasma-sprayed La 0.5 Sr 0.5 CoO 3 (LSCO) coatings were examined and compared to free splat surfaces. The results show that free splat surfaces are relatively smooth, while adjacent surfaces at intersplat interfaces are quite rough. The observation implies that nonbonded splat-to-splat interfaces were never bonded, having fractured due to interface shear stress generated during splat cooling.