A process control tool has been developed for air plasma spraying of a NiAl (bond coat) and Al 2 O 3 (top coat) coating systems. The process is employed at Volvo Aero Corporation for abrasive purposes, such as knife-edge applications on compressor parts. In-flight particle temperatures, velocities and diameters were measured by the DPV2000 system. Several samples were sprayed and the coating microstructures were evaluated using Image Analysis techniques on optical and scanning electron microscope images. Top and bond coat thickness, oxides, porosity, grit blast residues, delaminations, surface roughness (on top, bond and substrate) and tensile strength were evaluated. Statistical regression analysis was then used to establish relationships between process parameters (i.e. current and primary gas flow), particle in-flight characteristics (i.e. velocity and temperature), microstructure properties, and mechanical properties. The equations derived were finally used for development of a tool, which can be used by the operator for on-line monitoring and control of the coating characteristics based on information of the current particle inflight characteristics. The tool makes it possible to continuously adjust the process set points, ensuring a high reproducibility and stability of the process.

The plasma spray deposition of a zirconia thermal barrier coating (TBC) on a gas turbine component has been examined using analytical and experimental techniques. The coating thickness was simulated by the use of commercial off-line programming software. The impinging jet was modelled by means of a finite difference elliptic code using a simplified turbulence model. Powder particle velocity, temperature history and trajectory were calculated using a stochastic discrete particle model. The heat transfer and fluid flow model were then used to calculate transient coating and substrate temperatures using the finite element method. The predicted thickness, temperature and velocity of the particles and the coating temperatures were compared with these measurements and good correlations were obtained. The coating microstructure was evaluated by optical and scanning microscopy techniques. Special attention was paid to the crack structures within the top coating. Finally, the correlation between the modelled parameters and the deposit microstructure was studied.

Plasma sprayed MCrAlY bondcoats play a major role in thermal barrier coatings. During service, oxide forms on both sides of the bond coat and must be minimized to prevent coating failures. Along with powder chemistry, coating microstructure significantly influences oxide growth. It is known that both coating microstructure and coating strength are strongly related to plasma spraying parameters. This present work examines the effect of inflight particle properties on the adhesion strength and microstructure of NiCrAlY and NiCoCrAlY bondcoats. The relation between particle velocity and temperature and coating properties is particularly important. Relatively small changes in spray parameters such as arc current and gas flows can have a major impact on sprayed particles and consequently coating microstructure. Through online control of particle states it is expected that the quality of plasma-sprayed MCrAlY coatings can be significantly improved.

Thermal barrier coatings are used in several industries to improve thermal efficiency. Examples are gas turbine engines and marine diesels. The performance and life of thermal barrier coated components depend on a variety of factors all related to the specific application. This paper gives an overview of some of the aspects to consider and put special attention to. The different features, in the microstructure, will be discussed with respect to their appearance and influence on the performance of the TBC. Thermal conductivity, microstructure, failure mechanisms and different applications are highlighted.

A traditional plasma spray gun consists of an anode and a cathode. During spraying small particles of anode material of either copper or tungsten, depending on the brand of the gun, will be worn off and deposited in the coating. The size and frequency of the particles from a copper anode has generally a dramatic appearance (in the beginning or at the end of its life) whereas a tungsten nozzle normally behaves more randomly during its life. Tungsten particles can therefore be expected anywhere in a plasma sprayed coating. Unfortunately the material properties of tungsten is not very compatible with a thermal barrier coating of partially stabilized zirconia and it is shown that a contamination will cause a catastrophic failure, if located in, for a thermal barrier, a critical region. The behavior of tungsten at elevated temperatures is investigated and clearly show the detrimental effect of tungsten on the life and performance of a thermal barrier coating.

Reproducibility is a current challenge for the thermal spray industry. Reproducibility associated problems represent a large cost every year not only in terms of rejections and rework, but also in costs for destructive testing and decreased production flow. Thermal spray coatings are moving in the direction of being considered only as a "band aid" to becoming a design element. One of the prerequisites for such a development is an increase in reproducibility for thermal spray coatings. The purpose of this paper is to outline a vision aiming in the direction of a future "ultimate spray booth", where thermal spraying is as reproducible and reliable as machining, grinding or other production processes. A way to increase reproducibility and reliability in the future spray shop involves utilising major parts of IT - technology. This also includes active co-operation design-production in the pre-spray process. This paper will deal with areas such as: operation drawings and lists through multimedia techniques, education programs for operators and designers through multimedia techniques, CAD/CAM, Off-line programming and simulation, On-line diagnostics of flame (particle diagnostics) and coating (temperature & Acoustic emission measurements), on-line Statistical Process Control and Knowledge Based System techniques.

Thermal barrier coatings are used in several industries to improve thermal efficiency, for example, of gas turbine engines. The performance and life of thermal barrier coated components depend on many factors. One important factor is the residual stresses in the coating and substrate. Residual stresses can be influenced by the parameters of the application process. Parameters affecting residual stresses include the condition of the substrate, the type of spray application process, and the prespray heat treatment of the substrate. Residual stresses can also change significantly during the life of a thermal barrier coated material. The goal of this work is to quantitatively evaluate the changes in residual stresses of the thermal barrier coating and the substrate during the stages of processing and during simulated in-service testing. Through-thickness residual stresses distributions of the coating and the substrate material were determined using a destructive laboratory method, called the "Modified Layer Removal Method." Thin thermal barrier coatings (less than 0.5 mm) were evaluated in this work. Residual stresses in thermal barrier coated specimens were evaluated at three stages of the processing history: (1) after grit blasting of the Hastelloy substrate, (2) after application of the bond coat, and (3) after spraying the top coat. The effect on residual stresses of substrate temperature during spraying is examined. Changes in the residual stresses for thin thermal barrier coatings are shown at selected stages during the processing history of the coated materials. Differences between residual stresses at the selected stages are identified and discussed. Changes to residual stress distribution due to in-service conditions are examined. The effect of bond coat oxidation is examined by long-term, high-temperature exposure. Also, residual stresses are evaluated for thick thermal barrier coatings after thermal shock testing.