The main goal of the project was to investigate the influence of different gas properties, in combination with different spraying parameters, on the wire arc spraying process. For this purpose, investigations with several gas compositions (pure nitrogen as well as nitrogen combined with hydrogen or ethene – compared to compressed air) have been carried out for different spraying materials which are currently being used in today’s industries, such as copper, carbon (St0.8) and stainless steels (316L). The preheating of the process gas as well as the variation of the gas pressure up to 1,400 kPa (14 bar) were also subject to research. The resulting coating properties have been analyzed in terms of oxide content, porosity and hardness as well as deposition efficiency and adhesive tensile strength. Additionally, in order to enhance the process stability, a system to detect the cause of cold shuts has been developed.

This study investigates the effect of different gas compositions on the size, velocity, and temperature of particles in a wire arc gas jet. In the experiments, two wire materials (316L and G3Si1) were sprayed via compressed air, nitrogen, and a nitrogen-hydrogen mixture and high-speed shadow imaging was used to record in-flight particle characteristics. Deposition efficiency was also measured along with the hardness and oxide content of the coatings. The spraying process, equipment, and test methods employed in the study are described and the results are presented and discussed.

This study investigates the cause of process instabilities in large and small scale arc spraying production equipment and in an experimental spray gun. Arc voltage and current, voltage drop at the wire contact sleeves, and wire feed velocity are recorded and spectrum analysis is used to predict the separation of unmelted wire pieces, or cold shots, during spraying with a view to quality assurance. A high-speed camera with pulsed LED illumination is used to observe droplet detachment and spray jet generation. For each case, applied diagnostics are presented and the results are interpreted with respect to the physical causes of instability and how to avoid them.

A real-time measuring system has been developed to record and analyze the fluctuations of burner voltage and current. The objective is to identify the occurrence of stripping unmolten wire pieces (cold shuts) and to detect corresponding spraying conditions. To identify voltage and current fluctuations causing cold shuts, high speed camera shots are synchronized with electrical measurements to analyze spraying parameters which were assumed leading to cold shuts. As a result, different cold shut conditions could be identified. The electrical cold shut identification then triggers a camera system, to capture online the size and velocity of cold shuts. Based on electrical measurements it is intended to detect wear of spraying equipment which leads to enhanced cold shuts occurrence during industrial spraying process.

The vacuum plasma spraying process has to be optimized for each task in order to obtain the required mechanical and electrical properties for the desired coatings. This paper deals with the characterization of plasma and powder spray jets at deposition conditions for Solid Oxide Fuel Cells layers. First, DC plasma jets under soft vacuum conditions are characterized by using an enthalpy probe system and a Schlieren optic installation. The influence of the inner contour of the plasma spray torch anode on the temperature and velocity profiles as well on the shape of the plasma jets are investigated. Second, Laser Doppler Anemometry (LDA) measurements were performed for (8 mol %) yttria stabilized zirconia (YSZ) powder (-20+5 µm) spray jets for two chamber pressures, different argon carrier gas flow rates and injection modes. The results show that a M3 Laval nozzle and a F4V nozzle with conical inner profile allow to obtain a larger plasma volume and a more uniform plasma than with a standard F4 anode nozzle resulting in a better treatment of solid particles in the plasma. LDA measurements, using a M3 anode nozzle, show that the penetration and the acceleration of particles in the core of the plasma jet have their optimum at 10 kPa with an inclined injection with respect to the plasma jet axis for a 3.75 slpm carrier gas flow rate.

ln co-operation with industrial companies, education and training institutes, and universities, an interactive multimedia learn-ing programme was developed. The project was sponsored over three years by the European Community. Structure and contents of this programme are based on the EWF-guideline “European Thermal Sprayer - Minimum requirements for education and training”. The multimedia programme contains the module of theoretical basis of the training course and covers training subjects as spraying processes, base and spray materials, bonding mechanisms, coating characteristics, measuring and testing, environmental and safety aspects. The interactive multimedia programme may be used to shorten the duration of the ETS-course, for spray company internal education and training, for settling into a new job concerning thermal spray technique, or for supporting a training course itself. The multimedia programme will be demonstrated during the poster sessions. Paper text in German.