Thermal spraying methods are processes which provide high energy for the melting and atomizing of powder, rod or wire shaped feedstock materials that are finally applied to a substrate. The coating can improve surface properties, such as wear resistance and corrosion protection of mechanical components, and add functional properties. In addition to a careful substrate preparation, the physical properties of the coating particles are decisive for the quality of the coating. Temperature, size, rate and velocity represent the classical quantities, which can be measured in situ using various diagnostics. Since many industrially used coating methods, such as for example wire arc spraying, are used under atmospheric conditions, another quality-determining parameter is the degree of oxidation. This particle property cannot be measured by established diagnostics and must therefore be qualitatively derived from the above mentioned quantities or subsequently be measured by means of destructive methods (microsections, EDX, etc.). For these reasons the aim of this work is the development and testing of a diagnostic for the in-flight measurement of particle oxidation. This innovative measurement method detects the entire particle plume from different directions using a 2D two-color-pyrometry and allows the calculation of spatially resolved three-dimensional temperature and intensity distributions based on a tomographic evaluation method. By additionally using measurements of the particle velocities (Laser-Doppler-Anemometry) and particle sizes (Particle Shape Imaging) the surface emissivity of the particles along the spraying direction can be calculated, which in turn allows quantitative conclusions on the degree of particle oxidation. Investigations on the wire arc spraying process have shown that the particle plume can be assumed to be optically thin and is thus suited for emission tomography. In addition, particle oxidation degrees could be measured which tend to correlate well with oxide contents in finished coatings. Especially in the case of using nitrogen as atomizing gas, the oxide content in the layer can be predicted very well with the aid of the in-flight measured emissivities.    «

Thermal spraying methods are processes which provide high energy for the melting and atomizing of powder, rod or wire shaped feedstock materials that are finally applied to a substrate. The coating can improve surface properties, such as wear resistance and corrosion protection of mechanical components, and add functional properties. In addition to a careful substrate preparation, the physical properties of the coating particles are decisive for the quality of the coating. Temperature, size, rat...    »