Enhancement and validation of diagnostic systems for the measurement of particle properties in high kinetic thermal spray processes

High kinetic thermal spray processes such as Cold Gas Spraying (CGS) or High Velocity Air Fuel Spraying (HVAF) are challenging for the application of diagnostic systems to measure in-flight particle characteristics. The particles are relatively cold, fast and often quite small. Fluctuations in the density of the fast-flowing working gas jets can cause additional difficulties. Initially, two particle tracking velocimetry (PTV) systems were used in this study. The Oseir HiWatch HR2 is based on shadow imaging and the Oseir HiWatch CS2 uses scattered light from a laser sheet. For the HR2, image processing routines were improved to enhance the contrast between particles and working gas striations. The particle sizing and velocimetry results were then compared with particle characteristics obtained using a Tecnar Cold Spray Meter (CSM) and a Tecnar Accuraspray unit. The former uses backscattered laser light and a double-slit mask, and the latter uses thermal radiation from the particles and a correlation method. In addition, particle size distributions measured by laser diffraction were included for validation. Although these systems are based on fundamentally different measurement principles, the overall results were in good agreement. Specific advantages and limitations of the systems are discussed, also with respect to their industrial application.