Previous studies have shown that gas shrouding is an effective means for controlling oxidation during HVOF spraying. In this present work, the authors attach a gas shroud to an oxyfuel torch with a longer barrel to further investigate the correlation between the state of HVOF sprayed particles and the density and oxygen content of the resulting layers. It is shown that with gas shielding, extended barrel length, and optimized spraying parameters, it is possible to accelerate powder particles to a velocity of over 750 m/sec with maintaining a high molten fraction, thereby producing very dense (zero porosity) stainless steel layers with oxygen contents less than 0.2% by weight. Paper includes a German-language abstract.

A new method to capture and evaluate the condition of thermal sprayed particles has been developed by using an agar gel target. HVOF sprayed Hastelloy C particles were collected by a gel target placed at the substrate position, i.e., 380mm downstream from the spray nozzle exit. In the surface layer of the target, a large number of fine particles were observed, whereas in the deeper part, globular particles were trapped. The ratio of particles in the surface layer with respect to the deeper part changed by spraying parameters. Furthermore, particles in the target were separated by cutting the gel, collected after resolving the agar, and then observed by SEM. Particles collected from the target's surface layer were fine particles (under 10µm) and fragments of dendritic crystals. These collected from the deeper part were mostly unmelted particles, some of which exposed dendrites. Results obtained by other techniques such as splat observation and in-flight diagnostics are compared with these results. It was concluded that by capturing thermal sprayed particles with a gel target, it is possible to visualize and quantify the melting condition of HVOF sprayed particles.

Thermoelectric (TE) power generation from waste heat is recently attracted much attention as one of energy-saving technologies. In this paper, Co-doped n-type iron silicide semiconductor was plasma sprayed under various spray conditions to find the optimum spray-forming conditions. Then Co-doped iron silicide TE device with thickness ranging from 3 to 5 mm and the area of over 100 cm square was produced in the form of a plate or on tube. The paper examines the microstructure and evaluates thermal and electric properties. Paper includes a German-language abstract.