Abstract
In HVSFS (High Velocity Suspension Spraying), a suspension is axially fed into the combustion chamber of a modified HVOF torch. The particle formation is strongly influenced by the phenomena occurring during the short dwell time in the combustion chamber and expansion nozzle, i.e. break up and evaporation of the liquid jet, particle formation, sintering and melting. Optimization of the spray torch has already led to an improved coating process but is still an important topic for the future. A deeper understanding of the suspension liquid / flame interaction is still necessary to control coating properties. It turns out, that among other process parameters, rheological properties and agglomeration behaviour of the suspension have a strong influence of the particle formation and hence resulting coating properties. As a result of using nano particles HVSF sprayed coatings show partly different microstructures compared to HVOF sprayed coatings. To gain a deeper understanding of the process particles were collected in-flight to get information about the size distribution and melting degree during the spray process. The paper will give an overview of the present state of HVSFS development at the IFKB and present experimental results.
