Abstract

Thermal spray technology is a widely used technique in the industry in which surfaces of components are coated by spraying a wide range of metals or ceramics. Considering the growing interest
in building nanostructured coatings due to their unique characteristics, a new technique called suspension plasma spraying is developed. Suspension plasma spraying (SPS) is one of the promising
methods that can be used to achieve coatings with fine microstructure and superior properties. Several significant parameters make this SPS process complex to understand and control. In particular,
the velocity and diameter of in-flight particles near the substrate, which depend on the plasma and
injection conditions, have a strong influence on the coating columnar structure. In this work, the
velocity of in-flight particles in the vicinity of the substrate and free jet was investigated by the
particle image velocimetry (PIV) method. This study is aimed at providing a better understanding
of the behavior of in-flight particles in the SPS process. A suspension of titania particles is used
here taking advantage to the abundance and chemical stability of titania and its use in different
SPS applications. Observations and results of this work showed that the trajectory and velocity of
micron-size particles, due to their small Stokes number, are strongly influenced by the presence of
the substrate. The PIV results make it possible to visualize the suspension injection into the plasma
with titania aqueous suspension. Particle velocity reported by PIV method corresponded likely to
un-molten particles in SPS process. The PIV measurements were finally compared with velocity
measurements carried out with a thermal-emission particle sensor in the same spray condition as
the PIV run.