2001 Volume 19 Issue 3 Pages 440-445
In-flight temperature and velocity of thermal sprayed ceramic particle at various spraying distances were measured and the effect of the temperature and velocity on the flattening behavior of the particle was investigated.
Several kinds of ceramic particles, such as an alumina, were sprayed at various spraying distances, and the particles were collected onto a mirror polished substrate. The velocity and temperature of the particles were measured by DPV-2000 system, which is an optical sensing device with on-line monitoring of the individual particle.
Both the velocity and temperature of the particles monotonously decreased with increasing of the spraying distance. This tendency is quite similar to that of metallic particle. The transition temperature change of the ceramic particles with spraying distance, however, showed an opposite tendency to that of the metallic particle, namely, the transition temperature rose with an increase of the spraying distance. From the observation results of the collided particles on the flat substrate surface, it was found that the partially melted particles were often observed on the shorter spraying distance. This indicates that in the case of the large particle or the shorter spraying distance, the ceramic particles were melted only on the surface. Coexistence of the melting and non-melting part in a particle makes a viscosity of the particle high, and the higher viscosity restrains the occurrence of the splashing on the flattening. This maybe causes the lower transition temperature at the shorter spraying distance range.
Consequently, it must take care that the temperature of thermal sprayed ceramic particle measured by the optical sensing device is only an information on the surface of the particle.