2000 Volume 18 Issue 3 Pages 390-396
A transition phenomenon in a flattening of thermal sprayed particle onto a flat substrate surface has been investigated. Our previous results showed that a splat morphology change transitionally from irregular splash shape to disk shape at certain temperature range with increasing a substrate temperature. The most interesting feature of the phenomenon lies in a drastic change at a certain narrow temperature range. The reason for this drastic change of the splat morphology is not always clear yet, because an in-situ observation of flattening is still difficult.
In this study, in-flight measurement of velocity and temperature of the particle was conducted and the transition temperature of the splat was measured. The transition phenomenon of the splat was investigated based on the measurement results of the particles. The transition temperature increases with increasing the velocity, temperature and diameter of the particles. From the result of a breakup phenomenon of a liquid film, Splashing parameter: K=We0.5 Re0.25 was introduced as a determinant of the splashing. The transition temperature increases with increasing Splashing parameter based on the measured data of the particle. However, from the relation with the transition temperature, it was found that only Splashing parameter could not determine the transition phenomenon and some new determinant based on the data of the flattening particle was required. Then, Flattening K value : Kf=0.5a1.25Re-0.3K was defined and seemed to correspond to the boundary line of the splat morphology. From this result, it was found that the flattening velocity increases with decreasing the substrate temperature.