Proposal of New Criterion for Splashing of Thermal Sprayed Particle onto Flat Substrate Surface

In the collision of a liquid droplet onto a flat surface, a splashing parameter (K=We^0.5Re^0.25) has been used to evaluate the flattening behavior, and a critical value of K (K^C) was introduced as a criterion for splashing. In order to evaluate K of thermal sprayed particle, in-flight measurement for the velocity and temperature of the particle was conducted in this study. As a flattening pattern of the thermal sprayed particle changed significantly with a substrate temperature, the transition temperature (T_t) was also measured by changing the substrate temperature. Both K and T_t showed a tendency of monotonous decreasing with increasing the spray distance and a strong linearity was recognized in a K-T_t relationship. This straight line corresponds to a critical value for the splashing. However, as the influence of substrate temperature on the flattening is essentially independent of K, a new criterion for the splashing in the flattening of the particle was proposed in the study. That is, a splashing parameter on flattening was proposed, which considers the ratio of the flattening velocity to the impact velocity of the particle.