The effects of the plasma gas composition on the formations of the splat, the single passed spraying bea d, and the coating and the resultant coating properties were investigated using an Al2O3-13 wt.%TiO2 commercial grade clad powder. The plasma gas consisted of the argon gas and the hydrogen gas. By controlling the plasma gas compositions in the atmospheric plasma spraying process, both particle velocity and enthalpy were designed to change under the constant feeding parameters, spray distance, cooling condition, and spray current. Splat morphology was examined using the scanning electron microscopy, and the effects of the plasma gas composition on the splashing degree were considered. The splashing degree of the splat was increased with the increases of the hydrogen gas flow rate and the argon gas flow rate. And also the chemistry of the impacting particle might affect the splashing behaviors. The geometries of the single passed spaying beads were evaluated by observing the plane-view morphology and the cross sectional morphology using the SEM and image analyzer. While the argon gas decreased the bead width and thickness, the bead width and thickness were increased with the increase of the hydrogen gas fraction in the plasma gas. In addition, the argon gas fraction increased the bead symmetry, which implies that the trajectories of the in-flight particles are largely dependent on the plasma gas composition. According to gas compositions, coating thickness, porosity, microhardness, and bond strength were measured. Cross-sectional coating morphologies were observed using SEM. Microharndess as well as coating thickness and porosity seemed to be dependent on the melting state of the inflight particle largely affected by the enthalpy of the plasma jet stream. Meanwhile, the bond strength of coating depended on the velocity of the plasma jet affecting the particle impacting velocity and the contact interface properties. Thus, the coating properties were dependent on the plasma gas compositions and this means that the coating properties can be tailored by controlling the plasma gas compositions.

Keywords: alumina-titania, splat formation, single passed spraying bead