On the relationships between the geometric processing parameters of APS and the Al2O3-TiO2 deposit shapes

Controlling the quality of thermal spraying requires a profound knowledge of the phenomena involved. The reproducibility of deposit characteristics is not always reached. This study aims to illustrate the impact of some geometric processing parameters on the morphologies of beads, to ultimately develop a quantitative model for atmospheric plasma spraying (APS) permitting property forecasts. A commercial available powder made of Al2O3-TiO2 (13% by weight) was plasma sprayed onto steel plates. Beads (deposits) were formed by consecutive passages of the torch in front of the plates. The following geometric processing parameters were studied: the spray distance, the spray angle, and the angular positioning of the powder injection. The as-sprayed deposit morphologies were measured by means of a laser sensor. The net deposit profiles were extracted and then fitted by Gaussian approximations. Analyses of the deposit morphologies are presented and a set of parameters is proposed to comprehensively describe the significant features of the deposit morphologies. Evolution of the morphologies of deposits as a function of the spray distance appears as nonlinear. The spray angle is one of the principal “levers” to influence the morphology of deposit (i.e., maximum height, degree of symmetry, etc.) and its position (i.e., offset). It is proved that the accurate angular position of the powder injection may also play a significant role to the positioning of deposit.