On the Effects of Processing Parameters on Pore Network Architecture and Characteristics of Al₂O₃-13% wt. TiO₂: Experimental Quantification and Prediction by Artificial Intelligence

The very singular pore network architecture of thermal spray coating results from the combination of several phenomena occurring during the coating buildup process. Close pores, usually of large dimensions, result from stacking defaults when impinging particles spread onto previously deposited layers. Intra-lamellar cracks, perpendicular to the substrate surface, develop mostly in ceramic lamellae during solidification. Inter-lamellar cracks, parallel to the substrate surface, depend significantly from the surface tension characteristics during the particle spreading stage. One way or another, these characteristics are related to the processing parameters implemented to manufacture the coating and they significantly modify the coating characteristics, their cohesion, their compliance and their impermeability, among the most significant. Al₂O₃-TiO₂ (13% wt.) coatings were atmospheric plasma sprayed implementing several sets of processing parameters, among which power parameters (i.e., arc current intensity, plasmas gas flow rates, etc.), feedstock injection parameters (i.e., carrier gas flow rate, injector internal diameter, etc.) and environment parameters (i.e., spray angle, etc.) were varied. Pore contents were analyzed implementing image analysis. Pore network connectivity was analyzed implementing an electrochemical test: the higher the passivation potential of the substrate, the higher the coating pore network connectivity.