Three-Dimensional Simulation of Porosity in Plasma-Sprayed Alumina Using Microtomography and Electrochemical Impedance Spectrometry for Finite Element Modeling of Properties O. Amsellem, F. Borit, D. Jeulin, V. Guipont, M. Jeandin, E. Boller, and F. Pauchet (Submitted February 3, 2011; in revised form July 11, 2011) Moving from a 2-dimensional to a 3-dimensional (3D) approach to microstructure and properties has been expected eagerly for a long while to result in a dramatic increase in the knowledge of thermally sprayed coatings. To meet these expectations, in the present study, microtomography and electro- chemical impedance spectroscopy (EIS) were carried out to simulate the microstructure of plasma- sprayed alumina. As-sprayed and excimer laser-processed deposits were studied. Some unexpected but relevant results, e.g., regarding pore orientation in the coatings, could be obtained. EIS led to the establishment of an equivalent electrical circuit representation of the microstructure which enabled modeling of the insulating properties as a function of interfaces and pore interconnection. The pore interconnection was studied by microtomography. From this 3D simulation, a finite element analysis of YoungÕs modulus properties was developed and compared to experiments. Using this approach, excimer laser surface processing was shown to be an innovative process to modify insulating characteristics of plasma-sprayed alumina. Keywords influence of process parameters, laser surface treatment, plasma spray forming, porosity of coatings 1. Introduction Alumina (Al 2 O 3 ) is used extensively for its electrical insulating properties because of its high dielectric strength (Ref 1). Thermal spraying, e.g., plasma spraying, is a prominent process for depositing low-cost high-perfor- mance dielectric coatings such as those made of pure alumina. Thermally sprayed alumina coatings show a composite microstructure because of the presence of defects, such as pores, inter-lamellar and intra-lamellar cracks, which can be considered as a second phase in an alumina matrix. These second phase features influence the mechanical behavior and electrical insulation of the coating dramatically (Ref 2, 3). Several studies were published relating physical properties to plasma-sprayed coating microstructure (Ref 4–8). The present study is based on the study of composite microstructures (according to the above mentioned definition, i.e., alumina + porosity) obtained by air plasma spraying (APS). Following an earlier 2-dimensional (2D) approaches to this issue (Ref 9, 10), a 3-dimensional (3D) approach is developed to relate pore and crack intercon- nection, which is difficult through 2D methods. Two 3D tools were used, first, microtomography (Ref 11), a dra- matic development of which dates back to a few years ago only and, second, electrochemical impedance spectros- copy (EIS), the potential of which for correlating micro- structure with coating properties was shown also recently (Ref 12, 13). The 3D approach allows the determination of thermo-mechanical and electrical properties, e.g., pri- marily the YoungÕs Modulus, which can be compared to those from the 2D approach (Ref 9, 10). To demonstrate the advantages of the 3D approach, a new excimer laser process of coating was developed as a tool to explore the performance of the 3D approach. The process is new because conventional excimer laser processing is generally restricted to metals (Ref 14), rather than to ceramics, the study of which is relatively unexplored (Ref 15, 16). 2. Materials and Processing 2.1 Materials and Spraying Three types (A, B, and C) of alumina composite coat- ings were AP sprayed onto grit-blasted stainless steel plates (AISI 304L, 25 9 30 9 2 mm 3 , Ra  4 lm) using a F. Borit, D. Jeulin, V. Guipont, and M. Jeandin, Evry, France; E. Boller, Grenoble, France; and O. Amsellem and F. Pauchet, Clamart, France. Contact e-mail: oamsellem@slb.com. JTTEE5 21:193–201 DOI: 10.1007/s11666-011-9687-0 1059-9630/$19.00 Ó ASM International Journal of Thermal Spray Technology Volume 21(2) March 2012—193 Peer Reviewed