Characterization of the deposition formation dynamics of Suspension plasma spray coatings using in-situ coating property measurements

Suspension plasma spraying (SPS) enables the production of finely grained nanometric or submicrometric coatings with unique mechanical, thermal, and structural properties. In SPS, a liquid carrier (ethanol/water) is used to transport the submicrometric feedstock into the useful core centerline region of the plasma jet. This condition brings about a series of important changes in the deposition state and microstructure of the deposited coatings compared to traditional plasma sprayed coatings. Considering complex deposition dynamics of SPS deposition technique, there is an extensive need to better understand the relationship between plasma spray conditions and stress evolution in coating during deposition. In this investigation a submicron (300 nm) yttria stabilized zirconia (YSZ) particles suspended in ethanol was spray deposited using a single electrode cascaded arc plasma torch. The suspension contained 25 wt% solid content. The stresses generated (termed evolving stress) during the deposition of the coatings were calculated using the change in curvature of the substrate measured using an in-situ coating property (ICP) sensor. Multitudes of coating morphologies ranging between porous lamellar to heavily segmented columnar structures were observed under the considered deposition parameters. The mechanisms for formation of multitudes of SPS coating morphologies were proposed based on ICP results.