A Comparative Study of YSZ Suspensions and Coatings

Abstract

The demand for suspensions that are used in thermal spray processes is expanding from research labs using the lab-prepared suspensions toward actual coating production in different industrial sectors. Industrial applications dictate the reduced production time and effort, which may in turn justify the development of the market for ready-to-use commercial suspensions. To this end, some of the powder suppliers have already taken steps forward by introducing, to the market, suspensions of some of the most used materials, such as yttria-stabilized zirconia (YSZ), alumina, and titania. However, there is a need to compare the suspension characteristics over time and the resultant coatings when using these suspensions when compared with the freshly prepared homemade suspensions. In this work, such a comparison is done using YSZ suspensions of the sub-micron to a few micron powders. In addition, some changes in the suspensions’ formula were performed as a tool to vary the coatings’ microstructures in a more predictable way, without any variation of the spray parameters. The coatings were generated while using both radial and axial injection of the suspensions into Oerlikon-Metco 3MB and Mettech Axial III plasma spray torches, respectively. A clear effect of suspension viscosity on the coating microstructure was observed using the 3MB torch with a radial injection of suspension (i.e., cross flow atomization). However, the viscosity role was not dominant when using the Axial III torch with an axial feed injection system (i.e., coaxial flow atomization).

Deposition of Columnar-Morphology Lanthanum Zirconate Thermal Barrier Coatings by Solution Precursor Plasma Spraying

“…Relatively small Stokes number (St\ 1) indicates increased probability of droplets approaching the substrate at more oblique angels (Ref 18, 39). Formation of columnar coatings from water based precursor solutions could be related to the small droplet sizes increasing the chance of having small Stokes numbers ( Ref 40,41). This is in accordance with the droplet size distribution measurements of atomized solutions as discussed above (17.4 and 15.9 lm for 0.5 and 0.125 M concentrations of water based solutions, respectively).…”

Influence of Substrate Shape and Roughness on Coating Microstructure in Suspension Plasma Spray

“…The injection of the suspension has also been an object of study [17]. Some of those conclusions showed that coating microstructure and performance are related to the suspension characteristics [18]. Ganvir et al [19] studied the evolution of the coating microstructure during spray.…”

Microstructure, mechanical and thermal properties of YSZ thermal barrier coatings deposited by axial suspension plasma spraying

“…The pseudo-columnar growth of the nano-structured suspension PS YSZ coatings has turned out to be sensitive to a number of deposition parameters like the average particle size, liquid carrier composition, flow rate, the ratio of solid to liquid, and stand-off distance [13,16,[20][21][22]. The formation of this characteristic microstructure is sought in the operation of strong drag force exerted on in-flight solidified drops by a working gas, which is surpassing the adhesion force on the impact on a flat surface [23,24].…”