A Comparative Study of YSZ Suspensions and Coatings

Abstract

The demand for suspensions 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 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. There is, however, a need to compare the suspension characteristics over time and the resultant coatings when using these suspensions as compared with the freshly prepared home-made suspensions. In this work, such 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 variation of spray parameters. The coatings were generated 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 radial injection of suspension (i.e. cross flow atomization). The viscosity role, however, was not dominant when using the Axial III torch with axial feed injection system (i.e. coaxial flow atomization).

In-Flight Mechanisms in Suspension Plasma Spraying: Issues and Perspectives

“…However, the viscosity and the surface tension directly influence the droplets size distribution during primary and secondary fragmentations. The droplet sizes are shown to be reduced as the viscosity and surface tension are decreased leading to smaller molted particles and to more columnar and porous coatings (Ref 84,85). It has to be underlined that the axial injection in Axial III plasma torch seems to be less dependent on the suspension properties and is a field of investigation of research and technology for an optimized injection (Ref 85).…”

Mechanical Properties and Sliding Wear Resistance of Suspension Plasma Sprayed YSZ Coatings

“…On the basis of literature review, it can be stated that from the wide range of SPS materials, the yttria stabilised zirconia (YSZ) is the most examined feedstock material [27][28][29]. Moreover, the depiction procedure of the YSZ is being systematically developed.…”