Abstract: Gas turbine engines employ a variety of abradable liners to decrease the clearance between the rotating components and the surrounding casing. There is normally a trade-off between porosity, (and concomitant permeability) and the abradability of the liner material, such that materials with good abradability are permeable to gas flow--resulting in performance losses. Permeability of porous liners is decreased by infiltrating the liner with a low-viscosity liquid containing a metal or metal oxide. After infiltration, the viscosity of the liquid is substantially increased to prevent its egress from the porous liner. Thereafter, the liner is heated at an elevated temperature to drive off the remaining liquid and provide an oxide which blocks the passages and decreases the permeability of the liner.

Abstract: For high temperature applications, ceramic coatings are plasma-sprayed onto various substrates. Plasma-spraying of ceramics onto non-conductive polymer surfaces often results in coatings which are poorly adherent. Adherent, non-spalling, ceramic layers can be achieved by first coating the non-conductive surface with an adhesively bonded, more conductive layer. It is postulated that the resulting more conductive coating is sufficient to prevent the build-up of electrostatic charges which can act to repel the plasma-sprayed particles. After the more conductive layer is applied (a bond coat may be employed, but is generally unnecessary), the ceramic powders are plasma-sprayed.