Wear of seal materials used in aircraft propulsion systems

The various types of seal locations in a gas turbine engine are described and the significance of wear for each type is reviewed. Starting with positive contact shaft seals, existing material selection guidelines are reviewed and the existing PV (contact pressure × sliding velocity) criteria for selecting seal materials are discussed together with the theoretical background for these criteria. Examples of wear mechanisms observed to operate in positive contact seals are shown. Design features that can extend the operating capabilities of positive contact seals, including pressure balancing and incorporation of hydrodynamic lift, are briefly discussed. It is concluded that, despite the benefits arising from these design features, improved positive contact seal materials from the standpoint of wear, erosion and oxidation resistance will be necessary for further improvements in seal performance and durability and to meet stringent future challenges. Materials used in noncontacting gas path seal applications are described and a review of wear studies performed on these materials is presented. Factors that promote drastic changes in the structure and wear behavior of highly porous gas path seal materials are discussed. A correlation between wear characteristics and a factor that includes material strength, ductility, specific heat and hotworking temperature is proposed for low porosity metallic gas path seal materials.