protective coatings for gas turbine blades

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APPENDIX J 937
protective coatings. Typical examples of these materials are Mar-M 509, a
high-chromium, carbide-strengthened, cobalt-base superalloy, and Rene 80, a
cast, precipitation-hardenable, nickel-base superalloy (Ref. 89). Many of the
newer superalloys for turbine rotor blades are cast and solidified in such a
manner as to align the crystals in the radial direction, called directional
solidification, or to produce a single crystal. The resulting turbine blades are
capable of operating at temperatures 100 to 200°F (55 to l10°C) above those of
conventionally cast blades.
In high-pressure turbines, the blades are typically made of superalloys
while high-strength, nickel-base alloys are used for the disks and rims. Since
the temperatures are much lower in the low-pressure turbine, the critical
components are not cooled and are frequently made from high-strength,
nickel-base alloys.