Rolls-Royce plc
Derby and Bristol, UK
Malcolm C. Thomas, Paul S. Korinko, Phil S. Burkholder
Allison Engine Company
[Rolls-Royce plc]
Indianapolis, Indiana USA
Ken Harris, Jacqueline B. Wahl
Cannon-Muskegon Corporation
[SPS Technologies, Inc.]
Muskegon, Michigan USA
ABSTRACT
Turbine inlet temperatures (TITs) have now reached 1650°C (3000°F) at maximum power for the latest large commercial turbofan engines, resulting in high fuel efficiency and thrust levels approaching or exceeding 445 kN (100 000 lbs.). High reliability and durability must be intrinsically designed into these turbine engines to meet operating economic targets and ETOPS certification requirements. This level of performance has been brought about by a combination of advances in air cooling for turbine blades and vanes, 3-D computerized design technology for stresses and airflow and the development and application of rhenium (Re) containing, high g¢ volume fraction nickel-base single crystal (SX) superalloys, with advanced coatings, including prime-reliant ceramic thermal barrier coatings (TBCs).
At high gas temperatures, several issues are critical to turbine engine performance retention, blade life and integrity. These are tip oxidation in particular for shroudless blades, internal oxidation for lightly cooled turbine blades and TBC adherence to both the airfoil and tip seal liner. A team approach has been used to develop an improvement to CMSX-4® alloy which contains 3% Re, by reducing sulfur (S) and phosphorus (P) levels in the alloy to < 2 ppm, combined with residual additions of lanthanum (La) + yttrium (Y) in the range 10-30 ppm. Results from cyclic, burner rig, dynamic oxidation testing at 1093°C (2000°F) show thirteen times the number of cycles to initial alumina scale spallation for CMSX-4 [La + Y] compared to standard CMSX-4. CMSX-4 (ULS) [La + Y] HP shroudless turbine blades are scheduled to commence engine testing in mid 1998.
Keywords: CMSX-4, Turbine, Durability, Lanthanum and Yttrium.
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