Improved performance rhenium containing single crystal alloy turbine blades utilizing ppm levels of the highly reactive elements lanthanum and yttrium
- Rolls-Royce PLC, Bristol (United Kingdom)
- Allison Engine Co., Indianapolis, IN (United States)
- Cannon-Muskegon Corp., MI (United States)
Turbine inlet temperatures have now approached 1650 C 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. Re additions to cast airfoil superalloys not only improve creep and thermomechanical fatigue strength but also environmental properties, including coating performance. It is now known that sulfur (S) at levels <10 ppm but >0.2 ppm in these alloys reduces the adherence of {alpha} alumina protective scales on these materials or their coatings by weakening the Van der Waal`s bond between the scale and the alloy substrate. A team approach has been used to develop an improvement to CMSX-4 alloy which contains 3% Re, by reducing 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 show thirteen times the number of cycles to initial alumina scale spallation for CMSX-4 [La + Y] compared to standard CMSX-4. The La assists with ppm chemistry control of the Y throughout the single crystal turbine blade castings through the formation of a continuous lanthanum oxide film between the molten and solidifying alloy and the ceramic core and prime coat of the shell mold. Y and La tie up the M2 ppm but >0.2 ppm residual S in the alloy as very stable Y and La sulfides and oxysulfides, thus preventing diffusion of the S atoms to the alumina scale layer under high temperature, cyclic oxidizing conditions. La also forms a stable phosphide. CMSX-4 (ULS) (La + Y) HP shroudless turbine blades will commence engine testing in May 1998.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 328343
- Report Number(s):
- CONF-980615--
- Journal Information:
- Journal of Engineering for Gas Turbines and Power, Journal Name: Journal of Engineering for Gas Turbines and Power Journal Issue: 1 Vol. 121; ISSN JETPEZ; ISSN 0742-4795
- Country of Publication:
- United States
- Language:
- English
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