Two complementary single crystal alloys have been developed from the MAR-M-247 composition, with the objectives of providing high creep-rupture strength, excellent oxidation resistance, good castability, practical solution heat-treatment ranges, high incipient melting points, and stable microstructures. The alloys, CM SX-2 and CM SX-3, are turbine blade and vane alloys, with CM SX-3 showing improved coated oxidation and corrosion resistance. Foundry performance characteristics studied using ten different single crystal casting processes to produce both solid and complex cored, thin-wall turbine blade and vane components were: “freckling” sensitivity, spurious grain formation, microporosity, and alloy/ceramic core reactions. Practical solution heat-treatment ranges (difference between the γ′ solvus and the incipient melting temperatures) have been established and vary from 45–50°F for CM SX-3 and 50–55°F for CM SX-2 measured without prior homogenization treatments. Extensive machined-from-blade (MFB) mechanical property work is reported. Alloy stability investigations were undertaken using prior tested MFB stress-rupture specimens. Environmental evaluations using both bare and coated single crystal specimens, subjected to separate cyclic/dynamic oxidation, and corrosion testing in burner-type rigs are also reviewed. A new γ′ microstructure/heat-treatment technology has been found to be particularly applicable to CM SX-2 and CM SX-3 alloys, because of their low γ/γ′ mismatch and suitable γ′ chemistry. This technology further increases the creep-rupture capability of both alloys by 10–40°F, depending on test temperature.
- International Gas Turbine Institute
Development of the Single Crystal Alloys CM SX-2 and CM SX-3 for Advanced Technology Turbine Engines
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Harris, K, Erickson, GL, & Schwer, RE. "Development of the Single Crystal Alloys CM SX-2 and CM SX-3 for Advanced Technology Turbine Engines." Proceedings of the ASME 1983 International Gas Turbine Conference and Exhibit. Volume 5: Ceramics; Structures and Dynamics; Controls, Diagnostics and Instrumentation; Education; Process Industries. Phoenix, Arizona, USA. March 27–31, 1983. V005T11A006. ASME. https://doi.org/10.1115/83-GT-244
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