A team approach involving a turbine engine company [Rolls-Royce], its single crystal casting facilities and a superalloy developer and ingot manufacturer [Cannon-Muskegon], utilizing the concepts of simultaneous engineering, has been used to successfully develop CMSX-4 alloy for turbine blade applications. CMSX-4 alloy is a second generation nickel-base single crystal superalloy containing 3% (wt) rhenium (Re) and 70% volume fraction of the coherent γ′ precipitate strengthening phase. Its finely balanced composition offers an attractive range of properties for turbine airfoil applications. In particular the alloy’s combination of high strength in relation to creep-rupture, mechanical and thermal fatigue, good phase stability following extensive high temperature, stressed exposure and oxidation, hot corrosion and coating performance, are attractive for turbine engine applications where engine performance and turbine airfoil durability are of prime importance.
The paper details the single crystal casting process and heat treatment manufacturing development for turbine blades in CMSX-4 alloy. Competitive single crystal casting yields are being achieved in production and extensive vacuum heat treatment experience confirms CMSX-4 alloy to have a practical production solution heat treat / homogenization “window”.
The creep-rupture data-base on CMSX-4 alloy now includes 325 data points from seventeen heats including fourteen 3630 kg (8000 lb) production size heats. An appreciable portion of this data was machined-from-blade (MFB) properties which indicate turbine blade component capabilities based on single crystal casting process, component configuration and heat treatment. The use of hot-isostatic-pressing (HIP) has been shown to eliminate single crystal casting micropores which along with the essential absence of γ/γ′ eutectic phase, carbides, stable oxide, nitride and sulphide inclusions results in remarkably high mechanical fatigue properties, with smooth and particularly notched specimens. The Re addition has been shown to not only benefit creep and mechanical fatigue strength (with and without HIP), but also bare oxidation, hot corrosion (sulphidation) and coating performance.
The high level of balanced properties determined by extensive laboratory evaluation has been confirmed during engine testing the Rolls-Royce Pegasus turbofan.