M. V. Nathal, R. A. MacKay, T. P. Gabb, J. L. Smialek, NASA Glenn Research Center, Cleveland, OH
Second-generation single crystal alloys are typically used in the production of turbine blades for subsonic aircraft engines. These alloys have good high temperature creep resistance and demonstrate a range of oxidation resistance and alloy densities. More advanced, third and fourth-generation single crystal turbine blade alloys have excellent high temperature creep but have very high alloy densities because of the nature and amount of refractory metals used in these alloys. These latter alloys typically have more limited applications as a result. We have taken the approach of designing new single crystal alloys with high temperature creep and oxidation resistances that meet or exceed the performance of second-generation single crystal alloys and do so at a reduced alloy density. Lower blade alloy density can provide significant reductions in total engine weight, because the size of the rotating disk, shaft, and other supporting structures can be concurrently reduced. Thus, lower density and stronger turbine blade alloys provide improved engine performance, reduced fuel burn, and reduced emissions for subsonic aircraft. Results from creep rupture testing, cyclic oxidation testing, microstructural stability tests, and density measurements will be presented for the low density superalloy single crystals and compared with published data from several production turbine blade alloys. To gain an understanding of the fundamental effects of alloying elements on mechanical and environmental behavior, a number of microstructural features were examined, including g’ precipitate size and volume fraction, microstructural stability, phase chemistries, and oxide scale formation. The goal of this work is to improve the ability to predict alloy behavior in order to tailor these alloys for specific turbine engine applications.
Summary: Second-generation single crystal alloys typically used in the production of turbine blades for subsonic aircraft engines have good high temperature creep resistance and demonstrate a range of oxidation resistance and alloy densities. More advanced, third and fourth-generation single crystal turbine blade alloys have excellent high temperature creep but have very high alloy densities because of the nature and amount of refractory metals used in these alloys. We have taken the approach of designing new single crystal alloys with high temperature creep and oxidation resistances that meet or exceed the performance of second-generation single crystal alloys and do so at a reduced alloy density. Results from creep rupture testing, cyclic oxidation testing, microstructural stability tests, and density measurements will be presented for the low density superalloy single crystals and compared with published data from several production turbine blade alloys. The goal of this work is to improve the ability to predict alloy behavior in order to tailor these alloys for specific turbine engine applications.
