Computational Materials Design of Castable SX NI-Based Superalloys for IGT Blade Components
Improvements to the efficiency of advanced power systems is a critical technological concern. Higher efficiencies can reduce harmful byproduct such as CO2 and NOx emissions while utilizing coal resources more effectively. In order to improve the thermal efficiency of modern power plant technologies, the materials of the turbine blades and vanes must possess superior creep rupture resistance to endure the higher inlet temperatures associated with higher efficiencies. Ni-based single crystal (SX) superalloy blades, seen widely in aerospace engines, possess high creep strength in comparison with conventionally cast and directionally solidified (DS) blades. However, industrial gas turbines (IGTs) require much larger sized castings than aerospace engines, and the use of SX superalloys in IGTs is limited because of the low casting yield due to defects associated with large size and slow solidification, such as freckling, high/low angle boundary (HAB/LAB) formation, grain nucleation, and shrinkage/porosity. QuesTek Innovations LLC, a leader in integrated computational materials engineering (ICME), has designed a highly castable SX Ni-based superalloy (QTSX) that can be cast effectively as large, defect-free IGT components and provides creep performance comparable to state-of-the-art aeroturbine blades materials, thereby allowing higher gas temperatures and increased thermal efficiency. Upon completion of a DOE Phase I and Phase II SBIR, QuesTek Innovations LLC, teamed with Siemens Power Generation Inc. and PCC Airfoils (PCC), has developed an ICME framework and an innovative composition with 1wt% Re for a single crystal Ni-base superalloy IGT blades that exhibits the processability of Re-free alloy but with the comparable performance of 3wt% Re 2nd Gen SX superalloys. Under this program, the solidification characteristics of the new alloy were compared against a commercially available single crystal Ni-base superalloy, Rene N5. Single crystal casting trials were performed on physically large geometries with cross-section transitions that were representative of large IGT blades. Under nominally identical casting conditions, the QuesTek alloy was found to exhibit no evidence of casting defects (100% yield rate) while both “freckle” defects and misoriented grains were observed in the Rene N5 castings. Characterization and testing of alloys has been performed, and the microstructure and mechanical properties have been validated. Preliminary assessment of the microstructural stability, oxidation resistance, and creep performance of the newly developed QuesTek alloy are extremely promising as they are comparable to Rene N5 (3wt %Re) despite containing a lower overall concentration of Re (1wt %) in the alloy. Full-scale blade castings using QTSX have been produced at PCC to demonstrate the full processability potential of the new alloy. An US Patent has been filed based on the new alloy invention (Application No. 14/723,074).
- Research Organization:
- US Department of Energy (USDOE), Washington DC (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0009592
- OSTI ID:
- 1481883
- Type / Phase:
- SBIR (Phase IIA)
- Report Number(s):
- Final Report
- Country of Publication:
- United States
- Language:
- English
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