QuesTek's Single Crystal Nickel Answers the Department Of Energy's Call
SituationThe U.S. Department of Energy needed to utilize better materials with improved casting yields for the wide-spread use of single crystal superalloys in industrial gas turbines. To that end, DOE’s National Energy Technology Laboratory (NETL) Small Business Innovation Research (SBIR) generated a solicitation addressing Advanced Fossil Energy Technology Research.
ChallengesNickel-based superalloys are used in hot gas path components in gas turbines due to their excellent creep resistance. To achieve their maximum mechanical capability, these materials must be cast as single crystals. However, prior to funding research into development of castable, single crystal nickel-based superalloys, the industry typically utilized conventionally cast or directionally solidified blades.
The DOE arrived at an impasse: casting capability had improved but not enough due to defects formed during the slow cooling of large Industrial Gas Turbine (IGT) blades, partly due to high rhenium (Re) content necessary for enhanced creep performance. Consequently, this has hampered the adoption of single crystal blades in IGT use.
Then there was the environmental component. The traditional use of coal resources created CO2 and NOx emissions that emitted higher levels of pollutants.
The innovation simply wasn’t there, and that prompted DOE to:
- Seek research and development to explore compositional adjustments to the alloy system in order to increase the yield rates of single crystal castings for high-temperature gas turbine applications.
- Push the boundaries of existing materials through the design and development of a novel material composition that could improve casting yield and IGT blade performance, impacting the thermal efficiency of Integrated Gasification Combined Cycle (IGCC) and other advanced power plants.
SolutionThrough Phase I, Phase II and Phase IIA SBIR programs, QuesTek successfully designed, developed, and demonstrated a novel, castable single crystal nickel superalloy that contained 1% rhenium (a lower percentage than next generation, high performance IGT blade alloys), and exhibited high casting yield rates and good application-specific performance.
A Materials Genome-based ICME approach was applied to the design of the alloy to meet critical high temperature performance requirements and demanding processing conditions. By tightly controlling alloy solidification behavior, QuesTek designed a 1wt% rhenium alloy with the processability of a rhenium-free alloy, while its improved partitioning in the solid state delivered the creep performance of a 3wt% rhenium alloy.
OutcomesQuesTek applied an ICME approach to design, develop and demonstrate a novel alloy that met the DOE’s desired goals. The new design could cast effectively as large IGT blade components, provide hot corrosion resistance and creep performance comparable to state-of-the-art SX aeroturbine blades.
Through QuesTek’s leadership and innovation, a material now exists to propel the industry to push efficiencies to the next level.