Abstract
The development of high-temperature heavy-duty turbine disk materials is critical for improving the overall efficiency of combined cycle power plants. An alloy development strategy to this end involves superalloys strengthened by ‘compact’ γ′-γ″ coprecipitates. Compact morphology of coprecipitates consists of a cuboidal γ′ precipitate such that γ″ discs coat its six {001} faces. The present work is an attempt to investigate the microstructure and creep behavior of a fully aged alloy exhibiting compact coprecipitates. We conducted heat treatments, detailed microstructural characterization, and creep testing at 1200 °F (649 °C) on an IN718-variant alloy. Our results indicate that aged IN718-27 samples exhibit a relatively uniform distribution of compact coprecipitates, irrespective of the cooling rate. However, the alloy ruptured at low strains during creep tests at 1200 °F (649 °C). At 100 ksi (689 MPa) load, the alloy fails around 0.1% strain, and 75 ksi (517 MPa) loading causes rupture at 0.3% strain. We also report extensive intergranular failure in all the tested samples, which is attributed to cracking along grain boundary precipitates. The results suggest that while the compact coprecipitates are indeed thermally stable during thermomechanical processing, the microstructure of the alloy needs to be optimized for better creep strength and rupture life.
Highlights
The world’s most efficient combined-cycle power plant pairs heavy-duty gas turbines with steam turbines, currently operating at an efficiency of 63.08% [1]
We studied an IN718-variant alloy to evaluate if the alloy might be a suitable generation gas turbine disk material
The microstructure of aged IN718-27 subjected to 28 ◦C/min cooling after solution treatment (IN718-27 FC) was studied using BSE imaging and Scanning Transmission Electron Microscopy (STEM)-Energy Dispersive X-ray Spectroscopy (EDS) (Figure 2) mapping
Summary
The world’s most efficient combined-cycle power plant pairs heavy-duty gas turbines with steam turbines, currently operating at an efficiency of 63.08% [1]. For a 1000 MW power plant, a 1% increase in engine efficiency could potentially reduce the cost of power generation by $50 million a year [2]. Higher engine efficiency can result in better fuel economy and reduced greenhouse gas emissions. One way to increase the efficiency of combined-cycle power plants is to improve gas turbine efficiency. A roadblock in raising gas turbine efficiency is the current temperature performance of turbine disk materials. Developing the next-generation advanced cycle, potentially operating at an efficiency of 65% or more, requires a turbine disk material that can operate at or above 1200 ◦F (649 ◦C)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
