Abstract
Industrial gas turbines (IGT) require novel single-crystal superalloys with demonstrably superior corrosion resistance to those used for aerospace applications and thus higher Cr contents. Multi-scale modeling approaches are aiding in the design of new alloy grades; however, the CALPHAD databases on which these rely remain unproven in this composition regime. A set of trial nickel-based superalloys for IGT blades is investigated, with carefully designed chemistries which isolate the influence of individual additions. Results from an extensive experimental characterization campaign are compared with CALPHAD predictions. Insights gained from this study are used to derive guidelines for optimized gas turbine alloy design and to gauge the reliability of the CALPHAD databases.
Highlights
NICKEL-BASED superalloys have emerged as the materials of choice for high-temperature industrial gas turbine (IGT) applications due to their unique combination of resistance to loading under static, fatigue, and creep conditions, as well as to environmental degradation.[1]
Chemical compositions determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and electron probe microanalysis (EPMA) are in good overall agreement with nominal values
Secondary particles form after the homogenization step during cooling from around 1260 °C, while tertiary ones precipitate during the subsequent aging heat treatments at 1120 °C and 845 °C
Summary
NICKEL-BASED superalloys have emerged as the materials of choice for high-temperature industrial gas turbine (IGT) applications due to their unique combination of resistance to loading under static, fatigue, and creep conditions, as well as to environmental degradation.[1] Materials tailored to particular gas turbine specifications are required, as a simple adaptation or modification of aeroengine alloys cannot yield optimal results due to distinct design factors including weight restriction, operating time, fuel quality, and cyclic duty.[2]. The latter tend to either possess (1) a high Al/Cr ratio and exhibit good creep properties, but weak corrosion resistance, having been developed for aerospace applications, or (2) a low Al/Cr ratio, Manuscript submitted March 8, 2020. Only few compositions satisfy both requirements and populate the envisioned area above 13.2 at. pct Cr and 8.5 at. pct Al
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