The structural and surface stabilities of two experimental c-Ni+c¢-Ni 3 Al-base alloys containing Pt or Ir were investigated. These alloys are representative of alloys currently being developed to occupy a unique domain with a good combination of high-temperature strength and resistance to oxidation and hot corrosion. Structural characterization included differential thermal analysis (DTA), transmission synchrotron X-ray analysis, precipitate morphology evolution, phase-partitioning behavior, transmission electron microscopy (TEM), dislocation analysis, and isothermal precipitate-coarsening behavior. Electron microprobe investigations showed that Pt partitions largely to the c¢ phase, while Ir partitions more to the c phase. As a consequence, the influence of these two elements on the c-c¢ lattice-parameter mismatch was quite different. Specifically, synchrotron X-ray analysis confirmed a positive c-c¢ misfit in both the Pt-and Ir-modified alloys in the temperature range 700°C to 1200°C; however, the Pt partitioning to the c¢ phase resulted in a much larger misfit. The coarsening kinetics of both alloys followed a cubic time dependence and Pt addition was more effective than Ir in slowing the coarsening rate. Thermodynamic predictions about elemental partitioning and about the solidus, liquidus, and c¢ solvus temperatures were made using the software package PANDAT; the results of these predictions were compared with experimental measurements.
As future land-based gas turbine engines are being designed to operate with inlet temperatures exceeding 1300°C (2370°F), efforts at NETL have been focused on developing advanced materials systems that are integrated with novel airfoil cooling architectures. Recent achievements in the areas of low cost diffusion bond coat systems applied to single- and poly-crystalline nickel-based superalloys, as well as development of thin nickel-based oxide dispersion strengthened layers are presented in this paper. Integration of these material systems with commercially cast, novel, pin-fin internal cooling airfoil arrays, tripod film cooling hole architectures, trailing edge cooling geometries, and near surface micro-channel concepts is also presented.
Advanced coating systems in conjunction with novel internal airfoil cooling configurations continue to be a critical research focus to provide enhanced oxidation protection and cooling of commercial metal alloys as future land-based gas turbines are being designed for inlet gas temperature operations of >1300–1400°C. With the application of densified oxide dispersion strengthened (ODS) coatings on cast near surface embedded micro-channel (NSEMC) airfoil surfaces, improvements of >50–70% in heat removal capabilities are projected over that of conventional, smooth-channeled, internally-cooled, airfoil configurations. For turbine inlet and airfoil surface design temperatures exceeding 1400–1600°C, oxide-coated, silicon carbide-based ceramic matric composites (CMCs) have been developed. In this paper we will review our recent advancements that have been made with respect to ODS coating development and the oxidation stability of CMCs during bench-scale laboratory testing.
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