TECHNICAL: The single-phase beta (Ni,Pt)Al coating is an accepted industrial standard as the bond coat in state-of-the-art thermal barrier coating (TBC) systems that protect superalloys against high-temperature oxidation. This coating faces challenges when applied to single crystal superalloys with increased content of refractory elements (e.g., the 3rd-generation and potential 4th-generation superalloys) due to formation of brittle topologically close-packed (TCP) phases and formation of a secondary reaction zone (SRZ) near the bond coat/superalloy interface. This GOALI collaborative effort between Tennessee Technological University (TTU) and General Electric Aircraft Engines (GEAE), with additional participation from Oak Ridge National Laboratory (ORNL), explores a new bond coat system. Compared to the (Ni,Pt)Al bond coat, the new Pt-enriched gamma-gamma prime, two-phase bond coat offers the advantages of a higher creep strength, better compatibility between the coating and superalloy substrate, improved metallurgical stability, and reduced manufacturing cost. This research focuses on (1) elucidating the effect of alloying elements in superalloy substrates on coating oxidation performance through synthesis of the gamma-gamma prime coatings on cast model alloys with well-controlled compositions; (2) clarifying the effect of Pt in the coating on counteracting detrimental effects of some refractory elements from the superalloy substrate; (3) assessing the long-term stability of this new bond coat system to account for interdiffusion with the substrate and evolution of the microstructure. GEAE will provide overall design guidelines for both cast model alloys and coatings and will supply single-crystal superalloy materials and TBC coatings. Custom-designed bond coats with optimal composition and microstructure will be identified for GEAE's Ni-base superalloys with the emphasis on newer-generation single crystals. The performance of the coated alloys will be evaluated by laboratory oxidation tests at TTU and ORNL, as well as tests in simulated engine environments at GEAE's facilities. NONTECHNICAL: This research will not only offer new bond coat candidates for the next-generation single-crystal superalloys but also provide a basis for the design of future superalloys and TBC systems. The project allows the PI, a young female faculty member at TTU, to further her research in the field of high-temperature coatings. An important aspect of this GOALI research is to provide the opportunity for undergraduate and graduate students to perform research in an academic/industry team environment. Short-term visits at GEAE will help students appreciate real industrial challenges in materials design/fabrication and better prepare them for future careers. Female students will be encouraged to participate and one female Ph.D. student will be recruited to work on the project. Through an outreach program, "Engineering a Future", recently initiated by TTU and the local Society of Women Engineers, the PI plans to introduce the wonderful world of materials to the girls in 5th-8th grades across the Mid-Tennessee via a hands-on learning workshop to foster scientific curiosity. An arc melter, to be acquired for conducting the research, will be a timely addition to the overall materials research facility at TTU, as materials processing has been listed as a thrust research area of the university. The research will build long-term research collaborations with leading industrial companies and national laboratories, thus enhancing the research quality and capability of TTU, the only dedicated technological university in the State of Tennessee.
