GOALI: Fundamental Investigation of the Synthesis, Characterization, and Performance of a NiAl Diffusion Coating Doped with a Reactive Element by Chemical Vapor Deposition

9801042 Lee Thermal barrier coatings (TBCs) consist of a strain-tolerant ceramic layer and a metallic bond coat, which provides oxidation protection to metal alloys. The dominant failure mode observed in these material systems is the progressive fracture of the interface region between the bond coat surface and its oxide scale upon exposure to oxidation. One potent avenue for improving the scale adhesion at the bond coat surface is to incorporate one or more reactive elements, such as Hf or Zr, into a NiAl diffusion coating formed by aluminizing the surface of a Ni-based superalloy. This grant results from recent manufacturing advances in aluminizing by chemical vapor deposition (CVD). In contrast to the close-batch pack cementation and gas phase pack methods traditionally used for aluminizing, the dynamic nature of the open-flow CVD technique offers the promise of proactively controlling dopant concentration and distribution in the coating matrix. Previous studies with bulk alloys and intermetallics have shown that, in order for the beneficial effect to be operative, a reactive element must be present in a well-controlled level and distribution in the matrix material. Stevens Institute of Technology in collaboration with General Electric Aircraft Engines (GEAE) is exploring the synthesis, characterization, and performance issues associated with the CVD doping concept. This is accomplished under the NSF-GOALI concept, which is ideal for long-term exploration by collaborative university- industry research activities. This research project effectively integrates Stevens' strengths in conducting kinetic experiments, coating characterization, and mathematical modeling with GEAE's expertise as a leading aircraft engine manufacturer with unique characterization and test facilities. The Division of Materials Research and the MPS Office of Multidisciplinary Activities jointly fund this grant. %%% Extending the surface functionality of advanced metallic and ceramic materials has been a vital area of research and development for high temperature structural applications. Currently a strong technological need exists to improve the performance of 'traditional' structural materials, such as Ni-based superalloys, via surface coating and modification approaches. ***