Nanocrystalline bond coat development

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Gas turbine engines are considered to be amongst the most hostile operating environments for conventional material systems. Increasing demands for higher engine performance, thermal efficiency and durability of components have led to the development of thermal barrier coating (TBC) systems. These systems are typically used on the hot section components of gas turbine engines, such as blades, vanes and combustors for protection against high temperature oxidation and corrosion. TBCs typically consist of an yttria-partially-stabilized zirconia top coat and a MCrAlY (where M can be Ni and/or Co) bond coat usually applied by thermal spray techniques such as plasma and/or HVOF spraying on the superalloy base metal to be protected. The full potential of TBC systems is yet to be reached due to premature failure, usually occurring at the bond coat-top coat interface. Recent studies have shown promising solutions to obtain enhanced performance TBC. In particular, nanocrystalline bond coats have been produced by HVOF. Although these bond coats exhibited partial grain growth compared to the original nanocrystalline feedstock powder, they exhibited improved oxidation and corrosion behaviour, thus enhancing the TBC performances. However, these studies have revealed that the use of HVOF to produce the bond coat promotes the formation of detrimental oxides due to unavoidable in-flight oxidation of the feedstock powder. The production of nanocrystalline bond coat without the formation of harmful oxides and grain growth during spraying is sought as the solution to producing enhanced TBC systems. The long term objective of this research project is to successfully produce enhanced TBC systems that will exhibit better performances with respect to delamination/cracking, by first producing non-oxidized nanocrystalline MCrAlY bond coats using both CGDS and p-CGDS techniques combined with nanocrystalline powder production using existing milling techniques (shorter term objective).It is expected that non-oxidized nanocrystalline bond coats will exhibit superior performances with respect to delamination/cracking.