Abstract

Two aspects of the durability of modified ZrO/sub 2/ ceramic thermal barrier coatings for gas turbine airfoils are being investigated in this program. First, adherence of coatings of these materials has historically been difficult to achieve due to mismatch in thermal expansion coefficients and other properties between ceramic coatings and metallic substrates. Second, if the ceramic coatings are discontinuous, as for many plasma sprayed coatings, then condensate from the combustion environment may permeate the coating and volume changes in this condensate during subsequent service cycles may produce coating spallation. The adherence problem was approached by seeking to sputter deposit ceramic coatings over either sputter-etched, closely spaced, high aspect ratio substrate surface cones or by sputter depositing ceramic coatings over sputtered CoCrAlY coatings containing a very high density of columnar voids (leaders). The objective in both instances was to provide a compliant fibrous metal attachment between metal substrate and ceramic coating to absorb property mismatches. The permeability problem was approached both by coating a segmented (fibrous columnar) ceramic layer with a continuous and impervious metal sealing layer that is not required to provide structural strength or insulation, and by coating the segmented ceramic layer with a continuous layer of the samemore » ceramic material.« less

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