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SUMMARYThe effects of yttrium concentration in NiA1Y and NiCrY and of chromium and aluminum concentrations in NiCrA1Y bond coatings on the cyclic furnace life of thermal barrier coatings were studied. Also, the effect of bond coating thickness on life was studied. The evaluations were done in cyclic furnace tests between 990 0 -280 0 and 109S o -280 0 C on solid specimens.On the basis of the data obtained in this study, it was established that the presence and the concentratign of yttrium in the bond coating is very critical. Without yttrium in the Ni-Cr. Ni-Al, and Ni-Cr-A1 bond coatings, the thermal barrter systems fail'very rapidly. The optimization of yttrium, and to a lesser extent, chromium and aluminum concentrations in t~e nickel-base alloy bond coatings leads to a very significant improvement of the thermal barrier systems.

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