Abstract
Abstract : Reactive element (RE) additions are of considerable interest for thermal barrier coating materials. The kinetics of alumina scale growth are controlled by oxygen inward diffusion and/or aluminum outward diffusion along the grain boundaries (gbs). The focus of the program was to determine how RE additions (Y, Hf) affect anion and cation diffusion in alumina. At 1300 C, 500 ppm yttrium slows oxygen gb diffusion by a factor of 5, and increases the corresponding activation enthalpy from 407 20 to 486 34 kJ/mol. Studies on alumina specimens incorporating Ni marker particles suggested that Y also slows Ni outward diffusion. It was also determined that Y-doping retards Cr diffusion in the gb regime by over an order of magnitude.
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