Structure of and ion segregation to an alumina grain boundary: Implications for growth and creep

Milas, Ivan; Hinnemann, Berit; Carter, Emily A.
May 2008
Journal of Materials Research;May2008, Vol. 23 Issue 5, p34
Academic Journal
Using the periodic density-functional theory (DFT), we investigated the structure and cohesive properties of the a-alumina S11 tilt grain boundary, with and without segregated elements, as a model for the thermally grown oxide in jet engine thermal-barrier coatings. We identified a new low-energy structure different from what was proposed previously based on electron microscopy and classical potential simulations. We explore the structure and energy landscape at the grain boundary for segregated Al, O, and early transition metals (TMs) Y and Hf. We predict that the TMs preferentially adsorb at the same sites as Al, while some adsites favored by O remain unblocked by TMs. All segregated atoms have a limited effect on grain boundary adhesion, suggesting that adhesion energies alone cannot be used for predictions of creep inhibition. These findings provide some new insights into how TM dopants affect alumina growth and creep kinetics.


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