Effect of atmosphere composition on lifetime and oxidation behavior of EB-PVD TBC with NiPtAl bondcoats

摘要

NiPtAl coatings are widely used as bondcoats for thermal barrier coating (TBC) systems during high temperature exposure. Pt modified aluminide coatings on the CMSX-4 Ni-base alloy were oxidized at 1150°C in different atmospheres. Cross-section oxide layer morphologies on the NiPtAl coatings after TBC failure were similar in air with that in air+15%H_2O. The surface morphologies of as-received low and high-Pt bondcoats showed great effect on the oxide layer growth and morphologies due to the different compositions within the two bondcoats. The irregular alumina surface on the low-Pt bondcoat was showed due to the slipping of the NiPtAl grains. Raman spectroscopy illustrated that the alumina mainly consisted θ and α-Al_2O_3 during the Ar+20%O_2 exposure, however, only α-Al_2O_3 could be found in Ar+4%H_2+2%H_2O during short time exposure. Low oxygen partial pressure of Ar+4%H_2+2%H_2O perhaps is the reason that spinel and θ-Al_2O_3 can not formed, and directly promotes the α-Al_2O_3 formation.