In situ synthesis of α-alumina layer on thermal barrier coating for protection against CMAS (CaO–MgO–Al2O3–SiO2) corrosion

Abstract

In general, it is accepted that thermal barrier coating (TBC) with good CMAS (CaO–MgO–Al2O3–SiO2) corrosion resistance has long lifetime. A columnar Al film was firstly deposited in this work at the top of 7wt.% yttria-stabilized zirconia (7YSZ) TBC by magnetron sputtering. Then a vacuum treatment of Al-deposited TBC was carried out at 700°C for 1h and 900°C for 5h. An α-Al2O3 layer was in situ synthesized at the top of 7YSZ TBC through the reaction of Al and ZrO2 after vacuum heat treatment. The CMAS corrosion resistance of as-sprayed TBC and treated TBC was compared after isothermal test of 1200°C for 24h. The results indicated that the Al-deposited TBC after vacuum heat treatment has better CMAS corrosion resistance than the as-sprayed TBC. Two mechanisms are considered to contribute to the protective effect of in situ synthesized α-Al2O3 layer: the first is α-Al2O3 partially filling existed open pores and cracks in the top 7YSZ coating to hinder the penetration of molten CMAS; and the second is α-Al2O3 reacted with CMAS forming CaAl2Si2O8 and MgAl2O4 that play the role in inhibiting further infiltration of CMAS.