IMPERMEABLE THIN AL2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

Mao, Scott X.

University of Pittsburgh (United States)

关键词: Vanadates;    Zirconium Oxides;    Sulfates;    Physical Vapor Deposition;    Corrosive Effects;   

DOI  :  10.2172/814918
RP-ID  :  NONE
RP-ID  :  FC26-01NT41189
RP-ID  :  814918

美国|英语

来源: UNT Digital Library

【 摘 要 】

In order to improve the hot corrosion resistance of conventional YSZ TBC system, the overlay of Al{sub 2}O{sub 3} coating was deposited on the TBC by EB-PVD techniques. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD). It has been found that TBC will react with V{sub 2}O{sub 5} to form YVO{sub 4}. A substantial amount of M-phase was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ. Al{sub 2}O{sub 3} overlay coating deposited by EB-PVD was dense, continues and adherent to the TBC. As a result, overlay Al{sub 2}O{sub 3} coating can prevent the YSZ from the attack by molten salts containing vanadium and arrest the penetration of salts into the YSZ along porous and cracks in the YSZ TBC, although there were some cracks in overlay Al{sub 2}O{sub 3} coating and at the interface between alumina and zirconia formed during hot corrosion tests due to the presence of tensile stress in the alumina coating. In the next reporting period, we will study the mechanisms of cracking of the overlay Al{sub 2}O{sub 3} layer and finish the hot corrosion tests of TBC with Al{sub 2}O{sub 3} coating deposited by high velocity oxy-fuel (HVOF) technique. The hot corrosion test of TBC with EB-PVD deposited Al{sub 2}O{sub 3} coating will be again performed. However before hot corrosion tests, a post-annealing will be carried out in vacuum (residual pressure 10{sup -3} Pa) at 1273K for 1h in order to transform the as-sputtered Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay.