Hot Corrosion Behavior of YSZ Thermal Barrier Coatings Modified by Laser Remelting and Al Deposition

Thermal barrier coatings that are widely used to protect the turbine blades of gas turbines from failure are subjected to hot corrosion conditions. The present study aims to improve their hot corrosion resistance by modifying the plasma-sprayed yttria-stabilized zirconia topcoat by laser remelting and Al deposition. First, a dense remelted layer with some vertical cracks was obtained by laser remelting. Then, Al film was deposited on the surface of laser-remelted coatings by magnetron sputtering, and the dense α -Al 2 O 3 overlay was in situ synthesized through the reaction of Al and ZrO 2 during vacuum heat treatment. Hot corrosion tests of all coatings were conducted in a mixture of 55 wt.% V 2 O 5 and 45 wt.% Na 2 SO 4 corrosive salts at 1000 °C for 30 h. The defects such as pores and microcracks in the as-sprayed coatings provided paths for molten salt penetration, which led to the worst hot corrosion resistance of the as-sprayed coatings. The minimal surface roughness of the dense laser-remelted coatings was the main reason for improving the hot corrosion resistance. However, the resistance of laser-remelted coatings to hot corrosion was significantly improved when they were modified by Al deposition, which is mainly due to the reduced reaction surface between molten salts and yttria stabilizer. The corresponding hot corrosion mechanism was discussed.