Investigation of the hot corrosion effects on the lifetime of TBCs with and without TC

Abstract

This paper investigates the influence of hot corrosion on the lifetime of TBCs with and without top coat under cyclic thermal loading. The tests were performed on two types of samples: Type A coating consisting solely of a bond coat (BC) fabricated by the HVOF method, and type B coating comprising a BC fabricated by the HVOF method and a TC fabricated by the APS method. The lifetime and degradation mechanism of these two types of coatings under hot corrosion in the presence of sulfate and vanadate molten salts were compared. The lifetime of type A and B coatings under the hot corrosion test is 31 and 24 cycles, respectively. Results indicate that the TGO acts as a barrier against the penetration of corrosive salts and delays the degradation of the type A coating. XRD patterns reveal that the reaction products of BC with molten salts are (Co,Ni)3(VO4)2 and (Cr,Al)VO4. In the type B coating, YVO4 is formed as a hot corrosion product due to the reaction of molten salts with yttria. With the depletion of yttria, the phase transition of zirconia from tetragonal to monoclinic causes volumetric expansion and coating degradation.