Functional Intermediate Layers for the Improvement of Thermal Barrier Coatings Performance

摘要

Thermal Barrier Coatings have been widely used on of gas turbines components in the aeronautical industry and power generation with the objective of extending the performance and life cycle of these machines. The goal is to protect metallic components, in general Nickel or Cobalt based superalloys that suffer degradation from corrosion, oxidation or excessive heating load during service in thermally aggressive environments. A TBC is usually constituted of a metallic bond coat and a ceramic top coat. The bond coat is usually a metallic alloy with the function of protecting the substrate from oxidation and hot corrosion, forming a protective oxide layer at the metallic-ceramic interface and helping in the adhesion. Some of the problems of a TBC in service are bond coat delamination due to the infiltration of gases at high temperature, the differences of thermal expansion coefficient between metallic and ceramic layers, the growth of an oxide layer that takes place under specific thermal conditions on the bond coat (TGO) and Al diffusion from the substrate. Extensive research has been made to improve the adhesion and high temperature oxidation resistance of the TBCs. Some possibilities have been explored, as the gradation of successive metal-ceramic layers (FGM), diffusion barrier layers and intermediate layers. In this work, the possibility of using an intermediate layer between the bond coat and the ceramic top coat is evaluated. The intermediate layer is a Cr_3C_2 applied by PVD. The results are discussed based on the oxidation and microstructural characteristics of the obtained coatings.