COMPOSITIONALLY GRADED THERMAL BARRIER COATINGS FOR HIGH-TEMPERATURE AERO GAS-TURBINE COMPONENTS

A new type of compositionally graded thermal barrier coating is being developed for the hot-end components of aero gas turbine engines. An electron beam physical vapour deposition process has been employed to co-deposit MCrAlY and partially stabilised zirconia on superalloy substrates. The compositional profile, across the thickness of the coating, is designed by an in-house computer program. The program takes into account the physical properties of the substrate and coating materials, as well as the most important performance requirements. The resulting graded coating is therefore tailored to match the properties of the substrate at the coating-substrate interface and those of the external environment at its outer surface. One advantage of such coatings is that problems associated with interfaces in conventional multi-layered coatings are eliminated. Fabricated coatings were subjected to a number of tests and characterisation studies, including thermal cycling and thermal shock tests, and microanalyses. Effects of process parameters such as substrate temperature and ion-assisted deposition on the microstructure and properties of the coatings, in particular their thermal stability, were investigated. It was found that the thermal stability of the coatings largely depends on their density and microstructure, and that by controlling the density across the thickness a corrosion resistant and strain tolerant coating can be produced.