Isothermal oxidation behavior of a thermal barrier coating prepared using EB-PVD

A novel two-layer structural thermal barrier coating (TBC) system with a similar to 150-mu m-thick CoCrAlY bond coat (BC) and a similar to 60-mu m-thick yttria stabilized zirconia (YSZ) ceramic top coat (TC) was prepared on superalloy K444 matrix using electron beam physical vapor deposition (EB-PVD). This deposited coating was characterized using isothermal oxidation tests (1000 degrees Cx200h). The results indicated that the deposited coating had a dense structure and close bonding between the layers. The thermally grown oxide (TGO) layer (predominantly alumina) that formed at the interface between the TC and the BC as a consequence of the oxidation process was effective in preventing the further oxidation of the BC. In the later stages of the oxidation process, embedded oxides of chromium/cobalt were observed among the TC's columnar grains, and the TGO underwent densification thinning. Through observations of the growth behavior of the TGO, the element diffusion, displacement reaction, and volatilization of the oxides were found to be related to the weight loss in the coating and the densification thinning of the TGO. These coatings displayed superior high-temperature oxidation resistance properties. Copyright (c) 2014 John Wiley & Sons, Ltd.