Title: Failure mechanisms of APS-YSZ-CoNiCrAlY thermal barrier coating under isothermal oxidation and solid particle erosion

Abstract

The high temperature oxidation and solid particle erosion of air plasma sprayed thermal barrier coating (APS-TBC) system was studied experimentally. The APS-TBC consists of an 8 wt% yttria partially stabilized zirconia (YSZ) top coat and CoNiCrAlY bond coat deposited on Inconel 718 substrate via atmospheric plasma spraying process. Isothermal oxidation tests of APS TBCs were conducted at 1050°C, 1100°C and 1150°C in air for up to 1970 hours. Solid particle erosion tests were also conducted for both as-deposited and isothermally exposed TBC specimens at selected particle impingement angles and velocities at ambient temperature. The scanning electron microscopy (SEM) shows the formation of thermally grown oxide (TGO) scale due to oxidation of CoNiCrAlY bond coat, and the oxidation kinetics of TGO growth is described by the parabolic rate formulae. The failure of APS-TBC system under isothermal oxidation is associated with the spallation of the top coat through propagation and coalescence of cracks along the coating interface affected by the TGO growth. The solid particle erosion rate of the top coat was found to increases with the impingement angle, and reaches the maximum erosion rate at normal impingement of particles. The erosion resistance of the APS-TBC was observed to increases after TBC specimen were exposed at 1100°C and 1150°C for 72 hours, probably due to the sintering effect on the top coat resulting in reduction of top coat porosity.