Abstract
In this study, we examined the influence of specimen shape and the bond coating (BC) process of a thermal barrier coating (TBC) on thermally grown oxide (TGO) growth using an advanced gas turbine system. Three differently shaped substrates were prepared: one was a flat plate substrate without restraints and the other two were round bar substrates with restraints. BCs were then applied by low-pressure plasma spraying (LPPS) or cold spraying (CS). An yttria-stabilized zirconia top coat was fabricated subsequently on the bond-coated layer by air plasma spraying. The coatings were oxidized isothermally at 1000°C for different periods of up to 1000 h and the TGO growth for each was compared. We found that the TGO growth on the round bars with restraints was faster than that on the flat plate bar. In addition, the TGO growth on the TBC treated using LPPS-BC was faster than that on the TBC treated using CS. We believe that the difference in the residual stresses between the flat plate specimen and the round bar specimens as well as differences in the microstructures between the TBCs that were treated with LPPS and CS-BC were responsible for faster TGO growth. Understanding the parameters that affect the TGO growth rate during service will allow predictions of the life span of a coating system.
