Abstract
The aim of this study is to measure residual stress profiles in conventional and continuously graded thermal barrier coatings (TBCs), including those with laser-drilled effusion holes added to improve heat protection. Three sets of TBCs with different bond coat-topcoat interfaces were produced on Haynes 188 substrates. Two sample sets were prepared by plasma spraying NiCrAlY and YSZ powders, in one case, at fixed feedrates, and in the other, at feedrates simultaneously changing in opposite directions. A third sample set was obtained by combining a cold-sprayed CoNiCrAlY bond coat with a plasma-sprayed YSZ topcoat. Residual stress profiles were measured by means of incremental-step hole drilling and speckle interferometry. An original test method was also developed and is used to determine residual stress gradients before and after effusion hole drilling. The results are presented and discussed along with best practices for controlling residual stresses.
