Mesoscopic nonlinear elastic modulus of thermal barrier coatings determined by cylindrical punch indentation

Cylindrical punch indentations are performed to determine the effective mod ulus of a plasma-sprayed ZrO2-8 wt% Y2O3 thermal barrier coating (TBC) as a function of coating depth. Cylindrical punch indentations offer significan t advantages over pointed (Vickers, Berkovich, or Knoop) indentations for m aterials that do not exhibit linear elastic behavior. Cyclic loading with a cylindrical punch clearly shows the TBCs to exhibit nonlinear elastic beha vior with significant hysteresis that is related to the compaction and inte rnal sliding within the plasma-spray splat microstructure. Also, the effect of a high-heat-flux laser treatment is shown to produce a gradient both in the effective TBC modulus and degree of loading/unloading hysteresis with depth.