Stress distributions in plasma-sprayed thermal barrier coati(8)

Stress distributions in plasma-sprayed thermal barrier coatings as a function of interface roughness and oxide scale thickness

34M.Ahrensetal./SurfaceandCoatingsTechnology161(2002)

26–35

Fig.10.TheradialstressabovethebottomofthevalleyasafunctionofRfordifferentoxidethicknesses(1,3,6,10mm),differentamplitudesandperiod

lengths.

cracksbelongingtoadjacentpeaksfinallyleadstospallation.AsstressconversionisdelayedforhigheramplitudesAonewouldexpectlongerlifetimesinthiscase,whichmaybeinaccordancewithourrecentlyperformedthermalcyclingexperiments.Here,afteradefinednumberofcycles,TBCswithhigherbondcoatroughnessshowedasmallernumberofcracksabove100mmclosetotheTBC–BCinterfacethanTBCswithlowerinterfaceroughnessw7x.Calculationsonstressdistributioncomparabletothosepresentedherearegiveninw14x.Theywereperformedforaninterfaceroughnessconsistingofsingleandperiodicpeakswhereasthepeaksweremodelledasrectangleswithsemicirclesontop.Inthisway,itwaspossibletovarythecurvatureandpeakheightindepen-dently.Thedependencesoftheradialstressatthepeaktiponitsheightaresimilartoourresults,asarethecalculationsofstresslevelsfordifferentoxidethick-

Fig.11.Radialstressatthebottomofthevalleyasafunctionofoxidethicknessfordifferentamplitudes,A,andperiodlengths,L.Left:fixedL,amplitudes:0.5–20mm;right:fixedA,periodlengths:40–200mm.