2004 Volume 47 Issue 3 Pages 318-323
It is possible to measure nondestructively the residual stress in the interior of the top coating in the thermal barrier coating (TBC) using hard synchrotron X-rays, which have a large penetration depth and high brightness. A new hybrid method is proposed to estimate the distribution of the spalling stress in the top coating by combining the synchrotron data with the stress data measured by the conventional X-ray method utilizing a Cr-Kα radiation. The new hybrid method was applied to estimate the distribution of the spalling stress in the top coating of TBC which had a zirconia top coating with a thickness of 0.24mm and a NiCoCrAlY bond coating with a thickness of 0.2mm. The residual stress, σ11-σ33, within the top coating was determined by synchrotron X-rays of 73keV energy level, where σ33 was the stress perpendicular to the surface and σ11 was an in-plane stress. The distribution of residual in-plane stresses, σ11 and σ22, in the top and the bond coating was determined with the conventional X-ray method by repeating the measurement after successive removal of the surface layer. From the data obtained by synchrotron and conventional X-rays, the distribution of stress component, σ33, responsible for spalling was determined. The estimated value of the spalling stress was very small beneath the surface and increased to about 75MPa near the interface between the top and the bond coating.