Microstructure and surface residual stress of plasma sprayed nanostructured and conventional ZrO₂-8wt%Y₂O₃ thermal barrier coatings

The nanostructured agglomerate feedstock which can be used for plasma spraying was obtained successfully by the reconstituting nanoparticle technique. Nanostructured and conventional ZrO₂-8wt%Y₂O₃ (8YSZ) thermal barrier coatings (TBCs) have been prepared by atmospheric plasma spraying (APS) on NiCoCrAlY coated 45# steel substrates. The microstructure and phase composition of feedstock and corresponding coating were characterized by SEM and XRD. The elastic modulus was tested by the nanoindenter instrument. The surface residual stresses were examined by XRD stress test equipment. The numerical value probability statistics of surface residual stress by the Weibull distribution theory was implemented under different thermal spray parameters. The value of residual stresses increased with increasing the thickness of the ceramic coating. The surface residual stress of nanostructured 8YSZ coating is lower than that of the conventional 8YSZ coating. A physical mechanical model is put forward to explain the causation of the variation of residual stresses. At the same time, the variation characteristic of surface residual stress is discussed by introducing the closed form solution of residual stress of laminar layer plate.