Evolution of residual stress in air plasma sprayed yttria stabilised zirconia thermal barrier coatings after isothermal treatment

The evolution of residual stresses in yttria stabilised zirconia (YSZ) thermal barrier coatings (TBCs) produced by air plasma-spray technique after thermal treatments at 1150 °C was investigated. The residual stresses in YSZ layer were measured using the Raman spectroscopy and curvature method, respectively. Generally, the YSZ layer was under compressive stress in as-deposited condition, but changed to tensile after thermal treatment for 30 hours partly due to the monoclinic to tetragonal phase transformation in YSZ layer. With prolonged thermal treatment, the residual stress gradually transformed from tensile to compressive, which can be attributed to the sintering in the YSZ layer. In addition, the β-NiAl to γ/γ′-Ni3Al phase transformation in the bond coat also plays an important role on the stress in the YSZ layer.