Effect of residual stress on high temperature oxidation behaviour of yttria stabilized zirconia - lanthanum zirconate thermal barrier composite coatings

• YSZ/LZ composite TBC deposited using APS method and evaluated under cyclic exposure • The 80%YSZ/20%LZ showed 45% lower oxidation than monolithic YSZ and LZ coating • Uniform and smallest thickness of TGO layer observed 80% YSZ/ 20%LZ composite coating after thermal cycling • Residual stress relaxation reduced to 8% of the composite 80% YSZ/ 20% LZ coating. Residual stress formation during the coating process influences the oxidation resistance and durability of atmospheric plasma-sprayed thermal barrier coatings (TBC). This study examines the residual stress and oxidation resistance of TBC coating composed of yttria-stabilized zirconia (YSZ), lanthanum zirconate (LZ) and composite coatings applied on Inconel-718 substrates. The influence of compositional variation on thermal and mechanical stability under thermal cycling exposure was evaluated. Surface morphology studies confirmed the formation of lamellar microstructures characterized by variation in composition porosity and splat boundary dispersion. The oxidation kinetics demonstrated, with the 80%YSZ/20%LZ composite showing the minimal cumulative weight gain of 0.00784 g/cm 2 after 100 hours, in comparison with 0.01416 g/cm 2 for 100%YSZ. Residual stress measurements indicated considerable stress relaxation in monolithic coatings (34% for YSZ and 32% for LZ) following thermal cycling conditions. However, the 80%YSZ/20%LZ coating exhibited minimal stress relaxation at approximately 8% maintaining a stable compressive stress. The performance of the coating was due to the combined effect between YSZ-induced strain tolerance and LZ-induced reduction in oxygen diffusivity, which together suppress excessive growth of thermally grown oxide. In comparison, the optimized 80%YSZ/20%LZ system exhibited enhanced oxidation resistance and residual stress stability underscoring its suitability for high temperature turbine applications.