Thermochemical and Thermomechanical study on Composite Coatings (Al 2O 3+ZrO 2•5CaO)

Premature failure is the major apprehension in graded coating systems. To determine the life span of the topcoat (Al₂O₃+ZrO₂•5CaO), Muffle furnace technique was adopted.The topcoat thicknesses were varied in 100, 200 & 300 µm and applied on Cast iron substrate. A controlled heating (600 ±2°C) and ambient cooling in the cycle were carried out until the fracture acknowledges at the surface of the topcoat. Results obtained from SEM micrograph and EDX analysis revealed that thermochemical and thermomechanical stresses lead to premature failure of the topcoat.The coating reported failing from the bond coat and the same is remained intact with the substrate. After 312 thermal cyclic tests, spallation acknowledges in the case of 100 µm topcoat. The mechanism of failure for the above said graded composite coating discussed in detail.