Effect of Top-Coat Thickness and Interface Fluctuation on the Residual Stress in APS-TBCs

This study focused on the numerical simulation of the distribution of residual stress in yttria-stabilized zirconia (YSZ) coatings prepared with atmospheric plasma spraying (APS). We particularly investigated the stress distribution around the interface between the top coat and bond coat. During thermal spray deposition, droplets and particles deposit on the substrate in a complex manner, causing interface waviness and non-uniform stress distribution. Therefore, residual stress is an important consideration when preparing thermal barrier coatings (TBCs). Residual stresses directly affect the performance of bond coats (BCs) and ceramic top coats (TCs). To accurately evaluate residual stress, we considered interface waviness and the thickness of the ceramic top coat and conducted a detailed analysis of stress distribution. The results show that compressive stress exists at the TC/BC interface, which may be caused by the mismatch in the thermal expansion coefficient between the YSZ top coat and the substrate, potentially leading to coating delamination. Moreover, the residual stress at the TC/BC interface significantly increases with an increasing YSZ thickness. When the top-coat thickness exceeds 300 μm, stress concentration and failure of the coating are likely to occur. Meanwhile, the optimized thermal spray experiment results confirm that the residual stress at the BC/YSZ interface of the thermal barrier coating is tensile stress, with a maximum value of 155 MPa, which is consistent with the finite element calculation results. Furthermore, the failure modes of TBCs with rough interface conditions are discussed in detail. Our research provides important guidance for TBC design and optimizing their performance.