Investigation of the effect of BC layer surface roughness and TC layer porosity on stress values in plasma sprayed coatings based on SEM images

This study investigates the effect of BC surface roughness and TC porosity on the stress values in atmospheric plasma sprayed (APS) thermal barrier coatings using the finite element method based on SEM images. Thermal aging treatment was performed at 1100 degrees C for 12 h on TBC samples with different BC surface roughness. Grinding and grit blasting treatments were performed on the BC surface to achieve different roughnesses. It was observed that increasing the BC surface roughness increases the contact surface with oxygen and Al diffusion paths towards the BC/TC interface, increasing the TGO thickness. The finite element results show that in the initial state without the TGO layer, after the heating stage, the stress is tensile in the peak areas of the interface and compressive in the valley areas, and with the TGO growth, the stress in the peak becomes compressive and in the valley becomes tensile. By increasing the BC surface roughness from Ra= 1.3 mu m to Ra= 3.7 mu m, the maximum tensile stress in the valley region of the TGO/TC interface reached from 34.84 MPa to 91.70 MPa. As a result, increasing the surface roughness increases the stress values in TBCs. The TC porosity shifts the stress concentration sites to the boundary of pores and reduces the stress at the TGO/TC interface. For this reason, cracks have initiated from the discontinuities within the TC layer in the coating with the highest BC surface roughness.