Evolution of the residual stress in porous ceramic abradable coatings under thermal exposure

Porous dysprosium-stabilized zirconia (DySZ) based abradable coatings were fabricated on DD5 superalloy by atmospheric plasma spraying technique (APS). The residual stress of the porous coating after thermal aging at 1100 degrees C was characterized using Raman spectroscopy and Photoluminescence piezo-spectroscopy (PLPS) techniques. The results indicated that the residual stress of the porous topcoat was smaller than the theoretically predicted due to a large number of pores and cracks inside the coating. Based on the stress evolution behavior of the porous coating exposed to thermal aging, a rational failure threshold stress was suggested. In addition, the effect of coating depth, pores and monoclinic ZrO2 phase on the stress distribution were analyzed on the polished cross-section specimens. Meanwhile, the stress distribution along the TGO direction showed a strong correlation with the local geometry, and the number of points showing tensile stress increased with prolongation of thermal exposure. Evidence revealed that the initiation and propagation of micro-cracks prefer to occur at locations with high curvature and tip edge of the convex area. The research in this paper provides enlightenment for life prediction and structural optimization.