Tailoring Periodic Vertical Cracks in Thermal Barrier Coatings Enabling High Strain Tolerance

Abstract

Lifetime is a basic support for the thermal insulation function of thermal barrier coatings (TBCs). Therefore, extending the life span is essential to develop next-generation TBCs. For this objective, the columnar structure formed by vertical cracks appears to make sense. However, the underlying mechanism is still unclear. This work scrutinizes the influence of periodic vertical cracks on cracking behavior in order to tailor high strain tolerant TBCs. A finite element model was evolved to explore the crack behavior influenced by thermal mismatch strain between substrate and coating. The virtual crack closure technique (VCCT) was used to describe the propagation of crack under load. It is found clearly that the space between two vertical cracks (short for SVC) along the in-plane direction has a noteworthy influence on the strain tolerance of TBCs. Results indicate that the strain energy release rate (SERR) and stresses at the pre-crack tip increase continuously with the increase of the SVC, suggesting that the driving force for cracks is increasing. The crack is not propagated when the SVC is very small, whereas the crack grows continuously with the increase of the SVC. The growth of a crack can be prevented by reducing the SVC. A critical value for the SVC was found. When the SVC is less than the critical value, the SERR can be dramatically reduced. Thus, the SVC of periodic cracks can be tailored to obtain TBCs with high strain tolerance.

Sintering-Induced Failure Mechanism of Thermal Barrier Coatings and Sintering-Resistant Design

“…TBCs with vertically cracked structures exhibit scale-sensitive stiffening behavior, as shown in Figure 16a,b. For a model with w/h = 20, the gap between two neighboring vertical cracks is very large, which is similar to the case of no vertical cracks [82]. Given that, the macroscopic and microscopic elastic moduli of TC are equal.…”

Progress update on extending the durability of air plasma sprayed thermal barrier coatings

“…Segmentation cracks, which refer to cracks greater than half of the coating thickness and perpendicular to the coating/substrate interface, have been recognized to enhance the strain tolerance and durability of TBCs, particularly for thick coatings [69,70]. The microstructure of segmentation coatings, also known as s dense vertically cracked coatings, differs remarkably from that of the traditional APS TBCs.…”

“…5. Typical microstructure of APS coating with (a) conventional lamellar structure;(b) periodic vertical cracks[70]. Fig.6.…”

Introducing segmentation cracks in air plasma‐sprayed thermal barrier coatings by controlling residual stress

“…The geometries of the segmentation cracks including crack spacing, width, and depth, which are determined by the residual stress in the coating, have a significant effect on the initiation and propagation of interfacial cracks 7,8 . Therefore, accurately measuring the stress in the topcoat during deposition and controlling the deposition parameters could enable the manipulation of the stress state and achieve desirable geometries of the segmentation cracks 9–11 …”

“…7,8 Therefore, accurately measuring the stress in the topcoat during deposition and controlling the deposition parameters could enable the manipulation of the stress state and achieve desirable geometries of the segmentation cracks. [9][10][11] To date, various techniques such as X-ray diffraction, curvature measurement, and Raman spectroscopy have been applied to measure the stress in the YSZ topcoat. X-ray diffraction is nondestructive.…”