Fracture resistance of atmospheric plasma sprayed thermal barrier coatings

A novel comparison of bending and wedge opening tests in combination with in-situ observation is used to assess the crack resistance behaviour for segmentation and delamination of thick stand-alone and thin attached atmospheric plasma sprayed thermal barrier coatings. The crack growth was monitored in-situ with optical and scanning electron microscopy. The controlled crack growth experiments verified an increase of resistance with crack extension for both segmentation and delamination cracks. Propagation of long cracks in delamination orientation verified R-curve behaviour with plateau values of ~ 150 N/m. The macro-crack followed in both orientations pre-existing inter- and intra-splat cracks. The sharp microcrack deflections generate a tortuous crack path which gives rise to crack surface interaction and thereby toughening.