Segmentation Crack Formation and Propagation Dynamics in Air Plasma Sprayed Coatings

Segmentation Cracks (SCs) in Air Plasma Sprayed (APS) coatings have been widely recognized to impart high in-plane strain tolerance, fracture toughness, and longevity. This combination has allowed wide spread use of vertically cracked coatings of Yttria Stabilized Zirconia (YSZ) in the gas turbine engines. But the industrial drive for more efficient Thermal Barrier Coatings (TBCs) requires processing and implementation of dense vertically cracked structures in ceramics. However, the literature addressing the formation and propagation of such cracks, and their relationship to process conditions and performance is still unresolved.

This study seeks to characterize the formation dynamics of Segmentation Cracks by studying the microstructural features attained by each incremental coating layer deposited on pre-heated underlying coating which mimic the real time deposition of APS coatings. The concept here is to understand the factors affecting the adhesion and micro-crack pattern of the individual splats, which will then allow identification of conditions at which the inter-splat cracking is coherent throughout the incremental layer of the coating deposited, that leads to initiation and progression of Segmentation Cracks through successive coating build-up.