Local cohesion of splats in hybrid plasma spray coating as observed by in-situ experiment

Hybrid plasma spraying combines spraying of dry coarse powders and liquids (suspensions and/or solutions). Introduction of secondary miniature phase from the liquid may provide new coating functionality but also may have a significant influence on the local coating cohesion – increasing or decreasing it, depending on the materials combination and deposition conditions. In this study, cohesion of dissimilar splats within the early-stage experimental hybrid thermal barrier coating (TBC) was evaluated by in-situ SEM three-point bending (3PB) observation coupled with high-resolution strain mapping. Loading was carried out on the annealed sample simulating in-service thermal exposure. Observed coating failure confirmed that the coating exhibits a rather high intersplat cohesion lowering its strain-tolerance, which was presumably the reason for the relatively low thermal cycling resistance of the deposit.