Design against fracture of functionally graded thermal barrier coatings using transformation toughening

This study presents a new theoretical model for design against fracture of zirconia-toughened functionally graded thermal barrier coatings (FG TBCs). A micromechanics-based model, which investigates the effect of the mismatch in material properties of the constituent phases on the transformation toughening mechanism in zirconia-enriched multi-phase composites, has been incorporated with the lamination theory. The developed model enables to engineer ZrO2-toughened multi-phase FG TBCs with required or pre-determined fracture properties by utilizing the synergetic characteristics of their constituent phases. A simulation for ZrO2/Ni FG TBC plates subjected to thermal shock loadings has been conducted. The results demonstrated that within the compositional gradation investigated, the substrate metal (Ni)-rich compositional gradation contributed to high fracture-resistant properties based on fracture-mechanics considerations. This tendency was theoretically and experimentally confirmed with results available in the open literature.