Effect of using unpyrolyzed powder on mechanical properties of vertically cracked thermal barrier coatings

Abstract

In this study, thermal barrier coatings with segmentation cracks produced using synthesized unpyrolyzed powder (UP TBC) and dense vertically cracked (DVC) thermal barrier coatings with varying vertical crack density and porosity were produced by air plasma spray technique. The mechanical properties of the coatings including microhardness, Young's modulus and fracture toughness were evaluated by indentation technique and the correlation of the results with porosity is discussed. The results of elastic modulus indicated that higher percentage of porosity results in a lower elastic modulus and consequently lower fracture toughness for DVC TBCs. In the case of the UP TBC samples, the porosity percentage, compared to the conventional one, is higher but in contrary a higher elastic modulus was measured; probably due to the existence of submicron size unmelted zones. The results of fracture toughness measurement showed that the UP TBC has a lower elastic modulus compared to that of DVC TBCs. However, due to non-melted zones which are consisted of unpyrolyzed particles, UP TBC demonstrates a higher fracture toughness than the DVC TBCs.