Atmospheric plasma sprayed thick thermal barrier coatings: Microstructure, thermal shock behaviors and failure mechanism

Abstract

Advanced thick thermal barrier coatings (TTBCs) have attracted extensive attentions due to the embedded segmentation-crack structure and excellent thermal insulation performance. The thermal shock life and failure behaviors of advanced TTBCs still remain a challenge. The objective of this work is to well understand the effect of microstructure on the coating cracking behavior in atmospheric plasma sprayed TTBCs system, in which the extended Raman spectroscopy (RS) techniques are used to obtain an in-depth understanding on how the oxidation affects the stress distribution in coatings and in turn, the causes of the observed cracking. Results show that the TTBCs deposited by the highly purified feedstock exhibit excellent thermal shock life at 1100 ℃ due to the well-proportioned and compact structure and built-in vertical cracks. After thermal shock test, the broken regions usually occur at the horizontal cracks and vertical cracks area within top-coat, and top-coat/bondcoat interface, which may suggest that each structural mutation parts are prone to causing the TTBCs instabilities. Cracks are propagated and extended under thermal tensile stress. The coating failure is most possibly dominated by the accumulated residual stress generated due to thermal expansion mismatch between the substrate and top-coat. In addition, the good thermal shock resistance have a close relationship with the newly formed vertical cracks at the bottom of ceramic coating near the top-coat/bondcoat interface.