Mechanical properties of single columnar in thermal barrier coatings with porous columnar microstructure

Abstract

The shear test and cantilever bending one for the single column of a suspension plasma sprayed thermal barrier coating (SPS-TBC) were carried out to evaluate the mechanical properties of the single column. The fracture of the single column occurred at the porous layer in the column near the top-coat/bond-coat (TC/BC) interface in the shear test. The cantilever bending test revealed that the SPS-TBC has a low Young’s modulus in the out-of-plane direction (E_o) compared with that in the in-plane direction and a strong anisotropy in the elastic modulus. The shear strength and E_o of the single column increased with thermal exposure, and the increasing ratio of shear strength was higher than that of E_o. It was found from the FEM analysis result that Young’s modulus of porous layer (E_p) is as low as 0.1% that of the dense layer (E_d). From these results, it was concluded that, in the SPS-TBC, the mechanical properties and their change by the thermal exposure are dominated by the mechanical properties of the porous layer within the single column. These results suggest that SPS-TBC has superior thermal cyclic resistance.