Observation of microstructure in thermal barrier coatings prepared by laser hybrid spraying process using fluorescent dye infiltration technique

摘要

It was found that the observation of resin infiltrated coatings by CLSM was a very effective way of visualizing the three dimensional structure and differentiating the original defects from ones induced by metal-lographical procedures. In case of as-sprayed coating, the sprayed top-coat was abruptly spalled just at the third time of cyclic thermal shock test. On the other hand, the laser treated coating, which has a higher crack density of 3.1 mm~(-1) (the average distance to the neighbor crack was near the thickness of top coating) and average crack depth of 160 μm (about a half of the thickness of top coating), survived even after 17 cycles of thermal shock test. In the case of coatings prepared by plasma-laser hybrid spraying process, the crack formation behaviors of coatings was different from the post-treated coatings. The feature of cracks in the coating, prepared by hybrid spraying processes, was characterized as a feather-like structure with a significant number of branching cracks which was not observed in the post-treated coatings. From the study of the microstructure of hybrid sprayed coatings and the relation with the thermal shock resistance, the processing conditions for producing the coatings, which have desirable properties against the cyclic thermal shock was suggested (portion of hybrid process (50%), P_ρ (120) and E_ρ (2.4)).