THERMAL-SHOCK TESTING OF BURNER CANS COATED WITH A THICK THERMAL BARRIER COATING

Thick (1.8 mm) thermal barrier coatings were air-plasma-sprayed onto t wo different substrate geometries, including small circular substrates and burner cans. Two different top-coating spray parameters were used , where the settings of the substrate temperature and the lamella thic kness were varied. A segmentation crack network was found in the top c oatings sprayed using a high substrate temperature and a high lamella thickness. The density of segmentation cracks was found to be independ ent of substrate geometry. No segmentation cracks were found in the to p-coatings when a low substrate temperature and a low lamella thicknes s were used. In the segmented burner can, after 1000 thermal shock cyc les, the segmentation crack network was still stable and no severe cra cks had formed in the top coating. In the nonsegmented burner can, cra cks were formed after only 35 thermal shock cycles. Among the crack ty pes, horizontally oriented cracks were found in the top coating close to, and sometimes reaching, the bond coating. Cracks of this type are not tolerated in thermal barrier coatings because they can cause failu re of the coating. Regarding the lifetime of the segmented burner can, it is believed the failure will be dependent on other mechanisms, suc h as bond-coating oxidation or top-coating decomposition.