Improvement of Oxidation and Delamination Resistant Properties in Thermal Barrier Coatings by Means of Plasma Thermal Spraying

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We suggested that degradation of thermal barrier coating (TBC) was induced by thermal stress due to formation and growth of thermally grown oxide (TGO) in YSZ top coat and MCrAlY bond coat, and by the decrease in bonding strength due to formation of many pores in TGO. In order to inhibit of formation of pores in TGO, an improvement of chemical composition of bond coat material was considered. Ce and Si added MCrAlY bond coat material was developed. As a result, morphology of the TGO changed drastically, namely TGO grew up from the interior of the bond coat like wooden root (wedge shaped TGO). Furthermore, the developed material also inhibited the growth of nickel and cobalt oxides, which have bad influence on formation of pores. And four point bending test was carried out to evaluated the interface strength. The strain of developed bond coat material used for TBC was three times higher than conventional one. Accordingly, the improvement of delamination resistant property using the developed bond coat material was successful.Also, a technique of laser remelting to a bond coat was developed to improve the oxidation resistant property. An objective of laser remelting is to produce a dense and less impure TGO. As a result, if conventional bond material (MCrAlY) was used, TGO thickness decreased and dense alumina formed. Moreover, laser remetled TBC was found to have stronger bending strength than the standard TBC, probably due to disappearance of pores in TGO.The improvement of oxidation and delamination resistant properties was succeeded by means of modification of bond coat material and usage of laser remelting technique.