Abstract:The stratified gradient thermal barrier coatings (TBCs) were obtained by laser cladding of ZrO2and NiCoCrAlY mixture powder. The coatings were four-layer structure: cellular dendritic ZrO2, dense ZrO2, Ni-based alloy bonding coating and substrate. The formation of the stratified TBCs was attributed to the insolubility of ZrO2in the Nibased alloy and the lower density of ZrO2than that of Ni-based alloy when both of them were in melted condition. The formation of two-layered ZrO2was related to the presence of Al in the Ni-based alloy, i) Al could be preoxidized into Al2O3that could be segregated in the grain boundaries of ZrO2during solidification process; ii) Al could be partially preoxidized into Al2O3, then Al and Al2O3could be segregated simultaneously at the grain boundaries of ZrO2during solidification process. Two formation processes were presented.

Key words: laser cladding; thermal barrier coatings; formation mechanismsDocument code: A