Cyclic oxidation behavior of thermal barrier coatings on single crystal superalloys

The thermal barrier coatings (TBC), which Ni30Cr12Al0.3Y bond coating was deposited by magnetron sputtering and ZrO₂ ceramic top coating was deposited by electron beam-physical vapor deposition (EB-PVD), was produced on Ni-base superalloy. The bond coatings, which the mean grain size was less than 100 nm, were nanostructured coatings, and had good oxidation-resistance. The ceramic topcoats, which were columnar structure, permitted larger strain in the coatings. The as-deposited ceramic coatings consisted of large quantity nonequilibrium tetragonal (t′), a small amount cubic (c) and monoclinic (m) phases. The t′ phases, which had important role to the stabilization of zirconia at high temperature, can not directly transform into m phase during cooling. During cyclic oxidation at 1050°C, the scale of the cast alloy had spalled after two cycles. After 100 cycles, the surface scale of single-crystal superalloy was mainly composed of NiO,Cr₂O₃, a little Al₂O₃ and pores by the Kirkendall effect. However, the ceramic coatings, which had microcrack, have not spalled and the thermally grown oxide (TGO) was Al₂O₃. There were some microcrack between TGO and bond coating after 300 cycles.