Thermal barrier coating (TBC) was applied to Co based superalloy specimens, where bond coat was CoNiCrAlY deposited by high velocity oxygen fuel (HVOF) spraying and top coat was 8mass% yttria stabilized zirconia (YSZ) by atmospheric plasma spraying. After the specimens were heated and held at high temperature, tensile tests and edge indent tests of the specimens were carried out to measure interfacial fracture toughness and delamination energy of the coating, respectively. The results showed that Al2O3 oxide was formed along the interface between the top coat and the bond coat, and the thickness of Al2O3, BAl, increased with increasing heating temperature T and holding time t. The growth behavior of Al2O3 layer was expressed by the equation: BAl=A·exp(-Q/RT)·tn, where Q is apparent activation energy, R is gas constant, and A and n are constants. The interfacial fracture toughness and the delamination energy increased with increasing BAl when it was less than about 2μm, while when BAl exceeded 8-10μm, both of them decreased drastically. By using a critical oxide layer thickness where the delamination strength was still maintained, a combination of operation temperature and time during which the delamination of coating would not occur was determinated.
