Abstract
NiCoCrAlY is usually used as the material to bond-coat in thermal barrier coating systems under high temperatures. Using NiCoCrAlY and adding different amounts of the active element Ti (0, 0.1, 0.3, and 0.5; wt%), the relationship between oxide peg size and thermally grown oxide spalling resistance is ascertained by examining specimens subjected to a cyclic oxidation experiment. Oxide pegs, consisting of a Y- and Ti-rich oxide core and an outer Al2O3 sheath, are formed by Ti and Al successively reacting with oxygen after the rapid generation of Y-rich oxide. The size of the oxide pegs with higher Ti concentrations is on average bigger in the alloy. Severe thermally grown oxide spalling occurred in the 0.5 wt% Ti specimen, but in the 0.3 wt% Ti specimen, it displayed the best adherence with the alloy due to the presence of fine pegs. Cavities existed at the interface between the inner oxide core and outer Al2O3 sheath of larger pegs serve as microcrack sources and further induce severe scale failure combined with the initial interface crack between the scale and alloy.
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