Abstract
An advanced Ni-base single-crystal superalloy, TMS-238, has the highest temperature capability, but there is still potential to improve its high-temperature properties. In the present study, aiming for that further improvement, TMS-238 was melted in a CaO crucible, which replaced an Al2O3 crucible. Creep tests at 1100 °C/137 MPa and cyclic oxidation tests at 1100 °C were conducted to compare the high-temperature properties of TMS-238 melted in an Al2O3vs a CaO crucible. Regardless of the melting crucible, the creep properties of the samples were equivalent. Meanwhile, TMS-238 melted in a CaO crucible exhibited better oxidation resistance. Although the composition of the oxide scale was almost the same, the sample melted in an Al2O3 crucible had its oxide scale spalled, while a continuous oxide scale was formed on the sample melted in a CaO crucible. Dissolved Ca capturing S as CaS and preventing segregation of S at the metal-oxide interface is a possible reason for the improvement of the oxide scale adhesiveness. The results indicated that melting in a CaO crucible can improve the oxidation resistance of the original superalloys while maintaining their creep properties.
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